diff options
Diffstat (limited to 'kernel')
| -rw-r--r-- | kernel/futex.c | 71 |
1 files changed, 65 insertions, 6 deletions
diff --git a/kernel/futex.c b/kernel/futex.c index 439fbede963d..4894c0934205 100644 --- a/kernel/futex.c +++ b/kernel/futex.c @@ -1198,11 +1198,67 @@ static void wait_for_owner_exiting(int ret, struct task_struct *exiting) put_task_struct(exiting); } +static int handle_exit_race(u32 __user *uaddr, u32 uval, + struct task_struct *tsk) +{ + u32 uval2; + + /* + * If the futex exit state is not yet FUTEX_STATE_DEAD, wait + * for it to finish. + */ + if (tsk && tsk->futex_state != FUTEX_STATE_DEAD) + return -EAGAIN; + + /* + * Reread the user space value to handle the following situation: + * + * CPU0 CPU1 + * + * sys_exit() sys_futex() + * do_exit() futex_lock_pi() + * futex_lock_pi_atomic() + * exit_signals(tsk) No waiters: + * tsk->flags |= PF_EXITING; *uaddr == 0x00000PID + * mm_release(tsk) Set waiter bit + * exit_robust_list(tsk) { *uaddr = 0x80000PID; + * Set owner died attach_to_pi_owner() { + * *uaddr = 0xC0000000; tsk = get_task(PID); + * } if (!tsk->flags & PF_EXITING) { + * ... attach(); + * tsk->futex_state = } else { + * FUTEX_STATE_DEAD; if (tsk->futex_state != + * FUTEX_STATE_DEAD) + * return -EAGAIN; + * return -ESRCH; <--- FAIL + * } + * + * Returning ESRCH unconditionally is wrong here because the + * user space value has been changed by the exiting task. + * + * The same logic applies to the case where the exiting task is + * already gone. + */ + if (get_futex_value_locked(&uval2, uaddr)) + return -EFAULT; + + /* If the user space value has changed, try again. */ + if (uval2 != uval) + return -EAGAIN; + + /* + * The exiting task did not have a robust list, the robust list was + * corrupted or the user space value in *uaddr is simply bogus. + * Give up and tell user space. + */ + return -ESRCH; +} + /* * Lookup the task for the TID provided from user space and attach to * it after doing proper sanity checks. */ -static int attach_to_pi_owner(u32 uval, union futex_key *key, +static int attach_to_pi_owner(u32 __user *uaddr, u32 uval, union futex_key *key, struct futex_pi_state **ps, struct task_struct **exiting) { @@ -1213,12 +1269,15 @@ static int attach_to_pi_owner(u32 uval, union futex_key *key, /* * We are the first waiter - try to look up the real owner and attach * the new pi_state to it, but bail out when TID = 0 [1] + * + * The !pid check is paranoid. None of the call sites should end up + * with pid == 0, but better safe than sorry. Let the caller retry */ if (!pid) - return -ESRCH; + return -EAGAIN; p = futex_find_get_task(pid); if (!p) - return -ESRCH; + return handle_exit_race(uaddr, uval, NULL); if (unlikely(p->flags & PF_KTHREAD)) { put_task_struct(p); @@ -1237,7 +1296,7 @@ static int attach_to_pi_owner(u32 uval, union futex_key *key, * FUTEX_STATE_DEAD, we know that the task has finished * the cleanup: */ - int ret = (p->futex_state = FUTEX_STATE_DEAD) ? -ESRCH : -EAGAIN; + int ret = handle_exit_race(uaddr, uval, p); raw_spin_unlock_irq(&p->pi_lock); /* @@ -1303,7 +1362,7 @@ static int lookup_pi_state(u32 __user *uaddr, u32 uval, * We are the first waiter - try to look up the owner based on * @uval and attach to it. */ - return attach_to_pi_owner(uval, key, ps, exiting); + return attach_to_pi_owner(uaddr, uval, key, ps, exiting); } static int lock_pi_update_atomic(u32 __user *uaddr, u32 uval, u32 newval) @@ -1419,7 +1478,7 @@ static int futex_lock_pi_atomic(u32 __user *uaddr, struct futex_hash_bucket *hb, * attach to the owner. If that fails, no harm done, we only * set the FUTEX_WAITERS bit in the user space variable. */ - return attach_to_pi_owner(uval, key, ps, exiting); + return attach_to_pi_owner(uaddr, newval, key, ps, exiting); } /** |