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Linux/fs/select.c

  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 <linux/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 timespec64 *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 u64 select_estimate_accuracy(struct timespec64 *tv)
 75 {
 76         u64 ret;
 77         struct timespec64 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_ts64(&now);
 87         now = timespec64_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 timespec64 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 timespec64 *to, time64_t sec, long nsec)
274 {
275         struct timespec64 ts = {.tv_sec = sec, .tv_nsec = nsec};
276 
277         if (!timespec64_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_ts64(to);
285                 *to = timespec64_add_safe(*to, ts);
286         }
287         return 0;
288 }
289 
290 static int poll_select_copy_remaining(struct timespec64 *end_time,
291                                       void __user *p,
292                                       int timeval, int ret)
293 {
294         struct timespec64 rts64;
295         struct timespec rts;
296         struct timeval rtv;
297 
298         if (!p)
299                 return ret;
300 
301         if (current->personality & STICKY_TIMEOUTS)
302                 goto sticky;
303 
304         /* No update for zero timeout */
305         if (!end_time->tv_sec && !end_time->tv_nsec)
306                 return ret;
307 
308         ktime_get_ts64(&rts64);
309         rts64 = timespec64_sub(*end_time, rts64);
310         if (rts64.tv_sec < 0)
311                 rts64.tv_sec = rts64.tv_nsec = 0;
312 
313         rts = timespec64_to_timespec(rts64);
314 
315         if (timeval) {
316                 if (sizeof(rtv) > sizeof(rtv.tv_sec) + sizeof(rtv.tv_usec))
317                         memset(&rtv, 0, sizeof(rtv));
318                 rtv.tv_sec = rts64.tv_sec;
319                 rtv.tv_usec = rts64.tv_nsec / NSEC_PER_USEC;
320 
321                 if (!copy_to_user(p, &rtv, sizeof(rtv)))
322                         return ret;
323 
324         } else if (!copy_to_user(p, &rts, sizeof(rts)))
325                 return ret;
326 
327         /*
328          * If an application puts its timeval in read-only memory, we
329          * don't want the Linux-specific update to the timeval to
330          * cause a fault after the select has completed
331          * successfully. However, because we're not updating the
332          * timeval, we can't restart the system call.
333          */
334 
335 sticky:
336         if (ret == -ERESTARTNOHAND)
337                 ret = -EINTR;
338         return ret;
339 }
340 
341 #define FDS_IN(fds, n)          (fds->in + n)
342 #define FDS_OUT(fds, n)         (fds->out + n)
343 #define FDS_EX(fds, n)          (fds->ex + n)
344 
345 #define BITS(fds, n)    (*FDS_IN(fds, n)|*FDS_OUT(fds, n)|*FDS_EX(fds, n))
346 
347 static int max_select_fd(unsigned long n, fd_set_bits *fds)
348 {
349         unsigned long *open_fds;
350         unsigned long set;
351         int max;
352         struct fdtable *fdt;
353 
354         /* handle last in-complete long-word first */
355         set = ~(~0UL << (n & (BITS_PER_LONG-1)));
356         n /= BITS_PER_LONG;
357         fdt = files_fdtable(current->files);
358         open_fds = fdt->open_fds + n;
359         max = 0;
360         if (set) {
361                 set &= BITS(fds, n);
362                 if (set) {
363                         if (!(set & ~*open_fds))
364                                 goto get_max;
365                         return -EBADF;
366                 }
367         }
368         while (n) {
369                 open_fds--;
370                 n--;
371                 set = BITS(fds, n);
372                 if (!set)
373                         continue;
374                 if (set & ~*open_fds)
375                         return -EBADF;
376                 if (max)
377                         continue;
378 get_max:
379                 do {
380                         max++;
381                         set >>= 1;
382                 } while (set);
383                 max += n * BITS_PER_LONG;
384         }
385 
386         return max;
387 }
388 
389 #define POLLIN_SET (POLLRDNORM | POLLRDBAND | POLLIN | POLLHUP | POLLERR)
390 #define POLLOUT_SET (POLLWRBAND | POLLWRNORM | POLLOUT | POLLERR)
391 #define POLLEX_SET (POLLPRI)
392 
393 static inline void wait_key_set(poll_table *wait, unsigned long in,
394                                 unsigned long out, unsigned long bit,
395                                 unsigned int ll_flag)
396 {
397         wait->_key = POLLEX_SET | ll_flag;
398         if (in & bit)
399                 wait->_key |= POLLIN_SET;
400         if (out & bit)
401                 wait->_key |= POLLOUT_SET;
402 }
403 
404 int do_select(int n, fd_set_bits *fds, struct timespec64 *end_time)
405 {
406         ktime_t expire, *to = NULL;
407         struct poll_wqueues table;
408         poll_table *wait;
409         int retval, i, timed_out = 0;
410         u64 slack = 0;
411         unsigned int busy_flag = net_busy_loop_on() ? POLL_BUSY_LOOP : 0;
412         unsigned long busy_end = 0;
413 
414         rcu_read_lock();
415         retval = max_select_fd(n, fds);
416         rcu_read_unlock();
417 
418         if (retval < 0)
419                 return retval;
