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TOMOYO Linux Cross Reference
Linux/kernel/fork.c

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  1 /*
  2  *  linux/kernel/fork.c
  3  *
  4  *  Copyright (C) 1991, 1992  Linus Torvalds
  5  */
  6 
  7 /*
  8  *  'fork.c' contains the help-routines for the 'fork' system call
  9  * (see also entry.S and others).
 10  * Fork is rather simple, once you get the hang of it, but the memory
 11  * management can be a bitch. See 'mm/memory.c': 'copy_page_range()'
 12  */
 13 
 14 #include <linux/slab.h>
 15 #include <linux/init.h>
 16 #include <linux/unistd.h>
 17 #include <linux/module.h>
 18 #include <linux/vmalloc.h>
 19 #include <linux/completion.h>
 20 #include <linux/personality.h>
 21 #include <linux/mempolicy.h>
 22 #include <linux/sem.h>
 23 #include <linux/file.h>
 24 #include <linux/fdtable.h>
 25 #include <linux/iocontext.h>
 26 #include <linux/key.h>
 27 #include <linux/binfmts.h>
 28 #include <linux/mman.h>
 29 #include <linux/mmu_notifier.h>
 30 #include <linux/fs.h>
 31 #include <linux/nsproxy.h>
 32 #include <linux/capability.h>
 33 #include <linux/cpu.h>
 34 #include <linux/cgroup.h>
 35 #include <linux/security.h>
 36 #include <linux/hugetlb.h>
 37 #include <linux/seccomp.h>
 38 #include <linux/swap.h>
 39 #include <linux/syscalls.h>
 40 #include <linux/jiffies.h>
 41 #include <linux/futex.h>
 42 #include <linux/compat.h>
 43 #include <linux/kthread.h>
 44 #include <linux/task_io_accounting_ops.h>
 45 #include <linux/rcupdate.h>
 46 #include <linux/ptrace.h>
 47 #include <linux/mount.h>
 48 #include <linux/audit.h>
 49 #include <linux/memcontrol.h>
 50 #include <linux/ftrace.h>
 51 #include <linux/proc_fs.h>
 52 #include <linux/profile.h>
 53 #include <linux/rmap.h>
 54 #include <linux/ksm.h>
 55 #include <linux/acct.h>
 56 #include <linux/tsacct_kern.h>
 57 #include <linux/cn_proc.h>
 58 #include <linux/freezer.h>
 59 #include <linux/delayacct.h>
 60 #include <linux/taskstats_kern.h>
 61 #include <linux/random.h>
 62 #include <linux/tty.h>
 63 #include <linux/blkdev.h>
 64 #include <linux/fs_struct.h>
 65 #include <linux/magic.h>
 66 #include <linux/perf_event.h>
 67 #include <linux/posix-timers.h>
 68 #include <linux/user-return-notifier.h>
 69 #include <linux/oom.h>
 70 #include <linux/khugepaged.h>
 71 #include <linux/signalfd.h>
 72 #include <linux/uprobes.h>
 73 #include <linux/aio.h>
 74 
 75 #include <asm/pgtable.h>
 76 #include <asm/pgalloc.h>
 77 #include <asm/uaccess.h>
 78 #include <asm/mmu_context.h>
 79 #include <asm/cacheflush.h>
 80 #include <asm/tlbflush.h>
 81 
 82 #include <trace/events/sched.h>
 83 
 84 #define CREATE_TRACE_POINTS
 85 #include <trace/events/task.h>
 86 
 87 /*
 88  * Protected counters by write_lock_irq(&tasklist_lock)
 89  */
 90 unsigned long total_forks;      /* Handle normal Linux uptimes. */
 91 int nr_threads;                 /* The idle threads do not count.. */
 92 
 93 int max_threads;                /* tunable limit on nr_threads */
 94 
 95 DEFINE_PER_CPU(unsigned long, process_counts) = 0;
 96 
 97 __cacheline_aligned DEFINE_RWLOCK(tasklist_lock);  /* outer */
 98 
 99 #ifdef CONFIG_PROVE_RCU
100 int lockdep_tasklist_lock_is_held(void)
101 {
102         return lockdep_is_held(&tasklist_lock);
103 }
104 EXPORT_SYMBOL_GPL(lockdep_tasklist_lock_is_held);
105 #endif /* #ifdef CONFIG_PROVE_RCU */
106 
107 int nr_processes(void)
108 {
109         int cpu;
110         int total = 0;
111 
112         for_each_possible_cpu(cpu)
113                 total += per_cpu(process_counts, cpu);
114 
115         return total;
116 }
117 
118 void __weak arch_release_task_struct(struct task_struct *tsk)
119 {
120 }
121 
122 #ifndef CONFIG_ARCH_TASK_STRUCT_ALLOCATOR
123 static struct kmem_cache *task_struct_cachep;
124 
125 static inline struct task_struct *alloc_task_struct_node(int node)
126 {
127         return kmem_cache_alloc_node(task_struct_cachep, GFP_KERNEL, node);
128 }
129 
130 static inline void free_task_struct(struct task_struct *tsk)
131 {
132         kmem_cache_free(task_struct_cachep, tsk);
133 }
134 #endif
135 
136 void __weak arch_release_thread_info(struct thread_info *ti)
137 {
138 }
139 
140 #ifndef CONFIG_ARCH_THREAD_INFO_ALLOCATOR
141 
142 /*
143  * Allocate pages if THREAD_SIZE is >= PAGE_SIZE, otherwise use a
144  * kmemcache based allocator.
145  */
146 # if THREAD_SIZE >= PAGE_SIZE
147 static struct thread_info *alloc_thread_info_node(struct task_struct *tsk,
148                                                   int node)
149 {
150         struct page *page = alloc_pages_node(node, THREADINFO_GFP_ACCOUNTED,
151                                              THREAD_SIZE_ORDER);
152 
153         return page ? page_address(page) : NULL;
154 }
155 
156 static inline void free_thread_info(struct thread_info *ti)
157 {
158         free_memcg_kmem_pages((unsigned long)ti, THREAD_SIZE_ORDER);
159 }
160 # else
161 static struct kmem_cache *thread_info_cache;
162 
163 static struct thread_info *alloc_thread_info_node(struct task_struct *tsk,
164                                                   int node)
165 {
166         return kmem_cache_alloc_node(thread_info_cache, THREADINFO_GFP, node);
167 }
168 
169 static void free_thread_info(struct thread_info *ti)
170 {
171         kmem_cache_free(thread_info_cache, ti);
172 }
173 
174 void thread_info_cache_init(void)
175 {
176         thread_info_cache = kmem_cache_create("thread_info", THREAD_SIZE,
177                                               THREAD_SIZE, 0, NULL);
178         BUG_ON(thread_info_cache == NULL);
179 }
180 # endif
181 #endif
182 
183 /* SLAB cache for signal_struct structures (tsk->signal) */
184 static struct kmem_cache *signal_cachep;
185 
186 /* SLAB cache for sighand_struct structures (tsk->sighand) */
187 struct kmem_cache *sighand_cachep;
188 
189 /* SLAB cache for files_struct structures (tsk->files) */
190 struct kmem_cache *files_cachep;
191 
192 /* SLAB cache for fs_struct structures (tsk->fs) */
193 struct kmem_cache *fs_cachep;
194 
195 /* SLAB cache for vm_area_struct structures */
196 struct kmem_cache *vm_area_cachep;
197 
198 /* SLAB cache for mm_struct structures (tsk->mm) */
199 static struct kmem_cache *mm_cachep;
200 
201 static void account_kernel_stack(struct thread_info *ti, int account)
202 {
203         struct zone *zone = page_zone(virt_to_page(ti));
204 
205         mod_zone_page_state(zone, NR_KERNEL_STACK, account);
206 }
207 
208 void free_task(struct task_struct *tsk)
209 {
210         account_kernel_stack(tsk->stack, -1);
211         arch_release_thread_info(tsk->stack);
212         free_thread_info(tsk->stack);
213         rt_mutex_debug_task_free(tsk);
214         ftrace_graph_exit_task(tsk);
215         put_seccomp_filter(tsk);
216         arch_release_task_struct(tsk);
217         free_task_struct(tsk);
218 }
219 EXPORT_SYMBOL(free_task);
220 
221 static inline void free_signal_struct(struct signal_struct *sig)
222 {
223         taskstats_tgid_free(sig);
224         sched_autogroup_exit(sig);
225         kmem_cache_free(signal_cachep, sig);
226 }
227 
228 static inline void put_signal_struct(struct signal_struct *sig)
229 {
230         if (atomic_dec_and_test(&sig->sigcnt))
231                 free_signal_struct(sig);
232 }
233 
234 void __put_task_struct(struct task_struct *tsk)
235 {
236         WARN_ON(!tsk->exit_state);
237         WARN_ON(atomic_read(&tsk->usage));
238         WARN_ON(tsk == current);
239 
240         security_task_free(tsk);
241         exit_creds(tsk);
242         delayacct_tsk_free(tsk);
243         put_signal_struct(tsk->signal);
244 
245         ccs_free_task_security(tsk);
246         if (!profile_handoff_task(tsk))
247                 free_task(tsk);
248 }
249 EXPORT_SYMBOL_GPL(__put_task_struct);
250 
251 void __init __weak arch_task_cache_init(void) { }
252 
253 void __init fork_init(unsigned long mempages)
254 {
255 #ifndef CONFIG_ARCH_TASK_STRUCT_ALLOCATOR
256 #ifndef ARCH_MIN_TASKALIGN
257 #define ARCH_MIN_TASKALIGN      L1_CACHE_BYTES
258 #endif
259         /* create a slab on which task_structs can be allocated */
260         task_struct_cachep =
261                 kmem_cache_create("task_struct", sizeof(struct task_struct),
262                         ARCH_MIN_TASKALIGN, SLAB_PANIC | SLAB_NOTRACK, NULL);
263 #endif
264 
265         /* do the arch specific task caches init */
266         arch_task_cache_init();
267 
268         /*
269          * The default maximum number of threads is set to a safe
270          * value: the thread structures can take up at most half
271          * of memory.
