kernel/futex_compat.c

   1 // SPDX-License-Identifier: GPL-2.0
   2 /*
   3  * linux/kernel/futex_compat.c
   4  *
   5  * Futex compatibililty routines.
   6  *
   7  * Copyright 2006, Red Hat, Inc., Ingo Molnar
   8  */
   9
  10 #include <linux/linkage.h>
  11 #include <linux/compat.h>
  12 #include <linux/nsproxy.h>
  13 #include <linux/futex.h>
  14 #include <linux/ptrace.h>
  15 #include <linux/syscalls.h>
  16
  17 #include <linux/uaccess.h>
  18
  19
  20 /*
  21  * Fetch a robust-list pointer. Bit 0 signals PI futexes:
  22  */
  23 static inline int
  24 fetch_robust_entry(compat_uptr_t *uentry, struct robust_list __user **entry,
  25                    compat_uptr_t __user *head, unsigned int *pi)
  26 {
  27         if (get_user(*uentry, head))
  28                 return -EFAULT;
  29
  30         *entry = compat_ptr((*uentry) & ~1);
  31         *pi = (unsigned int)(*uentry) & 1;
  32
  33         return 0;
  34 }
  35
  36 static void __user *futex_uaddr(struct robust_list __user *entry,
  37                                 compat_long_t futex_offset)
  38 {
  39         compat_uptr_t base = ptr_to_compat(entry);
  40         void __user *uaddr = compat_ptr(base + futex_offset);
  41
  42         return uaddr;
  43 }
  44
  45 /*
  46  * Walk curr->robust_list (very carefully, it's a userspace list!)
  47  * and mark any locks found there dead, and notify any waiters.
  48  *
  49  * We silently return on any sign of list-walking problem.
  50  */
  51 void compat_exit_robust_list(struct task_struct *curr)
  52 {
  53         struct compat_robust_list_head __user *head = curr->compat_robust_list;
  54         struct robust_list __user *entry, *next_entry, *pending;
  55         unsigned int limit = ROBUST_LIST_LIMIT, pi, pip;
  56         unsigned int uninitialized_var(next_pi);
  57         compat_uptr_t uentry, next_uentry, upending;
  58         compat_long_t futex_offset;
  59         int rc;
  60
  61         if (!futex_cmpxchg_enabled)
  62                 return;
  63
  64         /*
  65          * Fetch the list head (which was registered earlier, via
  66          * sys_set_robust_list()):
  67          */
  68         if (fetch_robust_entry(&uentry, &entry, &head->list.next, &pi))
  69                 return;
  70         /*
  71          * Fetch the relative futex offset:
  72          */
  73         if (get_user(futex_offset, &head->futex_offset))
  74                 return;
  75         /*
  76          * Fetch any possibly pending lock-add first, and handle it
  77          * if it exists:
  78          */
  79         if (fetch_robust_entry(&upending, &pending,
  80                                &head->list_op_pending, &pip))
  81                 return;
  82
  83         next_entry = NULL;      /* avoid warning with gcc */
  84         while (entry != (struct robust_list __user *) &head->list) {
  85                 /*
  86                  * Fetch the next entry in the list before calling
  87                  * handle_futex_death:
  88                  */
  89                 rc = fetch_robust_entry(&next_uentry, &next_entry,
  90                         (compat_uptr_t __user *)&entry->next, &next_pi);
  91                 /*
  92                  * A pending lock might already be on the list, so
  93                  * dont process it twice:
  94                  */
  95                 if (entry != pending) {
  96                         void __user *uaddr = futex_uaddr(entry, futex_offset);
  97
  98                         if (handle_futex_death(uaddr, curr, pi))
  99                                 return;
 100                 }
 101                 if (rc)
 102                         return;
 103                 uentry = next_uentry;
 104                 entry = next_entry;
 105                 pi = next_pi;
 106                 /*
 107                  * Avoid excessively long or circular lists:
 108                  */
 109                 if (!--limit)
 110                         break;
 111
 112                 cond_resched();
 113         }
 114         if (pending) {
 115                 void __user *uaddr = futex_uaddr(pending, futex_offset);
 116
 117                 handle_futex_death(uaddr, curr, pip);
 118         }
 119 }
 120
 121 COMPAT_SYSCALL_DEFINE2(set_robust_list,
 122                 struct compat_robust_list_head __user *, head,
 123                 compat_size_t, len)
 124 {
 125         if (!futex_cmpxchg_enabled)
 126                 return -ENOSYS;
 127
 128         if (unlikely(len != sizeof(*head)))
 129                 return -EINVAL;
 130
 131         current->compat_robust_list = head;
 132
 133         return 0;
 134 }
 135
 136 COMPAT_SYSCALL_DEFINE3(get_robust_list, int, pid,
 137                         compat_uptr_t __user *, head_ptr,
 138                         compat_size_t __user *, len_ptr)
 139 {
 140         struct compat_robust_list_head __user *head;
 141         unsigned long ret;
 142         struct task_struct *p;
 143
 144         if (!futex_cmpxchg_enabled)
 145                 return -ENOSYS;
 146
 147         rcu_read_lock();
 148
 149         ret = -ESRCH;
 150         if (!pid)
 151                 p = current;
 152         else {
 153                 p = find_task_by_vpid(pid);
 154                 if (!p)
 155                         goto err_unlock;
 156         }
 157
 158         ret = -EPERM;
 159         if (!ptrace_may_access(p, PTRACE_MODE_READ_REALCREDS))
 160                 goto err_unlock;
 161
 162         head = p->compat_robust_list;
 163         rcu_read_unlock();
 164
 165         if (put_user(sizeof(*head), len_ptr))
 166                 return -EFAULT;
 167         return put_user(ptr_to_compat(head), head_ptr);
 168
 169 err_unlock:
 170         rcu_read_unlock();
 171
 172         return ret;
 173 }
 174
 175 COMPAT_SYSCALL_DEFINE6(futex, u32 __user *, uaddr, int, op, u32, val,
 176                 struct compat_timespec __user *, utime, u32 __user *, uaddr2,
 177                 u32, val3)
 178 {
 179         struct timespec ts;
 180         ktime_t t, *tp = NULL;
 181         int val2 = 0;
 182         int cmd = op & FUTEX_CMD_MASK;
 183
 184         if (utime && (cmd == FUTEX_WAIT || cmd == FUTEX_LOCK_PI ||
 185                       cmd == FUTEX_WAIT_BITSET ||
 186                       cmd == FUTEX_WAIT_REQUEUE_PI)) {
 187                 if (compat_get_timespec(&ts, utime))
 188                         return -EFAULT;
 189                 if (!timespec_valid(&ts))
 190                         return -EINVAL;
 191
 192                 t = timespec_to_ktime(ts);
 193                 if (cmd == FUTEX_WAIT)
 194                         t = ktime_add_safe(ktime_get(), t);
 195                 tp = &t;
 196         }
 197         if (cmd == FUTEX_REQUEUE || cmd == FUTEX_CMP_REQUEUE ||
 198             cmd == FUTEX_CMP_REQUEUE_PI || cmd == FUTEX_WAKE_OP)
 199                 val2 = (int) (unsigned long) utime;
 200
 201         return do_futex(uaddr, op, val, tp, uaddr2, val2, val3);
 202 }