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TOMOYO Linux Cross Reference
Linux/kernel/seccomp.c

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  1 /*
  2  * linux/kernel/seccomp.c
  3  *
  4  * Copyright 2004-2005  Andrea Arcangeli <andrea@cpushare.com>
  5  *
  6  * Copyright (C) 2012 Google, Inc.
  7  * Will Drewry <wad@chromium.org>
  8  *
  9  * This defines a simple but solid secure-computing facility.
 10  *
 11  * Mode 1 uses a fixed list of allowed system calls.
 12  * Mode 2 allows user-defined system call filters in the form
 13  *        of Berkeley Packet Filters/Linux Socket Filters.
 14  */
 15 
 16 #include <linux/atomic.h>
 17 #include <linux/audit.h>
 18 #include <linux/compat.h>
 19 #include <linux/sched.h>
 20 #include <linux/seccomp.h>
 21 #include <linux/slab.h>
 22 #include <linux/syscalls.h>
 23 
 24 #ifdef CONFIG_HAVE_ARCH_SECCOMP_FILTER
 25 #include <asm/syscall.h>
 26 #endif
 27 
 28 #ifdef CONFIG_SECCOMP_FILTER
 29 #include <linux/filter.h>
 30 #include <linux/pid.h>
 31 #include <linux/ptrace.h>
 32 #include <linux/security.h>
 33 #include <linux/tracehook.h>
 34 #include <linux/uaccess.h>
 35 
 36 /**
 37  * struct seccomp_filter - container for seccomp BPF programs
 38  *
 39  * @usage: reference count to manage the object lifetime.
 40  *         get/put helpers should be used when accessing an instance
 41  *         outside of a lifetime-guarded section.  In general, this
 42  *         is only needed for handling filters shared across tasks.
 43  * @prev: points to a previously installed, or inherited, filter
 44  * @len: the number of instructions in the program
 45  * @insnsi: the BPF program instructions to evaluate
 46  *
 47  * seccomp_filter objects are organized in a tree linked via the @prev
 48  * pointer.  For any task, it appears to be a singly-linked list starting
 49  * with current->seccomp.filter, the most recently attached or inherited filter.
 50  * However, multiple filters may share a @prev node, by way of fork(), which
 51  * results in a unidirectional tree existing in memory.  This is similar to
 52  * how namespaces work.
 53  *
 54  * seccomp_filter objects should never be modified after being attached
 55  * to a task_struct (other than @usage).
 56  */
 57 struct seccomp_filter {
 58         atomic_t usage;
 59         struct seccomp_filter *prev;
 60         struct bpf_prog *prog;
 61 };
 62 
 63 /* Limit any path through the tree to 256KB worth of instructions. */
 64 #define MAX_INSNS_PER_PATH ((1 << 18) / sizeof(struct sock_filter))
 65 
 66 /*
 67  * Endianness is explicitly ignored and left for BPF program authors to manage
 68  * as per the specific architecture.
 69  */
 70 static void populate_seccomp_data(struct seccomp_data *sd)
 71 {
 72         struct task_struct *task = current;
 73         struct pt_regs *regs = task_pt_regs(task);
 74         unsigned long args[6];
 75 
 76         sd->nr = syscall_get_nr(task, regs);
 77         sd->arch = syscall_get_arch();
 78         syscall_get_arguments(task, regs, 0, 6, args);
 79         sd->args[0] = args[0];
 80         sd->args[1] = args[1];
 81         sd->args[2] = args[2];
 82         sd->args[3] = args[3];
 83         sd->args[4] = args[4];
 84         sd->args[5] = args[5];
 85         sd->instruction_pointer = KSTK_EIP(task);
 86 }
 87 
 88 /**
 89  *      seccomp_check_filter - verify seccomp filter code
 90  *      @filter: filter to verify
 91  *      @flen: length of filter
 92  *
 93  * Takes a previously checked filter (by bpf_check_classic) and
 94  * redirects all filter code that loads struct sk_buff data
 95  * and related data through seccomp_bpf_load.  It also
 96  * enforces length and alignment checking of those loads.
 97  *
 98  * Returns 0 if the rule set is legal or -EINVAL if not.