272          */
273         max_threads = mempages / (8 * THREAD_SIZE / PAGE_SIZE);
274 
275         /*
276          * we need to allow at least 20 threads to boot a system
277          */
278         if (max_threads < 20)
279                 max_threads = 20;
280 
281         init_task.signal->rlim[RLIMIT_NPROC].rlim_cur = max_threads/2;
282         init_task.signal->rlim[RLIMIT_NPROC].rlim_max = max_threads/2;
283         init_task.signal->rlim[RLIMIT_SIGPENDING] =
284                 init_task.signal->rlim[RLIMIT_NPROC];
285 }
286 
287 int __attribute__((weak)) arch_dup_task_struct(struct task_struct *dst,
288                                                struct task_struct *src)
289 {
290         *dst = *src;
291         return 0;
292 }
293 
294 static struct task_struct *dup_task_struct(struct task_struct *orig)
295 {
296         struct task_struct *tsk;
297         struct thread_info *ti;
298         unsigned long *stackend;
299         int node = tsk_fork_get_node(orig);
300         int err;
301 
302         tsk = alloc_task_struct_node(node);
303         if (!tsk)
304                 return NULL;
305 
306         ti = alloc_thread_info_node(tsk, node);
307         if (!ti)
308                 goto free_tsk;
309 
310         err = arch_dup_task_struct(tsk, orig);
311         if (err)
312                 goto free_ti;
313 
314         tsk->stack = ti;
315 
316         setup_thread_stack(tsk, orig);
317         clear_user_return_notifier(tsk);
318         clear_tsk_need_resched(tsk);
319         stackend = end_of_stack(tsk);
320         *stackend = STACK_END_MAGIC;    /* for overflow detection */
321 
322 #ifdef CONFIG_CC_STACKPROTECTOR
323         tsk->stack_canary = get_random_int();
324 #endif
325 
326         /*
327          * One for us, one for whoever does the "release_task()" (usually
328          * parent)
329          */
330         atomic_set(&tsk->usage, 2);
331 #ifdef CONFIG_BLK_DEV_IO_TRACE
332         tsk->btrace_seq = 0;
333 #endif
334         tsk->splice_pipe = NULL;
335         tsk->task_frag.page = NULL;
336 
337         account_kernel_stack(ti, 1);
338 
339         return tsk;
340 
341 free_ti:
342         free_thread_info(ti);
343 free_tsk:
344         free_task_struct(tsk);
345         return NULL;
346 }
347 
348 #ifdef CONFIG_MMU
349 static int dup_mmap(struct mm_struct *mm, struct mm_struct *oldmm)
350 {
351         struct vm_area_struct *mpnt, *tmp, *prev, **pprev;
352         struct rb_node **rb_link, *rb_parent;
353         int retval;
354         unsigned long charge;
355 
356         uprobe_start_dup_mmap();
357         down_write(&oldmm->mmap_sem);
358         flush_cache_dup_mm(oldmm);
359         uprobe_dup_mmap(oldmm, mm);
360         /*
361          * Not linked in yet - no deadlock potential:
362          */
363         down_write_nested(&mm->mmap_sem, SINGLE_DEPTH_NESTING);
364 
365         mm->locked_vm = 0;
366         mm->mmap = NULL;
367         mm->mmap_cache = NULL;
368         mm->map_count = 0;
369         cpumask_clear(mm_cpumask(mm));
370         mm->mm_rb = RB_ROOT;
371         rb_link = &mm->mm_rb.rb_node;
372         rb_parent = NULL;
373         pprev = &mm->mmap;
374         retval = ksm_fork(mm, oldmm);
375         if (retval)
376                 goto out;
377         retval = khugepaged_fork(mm, oldmm);
378         if (retval)
379                 goto out;
380 
381         prev = NULL;
382         for (mpnt = oldmm->mmap; mpnt; mpnt = mpnt->vm_next) {
383                 struct file *file;
384 
385                 if (mpnt->vm_flags & VM_DONTCOPY) {
386                         vm_stat_account(mm, mpnt->vm_flags, mpnt->vm_file,
387                                                         -vma_pages(mpnt));
388                         continue;
389                 }
390                 charge = 0;
391                 if (mpnt->vm_flags & VM_ACCOUNT) {
392                         unsigned long len = vma_pages(mpnt);
393 
394                         if (security_vm_enough_memory_mm(oldmm, len)) /* sic */
395                                 goto fail_nomem;
396                         charge = len;
397                 }
398                 tmp = kmem_cache_alloc(vm_area_cachep, GFP_KERNEL);
399                 if (!tmp)
400                         goto fail_nomem;
401                 *tmp = *mpnt;
402                 INIT_LIST_HEAD(&tmp->anon_vma_chain);
403                 retval = vma_dup_policy(mpnt, tmp);
404                 if (retval)
405                         goto fail_nomem_policy;
406                 tmp->vm_mm = mm;
407                 if (anon_vma_fork(tmp, mpnt))
408                         goto fail_nomem_anon_vma_fork;
409                 tmp->vm_flags &= ~VM_LOCKED;
410                 tmp->vm_next = tmp->vm_prev = NULL;
411                 file = tmp->vm_file;
412                 if (file) {
413                         struct inode *inode = file_inode(file);
414                         struct address_space *mapping = file->f_mapping;
415 
416                         get_file(file);
417                         if (tmp->vm_flags & VM_DENYWRITE)
418                                 atomic_dec(&inode->i_writecount);
419                         mutex_lock(&mapping->i_mmap_mutex);
420                         if (tmp->vm_flags & VM_SHARED)
421                                 mapping->i_mmap_writable++;
422                         flush_dcache_mmap_lock(mapping);
423                         /* insert tmp into the share list, just after mpnt */
424                         if (unlikely(tmp->vm_flags & VM_NONLINEAR))
425                                 vma_nonlinear_insert(tmp,
426                                                 &mapping->i_mmap_nonlinear);
427                         else
428                                 vma_interval_tree_insert_after(tmp, mpnt,
429                                                         &mapping->i_mmap);
430                         flush_dcache_mmap_unlock(mapping);
431                         mutex_unlock(&mapping->i_mmap_mutex);
432                 }
433 
434                 /*
435                  * Clear hugetlb-related page reserves for children. This only
436                  * affects MAP_PRIVATE mappings. Faults generated by the child
437                  * are not guaranteed to succeed, even if read-only
438                  */
439                 if (is_vm_hugetlb_page(tmp))
440                         reset_vma_resv_huge_pages(tmp);
441 
442                 /*
443                  * Link in the new vma and copy the page table entries.
