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TOMOYO Linux Cross Reference
Linux/fs/select.c

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  1 /*
  2  * This file contains the procedures for the handling of select and poll
  3  *
  4  * Created for Linux based loosely upon Mathius Lattner's minix
  5  * patches by Peter MacDonald. Heavily edited by Linus.
  6  *
  7  *  4 February 1994
  8  *     COFF/ELF binary emulation. If the process has the STICKY_TIMEOUTS
  9  *     flag set in its personality we do *not* modify the given timeout
 10  *     parameter to reflect time remaining.
 11  *
 12  *  24 January 2000
 13  *     Changed sys_poll()/do_poll() to use PAGE_SIZE chunk-based allocation 
 14  *     of fds to overcome nfds < 16390 descriptors limit (Tigran Aivazian).
 15  */
 16 
 17 #include <linux/kernel.h>
 18 #include <linux/sched.h>
 19 #include <linux/syscalls.h>
 20 #include <linux/export.h>
 21 #include <linux/slab.h>
 22 #include <linux/poll.h>
 23 #include <linux/personality.h> /* for STICKY_TIMEOUTS */
 24 #include <linux/file.h>
 25 #include <linux/fdtable.h>
 26 #include <linux/fs.h>
 27 #include <linux/rcupdate.h>
 28 #include <linux/hrtimer.h>
 29 #include <linux/sched/rt.h>
 30 #include <linux/freezer.h>
 31 #include <net/busy_poll.h>
 32 #include <linux/vmalloc.h>
 33 
 34 #include <asm/uaccess.h>
 35 
 36 
 37 /*
 38  * Estimate expected accuracy in ns from a timeval.
 39  *
 40  * After quite a bit of churning around, we've settled on
 41  * a simple thing of taking 0.1% of the timeout as the
 42  * slack, with a cap of 100 msec.
 43  * "nice" tasks get a 0.5% slack instead.
 44  *
 45  * Consider this comment an open invitation to come up with even
 46  * better solutions..
 47  */
 48 
 49 #define MAX_SLACK       (100 * NSEC_PER_MSEC)
 50 
 51 static long __estimate_accuracy(struct timespec *tv)
 52 {
 53         long slack;
 54         int divfactor = 1000;
 55 
 56         if (tv->tv_sec < 0)
 57                 return 0;
 58 
 59         if (task_nice(current) > 0)
 60                 divfactor = divfactor / 5;
 61 
 62         if (tv->tv_sec > MAX_SLACK / (NSEC_PER_SEC/divfactor))
 63                 return MAX_SLACK;
 64 
 65         slack = tv->tv_nsec / divfactor;
 66         slack += tv->tv_sec * (NSEC_PER_SEC/divfactor);
 67 
 68         if (slack > MAX_SLACK)
 69                 return MAX_SLACK;
 70 
 71         return slack;
 72 }
 73 
 74 long select_estimate_accuracy(struct timespec *tv)
 75 {
 76         unsigned long ret;
 77         struct timespec now;
 78 
 79         /*
 80          * Realtime tasks get a slack of 0 for obvious reasons.
 81          */
 82 
 83         if (rt_task(current))
 84                 return 0;
 85 
 86         ktime_get_ts(&now);
 87         now = timespec_sub(*tv, now);
 88         ret = __estimate_accuracy(&now);
 89         if (ret < current->timer_slack_ns)
 90                 return current->timer_slack_ns;
 91         return ret;
 92 }
 93 
 94 
 95 
 96 struct poll_table_page {
 97         struct poll_table_page * next;
 98         struct poll_table_entry * entry;
 99         struct poll_table_entry entries[0];
100 };
101 
102 #define POLL_TABLE_FULL(table) \
103         ((unsigned long)((table)->entry+1) > PAGE_SIZE + (unsigned long)(table))
104 
105 /*
106  * Ok, Peter made a complicated, but straightforward multiple_wait() function.
107  * I have rewritten this, taking some shortcuts: This code may not be easy to
108  * follow, but it should be free of race-conditions, and it's practical. If you
109  * understand what I'm doing here, then you understand how the linux
110  * sleep/wakeup mechanism works.
111  *
112  * Two very simple procedures, poll_wait() and poll_freewait() make all the
113  * work.  poll_wait() is an inline-function defined in <linux/poll.h>,
114  * as all select/poll functions have to call it to add an entry to the
115  * poll table.
