Patch "net/smc: add fallback check to connect()" has been added to the 5.4-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

This is a note to let you know that I've just added the patch titled

    net/smc: add fallback check to connect()

to the 5.4-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     net-smc-add-fallback-check-to-connect.patch
and it can be found in the queue-5.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit f1b1b7b8dfcadb131fd0205339a035923001ffea
Author: Ursula Braun <ubraun@xxxxxxxxxxxxx>
Date:   Thu Dec 12 22:35:58 2019 +0100

    net/smc: add fallback check to connect()
    
    [ Upstream commit 86434744fedf0cfe07a9eee3f4632c0e25c1d136 ]
    
    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: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/net/smc/af_smc.c b/net/smc/af_smc.c
index 737b49909a7a..6a6d3b2aa5a9 100644
--- a/net/smc/af_smc.c
+++ b/net/smc/af_smc.c
@@ -854,6 +854,8 @@ static int smc_connect(struct socket *sock, struct sockaddr *addr,
 		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 *sock, int level, int optname,
 		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 *sock, int level, int optname,
 		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 *sock, int level, int optname,
 			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 *sock, int level, int optname,
 		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 *sock, int level, int optname,
 	default:
 		break;
 	}
+out:
 	release_sock(sk);
 
 	return rc;