420         n = retval;
421 
422         poll_initwait(&table);
423         wait = &table.pt;
424         if (end_time && !end_time->tv_sec && !end_time->tv_nsec) {
425                 wait->_qproc = NULL;
426                 timed_out = 1;
427         }
428 
429         if (end_time && !timed_out)
430                 slack = select_estimate_accuracy(end_time);
431 
432         retval = 0;
433         for (;;) {
434                 unsigned long *rinp, *routp, *rexp, *inp, *outp, *exp;
435                 bool can_busy_loop = false;
436 
437                 inp = fds->in; outp = fds->out; exp = fds->ex;
438                 rinp = fds->res_in; routp = fds->res_out; rexp = fds->res_ex;
439 
440                 for (i = 0; i < n; ++rinp, ++routp, ++rexp) {
441                         unsigned long in, out, ex, all_bits, bit = 1, mask, j;
442                         unsigned long res_in = 0, res_out = 0, res_ex = 0;
443 
444                         in = *inp++; out = *outp++; ex = *exp++;
445                         all_bits = in | out | ex;
446                         if (all_bits == 0) {
447                                 i += BITS_PER_LONG;
448                                 continue;
449                         }
450 
451                         for (j = 0; j < BITS_PER_LONG; ++j, ++i, bit <<= 1) {
452                                 struct fd f;
453                                 if (i >= n)
454                                         break;
455                                 if (!(bit & all_bits))
456                                         continue;
457                                 f = fdget(i);
458                                 if (f.file) {
459                                         const struct file_operations *f_op;
460                                         f_op = f.file->f_op;
461                                         mask = DEFAULT_POLLMASK;
462                                         if (f_op->poll) {
463                                                 wait_key_set(wait, in, out,
464                                                              bit, busy_flag);
465                                                 mask = (*f_op->poll)(f.file, wait);
466                                         }
467                                         fdput(f);
468                                         if ((mask & POLLIN_SET) && (in & bit)) {
469                                                 res_in |= bit;
470                                                 retval++;
471                                                 wait->_qproc = NULL;
472                                         }
473                                         if ((mask & POLLOUT_SET) && (out & bit)) {
474                                                 res_out |= bit;
475                                                 retval++;
476                                                 wait->_qproc = NULL;
477                                         }
478                                         if ((mask & POLLEX_SET) && (ex & bit)) {
479                                                 res_ex |= bit;
480                                                 retval++;
481                                                 wait->_qproc = NULL;
482                                         }
483                                         /* got something, stop busy polling */
484                                         if (retval) {
485                                                 can_busy_loop = false;
486                                                 busy_flag = 0;
487 
488                                         /*
489                                          * only remember a returned
490                                          * POLL_BUSY_LOOP if we asked for it
491                                          */
492                                         } else if (busy_flag & mask)
493                                                 can_busy_loop = true;
494 
495                                 }
496                         }
497                         if (res_in)
498                                 *rinp = res_in;
499                         if (res_out)
500                                 *routp = res_out;
501                         if (res_ex)
502                                 *rexp = res_ex;
503                         cond_resched();
504                 }
505                 wait->_qproc = NULL;
506                 if (retval || timed_out || signal_pending(current))
507                         break;
508                 if (table.error) {
509                         retval = table.error;
510                         break;
511                 }
512 
513                 /* only if found POLL_BUSY_LOOP sockets && not out of time */
514                 if (can_busy_loop && !need_resched()) {
515                         if (!busy_end) {
516                                 busy_end = busy_loop_end_time();
517                                 continue;
518                         }
519                         if (!busy_loop_timeout(busy_end))
520                                 continue;
521                 }
522                 busy_flag = 0;
523 
524                 /*
525                  * If this is the first loop and we have a timeout
526                  * given, then we convert to ktime_t and set the to
527                  * pointer to the expiry value.