 99  */
100 static int seccomp_check_filter(struct sock_filter *filter, unsigned int flen)
101 {
102         int pc;
103         for (pc = 0; pc < flen; pc++) {
104                 struct sock_filter *ftest = &filter[pc];
105                 u16 code = ftest->code;
106                 u32 k = ftest->k;
107 
108                 switch (code) {
109                 case BPF_LD | BPF_W | BPF_ABS:
110                         ftest->code = BPF_LDX | BPF_W | BPF_ABS;
111                         /* 32-bit aligned and not out of bounds. */
112                         if (k >= sizeof(struct seccomp_data) || k & 3)
113                                 return -EINVAL;
114                         continue;
115                 case BPF_LD | BPF_W | BPF_LEN:
116                         ftest->code = BPF_LD | BPF_IMM;
117                         ftest->k = sizeof(struct seccomp_data);
118                         continue;
119                 case BPF_LDX | BPF_W | BPF_LEN:
120                         ftest->code = BPF_LDX | BPF_IMM;
121                         ftest->k = sizeof(struct seccomp_data);
122                         continue;
123                 /* Explicitly include allowed calls. */
124                 case BPF_RET | BPF_K:
125                 case BPF_RET | BPF_A:
126                 case BPF_ALU | BPF_ADD | BPF_K:
127                 case BPF_ALU | BPF_ADD | BPF_X:
128                 case BPF_ALU | BPF_SUB | BPF_K:
129                 case BPF_ALU | BPF_SUB | BPF_X:
130                 case BPF_ALU | BPF_MUL | BPF_K:
131                 case BPF_ALU | BPF_MUL | BPF_X:
132                 case BPF_ALU | BPF_DIV | BPF_K:
133                 case BPF_ALU | BPF_DIV | BPF_X:
134                 case BPF_ALU | BPF_AND | BPF_K:
135                 case BPF_ALU | BPF_AND | BPF_X:
136                 case BPF_ALU | BPF_OR | BPF_K:
137                 case BPF_ALU | BPF_OR | BPF_X:
138                 case BPF_ALU | BPF_XOR | BPF_K:
139                 case BPF_ALU | BPF_XOR | BPF_X:
140                 case BPF_ALU | BPF_LSH | BPF_K:
141                 case BPF_ALU | BPF_LSH | BPF_X:
142                 case BPF_ALU | BPF_RSH | BPF_K:
143                 case BPF_ALU | BPF_RSH | BPF_X:
144                 case BPF_ALU | BPF_NEG:
145                 case BPF_LD | BPF_IMM:
146                 case BPF_LDX | BPF_IMM:
147                 case BPF_MISC | BPF_TAX:
148                 case BPF_MISC | BPF_TXA:
149                 case BPF_LD | BPF_MEM:
150                 case BPF_LDX | BPF_MEM:
151                 case BPF_ST:
152                 case BPF_STX:
153                 case BPF_JMP | BPF_JA:
154                 case BPF_JMP | BPF_JEQ | BPF_K:
155                 case BPF_JMP | BPF_JEQ | BPF_X:
156                 case BPF_JMP | BPF_JGE | BPF_K:
157                 case BPF_JMP | BPF_JGE | BPF_X:
158                 case BPF_JMP | BPF_JGT | BPF_K:
159                 case BPF_JMP | BPF_JGT | BPF_X:
160                 case BPF_JMP | BPF_JSET | BPF_K:
161                 case BPF_JMP | BPF_JSET | BPF_X:
162                         continue;
163                 default:
164                         return -EINVAL;
165                 }
166         }
167         return 0;
168 }
169 
170 /**
171  * seccomp_run_filters - evaluates all seccomp filters against @syscall
172  * @syscall: number of the current system call
173  *
174  * Returns valid seccomp BPF response codes.
