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 <koct9i@xxxxxxxxx>
Reported-by: Cyrill Gorcunov <gorcunov@xxxxxxxxxx>
Cc: Stable <stable@xxxxxxxxxxxxxxx> # 3.13+
Cc: Sasha Levin <sasha.levin@xxxxxxxxxx>
Cc: Jason Baron <jbaron@xxxxxxxxxx>
---
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);
--
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