444                  */
445                 *pprev = tmp;
446                 pprev = &tmp->vm_next;
447                 tmp->vm_prev = prev;
448                 prev = tmp;
449 
450                 __vma_link_rb(mm, tmp, rb_link, rb_parent);
451                 rb_link = &tmp->vm_rb.rb_right;
452                 rb_parent = &tmp->vm_rb;
453 
454                 mm->map_count++;
455                 retval = copy_page_range(mm, oldmm, mpnt);
456 
457                 if (tmp->vm_ops && tmp->vm_ops->open)
458                         tmp->vm_ops->open(tmp);
459 
460                 if (retval)
461                         goto out;
462         }
463         /* a new mm has just been created */
464         arch_dup_mmap(oldmm, mm);
465         retval = 0;
466 out:
467         up_write(&mm->mmap_sem);
468         flush_tlb_mm(oldmm);
469         up_write(&oldmm->mmap_sem);
470         uprobe_end_dup_mmap();
471         return retval;
472 fail_nomem_anon_vma_fork:
473         mpol_put(vma_policy(tmp));
474 fail_nomem_policy:
475         kmem_cache_free(vm_area_cachep, tmp);
476 fail_nomem:
477         retval = -ENOMEM;
478         vm_unacct_memory(charge);
479         goto out;
480 }
481 
482 static inline int mm_alloc_pgd(struct mm_struct *mm)
483 {
484         mm->pgd = pgd_alloc(mm);
485         if (unlikely(!mm->pgd))
486                 return -ENOMEM;
487         return 0;
488 }
489 
490 static inline void mm_free_pgd(struct mm_struct *mm)
491 {
492         pgd_free(mm, mm->pgd);
493 }
494 #else
495 #define dup_mmap(mm, oldmm)     (0)
496 #define mm_alloc_pgd(mm)        (0)
497 #define mm_free_pgd(mm)
498 #endif /* CONFIG_MMU */
499 
500 __cacheline_aligned_in_smp DEFINE_SPINLOCK(mmlist_lock);
501 
502 #define allocate_mm()   (kmem_cache_alloc(mm_cachep, GFP_KERNEL))
503 #define free_mm(mm)     (kmem_cache_free(mm_cachep, (mm)))
504 
505 static unsigned long default_dump_filter = MMF_DUMP_FILTER_DEFAULT;
506 
507 static int __init coredump_filter_setup(char *s)
508 {
509         default_dump_filter =
510                 (simple_strtoul(s, NULL, 0) << MMF_DUMP_FILTER_SHIFT) &
511                 MMF_DUMP_FILTER_MASK;
512         return 1;
513 }
514 
515 __setup("coredump_filter=", coredump_filter_setup);
516 
517 #include <linux/init_task.h>
518 
519 static void mm_init_aio(struct mm_struct *mm)
520 {
521 #ifdef CONFIG_AIO
522         spin_lock_init(&mm->ioctx_lock);
523         mm->ioctx_table = NULL;
524 #endif
525 }
526 
527 static struct mm_struct *mm_init(struct mm_struct *mm, struct task_struct *p)
528 {
529         atomic_set(&mm->mm_users, 1);
530         atomic_set(&mm->mm_count, 1);
531         init_rwsem(&mm->mmap_sem);
532         INIT_LIST_HEAD(&mm->mmlist);
533         mm->flags = (current->mm) ?
534                 (current->mm->flags & MMF_INIT_MASK) : default_dump_filter;
535         mm->core_state = NULL;
536         atomic_long_set(&mm->nr_ptes, 0);
537         memset(&mm->rss_stat, 0, sizeof(mm->rss_stat));
538         spin_lock_init(&mm->page_table_lock);
539         mm_init_aio(mm);
540         mm_init_owner(mm, p);
541         clear_tlb_flush_pending(mm);
542 
543         if (likely(!mm_alloc_pgd(mm))) {
544                 mm->def_flags = 0;
545                 mmu_notifier_mm_init(mm);
546                 return mm;
547         }
548 
549         free_mm(mm);
550         return NULL;
551 }
552 
553 static void check_mm(struct mm_struct *mm)
554 {
555         int i;
556 
557         for (i = 0; i < NR_MM_COUNTERS; i++) {
558                 long x = atomic_long_read(&mm->rss_stat.count[i]);
559 
560                 if (unlikely(x))
561                         printk(KERN_ALERT "BUG: Bad rss-counter state "
562                                           "mm:%p idx:%d val:%ld\n", mm, i, x);
563         }
564 
565 #if defined(CONFIG_TRANSPARENT_HUGEPAGE) && !USE_SPLIT_PMD_PTLOCKS
566         VM_BUG_ON(mm->pmd_huge_pte);
567 #endif
568 }
569 
570 /*
571  * Allocate and initialize an mm_struct.
572  */
573 struct mm_struct *mm_alloc(void)
574 {
575         struct mm_struct *mm;
576 
577         mm = allocate_mm();
578         if (!mm)
579                 return NULL;
580 
581         memset(mm, 0, sizeof(*mm));
582         mm_init_cpumask(mm);
583         return mm_init(mm, current);
584 }
585 
586 /*
587  * Called when the last reference to the mm
588  * is dropped: either by a lazy thread or by
589  * mmput. Free the page directory and the mm.
590  */
591 void __mmdrop(struct mm_struct *mm)
592 {
593         BUG_ON(mm == &init_mm);
594         mm_free_pgd(mm);
595         destroy_context(mm);
596         mmu_notifier_mm_destroy(mm);
597         check_mm(mm);
598         free_mm(mm);
599 }
600 EXPORT_SYMBOL_GPL(__mmdrop);
601 
602 /*
603  * Decrement the use count and release all resources for an mm.
604  */
605 void mmput(struct mm_struct *mm)
606 {
607         might_sleep();
608 
609         if (atomic_dec_and_test(&mm->mm_users)) {
610                 uprobe_clear_state(mm);
611                 exit_aio(mm);
612                 ksm_exit(mm);
613                 khugepaged_exit(mm); /* must run before exit_mmap */
614                 exit_mmap(mm);
615                 set_mm_exe_file(mm, NULL);
616                 if (!list_empty(&mm->mmlist)) {
617                         spin_lock(&mmlist_lock);
618                         list_del(&mm->mmlist);
619                         spin_unlock(&mmlist_lock);
620                 }
621                 if (mm->binfmt)
622                         module_put(mm->binfmt->module);
623                 mmdrop(mm);
624         }
625 }
626 EXPORT_SYMBOL_GPL(mmput);
627 
628 void set_mm_exe_file(struct mm_struct *mm, struct file *new_exe_file)
629 {
630         if (new_exe_file)
631                 get_file(new_exe_file);
632         if (mm->exe_file)
633                 fput(mm->exe_file);
634         mm->exe_file = new_exe_file;
635 }
636 
637 struct file *get_mm_exe_file(struct mm_struct *mm)
638 {
639         struct file *exe_file;
640 
641         /* We need mmap_sem to protect against races with removal of exe_file */
642         down_read(&mm->mmap_sem);
643         exe_file = mm->exe_file;
644         if (exe_file)
645                 get_file(exe_file);
646         up_read(&mm->mmap_sem);
647         return exe_file;
648 }
649 
650 static void dup_mm_exe_file(struct mm_struct *oldmm, struct mm_struct *newmm)
651 {
652         /* It's safe to write the exe_file pointer without exe_file_lock because
653          * this is called during fork when the task is not yet in /proc */
654         newmm->exe_file = get_mm_exe_file(oldmm);
655 }
656 
657 /**
658  * get_task_mm - acquire a reference to the task's mm
659  *
660  * Returns %NULL if the task has no mm.  Checks PF_KTHREAD (meaning
661  * this kernel workthread has transiently adopted a user mm with use_mm,
662  * to do its AIO) is not set and if so returns a reference to it, after
663  * bumping up the use count.  User must release the mm via mmput()
664  * after use.  Typically used by /proc and ptrace.
665  */
666 struct mm_struct *get_task_mm(struct task_struct *task)
667 {
668         struct mm_struct *mm;
669 
670         task_lock(task);
671         mm = task->mm;
672         if (mm) {
673                 if (task->flags & PF_KTHREAD)
674                         mm = NULL;
675                 else
676                         atomic_inc(&mm->mm_users);
677         }
678         task_unlock(task);
679         return mm;
680 }
681 EXPORT_SYMBOL_GPL(get_task_mm);
682 
683 struct mm_struct *mm_access(struct task_struct *task, unsigned int mode)
684 {
685         struct mm_struct *mm;
686         int err;
687 
688         err =  mutex_lock_killable(&task->signal->cred_guard_mutex);
689         if (err)
690                 return ERR_PTR(err);
691 
692         mm = get_task_mm(task);
693         if (mm && mm != current->mm &&
694                         !ptrace_may_access(task, mode)) {
695                 mmput(mm);
696                 mm = ERR_PTR(-EACCES);
697         }
698         mutex_unlock(&task->signal->cred_guard_mutex);
699 
700         return mm;
701 }
702 
703 static void complete_vfork_done(struct task_struct *tsk)
704 {
705         struct completion *vfork;
706 
707         task_lock(tsk);
708         vfork = tsk->vfork_done;
709         if (likely(vfork)) {
710                 tsk->vfork_done = NULL;
711                 complete(vfork);
712         }
713         task_unlock(tsk);
714 }
715 
716 static int wait_for_vfork_done(struct task_struct *child,
717                                 struct completion *vfork)
718 {
719         int killed;
720 
721         freezer_do_not_count();
722         killed = wait_for_completion_killable(vfork);
723         freezer_count();
724 
725         if (killed) {
726                 task_lock(child);
727                 child->vfork_done = NULL;
728                 task_unlock(child);
729         }
730 
731         put_task_struct(child);
732         return killed;
733 }
734 
735 /* Please note the differences between mmput and mm_release.
736  * mmput is called whenever we stop holding onto a mm_struct,
737  * error success whatever.
738  *
739  * mm_release is called after a mm_struct has been removed
740  * from the current process.
741  *
742  * This difference is important for error handling, when we
743  * only half set up a mm_struct for a new process and need to restore
744  * the old one.  Because we mmput the new mm_struct before
745  * restoring the old one. . .
