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author | Linus Torvalds <torvalds@g5.osdl.org> | 2006-11-04 21:03:00 (GMT) |
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committer | Linus Torvalds <torvalds@g5.osdl.org> | 2006-11-04 21:03:00 (GMT) |
commit | 10b1fbdb0a0ca91847a534ad26d0bc250c25b74f (patch) | |
tree | 67a3e6d7069e9281b0f5819f4acf91d7150a5d74 | |
parent | 45c18b0bb579b5c1b89f8c99f1b6ffa4c586ba08 (diff) | |
download | linux-fsl-qoriq-10b1fbdb0a0ca91847a534ad26d0bc250c25b74f.tar.xz |
Make sure "user->sigpending" count is in sync
The previous commit (45c18b0bb579b5c1b89f8c99f1b6ffa4c586ba08, aka "Fix
unlikely (but possible) race condition on task->user access") fixed a
potential oops due to __sigqueue_alloc() getting its "user" pointer out
of sync with switch_user(), and accessing a user pointer that had been
de-allocated on another CPU.
It still left another (much less serious) problem, where a concurrent
__sigqueue_alloc and swich_user could cause sigqueue_alloc to do signal
pending reference counting for a _different_ user than the one it then
actually ended up using. No oops, but we'd end up with the wrong signal
accounting.
Another case of Oleg's eagle-eyes picking up the problem.
This is trivially fixed by just making sure we load whichever "user"
structure we decide to use (it doesn't matter _which_ one we pick, we
just need to pick one) just once.
Acked-by: Oleg Nesterov <oleg@tv-sign.ru>
Cc: Andrew Morton <akpm@osdl.org>
Cc: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
-rw-r--r-- | kernel/signal.c | 15 |
1 files changed, 11 insertions, 4 deletions
diff --git a/kernel/signal.c b/kernel/signal.c index 7ed8d53..df18c16 100644 --- a/kernel/signal.c +++ b/kernel/signal.c @@ -267,18 +267,25 @@ static struct sigqueue *__sigqueue_alloc(struct task_struct *t, gfp_t flags, int override_rlimit) { struct sigqueue *q = NULL; + struct user_struct *user; - atomic_inc(&t->user->sigpending); + /* + * In order to avoid problems with "switch_user()", we want to make + * sure that the compiler doesn't re-load "t->user" + */ + user = t->user; + barrier(); + atomic_inc(&user->sigpending); if (override_rlimit || - atomic_read(&t->user->sigpending) <= + atomic_read(&user->sigpending) <= t->signal->rlim[RLIMIT_SIGPENDING].rlim_cur) q = kmem_cache_alloc(sigqueue_cachep, flags); if (unlikely(q == NULL)) { - atomic_dec(&t->user->sigpending); + atomic_dec(&user->sigpending); } else { INIT_LIST_HEAD(&q->list); q->flags = 0; - q->user = get_uid(t->user); + q->user = get_uid(user); } return(q); } |