175  */
176 static u32 seccomp_run_filters(struct seccomp_data *sd)
177 {
178         struct seccomp_filter *f = ACCESS_ONCE(current->seccomp.filter);
179         struct seccomp_data sd_local;
180         u32 ret = SECCOMP_RET_ALLOW;
181 
182         /* Ensure unexpected behavior doesn't result in failing open. */
183         if (unlikely(WARN_ON(f == NULL)))
184                 return SECCOMP_RET_KILL;
185 
186         /* Make sure cross-thread synced filter points somewhere sane. */
187         smp_read_barrier_depends();
188 
189         if (!sd) {
190                 populate_seccomp_data(&sd_local);
191                 sd = &sd_local;
192         }
193 
194         /*
195          * All filters in the list are evaluated and the lowest BPF return
196          * value always takes priority (ignoring the DATA).
197          */
198         for (; f; f = f->prev) {
199                 u32 cur_ret = BPF_PROG_RUN(f->prog, (void *)sd);
200 
201                 if ((cur_ret & SECCOMP_RET_ACTION) < (ret & SECCOMP_RET_ACTION))
202                         ret = cur_ret;
203         }
204         return ret;
205 }
206 #endif /* CONFIG_SECCOMP_FILTER */
207 
208 static inline bool seccomp_may_assign_mode(unsigned long seccomp_mode)
209 {
210         assert_spin_locked(&current->sighand->siglock);
211 
212         if (current->seccomp.mode && current->seccomp.mode != seccomp_mode)
213                 return false;
214 
215         return true;
216 }
217 
218 static inline void seccomp_assign_mode(struct task_struct *task,
219                                        unsigned long seccomp_mode)
220 {
221         assert_spin_locked(&task->sighand->siglock);
222 
223         task->seccomp.mode = seccomp_mode;
224         /*
225          * Make sure TIF_SECCOMP cannot be set before the mode (and
226          * filter) is set.
227          */
228         smp_mb__before_atomic();
229         set_tsk_thread_flag(task, TIF_SECCOMP);
230 }
231 
232 #ifdef CONFIG_SECCOMP_FILTER
233 /* Returns 1 if the parent is an ancestor of the child. */
234 static int is_ancestor(struct seccomp_filter *parent,
235                        struct seccomp_filter *child)
236 {
237         /* NULL is the root ancestor. */
238         if (parent == NULL)
239                 return 1;
240         for (; child; child = child->prev)
241                 if (child == parent)
242                         return 1;
243         return 0;
244 }
245 
246 /**
247  * seccomp_can_sync_threads: checks if all threads can be synchronized
248  *
249  * Expects sighand and cred_guard_mutex locks to be held.
250  *
251  * Returns 0 on success, -ve on error, or the pid of a thread which was
252  * either not in the correct seccomp mode or it did not have an ancestral
253  * seccomp filter.
254  */
255 static inline pid_t seccomp_can_sync_threads(void)
256 {
257         struct task_struct *thread, *caller;
258 
259         BUG_ON(!mutex_is_locked(&current->signal->cred_guard_mutex));
260         assert_spin_locked(&current->sighand->siglock);
261 
262         /* Validate all threads being eligible for synchronization. */
263         caller = current;
264         for_each_thread(caller, thread) {
265                 pid_t failed;
266 
267                 /* Skip current, since it is initiating the sync. */
268                 if (thread == caller)
269                         continue;
270 
271                 if (thread->seccomp.mode == SECCOMP_MODE_DISABLED ||
272                     (thread->seccomp.mode == SECCOMP_MODE_FILTER &&
273                      is_ancestor(thread->seccomp.filter,
274                                  caller->seccomp.filter)))
275                         continue;
276 
277                 /* Return the first thread that cannot be synchronized. */
278                 failed = task_pid_vnr(thread);
279                 /* If the pid cannot be resolved, then return -ESRCH */
280                 if (unlikely(WARN_ON(failed == 0)))
281                         failed = -ESRCH;
282                 return failed;
283         }
284 
285         return 0;
286 }
287 
288 /**
289  * seccomp_sync_threads: sets all threads to use current's filter
290  *
291  * Expects sighand and cred_guard_mutex locks to be held, and for
292  * seccomp_can_sync_threads() to have returned success already
293  * without dropping the locks.