116  */
117 static void __pollwait(struct file *filp, wait_queue_head_t *wait_address,
118                        poll_table *p);
119 
120 void poll_initwait(struct poll_wqueues *pwq)
121 {
122         init_poll_funcptr(&pwq->pt, __pollwait);
123         pwq->polling_task = current;
124         pwq->triggered = 0;
125         pwq->error = 0;
126         pwq->table = NULL;
127         pwq->inline_index = 0;
128 }
129 EXPORT_SYMBOL(poll_initwait);
130 
131 static void free_poll_entry(struct poll_table_entry *entry)
132 {
133         remove_wait_queue(entry->wait_address, &entry->wait);
134         fput(entry->filp);
135 }
136 
137 void poll_freewait(struct poll_wqueues *pwq)
138 {
139         struct poll_table_page * p = pwq->table;
140         int i;
141         for (i = 0; i < pwq->inline_index; i++)
142                 free_poll_entry(pwq->inline_entries + i);
143         while (p) {
144                 struct poll_table_entry * entry;
145                 struct poll_table_page *old;
146 
147                 entry = p->entry;
148                 do {
149                         entry--;
150                         free_poll_entry(entry);
151                 } while (entry > p->entries);
152                 old = p;
153                 p = p->next;
154                 free_page((unsigned long) old);
155         }
156 }
157 EXPORT_SYMBOL(poll_freewait);
158 
159 static struct poll_table_entry *poll_get_entry(struct poll_wqueues *p)
160 {
161         struct poll_table_page *table = p->table;
162 
163         if (p->inline_index < N_INLINE_POLL_ENTRIES)
164                 return p->inline_entries + p->inline_index++;
165 
166         if (!table || POLL_TABLE_FULL(table)) {
167                 struct poll_table_page *new_table;
168 
169                 new_table = (struct poll_table_page *) __get_free_page(GFP_KERNEL);
170                 if (!new_table) {
171                         p->error = -ENOMEM;
172                         return NULL;
173                 }
174                 new_table->entry = new_table->entries;
175                 new_table->next = table;
176                 p->table = new_table;
177                 table = new_table;
178         }
179 
180         return table->entry++;
181 }
182 
183 static int __pollwake(wait_queue_t *wait, unsigned mode, int sync, void *key)
184 {
185         struct poll_wqueues *pwq = wait->private;
186         DECLARE_WAITQUEUE(dummy_wait, pwq->polling_task);
187 
188         /*
189          * Although this function is called under waitqueue lock, LOCK
190          * doesn't imply write barrier and the users expect write
191          * barrier semantics on wakeup functions.  The following
192          * smp_wmb() is equivalent to smp_wmb() in try_to_wake_up()
193          * and is paired with smp_store_mb() in poll_schedule_timeout.
194          */
195         smp_wmb();
196         pwq->triggered = 1;
197 
198         /*
199          * Perform the default wake up operation using a dummy
200          * waitqueue.
201          *
202          * TODO: This is hacky but there currently is no interface to
203          * pass in @sync.  @sync is scheduled to be removed and once
204          * that happens, wake_up_process() can be used directly.
205          */
206         return default_wake_function(&dummy_wait, mode, sync, key);
207 }
208 
209 static int pollwake(wait_queue_t *wait, unsigned mode, int sync, void *key)
210 {
211         struct poll_table_entry *entry;
212 
213         entry = container_of(wait, struct poll_table_entry, wait);
214         if (key && !((unsigned long)key & entry->key))
215                 return 0;
216         return __pollwake(wait, mode, sync, key);
217 }
218 
219 /* Add a new entry */
220 static void __pollwait(struct file *filp, wait_queue_head_t *wait_address,
221                                 poll_table *p)
222 {
223         struct poll_wqueues *pwq = container_of(p, struct poll_wqueues, pt);
224         struct poll_table_entry *entry = poll_get_entry(pwq);
225         if (!entry)
226                 return;
227         entry->filp = get_file(filp);
228         entry->wait_address = wait_address;
229         entry->key = p->_key;
230         init_waitqueue_func_entry(&entry->wait, pollwake);
231         entry->wait.private = pwq;
232         add_wait_queue(wait_address, &entry->wait);
233 }
234 
235 int poll_schedule_timeout(struct poll_wqueues *pwq, int state,
236                           ktime_t *expires, unsigned long slack)
237 {
238         int rc = -EINTR;
239 
240         set_current_state(state);
241         if (!pwq->triggered)
242                 rc = schedule_hrtimeout_range(expires, slack, HRTIMER_MODE_ABS);
243         __set_current_state(TASK_RUNNING);
244 
245         /*
246          * Prepare for the next iteration.
247          *
248          * The following smp_store_mb() serves two purposes.  First, it's
249          * the counterpart rmb of the wmb in pollwake() such that data
250          * written before wake up is always visible after wake up.
251          * Second, the full barrier guarantees that triggered clearing
252          * doesn't pass event check of the next iteration.  Note that
253          * this problem doesn't exist for the first iteration as
254          * add_wait_queue() has full barrier semantics.