528                  */
529                 if (end_time && !to) {
530                         expire = timespec64_to_ktime(*end_time);
531                         to = &expire;
532                 }
533 
534                 if (!poll_schedule_timeout(&table, TASK_INTERRUPTIBLE,
535                                            to, slack))
536                         timed_out = 1;
537         }
538 
539         poll_freewait(&table);
540 
541         return retval;
542 }
543 
544 /*
545  * We can actually return ERESTARTSYS instead of EINTR, but I'd
546  * like to be certain this leads to no problems. So I return
547  * EINTR just for safety.
548  *
549  * Update: ERESTARTSYS breaks at least the xview clock binary, so
550  * I'm trying ERESTARTNOHAND which restart only when you want to.
551  */
552 int core_sys_select(int n, fd_set __user *inp, fd_set __user *outp,
553                            fd_set __user *exp, struct timespec64 *end_time)
554 {
555         fd_set_bits fds;
556         void *bits;
557         int ret, max_fds;
558         size_t size, alloc_size;
559         struct fdtable *fdt;
560         /* Allocate small arguments on the stack to save memory and be faster */
561         long stack_fds[SELECT_STACK_ALLOC/sizeof(long)];
562 
563         ret = -EINVAL;
564         if (n < 0)
565                 goto out_nofds;
566 
567         /* max_fds can increase, so grab it once to avoid race */
568         rcu_read_lock();
569         fdt = files_fdtable(current->files);
570         max_fds = fdt->max_fds;
571         rcu_read_unlock();
572         if (n > max_fds)
573                 n = max_fds;
574 
575         /*
576          * We need 6 bitmaps (in/out/ex for both incoming and outgoing),
577          * since we used fdset we need to allocate memory in units of
578          * long-words. 
579          */
580         size = FDS_BYTES(n);
581         bits = stack_fds;
582         if (size > sizeof(stack_fds) / 6) {
583                 /* Not enough space in on-stack array; must use kmalloc */
584                 ret = -ENOMEM;
585                 if (size > (SIZE_MAX / 6))
586                         goto out_nofds;
587 
588                 alloc_size = 6 * size;
589                 bits = kmalloc(alloc_size, GFP_KERNEL|__GFP_NOWARN);
590                 if (!bits && alloc_size > PAGE_SIZE)
591                         bits = vmalloc(alloc_size);
592 
593                 if (!bits)
594                         goto out_nofds;
595         }
596         fds.in      = bits;
597         fds.out     = bits +   size;
598         fds.ex      = bits + 2*size;
599         fds.res_in  = bits + 3*size;
600         fds.res_out = bits + 4*size;
601         fds.res_ex  = bits + 5*size;
602 
603         if ((ret = get_fd_set(n, inp, fds.in)) ||
604             (ret = get_fd_set(n, outp, fds.out)) ||
605             (ret = get_fd_set(n, exp, fds.ex)))
606                 goto out;
607         zero_fd_set(n, fds.res_in);
608         zero_fd_set(n, fds.res_out);
609         zero_fd_set(n, fds.res_ex);
610 
611         ret = do_select(n, &fds, end_time);
612 
613         if (ret < 0)
614                 goto out;
615         if (!ret) {
616                 ret = -ERESTARTNOHAND;
617                 if (signal_pending(current))
618                         goto out;
619                 ret = 0;
620         }
621 
622         if (set_fd_set(n, inp, fds.res_in) ||
623             set_fd_set(n, outp, fds.res_out) ||