294  *
295  */
296 static inline void seccomp_sync_threads(void)
297 {
298         struct task_struct *thread, *caller;
299 
300         BUG_ON(!mutex_is_locked(&current->signal->cred_guard_mutex));
301         assert_spin_locked(&current->sighand->siglock);
302 
303         /* Synchronize all threads. */
304         caller = current;
305         for_each_thread(caller, thread) {
306                 /* Skip current, since it needs no changes. */
307                 if (thread == caller)
308                         continue;
309 
310                 /* Get a task reference for the new leaf node. */
311                 get_seccomp_filter(caller);
312                 /*
313                  * Drop the task reference to the shared ancestor since
314                  * current's path will hold a reference.  (This also
315                  * allows a put before the assignment.)
316                  */
317                 put_seccomp_filter(thread);
318                 smp_store_release(&thread->seccomp.filter,
319                                   caller->seccomp.filter);
320                 /*
321                  * Opt the other thread into seccomp if needed.
322                  * As threads are considered to be trust-realm
323                  * equivalent (see ptrace_may_access), it is safe to
324                  * allow one thread to transition the other.
325                  */
326                 if (thread->seccomp.mode == SECCOMP_MODE_DISABLED) {
327                         /*
328                          * Don't let an unprivileged task work around
329                          * the no_new_privs restriction by creating
330                          * a thread that sets it up, enters seccomp,
331                          * then dies.
332                          */
333                         if (task_no_new_privs(caller))
334                                 task_set_no_new_privs(thread);
335 
336                         seccomp_assign_mode(thread, SECCOMP_MODE_FILTER);
337                 }
338         }
339 }
340 
341 /**
342  * seccomp_prepare_filter: Prepares a seccomp filter for use.
343  * @fprog: BPF program to install
344  *
345  * Returns filter on success or an ERR_PTR on failure.
346  */
347 static struct seccomp_filter *seccomp_prepare_filter(struct sock_fprog *fprog)
348 {
349         struct seccomp_filter *sfilter;
350         int ret;
351 
352         if (fprog->len == 0 || fprog->len > BPF_MAXINSNS)
353                 return ERR_PTR(-EINVAL);
354 
355         BUG_ON(INT_MAX / fprog->len < sizeof(struct sock_filter));
356 
357         /*
358          * Installing a seccomp filter requires that the task has
359          * CAP_SYS_ADMIN in its namespace or be running with no_new_privs.
360          * This avoids scenarios where unprivileged tasks can affect the
361          * behavior of privileged children.
362          */
363         if (!task_no_new_privs(current) &&
364             security_capable_noaudit(current_cred(), current_user_ns(),
365                                      CAP_SYS_ADMIN) != 0)
366                 return ERR_PTR(-EACCES);
367 
368         /* Allocate a new seccomp_filter */
369         sfilter = kzalloc(sizeof(*sfilter), GFP_KERNEL | __GFP_NOWARN);
370         if (!sfilter)
371                 return ERR_PTR(-ENOMEM);
372 
373         ret = bpf_prog_create_from_user(&sfilter->prog, fprog,
374                                         seccomp_check_filter);
375         if (ret < 0) {
376                 kfree(sfilter);
377                 return ERR_PTR(ret);
378         }
379 
380         atomic_set(&sfilter->usage, 1);
381 
382         return sfilter;
383 }
384 
385 /**
386  * seccomp_prepare_user_filter - prepares a user-supplied sock_fprog
387  * @user_filter: pointer to the user data containing a sock_fprog.
388  *
389  * Returns 0 on success and non-zero otherwise.
390  */
391 static struct seccomp_filter *
392 seccomp_prepare_user_filter(const char __user *user_filter)
393 {
394         struct sock_fprog fprog;
395         struct seccomp_filter *filter = ERR_PTR(-EFAULT);
396 
397 #ifdef CONFIG_COMPAT
398         if (is_compat_task()) {
399                 struct compat_sock_fprog fprog32;
400                 if (copy_from_user(&fprog32, user_filter, sizeof(fprog32)))
401                         goto out;
402                 fprog.len = fprog32.len;
403                 fprog.filter = compat_ptr(fprog32.filter);
404         } else /* falls through to the if below. */
405 #endif
406         if (copy_from_user(&fprog, user_filter, sizeof(fprog)))
407                 goto out;
408         filter = seccomp_prepare_filter(&fprog);
409 out:
410         return filter;
411 }
412 
413 /**
414  * seccomp_attach_filter: validate and attach filter
415  * @flags:  flags to change filter behavior
416  * @filter: seccomp filter to add to the current process
417  *
418  * Caller must be holding current->sighand->siglock lock.