255          */
256         smp_store_mb(pwq->triggered, 0);
257 
258         return rc;
259 }
260 EXPORT_SYMBOL(poll_schedule_timeout);
261 
262 /**
263  * poll_select_set_timeout - helper function to setup the timeout value
264  * @to:         pointer to timespec variable for the final timeout
265  * @sec:        seconds (from user space)
266  * @nsec:       nanoseconds (from user space)
267  *
268  * Note, we do not use a timespec for the user space value here, That
269  * way we can use the function for timeval and compat interfaces as well.
270  *
271  * Returns -EINVAL if sec/nsec are not normalized. Otherwise 0.
272  */
273 int poll_select_set_timeout(struct timespec *to, long sec, long nsec)
274 {
275         struct timespec ts = {.tv_sec = sec, .tv_nsec = nsec};
276 
277         if (!timespec_valid(&ts))
278                 return -EINVAL;
279 
280         /* Optimize for the zero timeout value here */
281         if (!sec && !nsec) {
282                 to->tv_sec = to->tv_nsec = 0;
283         } else {
284                 ktime_get_ts(to);
285                 *to = timespec_add_safe(*to, ts);
286         }
287         return 0;
288 }
289 
290 static int poll_select_copy_remaining(struct timespec *end_time, void __user *p,
291                                       int timeval, int ret)
292 {
293         struct timespec rts;
294         struct timeval rtv;
295 
296         if (!p)
297                 return ret;
298 
299         if (current->personality & STICKY_TIMEOUTS)
300                 goto sticky;
301 
302         /* No update for zero timeout */
303         if (!end_time->tv_sec && !end_time->tv_nsec)
304                 return ret;
305 
306         ktime_get_ts(&rts);
307         rts = timespec_sub(*end_time, rts);
308         if (rts.tv_sec < 0)
309                 rts.tv_sec = rts.tv_nsec = 0;
310 
311         if (timeval) {
312                 if (sizeof(rtv) > sizeof(rtv.tv_sec) + sizeof(rtv.tv_usec))
313                         memset(&rtv, 0, sizeof(rtv));
314                 rtv.tv_sec = rts.tv_sec;
315                 rtv.tv_usec = rts.tv_nsec / NSEC_PER_USEC;
316 
317                 if (!copy_to_user(p, &rtv, sizeof(rtv)))
318                         return ret;
319 
320         } else if (!copy_to_user(p, &rts, sizeof(rts)))
321                 return ret;
322 
323         /*
324          * If an application puts its timeval in read-only memory, we
325          * don't want the Linux-specific update to the timeval to
326          * cause a fault after the select has completed
327          * successfully. However, because we're not updating the
328          * timeval, we can't restart the system call.
329          */
330 
331 sticky:
332         if (ret == -ERESTARTNOHAND)
333                 ret = -EINTR;
334         return ret;
335 }
336 
337 #define FDS_IN(fds, n)          (fds->in + n)
338 #define FDS_OUT(fds, n)         (fds->out + n)
339 #define FDS_EX(fds, n)          (fds->ex + n)
340 
341 #define BITS(fds, n)    (*FDS_IN(fds, n)|*FDS_OUT(fds, n)|*FDS_EX(fds, n))
342 
343 static int max_select_fd(unsigned long n, fd_set_bits *fds)
344 {
345         unsigned long *open_fds;
346         unsigned long set;
347         int max;
348         struct fdtable *fdt;
349 
350         /* handle last in-complete long-word first */
351         set = ~(~0UL << (n & (BITS_PER_LONG-1)));
352         n /= BITS_PER_LONG;
353         fdt = files_fdtable(current->files);
354         open_fds = fdt->open_fds + n;
355         max = 0;
356         if (set) {
357                 set &= BITS(fds, n);
358                 if (set) {
359                         if (!(set & ~*open_fds))
360                                 goto get_max;
361                         return -EBADF;
362                 }
363         }
364         while (n) {
365                 open_fds--;
366                 n--;
367                 set = BITS(fds, n);
368                 if (!set)
369                         continue;
370                 if (set & ~*open_fds)
371                         return -EBADF;
372                 if (max)
373                         continue;
374 get_max:
375                 do {
376                         max++;
377                         set >>= 1;
378                 } while (set);
379                 max += n * BITS_PER_LONG;
380         }
381 
382         return max;
383 }
384 
385 #define POLLIN_SET (POLLRDNORM | POLLRDBAND | POLLIN | POLLHUP | POLLERR)
386 #define POLLOUT_SET (POLLWRBAND | POLLWRNORM | POLLOUT | POLLERR)
387 #define POLLEX_SET (POLLPRI)
388 
389 static inline void wait_key_set(poll_table *wait, unsigned long in,
390                                 unsigned long out, unsigned long bit,
391                                 unsigned int ll_flag)
392 {
393         wait->_key = POLLEX_SET | ll_flag;
394         if (in & bit)
395                 wait->_key |= POLLIN_SET;
396         if (out & bit)
397                 wait->_key |= POLLOUT_SET;
398 }
399 
400 int do_select(int n, fd_set_bits *fds, struct timespec *end_time)
401 {
402         ktime_t expire, *to = NULL;
403         struct poll_wqueues table;
404         poll_table *wait;
405         int retval, i, timed_out = 0;
406         unsigned long slack = 0;
407         unsigned int busy_flag = net_busy_loop_on() ? POLL_BUSY_LOOP : 0;
408         unsigned long busy_end = 0;
409 
410         rcu_read_lock();
411         retval = max_select_fd(n, fds);
412         rcu_read_unlock();
413 
414         if (retval < 0)
415                 return retval;
416         n = retval;
417 
418         poll_initwait(&table);
419         wait = &table.pt;
420         if (end_time && !end_time->tv_sec && !end_time->tv_nsec) {
421                 wait->_qproc = NULL;
422                 timed_out = 1;
423         }
424 