746  * Eric Biederman 10 January 1998
747  */
748 void mm_release(struct task_struct *tsk, struct mm_struct *mm)
749 {
750         /* Get rid of any futexes when releasing the mm */
751 #ifdef CONFIG_FUTEX
752         if (unlikely(tsk->robust_list)) {
753                 exit_robust_list(tsk);
754                 tsk->robust_list = NULL;
755         }
756 #ifdef CONFIG_COMPAT
757         if (unlikely(tsk->compat_robust_list)) {
758                 compat_exit_robust_list(tsk);
759                 tsk->compat_robust_list = NULL;
760         }
761 #endif
762         if (unlikely(!list_empty(&tsk->pi_state_list)))
763                 exit_pi_state_list(tsk);
764 #endif
765 
766         uprobe_free_utask(tsk);
767 
768         /* Get rid of any cached register state */
769         deactivate_mm(tsk, mm);
770 
771         /*
772          * If we're exiting normally, clear a user-space tid field if
773          * requested.  We leave this alone when dying by signal, to leave
774          * the value intact in a core dump, and to save the unnecessary
775          * trouble, say, a killed vfork parent shouldn't touch this mm.
776          * Userland only wants this done for a sys_exit.
777          */
778         if (tsk->clear_child_tid) {
779                 if (!(tsk->flags & PF_SIGNALED) &&
780                     atomic_read(&mm->mm_users) > 1) {
781                         /*
782                          * We don't check the error code - if userspace has
783                          * not set up a proper pointer then tough luck.
784                          */
785                         put_user(0, tsk->clear_child_tid);
786                         sys_futex(tsk->clear_child_tid, FUTEX_WAKE,
787                                         1, NULL, NULL, 0);
788                 }
789                 tsk->clear_child_tid = NULL;
790         }
791 
792         /*
793          * All done, finally we can wake up parent and return this mm to him.
794          * Also kthread_stop() uses this completion for synchronization.
795          */
796         if (tsk->vfork_done)
797                 complete_vfork_done(tsk);
798 }
799 
800 /*
801  * Allocate a new mm structure and copy contents from the
802  * mm structure of the passed in task structure.
803  */
804 struct mm_struct *dup_mm(struct task_struct *tsk)
805 {
806         struct mm_struct *mm, *oldmm = current->mm;
807         int err;
808 
809         if (!oldmm)
810                 return NULL;
811 
812         mm = allocate_mm();
813         if (!mm)
814                 goto fail_nomem;
815 
816         memcpy(mm, oldmm, sizeof(*mm));
817         mm_init_cpumask(mm);
818 
819 #if defined(CONFIG_TRANSPARENT_HUGEPAGE) && !USE_SPLIT_PMD_PTLOCKS
820         mm->pmd_huge_pte = NULL;
821 #endif
822         if (!mm_init(mm, tsk))
823                 goto fail_nomem;
824 
825         if (init_new_context(tsk, mm))
826                 goto fail_nocontext;
827 
828         dup_mm_exe_file(oldmm, mm);
829 
830         err = dup_mmap(mm, oldmm);
831         if (err)
832                 goto free_pt;
833 
834         mm->hiwater_rss = get_mm_rss(mm);
835         mm->hiwater_vm = mm->total_vm;
836 
837         if (mm->binfmt && !try_module_get(mm->binfmt->module))
838                 goto free_pt;
839 
840         return mm;
841 
842 free_pt:
843         /* don't put binfmt in mmput, we haven't got module yet */
844         mm->binfmt = NULL;
845         mmput(mm);
846 
847 fail_nomem:
848         return NULL;
849 
850 fail_nocontext:
851         /*
852          * If init_new_context() failed, we cannot use mmput() to free the mm
853          * because it calls destroy_context()
854          */
855         mm_free_pgd(mm);
856         free_mm(mm);
857         return NULL;
858 }
859 
860 static int copy_mm(unsigned long clone_flags, struct task_struct *tsk)
861 {
862         struct mm_struct *mm, *oldmm;
863         int retval;
864 
865         tsk->min_flt = tsk->maj_flt = 0;
866         tsk->nvcsw = tsk->nivcsw = 0;
867 #ifdef CONFIG_DETECT_HUNG_TASK
868         tsk->last_switch_count = tsk->nvcsw + tsk->nivcsw;
869 #endif
870 
871         tsk->mm = NULL;
872         tsk->active_mm = NULL;
873 
874         /*
875          * Are we cloning a kernel thread?
876          *
877          * We need to steal a active VM for that..
878          */
879         oldmm = current->mm;
880         if (!oldmm)
881                 return 0;
882 
883         if (clone_flags & CLONE_VM) {
884                 atomic_inc(&oldmm->mm_users);
885                 mm = oldmm;
886                 goto good_mm;
887         }
888 
889         retval = -ENOMEM;
890         mm = dup_mm(tsk);
891         if (!mm)
892                 goto fail_nomem;
893 
894 good_mm:
895         tsk->mm = mm;
896         tsk->active_mm = mm;
897         return 0;
898 
899 fail_nomem:
900         return retval;
901 }
902 
903 static int copy_fs(unsigned long clone_flags, struct task_struct *tsk)
904 {
905         struct fs_struct *fs = current->fs;
906         if (clone_flags & CLONE_FS) {
907                 /* tsk->fs is already what we want */
908                 spin_lock(&fs->lock);
909                 if (fs->in_exec) {
910                         spin_unlock(&fs->lock);
911                         return -EAGAIN;
912                 }
913                 fs->users++;
914                 spin_unlock(&fs->lock);
915                 return 0;
916         }
917         tsk->fs = copy_fs_struct(fs);
918         if (!tsk->fs)
919                 return -ENOMEM;
920         return 0;
921 }
922 
923 static int copy_files(unsigned long clone_flags, struct task_struct *tsk)
924 {
925         struct files_struct *oldf, *newf;
926         int error = 0;
927 
928         /*
929          * A background process may not have any files ...
930          */
931         oldf = current->files;
932         if (!oldf)
933                 goto out;
934 
935         if (clone_flags & CLONE_FILES) {
936                 atomic_inc(&oldf->count);
937                 goto out;
938         }
939 
940         newf = dup_fd(oldf, &error);
941         if (!newf)
942                 goto out;
943 
944         tsk->files = newf;
945         error = 0;
946 out:
947         return error;
948 }
949 
950 static int copy_io(unsigned long clone_flags, struct task_struct *tsk)
951 {
952 #ifdef CONFIG_BLOCK
953         struct io_context *ioc = current->io_context;
954         struct io_context *new_ioc;
955 
956         if (!ioc)
957                 return 0;
958         /*
959          * Share io context with parent, if CLONE_IO is set
960          */
961         if (clone_flags & CLONE_IO) {
962                 ioc_task_link(ioc);
963                 tsk->io_context = ioc;
964         } else if (ioprio_valid(ioc->ioprio)) {
965                 new_ioc = get_task_io_context(tsk, GFP_KERNEL, NUMA_NO_NODE);
966                 if (unlikely(!new_ioc))
967                         return -ENOMEM;
968 
969                 new_ioc->ioprio = ioc->ioprio;
970                 put_io_context(new_ioc);
971         }
972 #endif
973         return 0;
974 }
975 
976 static int copy_sighand(unsigned long clone_flags, struct task_struct *tsk)
977 {
978         struct sighand_struct *sig;
979 
980         if (clone_flags & CLONE_SIGHAND) {
981                 atomic_inc(&current->sighand->count);
982                 return 0;
983         }
984         sig = kmem_cache_alloc(sighand_cachep, GFP_KERNEL);
985         rcu_assign_pointer(tsk->sighand, sig);
986         if (!sig)
987                 return -ENOMEM;
988         atomic_set(&sig->count, 1);
989         memcpy(sig->action, current->sighand->action, sizeof(sig->action));
990         return 0;
991 }
992 
993 void __cleanup_sighand(struct sighand_struct *sighand)
994 {
995         if (atomic_dec_and_test(&sighand->count)) {
996                 signalfd_cleanup(sighand);
997                 kmem_cache_free(sighand_cachep, sighand);
998         }
999 }
1000 
1001 
1002 /*
1003  * Initialize POSIX timer handling for a thread group.
