[PATCH] net/smc: fix possible recursive locking in __smc_lgr_terminate()

syzbot reports a possible recursive locking in the SMC listen path:

  WARNING: possible recursive locking detected
    kworker/0:2 is trying to acquire lock: sk_lock-AF_SMC
      at __smc_lgr_terminate() (net/smc/smc_core.c:1580)
    but task is already holding lock: sk_lock-AF_SMC
      at smc_listen_work() (net/smc/af_smc.c:2463)

smc_listen_work() holds new_smc->sk while calling
smc_listen_decline() -> smc_conn_abort() -> smc_lgr_cleanup_early().
smc_conn_free() unregisters new_smc from lgr->conns_all before the
early cleanup, so __smc_lgr_terminate() walks the remaining
connections and locks another socket, not the one already held.

All sockets use the same sk_lock class, so lockdep cannot tell the
two instances apart and reports a possible recursive acquisition.
Annotate the per-connection lock as a nested acquisition, as
smc_listen_out() already does for the listener socket.

Reported-by: <redacted>
Closes: https://syzkaller.appspot.com/bug?extid=7ea1f5efd5de7e24f1de
Fixes: 2c7f14ed9c19 ("net/smc: fix LGR and link use-after-free issue")
Cc: <redacted> # v6.13+
Signed-off-by: Anfernee Cao <redacted>
---
 net/smc/smc_core.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/smc/smc_core.c b/net/smc/smc_core.c
index 9974149659c2..5911368ae520 100644
--- a/net/smc/smc_core.c
+++ b/net/smc/smc_core.c

@@ -1577,7 +1577,7 @@ static void __smc_lgr_terminate(struct smc_link_group *lgr, bool soft)
 		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);
+		lock_sock_nested(&smc->sk, SINGLE_DEPTH_NESTING);
 		smc_conn_kill(conn, soft);
 		release_sock(&smc->sk);
 		sock_put(&smc->sk); /* sock_hold above */

-- 
2.54.0.windows.1