425         if (end_time && !timed_out)
426                 slack = select_estimate_accuracy(end_time);
427 
428         retval = 0;
429         for (;;) {
430                 unsigned long *rinp, *routp, *rexp, *inp, *outp, *exp;
431                 bool can_busy_loop = false;
432 
433                 inp = fds->in; outp = fds->out; exp = fds->ex;
434                 rinp = fds->res_in; routp = fds->res_out; rexp = fds->res_ex;
435 
436                 for (i = 0; i < n; ++rinp, ++routp, ++rexp) {
437                         unsigned long in, out, ex, all_bits, bit = 1, mask, j;
438                         unsigned long res_in = 0, res_out = 0, res_ex = 0;
439 
440                         in = *inp++; out = *outp++; ex = *exp++;
441                         all_bits = in | out | ex;
442                         if (all_bits == 0) {
443                                 i += BITS_PER_LONG;
444                                 continue;
445                         }
446 
447                         for (j = 0; j < BITS_PER_LONG; ++j, ++i, bit <<= 1) {
448                                 struct fd f;
449                                 if (i >= n)
450                                         break;
451                                 if (!(bit & all_bits))
452                                         continue;
453                                 f = fdget(i);
454                                 if (f.file) {
455                                         const struct file_operations *f_op;
456                                         f_op = f.file->f_op;
457                                         mask = DEFAULT_POLLMASK;
458                                         if (f_op->poll) {
459                                                 wait_key_set(wait, in, out,
460                                                              bit, busy_flag);
461                                                 mask = (*f_op->poll)(f.file, wait);
462                                         }
463                                         fdput(f);
464                                         if ((mask & POLLIN_SET) && (in & bit)) {
465                                                 res_in |= bit;
466                                                 retval++;
467                                                 wait->_qproc = NULL;
468                                         }
469                                         if ((mask & POLLOUT_SET) && (out & bit)) {
470                                                 res_out |= bit;
471                                                 retval++;
472                                                 wait->_qproc = NULL;
473                                         }
474                                         if ((mask & POLLEX_SET) && (ex & bit)) {
475                                                 res_ex |= bit;
476                                                 retval++;
477                                                 wait->_qproc = NULL;
478                                         }
479                                         /* got something, stop busy polling */
480                                         if (retval) {
481                                                 can_busy_loop = false;
482                                                 busy_flag = 0;
483 
484                                         /*
485                                          * only remember a returned
486                                          * POLL_BUSY_LOOP if we asked for it
487                                          */
488                                         } else if (busy_flag & mask)
489                                                 can_busy_loop = true;
490 
491                                 }
492                         }
493                         if (res_in)
494                                 *rinp = res_in;
495                         if (res_out)
496                                 *routp = res_out;
497                         if (res_ex)
498                                 *rexp = res_ex;
499                         cond_resched();
500                 }
501                 wait->_qproc = NULL;
502                 if (retval || timed_out || signal_pending(current))
503                         break;
504                 if (table.error) {
505                         retval = table.error;
506                         break;
507                 }
508 
509                 /* only if found POLL_BUSY_LOOP sockets && not out of time */
510                 if (can_busy_loop && !need_resched()) {
511                         if (!busy_end) {
512                                 busy_end = busy_loop_end_time();
513                                 continue;
514                         }
515                         if (!busy_loop_timeout(busy_end))
516                                 continue;
517                 }
518                 busy_flag = 0;
519 
520                 /*
521                  * If this is the first loop and we have a timeout
522                  * given, then we convert to ktime_t and set the to
523                  * pointer to the expiry value.
524                  */
525                 if (end_time && !to) {
526                         expire = timespec_to_ktime(*end_time);
527                         to = &expire;
528                 }
529 
530                 if (!poll_schedule_timeout(&table, TASK_INTERRUPTIBLE,
531                                            to, slack))
532                         timed_out = 1;
533         }
534 
535         poll_freewait(&table);
536 
537         return retval;
538 }
539 
540 /*
541  * We can actually return ERESTARTSYS instead of EINTR, but I'd
542  * like to be certain this leads to no problems. So I return
543  * EINTR just for safety.