1004  */
1005 static void posix_cpu_timers_init_group(struct signal_struct *sig)
1006 {
1007         unsigned long cpu_limit;
1008 
1009         /* Thread group counters. */
1010         thread_group_cputime_init(sig);
1011 
1012         cpu_limit = ACCESS_ONCE(sig->rlim[RLIMIT_CPU].rlim_cur);
1013         if (cpu_limit != RLIM_INFINITY) {
1014                 sig->cputime_expires.prof_exp = secs_to_cputime(cpu_limit);
1015                 sig->cputimer.running = 1;
1016         }
1017 
1018         /* The timer lists. */
1019         INIT_LIST_HEAD(&sig->cpu_timers[0]);
1020         INIT_LIST_HEAD(&sig->cpu_timers[1]);
1021         INIT_LIST_HEAD(&sig->cpu_timers[2]);
1022 }
1023 
1024 static int copy_signal(unsigned long clone_flags, struct task_struct *tsk)
1025 {
1026         struct signal_struct *sig;
1027 
1028         if (clone_flags & CLONE_THREAD)
1029                 return 0;
1030 
1031         sig = kmem_cache_zalloc(signal_cachep, GFP_KERNEL);
1032         tsk->signal = sig;
1033         if (!sig)
1034                 return -ENOMEM;
1035 
1036         sig->nr_threads = 1;
1037         atomic_set(&sig->live, 1);
1038         atomic_set(&sig->sigcnt, 1);
1039         init_waitqueue_head(&sig->wait_chldexit);
1040         sig->curr_target = tsk;
1041         init_sigpending(&sig->shared_pending);
1042         INIT_LIST_HEAD(&sig->posix_timers);
1043 
1044         hrtimer_init(&sig->real_timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
1045         sig->real_timer.function = it_real_fn;
1046 
1047         task_lock(current->group_leader);
1048         memcpy(sig->rlim, current->signal->rlim, sizeof sig->rlim);
1049         task_unlock(current->group_leader);
1050 
1051         posix_cpu_timers_init_group(sig);
1052 
1053         tty_audit_fork(sig);
1054         sched_autogroup_fork(sig);
1055 
1056 #ifdef CONFIG_CGROUPS
1057         init_rwsem(&sig->group_rwsem);
1058 #endif
1059 
1060         sig->oom_score_adj = current->signal->oom_score_adj;
1061         sig->oom_score_adj_min = current->signal->oom_score_adj_min;
1062 
1063         sig->has_child_subreaper = current->signal->has_child_subreaper ||
1064                                    current->signal->is_child_subreaper;
1065 
1066         mutex_init(&sig->cred_guard_mutex);
1067 
1068         return 0;
1069 }
1070 
1071 static void copy_flags(unsigned long clone_flags, struct task_struct *p)
1072 {
1073         unsigned long new_flags = p->flags;
1074 
1075         new_flags &= ~(PF_SUPERPRIV | PF_WQ_WORKER);
1076         new_flags |= PF_FORKNOEXEC;
1077         p->flags = new_flags;
1078 }
1079 
1080 SYSCALL_DEFINE1(set_tid_address, int __user *, tidptr)
1081 {
1082         current->clear_child_tid = tidptr;
1083 
1084         return task_pid_vnr(current);
1085 }
1086 
1087 static void rt_mutex_init_task(struct task_struct *p)
1088 {
1089         raw_spin_lock_init(&p->pi_lock);
1090 #ifdef CONFIG_RT_MUTEXES
1091         plist_head_init(&p->pi_waiters);
1092         p->pi_blocked_on = NULL;
1093 #endif
1094 }
1095 
1096 #ifdef CONFIG_MM_OWNER
1097 void mm_init_owner(struct mm_struct *mm, struct task_struct *p)
1098 {
1099         mm->owner = p;
1100 }
1101 #endif /* CONFIG_MM_OWNER */
1102 
1103 /*
1104  * Initialize POSIX timer handling for a single task.
1105  */
1106 static void posix_cpu_timers_init(struct task_struct *tsk)
1107 {
1108         tsk->cputime_expires.prof_exp = 0;
1109         tsk->cputime_expires.virt_exp = 0;
1110         tsk->cputime_expires.sched_exp = 0;
1111         INIT_LIST_HEAD(&tsk->cpu_timers[0]);
1112         INIT_LIST_HEAD(&tsk->cpu_timers[1]);
1113         INIT_LIST_HEAD(&tsk->cpu_timers[2]);
1114 }
1115 
1116 static inline void
1117 init_task_pid(struct task_struct *task, enum pid_type type, struct pid *pid)
1118 {
1119          task->pids[type].pid = pid;
1120 }
1121 
1122 /*
1123  * This creates a new process as a copy of the old one,
1124  * but does not actually start it yet.
1125  *
1126  * It copies the registers, and all the appropriate
1127  * parts of the process environment (as per the clone
1128  * flags). The actual kick-off is left to the caller.
1129  */
1130 static struct task_struct *copy_process(unsigned long clone_flags,
1131                                         unsigned long stack_start,
1132                                         unsigned long stack_size,
1133                                         int __user *child_tidptr,
1134                                         struct pid *pid,
1135                                         int trace)
1136 {
1137         int retval;
1138         struct task_struct *p;
1139 
1140         if ((clone_flags & (CLONE_NEWNS|CLONE_FS)) == (CLONE_NEWNS|CLONE_FS))
1141                 return ERR_PTR(-EINVAL);
1142 
1143         if ((clone_flags & (CLONE_NEWUSER|CLONE_FS)) == (CLONE_NEWUSER|CLONE_FS))
1144                 return ERR_PTR(-EINVAL);
1145 
1146         /*
1147          * Thread groups must share signals as well, and detached threads
1148          * can only be started up within the thread group.
1149          */
1150         if ((clone_flags & CLONE_THREAD) && !(clone_flags & CLONE_SIGHAND))
1151                 return ERR_PTR(-EINVAL);
1152 
1153         /*
1154          * Shared signal handlers imply shared VM. By way of the above,
1155          * thread groups also imply shared VM. Blocking this case allows
1156          * for various simplifications in other code.
1157          */
1158         if ((clone_flags & CLONE_SIGHAND) && !(clone_flags & CLONE_VM))
1159                 return ERR_PTR(-EINVAL);
1160 
1161         /*
1162          * Siblings of global init remain as zombies on exit since they are
1163          * not reaped by their parent (swapper). To solve this and to avoid
1164          * multi-rooted process trees, prevent global and container-inits
1165          * from creating siblings.
1166          */
1167         if ((clone_flags & CLONE_PARENT) &&
1168                                 current->signal->flags & SIGNAL_UNKILLABLE)
1169                 return ERR_PTR(-EINVAL);
1170 
1171         /*
1172          * If the new process will be in a different pid or user namespace
1173          * do not allow it to share a thread group or signal handlers or
1174          * parent with the forking task.
1175          */
1176         if (clone_flags & CLONE_SIGHAND) {
1177                 if ((clone_flags & (CLONE_NEWUSER | CLONE_NEWPID)) ||
1178                     (task_active_pid_ns(current) !=
1179                                 current->nsproxy->pid_ns_for_children))
1180                         return ERR_PTR(-EINVAL);
1181         }
1182 
1183         retval = security_task_create(clone_flags);
1184         if (retval)
1185                 goto fork_out;
1186 
1187         retval = -ENOMEM;
1188         p = dup_task_struct(current);
1189         if (!p)
1190                 goto fork_out;
1191 
1192         ftrace_graph_init_task(p);
1193         get_seccomp_filter(p);
1194 
1195         rt_mutex_init_task(p);
1196 
1197 #ifdef CONFIG_PROVE_LOCKING
1198         DEBUG_LOCKS_WARN_ON(!p->hardirqs_enabled);
1199         DEBUG_LOCKS_WARN_ON(!p->softirqs_enabled);
1200 #endif
1201         retval = -EAGAIN;
1202         if (atomic_read(&p->real_cred->user->processes) >=
1203                         task_rlimit(p, RLIMIT_NPROC)) {
1204                 if (p->real_cred->user != INIT_USER &&
1205                     !capable(CAP_SYS_RESOURCE) && !capable(CAP_SYS_ADMIN))
1206                         goto bad_fork_free;
1207         }
1208         current->flags &= ~PF_NPROC_EXCEEDED;
1209 
1210         retval = copy_creds(p, clone_flags);
1211         if (retval < 0)
1212                 goto bad_fork_free;
1213 
1214         /*
1215          * If multiple threads are within copy_process(), then this check
1216          * triggers too late. This doesn't hurt, the check is only there
1217          * to stop root fork bombs.