419  *
420  * Returns 0 on success, -ve on error.
421  */
422 static long seccomp_attach_filter(unsigned int flags,
423                                   struct seccomp_filter *filter)
424 {
425         unsigned long total_insns;
426         struct seccomp_filter *walker;
427 
428         assert_spin_locked(&current->sighand->siglock);
429 
430         /* Validate resulting filter length. */
431         total_insns = filter->prog->len;
432         for (walker = current->seccomp.filter; walker; walker = walker->prev)
433                 total_insns += walker->prog->len + 4;  /* 4 instr penalty */
434         if (total_insns > MAX_INSNS_PER_PATH)
435                 return -ENOMEM;
436 
437         /* If thread sync has been requested, check that it is possible. */
438         if (flags & SECCOMP_FILTER_FLAG_TSYNC) {
439                 int ret;
440 
441                 ret = seccomp_can_sync_threads();
442                 if (ret)
443                         return ret;
444         }
445 
446         /*
447          * If there is an existing filter, make it the prev and don't drop its
448          * task reference.
449          */
450         filter->prev = current->seccomp.filter;
451         current->seccomp.filter = filter;
452 
453         /* Now that the new filter is in place, synchronize to all threads. */
454         if (flags & SECCOMP_FILTER_FLAG_TSYNC)
455                 seccomp_sync_threads();
456 
457         return 0;
458 }
459 
460 /* get_seccomp_filter - increments the reference count of the filter on @tsk */
461 void get_seccomp_filter(struct task_struct *tsk)
462 {
463         struct seccomp_filter *orig = tsk->seccomp.filter;
464         if (!orig)
465                 return;
466         /* Reference count is bounded by the number of total processes. */
467         atomic_inc(&orig->usage);
468 }
469 
470 static inline void seccomp_filter_free(struct seccomp_filter *filter)
471 {
472         if (filter) {
473                 bpf_prog_free(filter->prog);
474                 kfree(filter);
475         }
476 }
477 
478 /* put_seccomp_filter - decrements the ref count of tsk->seccomp.filter */
479 void put_seccomp_filter(struct task_struct *tsk)
480 {
481         struct seccomp_filter *orig = tsk->seccomp.filter;
482         /* Clean up single-reference branches iteratively. */
483         while (orig && atomic_dec_and_test(&orig->usage)) {
484                 struct seccomp_filter *freeme = orig;
485                 orig = orig->prev;
486                 seccomp_filter_free(freeme);
487         }
488 }
489 
490 /**
491  * seccomp_send_sigsys - signals the task to allow in-process syscall emulation
492  * @syscall: syscall number to send to userland
493  * @reason: filter-supplied reason code to send to userland (via si_errno)
494  *
495  * Forces a SIGSYS with a code of SYS_SECCOMP and related sigsys info.
496  */
497 static void seccomp_send_sigsys(int syscall, int reason)
498 {
499         struct siginfo info;
500         memset(&info, 0, sizeof(info));
501         info.si_signo = SIGSYS;
502         info.si_code = SYS_SECCOMP;
503         info.si_call_addr = (void __user *)KSTK_EIP(current);
504         info.si_errno = reason;
505         info.si_arch = syscall_get_arch();
506         info.si_syscall = syscall;
507         force_sig_info(SIGSYS, &info, current);
508 }
509 #endif  /* CONFIG_SECCOMP_FILTER */
510 
511 /*
512  * Secure computing mode 1 allows only read/write/exit/sigreturn.
513  * To be fully secure this must be combined with rlimit
514  * to limit the stack allocations too.
