From: Nicholas Carlini <nicholas@carlini.com>
Date: Tue, 31 Mar 2026 13:25:32 +0000 (+0200)
Subject: eventpoll: defer struct eventpoll free to RCU grace period
X-Git-Url: http://git.ipfire.org/gitweb.cgi?a=commitdiff_plain;h=07712db80857d5d09ae08f3df85a708ecfc3b61f;p=thirdparty%2Flinux.git

eventpoll: defer struct eventpoll free to RCU grace period

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>
---

diff --git a/fs/eventpoll.c b/fs/eventpoll.c
index 5714e900567c..4b43bf41296d 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);
 }
 
 /*