[PATCH 5.4 137/191] net/smc: add fallback check to connect()

[Greg Kroah-Hartman]

From: Ursula Braun <ubraun@xxxxxxxxxxxxx>

commit 86434744fedf0cfe07a9eee3f4632c0e25c1d136 upstream.

FASTOPEN setsockopt() or sendmsg() may switch the SMC socket to fallback
mode. Once fallback mode is active, the native TCP socket functions are
called. Nevertheless there is a small race window, when FASTOPEN
setsockopt/sendmsg runs in parallel to a connect(), and switch the
socket into fallback mode before connect() takes the sock lock.
Make sure the SMC-specific connect setup is omitted in this case.

This way a syzbot-reported refcount problem is fixed, triggered by
different threads running non-blocking connect() and FASTOPEN_KEY
setsockopt.

Reported-by: syzbot+96d3f9ff6a86d37e44c8@xxxxxxxxxxxxxxxxxxxxxxxxx
Fixes: 6d6dd528d5af ("net/smc: fix refcount non-blocking connect() -part 2")
Signed-off-by: Ursula Braun <ubraun@xxxxxxxxxxxxx>
Signed-off-by: Karsten Graul <kgraul@xxxxxxxxxxxxx>
Signed-off-by: Jakub Kicinski <jakub.kicinski@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 net/smc/af_smc.c |   14 ++++++++------
 1 file changed, 8 insertions(+), 6 deletions(-)

--- a/net/smc/af_smc.c
+++ b/net/smc/af_smc.c
@@ -854,6 +854,8 @@ static int smc_connect(struct socket *so
 		goto out;
 
 	sock_hold(&smc->sk); /* sock put in passive closing */
+	if (smc->use_fallback)
+		goto out;
 	if (flags & O_NONBLOCK) {
 		if (schedule_work(&smc->connect_work))
 			smc->connect_nonblock = 1;
@@ -1716,8 +1718,6 @@ static int smc_setsockopt(struct socket
 		sk->sk_err = smc->clcsock->sk->sk_err;
 		sk->sk_error_report(sk);
 	}
-	if (rc)
-		return rc;
 
 	if (optlen < sizeof(int))
 		return -EINVAL;
@@ -1725,6 +1725,8 @@ static int smc_setsockopt(struct socket
 		return -EFAULT;
 
 	lock_sock(sk);
+	if (rc || smc->use_fallback)
+		goto out;
 	switch (optname) {
 	case TCP_ULP:
 	case TCP_FASTOPEN:
@@ -1736,15 +1738,14 @@ static int smc_setsockopt(struct socket
 			smc_switch_to_fallback(smc);
 			smc->fallback_rsn = SMC_CLC_DECL_OPTUNSUPP;
 		} else {
-			if (!smc->use_fallback)
-				rc = -EINVAL;
+			rc = -EINVAL;
 		}
 		break;
 	case TCP_NODELAY:
 		if (sk->sk_state != SMC_INIT &&
 		    sk->sk_state != SMC_LISTEN &&
 		    sk->sk_state != SMC_CLOSED) {
-			if (val && !smc->use_fallback)
+			if (val)
 				mod_delayed_work(system_wq, &smc->conn.tx_work,
 						 0);
 		}
@@ -1753,7 +1754,7 @@ static int smc_setsockopt(struct socket
 		if (sk->sk_state != SMC_INIT &&
 		    sk->sk_state != SMC_LISTEN &&
 		    sk->sk_state != SMC_CLOSED) {
-			if (!val && !smc->use_fallback)
+			if (!val)
 				mod_delayed_work(system_wq, &smc->conn.tx_work,
 						 0);
 		}
@@ -1764,6 +1765,7 @@ static int smc_setsockopt(struct socket
 	default:
 		break;
 	}
+out:
 	release_sock(sk);
 
 	return rc;