624             set_fd_set(n, exp, fds.res_ex))
625                 ret = -EFAULT;
626 
627 out:
628         if (bits != stack_fds)
629                 kvfree(bits);
630 out_nofds:
631         return ret;
632 }
633 
634 SYSCALL_DEFINE5(select, int, n, fd_set __user *, inp, fd_set __user *, outp,
635                 fd_set __user *, exp, struct timeval __user *, tvp)
636 {
637         struct timespec64 end_time, *to = NULL;
638         struct timeval tv;
639         int ret;
640 
641         if (tvp) {
642                 if (copy_from_user(&tv, tvp, sizeof(tv)))
643                         return -EFAULT;
644 
645                 to = &end_time;
646                 if (poll_select_set_timeout(to,
647                                 tv.tv_sec + (tv.tv_usec / USEC_PER_SEC),
648                                 (tv.tv_usec % USEC_PER_SEC) * NSEC_PER_USEC))
649                         return -EINVAL;
650         }
651 
652         ret = core_sys_select(n, inp, outp, exp, to);
653         ret = poll_select_copy_remaining(&end_time, tvp, 1, ret);
654 
655         return ret;
656 }
657 
658 static long do_pselect(int n, fd_set __user *inp, fd_set __user *outp,
659                        fd_set __user *exp, struct timespec __user *tsp,
660                        const sigset_t __user *sigmask, size_t sigsetsize)
661 {
662         sigset_t ksigmask, sigsaved;
663         struct timespec ts;
664         struct timespec64 ts64, end_time, *to = NULL;
665         int ret;
666 
667         if (tsp) {
668                 if (copy_from_user(&ts, tsp, sizeof(ts)))
669                         return -EFAULT;
670                 ts64 = timespec_to_timespec64(ts);
671 
672                 to = &end_time;
673                 if (poll_select_set_timeout(to, ts64.tv_sec, ts64.tv_nsec))
674                         return -EINVAL;
675         }
676 
677         if (sigmask) {
678                 /* XXX: Don't preclude handling different sized sigset_t's.  */
679                 if (sigsetsize != sizeof(sigset_t))
680                         return -EINVAL;
681                 if (copy_from_user(&ksigmask, sigmask, sizeof(ksigmask)))
682                         return -EFAULT;
683 
684                 sigdelsetmask(&ksigmask, sigmask(SIGKILL)|sigmask(SIGSTOP));
685                 sigprocmask(SIG_SETMASK, &ksigmask, &sigsaved);
686         }
687 
688         ret = core_sys_select(n, inp, outp, exp, to);
689         ret = poll_select_copy_remaining(&end_time, tsp, 0, ret);
690 
691         if (ret == -ERESTARTNOHAND) {
692                 /*
693                  * Don't restore the signal mask yet. Let do_signal() deliver
694                  * the signal on the way back to userspace, before the signal
695                  * mask is restored.
696                  */
697                 if (sigmask) {
698                         memcpy(&current->saved_sigmask, &sigsaved,
699                                         sizeof(sigsaved));
700                         set_restore_sigmask();
701                 }
702         } else if (sigmask)
703                 sigprocmask(SIG_SETMASK, &sigsaved, NULL);
704 
705         return ret;
706 }
707 
708 /*
709  * Most architectures can't handle 7-argument syscalls. So we provide a
710  * 6-argument version where the sixth argument is a pointer to a structure
711  * which has a pointer to the sigset_t itself followed by a size_t containing
712  * the sigset size.
