From: Al Viro <viro@zeniv.linux.org.uk>
Date: Wed, 2 Sep 2020 15:30:48 +0000 (-0400)
Subject: fix regression in "epoll: Keep a reference on files added to the check list"
X-Git-Tag: v4.4.236~46
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=6504c100804870911f074fd67f280756b6805958;p=thirdparty%2Fkernel%2Fstable.git

fix regression in "epoll: Keep a reference on files added to the check list"

[ Upstream commit 77f4689de17c0887775bb77896f4cc11a39bf848 ]

epoll_loop_check_proc() can run into a file already committed to destruction;
we can't grab a reference on those and don't need to add them to the set for
reverse path check anyway.

Tested-by: Marc Zyngier <maz@kernel.org>
Fixes: a9ed4a6560b8 ("epoll: Keep a reference on files added to the check list")
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---

diff --git a/fs/eventpoll.c b/fs/eventpoll.c
index b8959d0d4c723..e5324642023d6 100644
--- a/fs/eventpoll.c
+++ b/fs/eventpoll.c
@@ -1720,9 +1720,9 @@ static int ep_loop_check_proc(void *priv, void *cookie, int call_nests)
 			 * during ep_insert().
 			 */
 			if (list_empty(&epi->ffd.file->f_tfile_llink)) {
-				get_file(epi->ffd.file);
-				list_add(&epi->ffd.file->f_tfile_llink,
-					 &tfile_check_list);
+				if (get_file_rcu(epi->ffd.file))
+					list_add(&epi->ffd.file->f_tfile_llink,
+						 &tfile_check_list);
 			}
 		}
 	}