1218          */
1219         retval = -EAGAIN;
1220         if (nr_threads >= max_threads)
1221                 goto bad_fork_cleanup_count;
1222 
1223         if (!try_module_get(task_thread_info(p)->exec_domain->module))
1224                 goto bad_fork_cleanup_count;
1225 
1226         p->did_exec = 0;
1227         delayacct_tsk_init(p);  /* Must remain after dup_task_struct() */
1228         copy_flags(clone_flags, p);
1229         INIT_LIST_HEAD(&p->children);
1230         INIT_LIST_HEAD(&p->sibling);
1231         rcu_copy_process(p);
1232         p->vfork_done = NULL;
1233         spin_lock_init(&p->alloc_lock);
1234 
1235         init_sigpending(&p->pending);
1236 
1237         p->utime = p->stime = p->gtime = 0;
1238         p->utimescaled = p->stimescaled = 0;
1239 #ifndef CONFIG_VIRT_CPU_ACCOUNTING_NATIVE
1240         p->prev_cputime.utime = p->prev_cputime.stime = 0;
1241 #endif
1242 #ifdef CONFIG_VIRT_CPU_ACCOUNTING_GEN
1243         seqlock_init(&p->vtime_seqlock);
1244         p->vtime_snap = 0;
1245         p->vtime_snap_whence = VTIME_SLEEPING;
1246 #endif
1247 
1248 #if defined(SPLIT_RSS_COUNTING)
1249         memset(&p->rss_stat, 0, sizeof(p->rss_stat));
1250 #endif
1251 
1252         p->default_timer_slack_ns = current->timer_slack_ns;
1253 
1254         task_io_accounting_init(&p->ioac);
1255         acct_clear_integrals(p);
1256 
1257         posix_cpu_timers_init(p);
1258 
1259         do_posix_clock_monotonic_gettime(&p->start_time);
1260         p->real_start_time = p->start_time;
1261         monotonic_to_bootbased(&p->real_start_time);
1262         p->io_context = NULL;
1263         p->audit_context = NULL;
1264         if (clone_flags & CLONE_THREAD)
1265                 threadgroup_change_begin(current);
1266         cgroup_fork(p);
1267 #ifdef CONFIG_NUMA
1268         p->mempolicy = mpol_dup(p->mempolicy);
1269         if (IS_ERR(p->mempolicy)) {
1270                 retval = PTR_ERR(p->mempolicy);
1271                 p->mempolicy = NULL;
1272                 goto bad_fork_cleanup_cgroup;
1273         }
1274         mpol_fix_fork_child_flag(p);
1275 #endif
1276 #ifdef CONFIG_CPUSETS
1277         p->cpuset_mem_spread_rotor = NUMA_NO_NODE;
1278         p->cpuset_slab_spread_rotor = NUMA_NO_NODE;
1279         seqcount_init(&p->mems_allowed_seq);
1280 #endif
1281 #ifdef CONFIG_TRACE_IRQFLAGS
1282         p->irq_events = 0;
1283         p->hardirqs_enabled = 0;
1284         p->hardirq_enable_ip = 0;
1285         p->hardirq_enable_event = 0;
1286         p->hardirq_disable_ip = _THIS_IP_;
1287         p->hardirq_disable_event = 0;
1288         p->softirqs_enabled = 1;
1289         p->softirq_enable_ip = _THIS_IP_;
1290         p->softirq_enable_event = 0;
1291         p->softirq_disable_ip = 0;
1292         p->softirq_disable_event = 0;
1293         p->hardirq_context = 0;
1294         p->softirq_context = 0;
1295 #endif
1296 #ifdef CONFIG_LOCKDEP
1297         p->lockdep_depth = 0; /* no locks held yet */
1298         p->curr_chain_key = 0;
1299         p->lockdep_recursion = 0;
1300 #endif
1301 
1302 #ifdef CONFIG_DEBUG_MUTEXES
1303         p->blocked_on = NULL; /* not blocked yet */
1304 #endif
1305 #ifdef CONFIG_MEMCG
1306         p->memcg_batch.do_batch = 0;
1307         p->memcg_batch.memcg = NULL;
1308 #endif
1309 #ifdef CONFIG_BCACHE
1310         p->sequential_io        = 0;
1311         p->sequential_io_avg    = 0;
1312 #endif
1313 
1314         /* Perform scheduler related setup. Assign this task to a CPU. */
1315         sched_fork(clone_flags, p);
1316 
1317         retval = perf_event_init_task(p);
1318         if (retval)
1319                 goto bad_fork_cleanup_policy;
1320         retval = audit_alloc(p);
1321         if (retval)
1322                 goto bad_fork_cleanup_policy;
1323         retval = ccs_alloc_task_security(p);
1324         if (retval)
1325                 goto bad_fork_cleanup_audit;
1326         /* copy all the process information */
1327         retval = copy_semundo(clone_flags, p);
1328         if (retval)
1329                 goto bad_fork_cleanup_audit;
1330         retval = copy_files(clone_flags, p);
1331         if (retval)
1332                 goto bad_fork_cleanup_semundo;
1333         retval = copy_fs(clone_flags, p);
1334         if (retval)
1335                 goto bad_fork_cleanup_files;
1336         retval = copy_sighand(clone_flags, p);
1337         if (retval)
1338                 goto bad_fork_cleanup_fs;
1339         retval = copy_signal(clone_flags, p);
1340         if (retval)
1341                 goto bad_fork_cleanup_sighand;
1342         retval = copy_mm(clone_flags, p);
1343         if (retval)
1344                 goto bad_fork_cleanup_signal;
1345         retval = copy_namespaces(clone_flags, p);
1346         if (retval)
1347                 goto bad_fork_cleanup_mm;
1348         retval = copy_io(clone_flags, p);
1349         if (retval)
1350                 goto bad_fork_cleanup_namespaces;
1351         retval = copy_thread(clone_flags, stack_start, stack_size, p);
1352         if (retval)
1353                 goto bad_fork_cleanup_io;
1354 
1355         if (pid != &init_struct_pid) {
1356                 retval = -ENOMEM;
1357                 pid = alloc_pid(p->nsproxy->pid_ns_for_children);
1358                 if (!pid)
1359                         goto bad_fork_cleanup_io;
1360         }
1361 
1362         p->set_child_tid = (clone_flags & CLONE_CHILD_SETTID) ? child_tidptr : NULL;
1363         /*
1364          * Clear TID on mm_release()?
1365          */
1366         p->clear_child_tid = (clone_flags & CLONE_CHILD_CLEARTID) ? child_tidptr : NULL;
1367 #ifdef CONFIG_BLOCK
1368         p->plug = NULL;
1369 #endif
1370 #ifdef CONFIG_FUTEX
1371         p->robust_list = NULL;
1372 #ifdef CONFIG_COMPAT
1373         p->compat_robust_list = NULL;
1374 #endif
1375         INIT_LIST_HEAD(&p->pi_state_list);
1376         p->pi_state_cache = NULL;
1377 #endif
1378         /*
1379          * sigaltstack should be cleared when sharing the same VM
1380          */
1381         if ((clone_flags & (CLONE_VM|CLONE_VFORK)) == CLONE_VM)
1382                 p->sas_ss_sp = p->sas_ss_size = 0;
1383 
1384         /*
1385          * Syscall tracing and stepping should be turned off in the
1386          * child regardless of CLONE_PTRACE.
1387          */
1388         user_disable_single_step(p);
1389         clear_tsk_thread_flag(p, TIF_SYSCALL_TRACE);
1390 #ifdef TIF_SYSCALL_EMU
1391         clear_tsk_thread_flag(p, TIF_SYSCALL_EMU);
1392 #endif
1393         clear_all_latency_tracing(p);
1394 
1395         /* ok, now we should be set up.. */
1396         p->pid = pid_nr(pid);
1397         if (clone_flags & CLONE_THREAD) {
1398                 p->exit_signal = -1;
1399                 p->group_leader = current->group_leader;
1400                 p->tgid = current->tgid;
1401         } else {
1402                 if (clone_flags & CLONE_PARENT)
1403                         p->exit_signal = current->group_leader->exit_signal;
1404                 else
1405                         p->exit_signal = (clone_flags & CSIGNAL);
1406                 p->group_leader = p;
1407                 p->tgid = p->pid;
1408         }
1409 
1410         p->pdeath_signal = 0;
1411         p->exit_state = 0;
1412 
1413         p->nr_dirtied = 0;
1414         p->nr_dirtied_pause = 128 >> (PAGE_SHIFT - 10);
1415         p->dirty_paused_when = 0;
1416 
1417         INIT_LIST_HEAD(&p->thread_group);
1418         p->task_works = NULL;
1419 
1420         /*
1421          * Make it visible to the rest of the system, but dont wake it up yet.
1422          * Need tasklist lock for parent etc handling!
1423          */
1424         write_lock_irq(&tasklist_lock);
1425 
1426         /* CLONE_PARENT re-uses the old parent */
1427         if (clone_flags & (CLONE_PARENT|CLONE_THREAD)) {
1428                 p->real_parent = current->real_parent;
1429                 p->parent_exec_id = current->parent_exec_id;
1430         } else {
1431                 p->real_parent = current;
1432                 p->parent_exec_id = current->self_exec_id;
1433         }
1434 
1435         spin_lock(&current->sighand->siglock);
1436 
1437         /*
1438          * Process group and session signals need to be delivered to just the
1439          * parent before the fork or both the parent and the child after the
1440          * fork. Restart if a signal comes in before we add the new process to
1441          * it's process group.
1442          * A fatal signal pending means that current will exit, so the new
1443          * thread can't slip out of an OOM kill (or normal SIGKILL).
