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author | Oleg Nesterov <oleg@redhat.com> | 2012-02-24 20:07:29 +0100 |
---|---|---|
committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2012-02-29 16:34:35 -0800 |
commit | d10e3b2952f0df0f23896e32ed54a5a6c916058e (patch) | |
tree | 8856b6b0cd68cfd6cdfb3f1f165af3f9efc44512 /fs/signalfd.c | |
parent | 391d7bfe9ce7a08a700f1ff3dc950a347b23e3cb (diff) | |
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epoll: ep_unregister_pollwait() can use the freed pwq->whead
commit 971316f0503a5c50633d07b83b6db2f15a3a5b00 upstream.
signalfd_cleanup() ensures that ->signalfd_wqh is not used, but
this is not enough. eppoll_entry->whead still points to the memory
we are going to free, ep_unregister_pollwait()->remove_wait_queue()
is obviously unsafe.
Change ep_poll_callback(POLLFREE) to set eppoll_entry->whead = NULL,
change ep_unregister_pollwait() to check pwq->whead != NULL under
rcu_read_lock() before remove_wait_queue(). We add the new helper,
ep_remove_wait_queue(), for this.
This works because sighand_cachep is SLAB_DESTROY_BY_RCU and because
->signalfd_wqh is initialized in sighand_ctor(), not in copy_sighand.
ep_unregister_pollwait()->remove_wait_queue() can play with already
freed and potentially reused ->sighand, but this is fine. This memory
must have the valid ->signalfd_wqh until rcu_read_unlock().
Reported-by: Maxime Bizon <mbizon@freebox.fr>
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'fs/signalfd.c')
-rw-r--r-- | fs/signalfd.c | 6 |
1 files changed, 5 insertions, 1 deletions
diff --git a/fs/signalfd.c b/fs/signalfd.c index 79c1eea..7ae2a57 100644 --- a/fs/signalfd.c +++ b/fs/signalfd.c @@ -33,7 +33,11 @@ void signalfd_cleanup(struct sighand_struct *sighand) { wait_queue_head_t *wqh = &sighand->signalfd_wqh; - + /* + * The lockless check can race with remove_wait_queue() in progress, + * but in this case its caller should run under rcu_read_lock() and + * sighand_cachep is SLAB_DESTROY_BY_RCU, we can safely return. + */ if (likely(!waitqueue_active(wqh))) return; |