713  */
714 SYSCALL_DEFINE6(pselect6, int, n, fd_set __user *, inp, fd_set __user *, outp,
715                 fd_set __user *, exp, struct timespec __user *, tsp,
716                 void __user *, sig)
717 {
718         size_t sigsetsize = 0;
719         sigset_t __user *up = NULL;
720 
721         if (sig) {
722                 if (!access_ok(VERIFY_READ, sig, sizeof(void *)+sizeof(size_t))
723                     || __get_user(up, (sigset_t __user * __user *)sig)
724                     || __get_user(sigsetsize,
725                                 (size_t __user *)(sig+sizeof(void *))))
726                         return -EFAULT;
727         }
728 
729         return do_pselect(n, inp, outp, exp, tsp, up, sigsetsize);
730 }
731 
732 #ifdef __ARCH_WANT_SYS_OLD_SELECT
733 struct sel_arg_struct {
734         unsigned long n;
735         fd_set __user *inp, *outp, *exp;
736         struct timeval __user *tvp;
737 };
738 
739 SYSCALL_DEFINE1(old_select, struct sel_arg_struct __user *, arg)
740 {
741         struct sel_arg_struct a;
742 
743         if (copy_from_user(&a, arg, sizeof(a)))
744                 return -EFAULT;
745         return sys_select(a.n, a.inp, a.outp, a.exp, a.tvp);
746 }
747 #endif
748 
749 struct poll_list {
750         struct poll_list *next;
751         int len;
752         struct pollfd entries[0];
753 };
754 
755 #define POLLFD_PER_PAGE  ((PAGE_SIZE-sizeof(struct poll_list)) / sizeof(struct pollfd))
756 
757 /*
758  * Fish for pollable events on the pollfd->fd file descriptor. We're only
759  * interested in events matching the pollfd->events mask, and the result
760  * matching that mask is both recorded in pollfd->revents and returned. The
761  * pwait poll_table will be used by the fd-provided poll handler for waiting,
762  * if pwait->_qproc is non-NULL.
763  */
764 static inline unsigned int do_pollfd(struct pollfd *pollfd, poll_table *pwait,
765                                      bool *can_busy_poll,
766                                      unsigned int busy_flag)
767 {
768         unsigned int mask;
769         int fd;
770 
771         mask = 0;
772         fd = pollfd->fd;
773         if (fd >= 0) {
774                 struct fd f = fdget(fd);
775                 mask = POLLNVAL;
776                 if (f.file) {
777                         mask = DEFAULT_POLLMASK;
778                         if (f.file->f_op->poll) {
779                                 pwait->_key = pollfd->events|POLLERR|POLLHUP;
780                                 pwait->_key |= busy_flag;
781                                 mask = f.file->f_op->poll(f.file, pwait);
782                                 if (mask & busy_flag)
783                                         *can_busy_poll = true;
784                         }
785                         /* Mask out unneeded events. */
786                         mask &= pollfd->events | POLLERR | POLLHUP;
787                         fdput(f);
788                 }
789         }
790         pollfd->revents = mask;
791 
792         return mask;
793 }
794 
795 static int do_poll(struct poll_list *list, struct poll_wqueues *wait,
796                    struct timespec64 *end_time)
797 {
798         poll_table* pt = &wait->pt;
799         ktime_t expire, *to = NULL;
800         int timed_out = 0, count = 0;
801         u64 slack = 0;
802         unsigned int busy_flag = net_busy_loop_on() ? POLL_BUSY_LOOP : 0;
803         unsigned long busy_end = 0;
804 
805         /* Optimise the no-wait case */
806         if (end_time && !end_time->tv_sec && !end_time->tv_nsec) {
807                 pt->_qproc = NULL;
808                 timed_out = 1;
809         }
810 
811         if (end_time && !timed_out)
812                 slack = select_estimate_accuracy(end_time);
813 
814         for (;;) {
815                 struct poll_list *walk;
816                 bool can_busy_loop = false;
817 
818                 for (walk = list; walk != NULL; walk = walk->next) {
819                         struct pollfd * pfd, * pfd_end;
820 
821                         pfd = walk->entries;
822                         pfd_end = pfd + walk->len;
823                         for (; pfd != pfd_end; pfd++) {
824                                 /*
825                                  * Fish for events. If we found one, record it
826                                  * and kill poll_table->_qproc, so we don't
827                                  * needlessly register any other waiters after
828                                  * this. They'll get immediately deregistered
829                                  * when we break out and return.