1444         */
1445         recalc_sigpending();
1446         if (signal_pending(current)) {
1447                 spin_unlock(&current->sighand->siglock);
1448                 write_unlock_irq(&tasklist_lock);
1449                 retval = -ERESTARTNOINTR;
1450                 goto bad_fork_free_pid;
1451         }
1452 
1453         if (likely(p->pid)) {
1454                 ptrace_init_task(p, (clone_flags & CLONE_PTRACE) || trace);
1455 
1456                 init_task_pid(p, PIDTYPE_PID, pid);
1457                 if (thread_group_leader(p)) {
1458                         init_task_pid(p, PIDTYPE_PGID, task_pgrp(current));
1459                         init_task_pid(p, PIDTYPE_SID, task_session(current));
1460 
1461                         if (is_child_reaper(pid)) {
1462                                 ns_of_pid(pid)->child_reaper = p;
1463                                 p->signal->flags |= SIGNAL_UNKILLABLE;
1464                         }
1465 
1466                         p->signal->leader_pid = pid;
1467                         p->signal->tty = tty_kref_get(current->signal->tty);
1468                         list_add_tail(&p->sibling, &p->real_parent->children);
1469                         list_add_tail_rcu(&p->tasks, &init_task.tasks);
1470                         attach_pid(p, PIDTYPE_PGID);
1471                         attach_pid(p, PIDTYPE_SID);
1472                         __this_cpu_inc(process_counts);
1473                 } else {
1474                         current->signal->nr_threads++;
1475                         atomic_inc(&current->signal->live);
1476                         atomic_inc(&current->signal->sigcnt);
1477                         list_add_tail_rcu(&p->thread_group,
1478                                           &p->group_leader->thread_group);
1479                 }
1480                 attach_pid(p, PIDTYPE_PID);
1481                 nr_threads++;
1482         }
1483 
1484         total_forks++;
1485         spin_unlock(&current->sighand->siglock);
1486         write_unlock_irq(&tasklist_lock);
1487         proc_fork_connector(p);
1488         cgroup_post_fork(p);
1489         if (clone_flags & CLONE_THREAD)
1490                 threadgroup_change_end(current);
1491         perf_event_fork(p);
1492 
1493         trace_task_newtask(p, clone_flags);
1494         uprobe_copy_process(p, clone_flags);
1495 
1496         return p;
1497 
1498 bad_fork_free_pid:
1499         if (pid != &init_struct_pid)
1500                 free_pid(pid);
1501 bad_fork_cleanup_io:
1502         if (p->io_context)
1503                 exit_io_context(p);
1504 bad_fork_cleanup_namespaces:
1505         exit_task_namespaces(p);
1506 bad_fork_cleanup_mm:
1507         if (p->mm)
1508                 mmput(p->mm);
1509 bad_fork_cleanup_signal:
1510         if (!(clone_flags & CLONE_THREAD))
1511                 free_signal_struct(p->signal);
1512 bad_fork_cleanup_sighand:
1513         __cleanup_sighand(p->sighand);
1514 bad_fork_cleanup_fs:
1515         exit_fs(p); /* blocking */
1516 bad_fork_cleanup_files:
1517         exit_files(p); /* blocking */
1518 bad_fork_cleanup_semundo:
1519         exit_sem(p);
1520 bad_fork_cleanup_audit:
1521         audit_free(p);
1522         ccs_free_task_security(p);
1523 bad_fork_cleanup_policy:
1524         perf_event_free_task(p);
1525 #ifdef CONFIG_NUMA
1526         mpol_put(p->mempolicy);
1527 bad_fork_cleanup_cgroup:
1528 #endif
1529         if (clone_flags & CLONE_THREAD)
1530                 threadgroup_change_end(current);
1531         cgroup_exit(p, 0);
1532         delayacct_tsk_free(p);
1533         module_put(task_thread_info(p)->exec_domain->module);
1534 bad_fork_cleanup_count:
1535         atomic_dec(&p->cred->user->processes);
1536         exit_creds(p);
1537 bad_fork_free:
1538         free_task(p);
1539 fork_out:
1540         return ERR_PTR(retval);
1541 }
1542 
1543 static inline void init_idle_pids(struct pid_link *links)
1544 {
1545         enum pid_type type;
1546 
1547         for (type = PIDTYPE_PID; type < PIDTYPE_MAX; ++type) {
1548                 INIT_HLIST_NODE(&links[type].node); /* not really needed */
1549                 links[type].pid = &init_struct_pid;
1550         }
1551 }
1552 
1553 struct task_struct *fork_idle(int cpu)
1554 {
1555         struct task_struct *task;
1556         task = copy_process(CLONE_VM, 0, 0, NULL, &init_struct_pid, 0);
1557         if (!IS_ERR(task)) {
1558                 init_idle_pids(task->pids);
1559                 init_idle(task, cpu);
1560         }
1561 
1562         return task;
1563 }
1564 
1565 /*
1566  *  Ok, this is the main fork-routine.
1567  *
1568  * It copies the process, and if successful kick-starts
1569  * it and waits for it to finish using the VM if required.
1570  */
1571 long do_fork(unsigned long clone_flags,
1572               unsigned long stack_start,
1573               unsigned long stack_size,
1574               int __user *parent_tidptr,
1575               int __user *child_tidptr)
1576 {
1577         struct task_struct *p;
1578         int trace = 0;
1579         long nr;
1580 
1581         /*
1582          * Determine whether and which event to report to ptracer.  When
1583          * called from kernel_thread or CLONE_UNTRACED is explicitly
1584          * requested, no event is reported; otherwise, report if the event
1585          * for the type of forking is enabled.
1586          */
1587         if (!(clone_flags & CLONE_UNTRACED)) {
1588                 if (clone_flags & CLONE_VFORK)
1589                         trace = PTRACE_EVENT_VFORK;
1590                 else if ((clone_flags & CSIGNAL) != SIGCHLD)
1591                         trace = PTRACE_EVENT_CLONE;
1592                 else
1593                         trace = PTRACE_EVENT_FORK;
1594 
1595                 if (likely(!ptrace_event_enabled(current, trace)))
1596                         trace = 0;
1597         }
1598 
1599         p = copy_process(clone_flags, stack_start, stack_size,
1600                          child_tidptr, NULL, trace);
1601         /*
1602          * Do this prior waking up the new thread - the thread pointer
1603          * might get invalid after that point, if the thread exits quickly.
1604          */
1605         if (!IS_ERR(p)) {
1606                 struct completion vfork;
1607 
1608                 trace_sched_process_fork(current, p);
1609 
1610                 nr = task_pid_vnr(p);
1611 
1612                 if (clone_flags & CLONE_PARENT_SETTID)
1613                         put_user(nr, parent_tidptr);
1614 
1615                 if (clone_flags & CLONE_VFORK) {
1616                         p->vfork_done = &vfork;
1617                         init_completion(&vfork);
1618                         get_task_struct(p);
1619                 }
1620 
1621                 wake_up_new_task(p);
1622 
1623                 /* forking complete and child started to run, tell ptracer */
1624                 if (unlikely(trace))
1625                         ptrace_event(trace, nr);
1626 
1627                 if (clone_flags & CLONE_VFORK) {
1628                         if (!wait_for_vfork_done(p, &vfork))
1629                                 ptrace_event(PTRACE_EVENT_VFORK_DONE, nr);
1630                 }
1631         } else {
1632                 nr = PTR_ERR(p);
1633         }
1634         return nr;
1635 }
1636 
1637 /*
1638  * Create a kernel thread.
1639  */
1640 pid_t kernel_thread(int (*fn)(void *), void *arg, unsigned long flags)
1641 {
1642         return do_fork(flags|CLONE_VM|CLONE_UNTRACED, (unsigned long)fn,
1643                 (unsigned long)arg, NULL, NULL);
1644 }
1645 
1646 #ifdef __ARCH_WANT_SYS_FORK
1647 SYSCALL_DEFINE0(fork)
1648 {
1649 #ifdef CONFIG_MMU
1650         return do_fork(SIGCHLD, 0, 0, NULL, NULL);
1651 #else
1652         /* can not support in nommu mode */
1653         return(-EINVAL);
1654 #endif
1655 }
1656 #endif
1657 
1658 #ifdef __ARCH_WANT_SYS_VFORK
1659 SYSCALL_DEFINE0(vfork)
1660 {
1661         return do_fork(CLONE_VFORK | CLONE_VM | SIGCHLD, 0, 
1662                         0, NULL, NULL);
1663 }
1664 #endif
1665 
1666 #ifdef __ARCH_WANT_SYS_CLONE
1667 #ifdef CONFIG_CLONE_BACKWARDS
1668 SYSCALL_DEFINE5(clone, unsigned long, clone_flags, unsigned long, newsp,
1669                  int __user *, parent_tidptr,
1670                  int, tls_val,
1671                  int __user *, child_tidptr)
1672 #elif defined(CONFIG_CLONE_BACKWARDS2)
1673 SYSCALL_DEFINE5(clone, unsigned long, newsp, unsigned long, clone_flags,
1674                  int __user *, parent_tidptr,
1675                  int __user *, child_tidptr,
1676                  int, tls_val)
1677 #elif defined(CONFIG_CLONE_BACKWARDS3)
1678 SYSCALL_DEFINE6(clone, unsigned long, clone_flags, unsigned long, newsp,
1679                 int, stack_size,
1680                 int __user *, parent_tidptr,
1681                 int __user *, child_tidptr,
1682                 int, tls_val)
1683 #else
1684 SYSCALL_DEFINE5(clone, unsigned long, clone_flags, unsigned long, newsp,
1685                  int __user *, parent_tidptr,
1686                  int __user *, child_tidptr,
1687                  int, tls_val)
1688 #endif
1689 {
1690         return do_fork(clone_flags, newsp, 0, parent_tidptr, child_tidptr);
1691 }
1692 #endif
1693 
1694 #ifndef ARCH_MIN_MMSTRUCT_ALIGN
1695 #define ARCH_MIN_MMSTRUCT_ALIGN 0
1696 #endif
1697 
1698 static void sighand_ctor(void *data)
1699 {
1700         struct sighand_struct *sighand = data;
1701 
1702         spin_lock_init(&sighand->siglock);
1703         init_waitqueue_head(&sighand->signalfd_wqh);
1704 }
1705 
1706 void __init proc_caches_init(void)
1707 {
1708         sighand_cachep = kmem_cache_create("sighand_cache",
1709                         sizeof(struct sighand_struct), 0,
1710                         SLAB_HWCACHE_ALIGN|SLAB_PANIC|SLAB_DESTROY_BY_RCU|
1711                         SLAB_NOTRACK, sighand_ctor);
1712         signal_cachep = kmem_cache_create("signal_cache",
1713                         sizeof(struct signal_struct), 0,
1714                         SLAB_HWCACHE_ALIGN|SLAB_PANIC|SLAB_NOTRACK, NULL);
1715         files_cachep = kmem_cache_create("files_cache",
1716                         sizeof(struct files_struct), 0,
1717                         SLAB_HWCACHE_ALIGN|SLAB_PANIC|SLAB_NOTRACK, NULL);
1718         fs_cachep = kmem_cache_create("fs_cache",
1719                         sizeof(struct fs_struct), 0,
1720                         SLAB_HWCACHE_ALIGN|SLAB_PANIC|SLAB_NOTRACK, NULL);
1721         /*
1722          * FIXME! The "sizeof(struct mm_struct)" currently includes the
1723          * whole struct cpumask for the OFFSTACK case. We could change
1724          * this to *only* allocate as much of it as required by the
1725          * maximum number of CPU's we can ever have.  The cpumask_allocation
1726          * is at the end of the structure, exactly for that reason.
