From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To: stable@vger.kernel.org
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	patches@lists.linux.dev,
	Xuanqiang Luo <luoxuanqiang@kylinos.cn>,
	Mahanta Jambigi <mjambigi@linux.ibm.com>,
	Paolo Abeni <pabeni@redhat.com>
Subject: [PATCH 5.10 261/389] net/smc: fix socket use-after-free during link group termination
Date: Mon, 17 Aug 2026 15:31:40 +0200
Message-ID: <20260817132549.377758240@linuxfoundation.org>
In-Reply-To: <20260817132538.796021292@linuxfoundation.org>
References: <20260817132538.796021292@linuxfoundation.org>
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5.10-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Xuanqiang Luo <luoxuanqiang@kylinos.cn>

commit f621d6ebeebb6374342571e4ddf45fdbc420f6cd upstream.

__smc_lgr_terminate() drops conns_lock after finding a connection in
lgr->conns_all, but before taking a reference on its socket. The connection
is embedded in the socket, and its registration reference protects it only
while the connection remains in the tree.

A concurrent close can unregister the connection and drop that reference,
freeing the socket before the termination worker reaches sock_hold().

The race is reachable when close overlaps link group termination.
Local stress testing reproduced the use-after-free and KASAN reported:

  BUG: KASAN: slab-use-after-free in __smc_lgr_terminate.part.0 [smc]
  Write of size 4 by task kworker/3:3
  Workqueue: events smc_lgr_terminate_work [smc]
  __smc_lgr_terminate.part.0 [smc]

The socket was allocated by smc_create(), freed through
slab_free_after_rcu_debug(), and was followed by:

  refcount_t: addition on 0; use-after-free.
  __smc_lgr_terminate.part.0 [smc]

Take the socket reference while conns_lock still protects the tree entry.
The unregister path then cannot drop the last reference until termination
has finished using the socket.

Fixes: 69318b5215f2 ("net/smc: improve abnormal termination locking")
Cc: stable@vger.kernel.org
Signed-off-by: Xuanqiang Luo <luoxuanqiang@kylinos.cn>
Reviewed-by: Mahanta Jambigi <mjambigi@linux.ibm.com>
Link: https://patch.msgid.link/20260723105454.87016-1-xuanqiang.luo@linux.dev
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 net/smc/smc_core.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/net/smc/smc_core.c
+++ b/net/smc/smc_core.c
@@ -919,10 +919,10 @@ static void __smc_lgr_terminate(struct s
 	read_lock_bh(&lgr->conns_lock);
 	node = rb_first(&lgr->conns_all);
 	while (node) {
-		read_unlock_bh(&lgr->conns_lock);
 		conn = rb_entry(node, struct smc_connection, alert_node);
 		smc = container_of(conn, struct smc_sock, conn);
 		sock_hold(&smc->sk); /* sock_put below */
+		read_unlock_bh(&lgr->conns_lock);
 		lock_sock(&smc->sk);
 		smc_conn_kill(conn, soft);
 		release_sock(&smc->sk);