515  */
516 static int mode1_syscalls[] = {
517         __NR_seccomp_read, __NR_seccomp_write, __NR_seccomp_exit, __NR_seccomp_sigreturn,
518         0, /* null terminated */
519 };
520 
521 #ifdef CONFIG_COMPAT
522 static int mode1_syscalls_32[] = {
523         __NR_seccomp_read_32, __NR_seccomp_write_32, __NR_seccomp_exit_32, __NR_seccomp_sigreturn_32,
524         0, /* null terminated */
525 };
526 #endif
527 
528 static void __secure_computing_strict(int this_syscall)
529 {
530         int *syscall_whitelist = mode1_syscalls;
531 #ifdef CONFIG_COMPAT
532         if (is_compat_task())
533                 syscall_whitelist = mode1_syscalls_32;
534 #endif
535         do {
536                 if (*syscall_whitelist == this_syscall)
537                         return;
538         } while (*++syscall_whitelist);
539 
540 #ifdef SECCOMP_DEBUG
541         dump_stack();
542 #endif
543         audit_seccomp(this_syscall, SIGKILL, SECCOMP_RET_KILL);
544         do_exit(SIGKILL);
545 }
546 
547 #ifndef CONFIG_HAVE_ARCH_SECCOMP_FILTER
548 void secure_computing_strict(int this_syscall)
549 {
550         int mode = current->seccomp.mode;
551 
552         if (mode == 0)
553                 return;
554         else if (mode == SECCOMP_MODE_STRICT)
555                 __secure_computing_strict(this_syscall);
556         else
557                 BUG();
558 }
559 #else
560 int __secure_computing(void)
561 {
562         u32 phase1_result = seccomp_phase1(NULL);
563 
564         if (likely(phase1_result == SECCOMP_PHASE1_OK))
565                 return 0;
566         else if (likely(phase1_result == SECCOMP_PHASE1_SKIP))
567                 return -1;
568         else
569                 return seccomp_phase2(phase1_result);
570 }
571 
572 #ifdef CONFIG_SECCOMP_FILTER
573 static u32 __seccomp_phase1_filter(int this_syscall, struct seccomp_data *sd)
574 {
575         u32 filter_ret, action;
576         int data;
577 
578         /*
579          * Make sure that any changes to mode from another thread have
580          * been seen after TIF_SECCOMP was seen.
581          */
582         rmb();
583 
584         filter_ret = seccomp_run_filters(sd);
585         data = filter_ret & SECCOMP_RET_DATA;
586         action = filter_ret & SECCOMP_RET_ACTION;
587 
588         switch (action) {
589         case SECCOMP_RET_ERRNO:
590                 /* Set low-order bits as an errno, capped at MAX_ERRNO. */
591                 if (data > MAX_ERRNO)
592                         data = MAX_ERRNO;
593                 syscall_set_return_value(current, task_pt_regs(current),
594                                          -data, 0);
595                 goto skip;
596 
597         case SECCOMP_RET_TRAP:
598                 /* Show the handler the original registers. */
599                 syscall_rollback(current, task_pt_regs(current));
600                 /* Let the filter pass back 16 bits of data. */
601                 seccomp_send_sigsys(this_syscall, data);
602                 goto skip;
603 
604         case SECCOMP_RET_TRACE:
605                 return filter_ret;  /* Save the rest for phase 2. */
606 
607         case SECCOMP_RET_ALLOW:
608                 return SECCOMP_PHASE1_OK;
609 
610         case SECCOMP_RET_KILL:
611         default:
612                 audit_seccomp(this_syscall, SIGSYS, action);
613                 do_exit(SIGSYS);
614         }
615 
616         unreachable();
617 
618 skip:
619         audit_seccomp(this_syscall, 0, action);
620         return SECCOMP_PHASE1_SKIP;
621 }
622 #endif
623 
624 /**
625  * seccomp_phase1() - run fast path seccomp checks on the current syscall
626  * @arg sd: The seccomp_data or NULL
627  *
628  * This only reads pt_regs via the syscall_xyz helpers.  The only change
629  * it will make to pt_regs is via syscall_set_return_value, and it will
630  * only do that if it returns SECCOMP_PHASE1_SKIP.
631  *
632  * If sd is provided, it will not read pt_regs at all.
633  *
634  * It may also call do_exit or force a signal; these actions must be
635  * safe.
