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[PATCH] send_sigqueue: simplify and fix the race 

send_sigqueue() checks PF_EXITING, then locks p->sighand->siglock.  This is
unsafe: 'p' can exit in between and set ->sighand = NULL.  The race is
theoretical, the window is tiny and irqs are disabled by the caller, so I
don't think we need the fix for -stable tree.

Convert send_sigqueue() to use lock_task_sighand() helper.

Also, delete 'p->flags & PF_EXITING' re-check, it is unneeded and the
comment is wrong.

Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
This commit is contained in:
Oleg Nesterov 2006-03-28 16:11:30 -08:00 committed by Linus Torvalds
parent a1d5e21e3e
commit 547679087b
1 changed files with 4 additions and 37 deletions
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41
kernel/signal.c
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@ -1309,12 +1309,10 @@ void sigqueue_free(struct sigqueue *q)
__sigqueue_free(q);
}
int
send_sigqueue(int sig, struct sigqueue *q, struct task_struct *p)
int send_sigqueue(int sig, struct sigqueue *q, struct task_struct *p)
{
unsigned long flags;
int ret = 0;
struct sighand_struct *sh;
BUG_ON(!(q->flags & SIGQUEUE_PREALLOC));
@ -1328,48 +1326,17 @@ send_sigqueue(int sig, struct sigqueue *q, struct task_struct *p)
*/
rcu_read_lock();
if (unlikely(p->flags & PF_EXITING)) {
if (!likely(lock_task_sighand(p, &flags))) {
ret = -1;
goto out_err;
}
retry:
sh = rcu_dereference(p->sighand);
spin_lock_irqsave(&sh->siglock, flags);
if (p->sighand != sh) {
/* We raced with exec() in a multithreaded process... */
spin_unlock_irqrestore(&sh->siglock, flags);
goto retry;
}
/*
* We do the check here again to handle the following scenario:
*
* CPU 0 CPU 1
* send_sigqueue
* check PF_EXITING
* interrupt exit code running
* __exit_signal
* lock sighand->siglock
* unlock sighand->siglock
* lock sh->siglock
* add(tsk->pending) flush_sigqueue(tsk->pending)
*
*/
if (unlikely(p->flags & PF_EXITING)) {
ret = -1;
goto out;
}
if (unlikely(!list_empty(&q->list))) {
/*
* If an SI_TIMER entry is already queue just increment
* the overrun count.
*/
if (q->info.si_code != SI_TIMER)
BUG();
BUG_ON(q->info.si_code != SI_TIMER);
q->info.si_overrun++;
goto out;
}
@ -1385,7 +1352,7 @@ retry:
signal_wake_up(p, sig == SIGKILL);
out:
spin_unlock_irqrestore(&sh->siglock, flags);
unlock_task_sighand(p, &flags);
out_err:
rcu_read_unlock();