544  *
545  * Update: ERESTARTSYS breaks at least the xview clock binary, so
546  * I'm trying ERESTARTNOHAND which restart only when you want to.
547  */
548 int core_sys_select(int n, fd_set __user *inp, fd_set __user *outp,
549                            fd_set __user *exp, struct timespec *end_time)
550 {
551         fd_set_bits fds;
552         void *bits;
553         int ret, max_fds;
554         size_t size, alloc_size;
555         struct fdtable *fdt;
556         /* Allocate small arguments on the stack to save memory and be faster */
557         long stack_fds[SELECT_STACK_ALLOC/sizeof(long)];
558 
559         ret = -EINVAL;
560         if (n < 0)
561                 goto out_nofds;
562 
563         /* max_fds can increase, so grab it once to avoid race */
564         rcu_read_lock();
565         fdt = files_fdtable(current->files);
566         max_fds = fdt->max_fds;
567         rcu_read_unlock();
568         if (n > max_fds)
569                 n = max_fds;
570 
571         /*
572          * We need 6 bitmaps (in/out/ex for both incoming and outgoing),
573          * since we used fdset we need to allocate memory in units of
574          * long-words. 
575          */
576         size = FDS_BYTES(n);
577         bits = stack_fds;
578         if (size > sizeof(stack_fds) / 6) {
579                 /* Not enough space in on-stack array; must use kmalloc */
580                 ret = -ENOMEM;
581                 if (size > (SIZE_MAX / 6))
582                         goto out_nofds;
583 
584                 alloc_size = 6 * size;
585                 bits = kmalloc(alloc_size, GFP_KERNEL|__GFP_NOWARN);
586                 if (!bits && alloc_size > PAGE_SIZE)
587                         bits = vmalloc(alloc_size);
588 
589                 if (!bits)
590                         goto out_nofds;
591         }
592         fds.in      = bits;
593         fds.out     = bits +   size;
594         fds.ex      = bits + 2*size;
595         fds.res_in  = bits + 3*size;
596         fds.res_out = bits + 4*size;
597         fds.res_ex  = bits + 5*size;
598 
599         if ((ret = get_fd_set(n, inp, fds.in)) ||
600             (ret = get_fd_set(n, outp, fds.out)) ||
601             (ret = get_fd_set(n, exp, fds.ex)))
602                 goto out;
603         zero_fd_set(n, fds.res_in);
604         zero_fd_set(n, fds.res_out);
605         zero_fd_set(n, fds.res_ex);
606 
607         ret = do_select(n, &fds, end_time);
608 
609         if (ret < 0)
610                 goto out;
611         if (!ret) {
612                 ret = -ERESTARTNOHAND;
613                 if (signal_pending(current))
614                         goto out;
615                 ret = 0;
616         }
617 
618         if (set_fd_set(n, inp, fds.res_in) ||
619             set_fd_set(n, outp, fds.res_out) ||
620             set_fd_set(n, exp, fds.res_ex))
621                 ret = -EFAULT;
622 
623 out:
624         if (bits != stack_fds)
625                 kvfree(bits);
626 out_nofds:
627         return ret;
628 }
629 
630 SYSCALL_DEFINE5(select, int, n, fd_set __user *, inp, fd_set __user *, outp,
631                 fd_set __user *, exp, struct timeval __user *, tvp)
632 {
633         struct timespec end_time, *to = NULL;
634         struct timeval tv;
635         int ret;
636 
637         if (tvp) {
638                 if (copy_from_user(&tv, tvp, sizeof(tv)))
639                         return -EFAULT;
640 
641                 to = &end_time;
642                 if (poll_select_set_timeout(to,
643                                 tv.tv_sec + (tv.tv_usec / USEC_PER_SEC),
644                                 (tv.tv_usec % USEC_PER_SEC) * NSEC_PER_USEC))
645                         return -EINVAL;
646         }
647 
648         ret = core_sys_select(n, inp, outp, exp, to);
649         ret = poll_select_copy_remaining(&end_time, tvp, 1, ret);
650 
651         return ret;
652 }
653 
654 static long do_pselect(int n, fd_set __user *inp, fd_set __user *outp,
655                        fd_set __user *exp, struct timespec __user *tsp,
656                        const sigset_t __user *sigmask, size_t sigsetsize)
657 {
658         sigset_t ksigmask, sigsaved;
659         struct timespec ts, end_time, *to = NULL;
660         int ret;
661 
662         if (tsp) {
663                 if (copy_from_user(&ts, tsp, sizeof(ts)))
664                         return -EFAULT;
665 
666                 to = &end_time;
667                 if (poll_select_set_timeout(to, ts.tv_sec, ts.tv_nsec))
668                         return -EINVAL;
669         }
670 
671         if (sigmask) {
672                 /* XXX: Don't preclude handling different sized sigset_t's.  */
673                 if (sigsetsize != sizeof(sigset_t))
674                         return -EINVAL;
675                 if (copy_from_user(&ksigmask, sigmask, sizeof(ksigmask)))
676                         return -EFAULT;
677 
678                 sigdelsetmask(&ksigmask, sigmask(SIGKILL)|sigmask(SIGSTOP));
679                 sigprocmask(SIG_SETMASK, &ksigmask, &sigsaved);
680         }
681 
682         ret = core_sys_select(n, inp, outp, exp, to);
683         ret = poll_select_copy_remaining(&end_time, tsp, 0, ret);
684 
685         if (ret == -ERESTARTNOHAND) {
686                 /*
687                  * Don't restore the signal mask yet. Let do_signal() deliver
688                  * the signal on the way back to userspace, before the signal
689                  * mask is restored.
