From: Nicholas Carlini <nicholas@carlini.com>
[ Upstream commit 07712db80857d5d09ae08f3df85a708ecfc3b61f ]
In certain situations, ep_free() in eventpoll.c will kfree the epi->ep
eventpoll struct while it still being used by another concurrent thread.
Defer the kfree() to an RCU callback to prevent UAF.
Fixes: f2e467a48287 ("eventpoll: Fix semi-unbounded recursion")
Signed-off-by: Nicholas Carlini <nicholas@carlini.com>
Signed-off-by: Christian Brauner <brauner@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
LLM Generated explanations, may be completely bogus:
Error: Failed to generate final synthesis
fs/eventpoll.c | 6 +++++-
1 file changed, 5 insertions(+), 1 deletion(-)
diff --git a/fs/eventpoll.c b/fs/eventpoll.c
index bcc7dcbefc419..a8e30414d996c 100644
--- a/fs/eventpoll.c
+++ b/fs/eventpoll.c
@@ -226,6 +226,9 @@ struct eventpoll {
*/
refcount_t refcount;
+ /* used to defer freeing past ep_get_upwards_depth_proc() RCU walk */
+ struct rcu_head rcu;
+
#ifdef CONFIG_NET_RX_BUSY_POLL
/* used to track busy poll napi_id */
unsigned int napi_id;
@@ -819,7 +822,8 @@ static void ep_free(struct eventpoll *ep)
mutex_destroy(&ep->mtx);
free_uid(ep->user);
wakeup_source_unregister(ep->ws);
- kfree(ep);
+ /* ep_get_upwards_depth_proc() may still hold epi->ep under RCU */
+ kfree_rcu(ep, rcu);
}
/*
--
2.53.0