From: Nicholas Carlini <[email protected]>
[ 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 <[email protected]>
Signed-off-by: Christian Brauner <[email protected]>
Signed-off-by: Sasha Levin <[email protected]>
(cherry picked from commit 5b1173b165421561db29f30afc7e97d940a398a9)
Signed-off-by: Eva Kurchatova <[email protected]>
https://virtuozzo.atlassian.net/browse/VSTOR-137490
Feature: fix epoll cve
---
fs/eventpoll.c | 6 +++++-
1 file changed, 5 insertions(+), 1 deletion(-)
diff --git a/fs/eventpoll.c b/fs/eventpoll.c
index 133a38f63677..6501b3e5bfc3 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);
}
/*
--
2.55.0
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