From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Subject: [PATCH] epoll: fix use-after-free in eventpoll_release_file From: Konstantin Khlebnikov To: Andrew Morton , linux-kernel@vger.kernel.org Cc: Cyrill Gorcunov , Sasha Levin , Jason Baron , Linus Torvalds , Stable Date: Tue, 17 Jun 2014 06:58:05 +0400 Message-ID: <20140617025805.29539.22007.stgit@zurg> MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: This fixes use-after-free of epi->fllink.next inside list loop macro. This loop actually releases elements in the body. List is rcu-protected but here we cannot hold rcu_read_lock because we need to lock mutex inside. 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. Bug is here since ae10b2b4eb01bedc91d29d5c5bb9e416fd806c40 ("epoll: optimize EPOLL_CTL_DEL using rcu") Signed-off-by: Konstantin Khlebnikov Reported-by: Cyrill Gorcunov Cc: Stable # 3.13+ Cc: Sasha Levin Cc: Jason Baron --- fs/eventpoll.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/fs/eventpoll.c b/fs/eventpoll.c index b73e062..b10b48c 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);