[Devel] [PATCH vz10 06/12] eventpoll: use hlist_is_singular_node() in __ep_remove()

[Eva Kurchatova]

From: Christian Brauner <brauner at kernel.org>

[ Upstream commit 3d9fd0abc94d8cd430cc7cd7d37ce5e5aae2cd2b ]

Replace the open-coded "epi is the only entry in file->f_ep" check
with hlist_is_singular_node(). Same semantics, and the helper avoids
the head-cacheline access in the common false case.

Link: https://patch.msgid.link/20260423-work-epoll-uaf-v1-1-2470f9eec0f5@kernel.org
Signed-off-by: Christian Brauner (Amutable) <brauner at kernel.org>
Stable-dep-of: a6dc643c6931 ("eventpoll: fix ep_remove struct eventpoll / struct file UAF")
Signed-off-by: Quentin Schulz <quentin.schulz at cherry.de>
Signed-off-by: Sasha Levin <sashal at kernel.org>
(cherry picked from commit 89dbf792b525ad7fa00b2cec747a5479efa1d323)
Signed-off-by: Eva Kurchatova <eva.kurchatova at virtuozzo.com>

https://virtuozzo.atlassian.net/browse/VSTOR-137490
Feature: fix epoll cve
---
 fs/eventpoll.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/eventpoll.c b/fs/eventpoll.c
index 6501b3e5bfc3..254f0a19d0f2 100644
--- a/fs/eventpoll.c
+++ b/fs/eventpoll.c
@@ -856,7 +856,7 @@ static bool __ep_remove(struct eventpoll *ep, struct epitem *epi, bool force)
 
 	to_free = NULL;
 	head = file->f_ep;
-	if (head->first == &epi->fllink && !epi->fllink.next) {
+	if (hlist_is_singular_node(&epi->fllink, head)) {
 		/* See eventpoll_release() for details. */
 		WRITE_ONCE(file->f_ep, NULL);
 		if (!is_file_epoll(file)) {
-- 
2.55.0