1727          */
1728         mm_cachep = kmem_cache_create("mm_struct",
1729                         sizeof(struct mm_struct), ARCH_MIN_MMSTRUCT_ALIGN,
1730                         SLAB_HWCACHE_ALIGN|SLAB_PANIC|SLAB_NOTRACK, NULL);
1731         vm_area_cachep = KMEM_CACHE(vm_area_struct, SLAB_PANIC);
1732         mmap_init();
1733         nsproxy_cache_init();
1734 }
1735 
1736 /*
1737  * Check constraints on flags passed to the unshare system call.
1738  */
1739 static int check_unshare_flags(unsigned long unshare_flags)
1740 {
1741         if (unshare_flags & ~(CLONE_THREAD|CLONE_FS|CLONE_NEWNS|CLONE_SIGHAND|
1742                                 CLONE_VM|CLONE_FILES|CLONE_SYSVSEM|
1743                                 CLONE_NEWUTS|CLONE_NEWIPC|CLONE_NEWNET|
1744                                 CLONE_NEWUSER|CLONE_NEWPID))
1745                 return -EINVAL;
1746         /*
1747          * Not implemented, but pretend it works if there is nothing to
1748          * unshare. Note that unsharing CLONE_THREAD or CLONE_SIGHAND
1749          * needs to unshare vm.
1750          */
1751         if (unshare_flags & (CLONE_THREAD | CLONE_SIGHAND | CLONE_VM)) {
1752                 /* FIXME: get_task_mm() increments ->mm_users */
1753                 if (atomic_read(&current->mm->mm_users) > 1)
1754                         return -EINVAL;
1755         }
1756 
1757         return 0;
1758 }
1759 
1760 /*
1761  * Unshare the filesystem structure if it is being shared
1762  */
1763 static int unshare_fs(unsigned long unshare_flags, struct fs_struct **new_fsp)
1764 {
1765         struct fs_struct *fs = current->fs;
1766 
1767         if (!(unshare_flags & CLONE_FS) || !fs)
1768                 return 0;
1769 
1770         /* don't need lock here; in the worst case we'll do useless copy */
1771         if (fs->users == 1)
1772                 return 0;
1773 
1774         *new_fsp = copy_fs_struct(fs);
1775         if (!*new_fsp)
1776                 return -ENOMEM;
1777 
1778         return 0;
1779 }
1780 
1781 /*
1782  * Unshare file descriptor table if it is being shared
1783  */
1784 static int unshare_fd(unsigned long unshare_flags, struct files_struct **new_fdp)
1785 {
1786         struct files_struct *fd = current->files;
1787         int error = 0;
1788 
1789         if ((unshare_flags & CLONE_FILES) &&
1790             (fd && atomic_read(&fd->count) > 1)) {
1791                 *new_fdp = dup_fd(fd, &error);
1792                 if (!*new_fdp)
1793                         return error;
1794         }
1795 
1796         return 0;
1797 }
1798 
1799 /*
1800  * unshare allows a process to 'unshare' part of the process
1801  * context which was originally shared using clone.  copy_*
1802  * functions used by do_fork() cannot be used here directly
1803  * because they modify an inactive task_struct that is being
1804  * constructed. Here we are modifying the current, active,
1805  * task_struct.
1806  */
1807 SYSCALL_DEFINE1(unshare, unsigned long, unshare_flags)
1808 {
1809         struct fs_struct *fs, *new_fs = NULL;
1810         struct files_struct *fd, *new_fd = NULL;
1811         struct cred *new_cred = NULL;
1812         struct nsproxy *new_nsproxy = NULL;
1813         int do_sysvsem = 0;
1814         int err;
1815 
1816         /*
1817          * If unsharing a user namespace must also unshare the thread.
1818          */
1819         if (unshare_flags & CLONE_NEWUSER)
1820                 unshare_flags |= CLONE_THREAD | CLONE_FS;
1821         /*
1822          * If unsharing a thread from a thread group, must also unshare vm.
1823          */
1824         if (unshare_flags & CLONE_THREAD)
1825                 unshare_flags |= CLONE_VM;
1826         /*
1827          * If unsharing vm, must also unshare signal handlers.
1828          */
1829         if (unshare_flags & CLONE_VM)
1830                 unshare_flags |= CLONE_SIGHAND;
1831         /*
1832          * If unsharing namespace, must also unshare filesystem information.
1833          */
1834         if (unshare_flags & CLONE_NEWNS)
1835                 unshare_flags |= CLONE_FS;
1836 
1837         err = check_unshare_flags(unshare_flags);
1838         if (err)
1839                 goto bad_unshare_out;
1840         /*
1841          * CLONE_NEWIPC must also detach from the undolist: after switching
1842          * to a new ipc namespace, the semaphore arrays from the old
1843          * namespace are unreachable.
1844          */
1845         if (unshare_flags & (CLONE_NEWIPC|CLONE_SYSVSEM))
1846                 do_sysvsem = 1;
1847         err = unshare_fs(unshare_flags, &new_fs);
1848         if (err)
1849                 goto bad_unshare_out;
1850         err = unshare_fd(unshare_flags, &new_fd);
1851         if (err)
1852                 goto bad_unshare_cleanup_fs;
1853         err = unshare_userns(unshare_flags, &new_cred);
1854         if (err)
1855                 goto bad_unshare_cleanup_fd;
1856         err = unshare_nsproxy_namespaces(unshare_flags, &new_nsproxy,
1857                                          new_cred, new_fs);
1858         if (err)
1859                 goto bad_unshare_cleanup_cred;
1860 
1861         if (new_fs || new_fd || do_sysvsem || new_cred || new_nsproxy) {
1862                 if (do_sysvsem) {
1863                         /*
1864                          * CLONE_SYSVSEM is equivalent to sys_exit().
1865                          */
1866                         exit_sem(current);
1867                 }
1868 
1869                 if (new_nsproxy)
1870                         switch_task_namespaces(current, new_nsproxy);
1871 
1872                 task_lock(current);
1873 
1874                 if (new_fs) {
1875                         fs = current->fs;
1876                         spin_lock(&fs->lock);
1877                         current->fs = new_fs;
1878                         if (--fs->users)
1879                                 new_fs = NULL;
1880                         else
1881                                 new_fs = fs;
1882                         spin_unlock(&fs->lock);
1883                 }
1884 
1885                 if (new_fd) {
1886                         fd = current->files;
1887                         current->files = new_fd;
1888                         new_fd = fd;
1889                 }
1890 
1891                 task_unlock(current);
1892 
1893                 if (new_cred) {
1894                         /* Install the new user namespace */
1895                         commit_creds(new_cred);
1896                         new_cred = NULL;
1897                 }
1898         }
1899 
1900 bad_unshare_cleanup_cred:
1901         if (new_cred)
1902                 put_cred(new_cred);
1903 bad_unshare_cleanup_fd:
1904         if (new_fd)
1905                 put_files_struct(new_fd);
1906 
1907 bad_unshare_cleanup_fs:
1908         if (new_fs)
1909                 free_fs_struct(new_fs);
1910 
1911 bad_unshare_out:
1912         return err;
1913 }
1914 
1915 /*
1916  *      Helper to unshare the files of the current task.
1917  *      We don't want to expose copy_files internals to
1918  *      the exec layer of the kernel.
1919  */
1920 
1921 int unshare_files(struct files_struct **displaced)
1922 {
1923         struct task_struct *task = current;
1924         struct files_struct *copy = NULL;
1925         int error;
1926 
1927         error = unshare_fd(CLONE_FILES, &copy);
1928         if (error || !copy) {
1929                 *displaced = NULL;
1930                 return error;
1931         }
1932         *displaced = task->files;
1933         task_lock(task);
1934         task->files = copy;
1935         task_unlock(task);
1936         return 0;
1937 }
1938 

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