diff options
| author | Eric Dumazet <edumazet@google.com> | 2026-06-23 17:30:29 +0000 |
|---|---|---|
| committer | Jakub Kicinski <kuba@kernel.org> | 2026-06-25 08:53:00 -0700 |
| commit | 7116764ca53ff529335d7ab7c364a69f094b23a5 (patch) | |
| tree | 31fae2d28997d256314f0b8bc89c71fef8c98e18 /net | |
| parent | 36323f54cd323122a1be89ab2c316a6e55a94e30 (diff) | |
| download | ath-7116764ca53ff529335d7ab7c364a69f094b23a5.tar.gz | |
tipc: fix UAF in cleanup_bearer() due to premature dst_cache_destroy()
TIPC UDP media bearer teardown calls dst_cache_destroy() on its
replicast caches before calling synchronize_net() to wait for
concurrent RCU readers (transmitters) to finish:
static void cleanup_bearer(struct work_struct *work)
{
...
list_for_each_entry_safe(rcast, tmp, &ub->rcast.list, list) {
dst_cache_destroy(&rcast->dst_cache);
list_del_rcu(&rcast->list);
kfree_rcu(rcast, rcu);
}
...
dst_cache_destroy(&ub->rcast.dst_cache);
udp_tunnel_sock_release(ub->sk);
synchronize_net();
...
}
This is highly buggy because dst_cache_destroy() immediately frees the
per-CPU cache memory (free_percpu()) and releases the cached dst
entries without any synchronization.
If a concurrent transmitter (e.g., tipc_udp_xmit()) is running on another
CPU under RCU protection, it can call dst_cache_get() concurrently,
leading to:
1. Use-After-Free on the per-CPU cache pointer itself (crash).
2. "rcuref - imbalanced put()" warning if it attempts to release a
dst that was concurrently released by dst_cache_destroy().
Furthermore, calling kfree(ub) immediately after synchronize_net() without
closing the socket first (or waiting after closing it) leaves a window
where a concurrent receiver (tipc_udp_recv()) could start after
synchronize_net(), access ub, and suffer a UAF when kfree(ub) runs.
To fix this, we must defer dst_cache_destroy() and kfree(ub) until after
we have ensured that no more readers can see the bearer/socket and all
existing readers have finished:
1. Defer rcast entry destruction (both dst_cache_destroy() and kfree())
to an RCU callback using call_rcu_hurry().
Using call_rcu_hurry() ensures the dst entries are released quickly.
2. Release the bearer socket using udp_tunnel_sock_release() (stops
new receive readers).
3. Call synchronize_net() to wait for all outstanding RCU readers
(both transmit and receive) to finish.
4. Now that it is safe, call dst_cache_destroy() on the main bearer
cache, and free ub.
Note: 3) and 4) can be changed later in net-next to also use
call_rcu_hurry() and get rid of the synchronize_net() latency.
Fixes: e9c1a793210f ("tipc: add dst_cache support for udp media")
Reported-by: syzbot+e14bc5d4942756023b77@syzkaller.appspotmail.com
Closes: https://lore.kernel.org/netdev/6a396a66.52ae72c2.136ac7.0003.GAE@google.com/T/#u
Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Jon Maloy <jmaloy@redhat.com>
Cc: tipc-discussion@lists.sourceforge.net
Reviewed-by: Xin Long <lucien.xin@gmail.com>
Link: https://patch.msgid.link/20260623173030.2925059-2-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Diffstat (limited to 'net')
| -rw-r--r-- | net/tipc/udp_media.c | 15 |
1 files changed, 11 insertions, 4 deletions
diff --git a/net/tipc/udp_media.c b/net/tipc/udp_media.c index 988b8a7f953ad..66f3cb87a0aaa 100644 --- a/net/tipc/udp_media.c +++ b/net/tipc/udp_media.c @@ -803,6 +803,14 @@ err: return err; } +static void rcast_free_rcu(struct rcu_head *rcu) +{ + struct udp_replicast *rcast = container_of(rcu, struct udp_replicast, rcu); + + dst_cache_destroy(&rcast->dst_cache); + kfree(rcast); +} + /* cleanup_bearer - break the socket/bearer association */ static void cleanup_bearer(struct work_struct *work) { @@ -811,18 +819,17 @@ static void cleanup_bearer(struct work_struct *work) struct tipc_net *tn; list_for_each_entry_safe(rcast, tmp, &ub->rcast.list, list) { - dst_cache_destroy(&rcast->dst_cache); list_del_rcu(&rcast->list); - kfree_rcu(rcast, rcu); + call_rcu_hurry(&rcast->rcu, rcast_free_rcu); } tn = tipc_net(sock_net(ub->sk)); - dst_cache_destroy(&ub->rcast.dst_cache); udp_tunnel_sock_release(ub->sk); - /* Note: could use a call_rcu() to avoid another synchronize_net() */ synchronize_net(); + + dst_cache_destroy(&ub->rcast.dst_cache); atomic_dec(&tn->wq_count); kfree(ub); } |