636  *
637  * If it returns SECCOMP_PHASE1_OK, the syscall passes checks and should
638  * be processed normally.
639  *
640  * If it returns SECCOMP_PHASE1_SKIP, then the syscall should not be
641  * invoked.  In this case, seccomp_phase1 will have set the return value
642  * using syscall_set_return_value.
643  *
644  * If it returns anything else, then the return value should be passed
645  * to seccomp_phase2 from a context in which ptrace hooks are safe.
646  */
647 u32 seccomp_phase1(struct seccomp_data *sd)
648 {
649         int mode = current->seccomp.mode;
650         int this_syscall = sd ? sd->nr :
651                 syscall_get_nr(current, task_pt_regs(current));
652 
653         switch (mode) {
654         case SECCOMP_MODE_STRICT:
655                 __secure_computing_strict(this_syscall);  /* may call do_exit */
656                 return SECCOMP_PHASE1_OK;
657 #ifdef CONFIG_SECCOMP_FILTER
658         case SECCOMP_MODE_FILTER:
659                 return __seccomp_phase1_filter(this_syscall, sd);
660 #endif
661         default:
662                 BUG();
663         }
664 }
665 
666 /**
667  * seccomp_phase2() - finish slow path seccomp work for the current syscall
668  * @phase1_result: The return value from seccomp_phase1()
669  *
670  * This must be called from a context in which ptrace hooks can be used.
671  *
672  * Returns 0 if the syscall should be processed or -1 to skip the syscall.
673  */
674 int seccomp_phase2(u32 phase1_result)
675 {
676         struct pt_regs *regs = task_pt_regs(current);
677         u32 action = phase1_result & SECCOMP_RET_ACTION;
678         int data = phase1_result & SECCOMP_RET_DATA;
679 
680         BUG_ON(action != SECCOMP_RET_TRACE);
681 
682         audit_seccomp(syscall_get_nr(current, regs), 0, action);
683 
684         /* Skip these calls if there is no tracer. */
685         if (!ptrace_event_enabled(current, PTRACE_EVENT_SECCOMP)) {
686                 syscall_set_return_value(current, regs,
687                                          -ENOSYS, 0);
688                 return -1;
689         }
690 
691         /* Allow the BPF to provide the event message */
692         ptrace_event(PTRACE_EVENT_SECCOMP, data);
693         /*
694          * The delivery of a fatal signal during event
695          * notification may silently skip tracer notification.
696          * Terminating the task now avoids executing a system
697          * call that may not be intended.
698          */
699         if (fatal_signal_pending(current))
700                 do_exit(SIGSYS);
701         if (syscall_get_nr(current, regs) < 0)
702                 return -1;  /* Explicit request to skip. */
703 
704         return 0;
705 }
706 #endif /* CONFIG_HAVE_ARCH_SECCOMP_FILTER */
707 
708 long prctl_get_seccomp(void)
709 {
710         return current->seccomp.mode;
711 }
712 
713 /**
714  * seccomp_set_mode_strict: internal function for setting strict seccomp
715  *
716  * Once current->seccomp.mode is non-zero, it may not be changed.
717  *
718  * Returns 0 on success or -EINVAL on failure.
719  */
720 static long seccomp_set_mode_strict(void)
721 {
722         const unsigned long seccomp_mode = SECCOMP_MODE_STRICT;
723         long ret = -EINVAL;
724 
725         spin_lock_irq(&current->sighand->siglock);
726 
727         if (!seccomp_may_assign_mode(seccomp_mode))
728                 goto out;
729 
730 #ifdef TIF_NOTSC
731         disable_TSC();
732 #endif
733         seccomp_assign_mode(current, seccomp_mode);
734         ret = 0;
735 
736 out:
737         spin_unlock_irq(&current->sighand->siglock);
738 
739         return ret;
740 }
741 
742 #ifdef CONFIG_SECCOMP_FILTER
743 /**
744  * seccomp_set_mode_filter: internal function for setting seccomp filter
745  * @flags:  flags to change filter behavior
746  * @filter: struct sock_fprog containing filter
747  *
748  * This function may be called repeatedly to install additional filters.
