[PATCH net] net/smc: avoid recursive sk_callback_lock in listen data_ready

[Runyu Xiao]

smc_listen() installs smc_clcsock_data_ready() as the underlying TCP
listen socket's sk_data_ready callback.  smc_clcsock_data_ready() then
immediately takes sk_callback_lock before looking up the SMC listener and
queuing smc_tcp_listen_work().

That is unsafe once the TCP listen socket is leaving TCP_LISTEN.  The TCP
close/flush path can run the installed sk_data_ready callback with
sk_callback_lock already held, so entering smc_clcsock_data_ready() again
tries to take the same rwlock recursively in the same thread.  The nvmet
TCP listener had to make the same state check before taking
sk_callback_lock for this reason.

This issue was found by our static analysis tool and then manually
reviewed against the current tree.

The grounded PoC kept the SMC listen callback installation path:

  smc_listen()
  smc_clcsock_replace_cb()
  sk_data_ready = smc_clcsock_data_ready()

It then modeled the close/flush carrier that invokes the installed
sk_data_ready callback while sk_callback_lock is already held.  Lockdep
reported the same-thread recursive acquisition:

  WARNING: possible recursive locking detected
  smc_clcsock_data_ready+0xa/0x4d [vuln_msv]
  smc_close_flush_work+0x1f/0x30 [vuln_msv]
  *** DEADLOCK ***

Return before taking sk_callback_lock when the underlying TCP socket is no
longer in TCP_LISTEN.  In that state there is no listen accept work to
queue for SMC, and avoiding the callback lock mirrors the fix used by the
TCP nvmet listener.

Fixes: 0558226cebee ("net/smc: Fix slab-out-of-bounds issue in fallback")
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Runyu Xiao <runyu.xiao@xxxxxxxxxx>
---
 net/smc/af_smc.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/net/smc/af_smc.c b/net/smc/af_smc.c
index 6421c2e1c84d..1af4e3c333ff 100644
--- a/net/smc/af_smc.c
+++ b/net/smc/af_smc.c
@@ -2631,6 +2631,9 @@ static void smc_clcsock_data_ready(struct sock *listen_clcsock)
 {
 	struct smc_sock *lsmc;
 
+	if (READ_ONCE(listen_clcsock->sk_state) != TCP_LISTEN)
+		return;
+
 	read_lock_bh(&listen_clcsock->sk_callback_lock);
 	lsmc = smc_clcsock_user_data(listen_clcsock);
 	if (!lsmc)
-- 
2.34.1