690                  */
691                 if (sigmask) {
692                         memcpy(&current->saved_sigmask, &sigsaved,
693                                         sizeof(sigsaved));
694                         set_restore_sigmask();
695                 }
696         } else if (sigmask)
697                 sigprocmask(SIG_SETMASK, &sigsaved, NULL);
698 
699         return ret;
700 }
701 
702 /*
703  * Most architectures can't handle 7-argument syscalls. So we provide a
704  * 6-argument version where the sixth argument is a pointer to a structure
705  * which has a pointer to the sigset_t itself followed by a size_t containing
706  * the sigset size.
707  */
708 SYSCALL_DEFINE6(pselect6, int, n, fd_set __user *, inp, fd_set __user *, outp,
709                 fd_set __user *, exp, struct timespec __user *, tsp,
710                 void __user *, sig)
711 {
712         size_t sigsetsize = 0;
713         sigset_t __user *up = NULL;
714 
715         if (sig) {
716                 if (!access_ok(VERIFY_READ, sig, sizeof(void *)+sizeof(size_t))
717                     || __get_user(up, (sigset_t __user * __user *)sig)
718                     || __get_user(sigsetsize,
719                                 (size_t __user *)(sig+sizeof(void *))))
720                         return -EFAULT;
721         }
722 
723         return do_pselect(n, inp, outp, exp, tsp, up, sigsetsize);
724 }
725 
726 #ifdef __ARCH_WANT_SYS_OLD_SELECT
727 struct sel_arg_struct {
728         unsigned long n;
729         fd_set __user *inp, *outp, *exp;
730         struct timeval __user *tvp;
731 };
732 
733 SYSCALL_DEFINE1(old_select, struct sel_arg_struct __user *, arg)
734 {
735         struct sel_arg_struct a;
736 
737         if (copy_from_user(&a, arg, sizeof(a)))
738                 return -EFAULT;
739         return sys_select(a.n, a.inp, a.outp, a.exp, a.tvp);
740 }
741 #endif
742 
743 struct poll_list {
744         struct poll_list *next;
745         int len;
746         struct pollfd entries[0];
747 };
748 
749 #define POLLFD_PER_PAGE  ((PAGE_SIZE-sizeof(struct poll_list)) / sizeof(struct pollfd))
750 
751 /*
752  * Fish for pollable events on the pollfd->fd file descriptor. We're only
753  * interested in events matching the pollfd->events mask, and the result
754  * matching that mask is both recorded in pollfd->revents and returned. The
755  * pwait poll_table will be used by the fd-provided poll handler for waiting,
756  * if pwait->_qproc is non-NULL.
