Commit ebe06187 authored Jun 17, 2014 by Konstantin Khlebnikov Committed by Linus Torvalds Jun 16, 2014

epoll: fix use-after-free in eventpoll_release_file



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 ae10b2b4 ("epoll: optimize EPOLL_CTL_DEL
using rcu")

Signed-off-by: Konstantin Khlebnikov <koct9i@gmail.com>
Reported-by: Cyrill Gorcunov <gorcunov@openvz.org>
Cc: Stable <stable@vger.kernel.org> # 3.13+
Cc: Sasha Levin <sasha.levin@oracle.com>
Cc: Jason Baron <jbaron@akamai.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent 68986c9f

fs/eventpoll.c

+2 −2

Original line number	Diff line number	Diff line
		@@ -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);