kernel/futex_compat.c

   1 /*
   2  * linux/kernel/futex_compat.c
   3  *
   4  * Futex compatibililty routines.
   5  *
   6  * Copyright 2006, Red Hat, Inc., Ingo Molnar
   7  */
   8
   9 #include <linux/linkage.h>
  10 #include <linux/compat.h>
  11 #include <linux/nsproxy.h>
  12 #include <linux/futex.h>
  13
  14 #include <asm/uaccess.h>
  15
  16
  17 /*
  18  * Fetch a robust-list pointer. Bit 0 signals PI futexes:
  19  */
  20 static inline int
  21 fetch_robust_entry(compat_uptr_t *uentry, struct robust_list __user **entry,
  22                    compat_uptr_t __user *head, unsigned int *pi)
  23 {
  24         if (get_user(*uentry, head))
  25                 return -EFAULT;
  26
  27         *entry = compat_ptr((*uentry) & ~1);
  28         *pi = (unsigned int)(*uentry) & 1;
  29
  30         return 0;
  31 }
  32
  33 static void __user *futex_uaddr(struct robust_list __user *entry,
  34                                 compat_long_t futex_offset)
  35 {
  36         compat_uptr_t base = ptr_to_compat(entry);
  37         void __user *uaddr = compat_ptr(base + futex_offset);
  38
  39         return uaddr;
  40 }
  41
  42 /*
  43  * Walk curr->robust_list (very carefully, it's a userspace list!)
  44  * and mark any locks found there dead, and notify any waiters.
  45  *
  46  * We silently return on any sign of list-walking problem.
  47  */
  48 void compat_exit_robust_list(struct task_struct *curr)
  49 {
  50         struct compat_robust_list_head __user *head = curr->compat_robust_list;
  51         struct robust_list __user *entry, *next_entry, *pending;
  52         unsigned int limit = ROBUST_LIST_LIMIT, pi, pip;
  53         unsigned int uninitialized_var(next_pi);
  54         compat_uptr_t uentry, next_uentry, upending;
  55         compat_long_t futex_offset;
  56         int rc;
  57
  58         if (!futex_cmpxchg_enabled)
  59                 return;
  60
  61         /*
  62          * Fetch the list head (which was registered earlier, via
  63          * sys_set_robust_list()):
  64          */
  65         if (fetch_robust_entry(&uentry, &entry, &head->list.next, &pi))
  66                 return;
  67         /*
  68          * Fetch the relative futex offset:
  69          */
  70         if (get_user(futex_offset, &head->futex_offset))
  71                 return;
  72         /*
  73          * Fetch any possibly pending lock-add first, and handle it
  74          * if it exists:
  75          */
  76         if (fetch_robust_entry(&upending, &pending,
  77                                &head->list_op_pending, &pip))
  78                 return;
  79
  80         next_entry = NULL;      /* avoid warning with gcc */
  81         while (entry != (struct robust_list __user *) &head->list) {
  82                 /*
  83                  * Fetch the next entry in the list before calling
  84                  * handle_futex_death:
  85                  */
  86                 rc = fetch_robust_entry(&next_uentry, &next_entry,
  87                         (compat_uptr_t __user *)&entry->next, &next_pi);
  88                 /*
  89                  * A pending lock might already be on the list, so
  90                  * dont process it twice:
  91                  */
  92                 if (entry != pending) {
  93                         void __user *uaddr = futex_uaddr(entry, futex_offset);
  94
  95                         if (handle_futex_death(uaddr, curr, pi))
  96                                 return;
  97                 }
  98                 if (rc)
  99                         return;
 100                 uentry = next_uentry;
 101                 entry = next_entry;
 102                 pi = next_pi;
 103                 /*
 104                  * Avoid excessively long or circular lists:
 105                  */
 106                 if (!--limit)
