Commit ebe06187 authored by Konstantin Khlebnikov's avatar Konstantin Khlebnikov Committed by Linus Torvalds

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: default avatarKonstantin Khlebnikov <koct9i@gmail.com>
Reported-by: default avatarCyrill 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: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 68986c9f
......@@ -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);
......
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