| From | Kamal Mostafa <> | Subject | [PATCH 3.13 149/198] epoll: fix use-after-free in eventpoll_release_file | Date | Tue, 15 Jul 2014 14:30:19 -0700 |
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3.13.11.5 -stable review patch. If anyone has any objections, please let me know.
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From: Konstantin Khlebnikov <koct9i@gmail.com>
commit ebe06187bf2aec10d537ce4595e416035367d703 upstream.
This fixes use-after-free of epi->fllink.next inside list loop macro. This loop actually releases elements in the body. The list is rcu-protected but here we cannot hold rcu_read_lock because we need to lock mutex inside.
The obvious solution is to use list_for_each_entry_safe(). RCU-ness isn't essential because nobody can change this list under us, it's final fput for this file.
The bug was introduced by ae10b2b4eb01 ("epoll: optimize EPOLL_CTL_DEL using rcu")
Signed-off-by: Konstantin Khlebnikov <koct9i@gmail.com> Reported-by: Cyrill Gorcunov <gorcunov@openvz.org> Cc: Sasha Levin <sasha.levin@oracle.com> Cc: Jason Baron <jbaron@akamai.com> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by: Kamal Mostafa <kamal@canonical.com> --- fs/eventpoll.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/fs/eventpoll.c b/fs/eventpoll.c index af90312..ead0046 100644 --- a/fs/eventpoll.c +++ b/fs/eventpoll.c @@ -910,7 +910,7 @@ static const struct file_operations eventpoll_fops = { void eventpoll_release_file(struct file *file) { struct eventpoll *ep; - struct epitem *epi; + struct epitem *epi, *next; /* * We don't want to get "file->f_lock" because it is not @@ -926,7 +926,7 @@ void eventpoll_release_file(struct file *file) * Besides, ep_remove() acquires the lock, so we can't hold it here. */ mutex_lock(&epmutex); - list_for_each_entry_rcu(epi, &file->f_ep_links, fllink) { + list_for_each_entry_safe(epi, next, &file->f_ep_links, fllink) { ep = epi->ep; mutex_lock_nested(&ep->mtx, 0); ep_remove(ep, epi); -- 1.9.1
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