830                                  */
831                                 if (do_pollfd(pfd, pt, &can_busy_loop,
832                                               busy_flag)) {
833                                         count++;
834                                         pt->_qproc = NULL;
835                                         /* found something, stop busy polling */
836                                         busy_flag = 0;
837                                         can_busy_loop = false;
838                                 }
839                         }
840                 }
841                 /*
842                  * All waiters have already been registered, so don't provide
843                  * a poll_table->_qproc to them on the next loop iteration.
844                  */
845                 pt->_qproc = NULL;
846                 if (!count) {
847                         count = wait->error;
848                         if (signal_pending(current))
849                                 count = -EINTR;
850                 }
851                 if (count || timed_out)
852                         break;
853 
854                 /* only if found POLL_BUSY_LOOP sockets && not out of time */
855                 if (can_busy_loop && !need_resched()) {
856                         if (!busy_end) {
857                                 busy_end = busy_loop_end_time();
858                                 continue;
859                         }
860                         if (!busy_loop_timeout(busy_end))
861                                 continue;
862                 }
863                 busy_flag = 0;
864 
865                 /*
866                  * If this is the first loop and we have a timeout
867                  * given, then we convert to ktime_t and set the to
868                  * pointer to the expiry value.
869                  */
870                 if (end_time && !to) {
871                         expire = timespec64_to_ktime(*end_time);
872                         to = &expire;
873                 }
874 
875                 if (!poll_schedule_timeout(wait, TASK_INTERRUPTIBLE, to, slack))
876                         timed_out = 1;
877         }
878         return count;
879 }
880 
881 #define N_STACK_PPS ((sizeof(stack_pps) - sizeof(struct poll_list))  / \
882                         sizeof(struct pollfd))
883 
884 int do_sys_poll(struct pollfd __user *ufds, unsigned int nfds,
885                 struct timespec64 *end_time)
886 {
887         struct poll_wqueues table;
888         int err = -EFAULT, fdcount, len, size;
889         /* Allocate small arguments on the stack to save memory and be
890            faster - use long to make sure the buffer is aligned properly
891            on 64 bit archs to avoid unaligned access */
892         long stack_pps[POLL_STACK_ALLOC/sizeof(long)];
893         struct poll_list *const head = (struct poll_list *)stack_pps;
894         struct poll_list *walk = head;
895         unsigned long todo = nfds;
896 
897         if (nfds > rlimit(RLIMIT_NOFILE))
898                 return -EINVAL;
899 
900         len = min_t(unsigned int, nfds, N_STACK_PPS);
901         for (;;) {
902                 walk->next = NULL;
903                 walk->len = len;
904                 if (!len)
905                         break;
906 
907                 if (copy_from_user(walk->entries, ufds + nfds-todo,
908                                         sizeof(struct pollfd) * walk->len))
909                         goto out_fds;
910 
911                 todo -= walk->len;
912                 if (!todo)
913                         break;
914 
915                 len = min(todo, POLLFD_PER_PAGE);
916                 size = sizeof(struct poll_list) + sizeof(struct pollfd) * len;
917                 walk = walk->next = kmalloc(size, GFP_KERNEL);
918                 if (!walk) {
919                         err = -ENOMEM;
920                         goto out_fds;
921                 }
922         }
923 
924         poll_initwait(&table);
925         fdcount = do_poll(head, &table, end_time);
926         poll_freewait(&table);
927 
928         for (walk = head; walk; walk = walk->next) {
929                 struct pollfd *fds = walk->entries;
930                 int j;
931 
932                 for (j = 0; j < walk->len; j++, ufds++)
933                         if (__put_user(fds[j].revents, &ufds->revents))
934                                 goto out_fds;
935         }