757  */
758 static inline unsigned int do_pollfd(struct pollfd *pollfd, poll_table *pwait,
759                                      bool *can_busy_poll,
760                                      unsigned int busy_flag)
761 {
762         unsigned int mask;
763         int fd;
764 
765         mask = 0;
766         fd = pollfd->fd;
767         if (fd >= 0) {
768                 struct fd f = fdget(fd);
769                 mask = POLLNVAL;
770                 if (f.file) {
771                         mask = DEFAULT_POLLMASK;
772                         if (f.file->f_op->poll) {
773                                 pwait->_key = pollfd->events|POLLERR|POLLHUP;
774                                 pwait->_key |= busy_flag;
775                                 mask = f.file->f_op->poll(f.file, pwait);
776                                 if (mask & busy_flag)
777                                         *can_busy_poll = true;
778                         }
779                         /* Mask out unneeded events. */
780                         mask &= pollfd->events | POLLERR | POLLHUP;
781                         fdput(f);
782                 }
783         }
784         pollfd->revents = mask;
785 
786         return mask;
787 }
788 
789 static int do_poll(unsigned int nfds,  struct poll_list *list,
790                    struct poll_wqueues *wait, struct timespec *end_time)
791 {
792         poll_table* pt = &wait->pt;
793         ktime_t expire, *to = NULL;
794         int timed_out = 0, count = 0;
795         unsigned long slack = 0;
796         unsigned int busy_flag = net_busy_loop_on() ? POLL_BUSY_LOOP : 0;
797         unsigned long busy_end = 0;
798 
799         /* Optimise the no-wait case */
800         if (end_time && !end_time->tv_sec && !end_time->tv_nsec) {
801                 pt->_qproc = NULL;
802                 timed_out = 1;
803         }
804 
805         if (end_time && !timed_out)
806                 slack = select_estimate_accuracy(end_time);
807 
808         for (;;) {
809                 struct poll_list *walk;
810                 bool can_busy_loop = false;
811 
812                 for (walk = list; walk != NULL; walk = walk->next) {
813                         struct pollfd * pfd, * pfd_end;
814 
815                         pfd = walk->entries;
816                         pfd_end = pfd + walk->len;
817                         for (; pfd != pfd_end; pfd++) {
818                                 /*
819                                  * Fish for events. If we found one, record it
820                                  * and kill poll_table->_qproc, so we don't
821                                  * needlessly register any other waiters after
822                                  * this. They'll get immediately deregistered
823                                  * when we break out and return.
824                                  */
825                                 if (do_pollfd(pfd, pt, &can_busy_loop,
826                                               busy_flag)) {
827                                         count++;
828                                         pt->_qproc = NULL;
829                                         /* found something, stop busy polling */
830                                         busy_flag = 0;
831                                         can_busy_loop = false;
832                                 }
833                         }
834                 }
835                 /*
836                  * All waiters have already been registered, so don't provide
837                  * a poll_table->_qproc to them on the next loop iteration.
838                  */
839                 pt->_qproc = NULL;
840                 if (!count) {
841                         count = wait->error;
842                         if (signal_pending(current))
843                                 count = -EINTR;
844                 }
845                 if (count || timed_out)
846                         break;
847 
848                 /* only if found POLL_BUSY_LOOP sockets && not out of time */
849                 if (can_busy_loop && !need_resched()) {
850                         if (!busy_end) {
851                                 busy_end = busy_loop_end_time();
852                                 continue;
853                         }
854                         if (!busy_loop_timeout(busy_end))
855                                 continue;
856                 }
857                 busy_flag = 0;
858 
859                 /*
860                  * If this is the first loop and we have a timeout
861                  * given, then we convert to ktime_t and set the to
862                  * pointer to the expiry value.
863                  */
864                 if (end_time && !to) {
865                         expire = timespec_to_ktime(*end_time);
866                         to = &expire;
867                 }
868 
869                 if (!poll_schedule_timeout(wait, TASK_INTERRUPTIBLE, to, slack))
870                         timed_out = 1;
871         }
872         return count;
873 }
874 
875 #define N_STACK_PPS ((sizeof(stack_pps) - sizeof(struct poll_list))  / \
876                         sizeof(struct pollfd))
877 
878 int do_sys_poll(struct pollfd __user *ufds, unsigned int nfds,
879                 struct timespec *end_time)
880 {
881         struct poll_wqueues table;
882         int err = -EFAULT, fdcount, len, size;
883         /* Allocate small arguments on the stack to save memory and be
884            faster - use long to make sure the buffer is aligned properly
885            on 64 bit archs to avoid unaligned access */
886         long stack_pps[POLL_STACK_ALLOC/sizeof(long)];
887         struct poll_list *const head = (struct poll_list *)stack_pps;
888         struct poll_list *walk = head;
889         unsigned long todo = nfds;
890 