 107                         break;
 108
 109                 cond_resched();
 110         }
 111         if (pending) {
 112                 void __user *uaddr = futex_uaddr(pending, futex_offset);
 113
 114                 handle_futex_death(uaddr, curr, pip);
 115         }
 116 }
 117
 118 asmlinkage long
 119 compat_sys_set_robust_list(struct compat_robust_list_head __user *head,
 120                            compat_size_t len)
 121 {
 122         if (!futex_cmpxchg_enabled)
 123                 return -ENOSYS;
 124
 125         if (unlikely(len != sizeof(*head)))
 126                 return -EINVAL;
 127
 128         current->compat_robust_list = head;
 129
 130         return 0;
 131 }
 132
 133 asmlinkage long
 134 compat_sys_get_robust_list(int pid, compat_uptr_t __user *head_ptr,
 135                            compat_size_t __user *len_ptr)
 136 {
 137         struct compat_robust_list_head __user *head;
 138         unsigned long ret;
 139         const struct cred *cred = current_cred(), *pcred;
 140
 141         if (!futex_cmpxchg_enabled)
 142                 return -ENOSYS;
 143
 144         if (!pid)
 145                 head = current->compat_robust_list;
 146         else {
 147                 struct task_struct *p;
 148
 149                 ret = -ESRCH;
 150                 rcu_read_lock();
 151                 p = find_task_by_vpid(pid);
 152                 if (!p)
 153                         goto err_unlock;
 154                 ret = -EPERM;
 155                 pcred = __task_cred(p);
 156                 /* If victim is in different user_ns, then uids are not
 157                    comparable, so we must have CAP_SYS_PTRACE */
 158                 if (cred->user->user_ns != pcred->user->user_ns) {
 159                         if (!ns_capable(pcred->user->user_ns, CAP_SYS_PTRACE))
 160                                 goto err_unlock;
 161                         goto ok;
 162                 }
 163                 /* If victim is in same user_ns, then uids are comparable */
 164                 if (cred->euid != pcred->euid &&
 165                     cred->euid != pcred->uid &&
 166                     !ns_capable(pcred->user->user_ns, CAP_SYS_PTRACE))
 167                         goto err_unlock;
 168 ok:
 169                 head = p->compat_robust_list;
 170                 rcu_read_unlock();
 171         }
 172
 173         if (put_user(sizeof(*head), len_ptr))
 174                 return -EFAULT;
 175         return put_user(ptr_to_compat(head), head_ptr);
 176
 177 err_unlock:
 178         rcu_read_unlock();
 179
 180         return ret;
 181 }
 182
 183 asmlinkage long compat_sys_futex(u32 __user *uaddr, int op, u32 val,
 184                 struct compat_timespec __user *utime, u32 __user *uaddr2,
 185                 u32 val3)
 186 {
 187         struct timespec ts;
 188         ktime_t t, *tp = NULL;
 189         int val2 = 0;
 190         int cmd = op & FUTEX_CMD_MASK;
 191
 192         if (utime && (cmd == FUTEX_WAIT || cmd == FUTEX_LOCK_PI ||
 193                       cmd == FUTEX_WAIT_BITSET ||
 194                       cmd == FUTEX_WAIT_REQUEUE_PI)) {
 195                 if (get_compat_timespec(&ts, utime))
 196                         return -EFAULT;
 197                 if (!timespec_valid(&ts))
 198                         return -EINVAL;
 199
 200                 t = timespec_to_ktime(ts);
 201                 if (cmd == FUTEX_WAIT)
 202                         t = ktime_add_safe(ktime_get(), t);
 203                 tp = &t;
 204         }
 205         if (cmd == FUTEX_REQUEUE || cmd == FUTEX_CMP_REQUEUE ||
 206             cmd == FUTEX_CMP_REQUEUE_PI || cmd == FUTEX_WAKE_OP)
 207                 val2 = (int) (unsigned long) utime;
 208
 209         return do_futex(uaddr, op, val, tp, uaddr2, val2, val3);
 210 }