749  * Every filter successfully installed will be evaluated (in reverse order)
750  * for each system call the task makes.
751  *
752  * Once current->seccomp.mode is non-zero, it may not be changed.
753  *
754  * Returns 0 on success or -EINVAL on failure.
755  */
756 static long seccomp_set_mode_filter(unsigned int flags,
757                                     const char __user *filter)
758 {
759         const unsigned long seccomp_mode = SECCOMP_MODE_FILTER;
760         struct seccomp_filter *prepared = NULL;
761         long ret = -EINVAL;
762 
763         /* Validate flags. */
764         if (flags & ~SECCOMP_FILTER_FLAG_MASK)
765                 return -EINVAL;
766 
767         /* Prepare the new filter before holding any locks. */
768         prepared = seccomp_prepare_user_filter(filter);
769         if (IS_ERR(prepared))
770                 return PTR_ERR(prepared);
771 
772         /*
773          * Make sure we cannot change seccomp or nnp state via TSYNC
774          * while another thread is in the middle of calling exec.
775          */
776         if (flags & SECCOMP_FILTER_FLAG_TSYNC &&
777             mutex_lock_killable(&current->signal->cred_guard_mutex))
778                 goto out_free;
779 
780         spin_lock_irq(&current->sighand->siglock);
781 
782         if (!seccomp_may_assign_mode(seccomp_mode))
783                 goto out;
784 
785         ret = seccomp_attach_filter(flags, prepared);
786         if (ret)
787                 goto out;
788         /* Do not free the successfully attached filter. */
789         prepared = NULL;
790 
791         seccomp_assign_mode(current, seccomp_mode);
792 out:
793         spin_unlock_irq(&current->sighand->siglock);
794         if (flags & SECCOMP_FILTER_FLAG_TSYNC)
795                 mutex_unlock(&current->signal->cred_guard_mutex);
796 out_free:
797         seccomp_filter_free(prepared);
798         return ret;
799 }
800 #else
801 static inline long seccomp_set_mode_filter(unsigned int flags,
802                                            const char __user *filter)
803 {
804         return -EINVAL;
805 }
806 #endif
807 
808 /* Common entry point for both prctl and syscall. */
809 static long do_seccomp(unsigned int op, unsigned int flags,
810                        const char __user *uargs)
811 {
812         switch (op) {
813         case SECCOMP_SET_MODE_STRICT:
814                 if (flags != 0 || uargs != NULL)
815                         return -EINVAL;
816                 return seccomp_set_mode_strict();
817         case SECCOMP_SET_MODE_FILTER:
818                 return seccomp_set_mode_filter(flags, uargs);
819         default:
820                 return -EINVAL;
821         }
822 }
823 
824 SYSCALL_DEFINE3(seccomp, unsigned int, op, unsigned int, flags,
825                          const char __user *, uargs)
826 {
827         return do_seccomp(op, flags, uargs);
828 }
829 
830 /**
831  * prctl_set_seccomp: configures current->seccomp.mode
832  * @seccomp_mode: requested mode to use
833  * @filter: optional struct sock_fprog for use with SECCOMP_MODE_FILTER
834  *
835  * Returns 0 on success or -EINVAL on failure.
836  */
837 long prctl_set_seccomp(unsigned long seccomp_mode, char __user *filter)
838 {
839         unsigned int op;
840         char __user *uargs;
841 
842         switch (seccomp_mode) {
843         case SECCOMP_MODE_STRICT:
844                 op = SECCOMP_SET_MODE_STRICT;
845                 /*
846                  * Setting strict mode through prctl always ignored filter,
847                  * so make sure it is always NULL here to pass the internal
848                  * check in do_seccomp().
849                  */
850                 uargs = NULL;
851                 break;
852         case SECCOMP_MODE_FILTER:
853                 op = SECCOMP_SET_MODE_FILTER;
854                 uargs = filter;
855                 break;
856         default:
857                 return -EINVAL;
858         }
859 
860         /* prctl interface doesn't have flags, so they are always zero. */
861         return do_seccomp(op, 0, uargs);
862 }
863 

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