891         if (nfds > rlimit(RLIMIT_NOFILE))
892                 return -EINVAL;
893 
894         len = min_t(unsigned int, nfds, N_STACK_PPS);
895         for (;;) {
896                 walk->next = NULL;
897                 walk->len = len;
898                 if (!len)
899                         break;
900 
901                 if (copy_from_user(walk->entries, ufds + nfds-todo,
902                                         sizeof(struct pollfd) * walk->len))
903                         goto out_fds;
904 
905                 todo -= walk->len;
906                 if (!todo)
907                         break;
908 
909                 len = min(todo, POLLFD_PER_PAGE);
910                 size = sizeof(struct poll_list) + sizeof(struct pollfd) * len;
911                 walk = walk->next = kmalloc(size, GFP_KERNEL);
912                 if (!walk) {
913                         err = -ENOMEM;
914                         goto out_fds;
915                 }
916         }
917 
918         poll_initwait(&table);
919         fdcount = do_poll(nfds, head, &table, end_time);
920         poll_freewait(&table);
921 
922         for (walk = head; walk; walk = walk->next) {
923                 struct pollfd *fds = walk->entries;
924                 int j;
925 
926                 for (j = 0; j < walk->len; j++, ufds++)
927                         if (__put_user(fds[j].revents, &ufds->revents))
928                                 goto out_fds;
929         }
930 
931         err = fdcount;
932 out_fds:
933         walk = head->next;
934         while (walk) {
935                 struct poll_list *pos = walk;
936                 walk = walk->next;
937                 kfree(pos);
938         }
939 
940         return err;
941 }
942 
943 static long do_restart_poll(struct restart_block *restart_block)
944 {
945         struct pollfd __user *ufds = restart_block->poll.ufds;
946         int nfds = restart_block->poll.nfds;
947         struct timespec *to = NULL, end_time;
948         int ret;
949 
950         if (restart_block->poll.has_timeout) {
951                 end_time.tv_sec = restart_block->poll.tv_sec;
952                 end_time.tv_nsec = restart_block->poll.tv_nsec;
953                 to = &end_time;
954         }
955 
956         ret = do_sys_poll(ufds, nfds, to);
957 
958         if (ret == -EINTR) {
959                 restart_block->fn = do_restart_poll;
960                 ret = -ERESTART_RESTARTBLOCK;
961         }
962         return ret;
963 }
964 
965 SYSCALL_DEFINE3(poll, struct pollfd __user *, ufds, unsigned int, nfds,
966                 int, timeout_msecs)
967 {
968         struct timespec end_time, *to = NULL;
969         int ret;
970 
971         if (timeout_msecs >= 0) {
972                 to = &end_time;
973                 poll_select_set_timeout(to, timeout_msecs / MSEC_PER_SEC,
974                         NSEC_PER_MSEC * (timeout_msecs % MSEC_PER_SEC));
975         }
976 
977         ret = do_sys_poll(ufds, nfds, to);
978 
979         if (ret == -EINTR) {
980                 struct restart_block *restart_block;
981 
982                 restart_block = &current->restart_block;
983                 restart_block->fn = do_restart_poll;
984                 restart_block->poll.ufds = ufds;
985                 restart_block->poll.nfds = nfds;
986 
987                 if (timeout_msecs >= 0) {
988                         restart_block->poll.tv_sec = end_time.tv_sec;
989                         restart_block->poll.tv_nsec = end_time.tv_nsec;
990                         restart_block->poll.has_timeout = 1;
991                 } else
992                         restart_block->poll.has_timeout = 0;
993 
994                 ret = -ERESTART_RESTARTBLOCK;
995         }
996         return ret;
997 }
998 
999 SYSCALL_DEFINE5(ppoll, struct pollfd __user *, ufds, unsigned int, nfds,
1000                 struct timespec __user *, tsp, const sigset_t __user *, sigmask,
1001                 size_t, sigsetsize)
1002 {
1003         sigset_t ksigmask, sigsaved;
1004         struct timespec ts, end_time, *to = NULL;
1005         int ret;
1006 
1007         if (tsp) {
1008                 if (copy_from_user(&ts, tsp, sizeof(ts)))
1009                         return -EFAULT;
1010 
1011                 to = &end_time;
1012                 if (poll_select_set_timeout(to, ts.tv_sec, ts.tv_nsec))
1013                         return -EINVAL;
1014         }
1015 
1016         if (sigmask) {
1017                 /* XXX: Don't preclude handling different sized sigset_t's.  */
1018                 if (sigsetsize != sizeof(sigset_t))
1019                         return -EINVAL;
1020                 if (copy_from_user(&ksigmask, sigmask, sizeof(ksigmask)))
1021                         return -EFAULT;
1022 
1023                 sigdelsetmask(&ksigmask, sigmask(SIGKILL)|sigmask(SIGSTOP));
1024                 sigprocmask(SIG_SETMASK, &ksigmask, &sigsaved);
1025         }
1026 
1027         ret = do_sys_poll(ufds, nfds, to);
1028 
1029         /* We can restart this syscall, usually */
1030         if (ret == -EINTR) {
1031                 /*
1032                  * Don't restore the signal mask yet. Let do_signal() deliver
1033                  * the signal on the way back to userspace, before the signal
1034                  * mask is restored.
1035                  */
1036                 if (sigmask) {
1037                         memcpy(&current->saved_sigmask, &sigsaved,
1038                                         sizeof(sigsaved));
1039                         set_restore_sigmask();
1040                 }
1041                 ret = -ERESTARTNOHAND;
1042         } else if (sigmask)
1043                 sigprocmask(SIG_SETMASK, &sigsaved, NULL);
1044 
1045         ret = poll_select_copy_remaining(&end_time, tsp, 0, ret);
1046 
1047         return ret;
1048 }
1049 

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