936 
937         err = fdcount;
938 out_fds:
939         walk = head->next;
940         while (walk) {
941                 struct poll_list *pos = walk;
942                 walk = walk->next;
943                 kfree(pos);
944         }
945 
946         return err;
947 }
948 
949 static long do_restart_poll(struct restart_block *restart_block)
950 {
951         struct pollfd __user *ufds = restart_block->poll.ufds;
952         int nfds = restart_block->poll.nfds;
953         struct timespec64 *to = NULL, end_time;
954         int ret;
955 
956         if (restart_block->poll.has_timeout) {
957                 end_time.tv_sec = restart_block->poll.tv_sec;
958                 end_time.tv_nsec = restart_block->poll.tv_nsec;
959                 to = &end_time;
960         }
961 
962         ret = do_sys_poll(ufds, nfds, to);
963 
964         if (ret == -EINTR) {
965                 restart_block->fn = do_restart_poll;
966                 ret = -ERESTART_RESTARTBLOCK;
967         }
968         return ret;
969 }
970 
971 SYSCALL_DEFINE3(poll, struct pollfd __user *, ufds, unsigned int, nfds,
972                 int, timeout_msecs)
973 {
974         struct timespec64 end_time, *to = NULL;
975         int ret;
976 
977         if (timeout_msecs >= 0) {
978                 to = &end_time;
979                 poll_select_set_timeout(to, timeout_msecs / MSEC_PER_SEC,
980                         NSEC_PER_MSEC * (timeout_msecs % MSEC_PER_SEC));
981         }
982 
983         ret = do_sys_poll(ufds, nfds, to);
984 
985         if (ret == -EINTR) {
986                 struct restart_block *restart_block;
987 
988                 restart_block = &current->restart_block;
989                 restart_block->fn = do_restart_poll;
990                 restart_block->poll.ufds = ufds;
991                 restart_block->poll.nfds = nfds;
992 
993                 if (timeout_msecs >= 0) {
994                         restart_block->poll.tv_sec = end_time.tv_sec;
995                         restart_block->poll.tv_nsec = end_time.tv_nsec;
996                         restart_block->poll.has_timeout = 1;
997                 } else
998                         restart_block->poll.has_timeout = 0;
999 
1000                 ret = -ERESTART_RESTARTBLOCK;
1001         }
1002         return ret;
1003 }
1004 
1005 SYSCALL_DEFINE5(ppoll, struct pollfd __user *, ufds, unsigned int, nfds,
1006                 struct timespec __user *, tsp, const sigset_t __user *, sigmask,
1007                 size_t, sigsetsize)
1008 {
1009         sigset_t ksigmask, sigsaved;
1010         struct timespec ts;
1011         struct timespec64 end_time, *to = NULL;
1012         int ret;
1013 
1014         if (tsp) {
1015                 if (copy_from_user(&ts, tsp, sizeof(ts)))
1016                         return -EFAULT;
1017 
1018                 to = &end_time;
1019                 if (poll_select_set_timeout(to, ts.tv_sec, ts.tv_nsec))
1020                         return -EINVAL;
1021         }
1022 
1023         if (sigmask) {
1024                 /* XXX: Don't preclude handling different sized sigset_t's.  */
1025                 if (sigsetsize != sizeof(sigset_t))
1026                         return -EINVAL;
1027                 if (copy_from_user(&ksigmask, sigmask, sizeof(ksigmask)))
1028                         return -EFAULT;
1029 
1030                 sigdelsetmask(&ksigmask, sigmask(SIGKILL)|sigmask(SIGSTOP));
1031                 sigprocmask(SIG_SETMASK, &ksigmask, &sigsaved);
1032         }
1033 
1034         ret = do_sys_poll(ufds, nfds, to);
1035 
1036         /* We can restart this syscall, usually */
1037         if (ret == -EINTR) {
1038                 /*
1039                  * Don't restore the signal mask yet. Let do_signal() deliver
1040                  * the signal on the way back to userspace, before the signal
1041                  * mask is restored.
1042                  */
1043                 if (sigmask) {
1044                         memcpy(&current->saved_sigmask, &sigsaved,
1045                                         sizeof(sigsaved));
1046                         set_restore_sigmask();
1047                 }
1048                 ret = -ERESTARTNOHAND;
1049         } else if (sigmask)
1050                 sigprocmask(SIG_SETMASK, &sigsaved, NULL);
1051 
1052         ret = poll_select_copy_remaining(&end_time, tsp, 0, ret);
1053 
1054         return ret;
1055 }
1056 

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