[PATCH net] net/smc: avoid fallback in case of non-blocking connect

[PATCH net] net/smc: avoid fallback in case of non-blocking connect

[Karsten Graul]

From: Ursula Braun <ubraun@linux.ibm.com>

FASTOPEN is not possible with SMC. sendmsg() with msg_flag MSG_FASTOPEN
triggers a fallback to TCP if the socket is in state SMC_INIT.
But if a nonblocking connect is already started, fallback to TCP
is no longer possible, even though the socket may still be in state
SMC_INIT.
And if a nonblocking connect is already started, a listen() call
does not make sense.

Reported-by: syzbot+bd8cc73d665590a1fcad@syzkaller.appspotmail.com
Fixes: 50717a37db032 ("net/smc: nonblocking connect rework")
Signed-off-by: Ursula Braun <ubraun@linux.ibm.com>
Signed-off-by: Karsten Graul <kgraul@linux.ibm.com>
---
 net/smc/af_smc.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/net/smc/af_smc.c b/net/smc/af_smc.c
index f5ea09258ab0..5b932583e407 100644
--- a/net/smc/af_smc.c
+++ b/net/smc/af_smc.c
@@ -263,7 +263,7 @@ static int smc_bind(struct socket *sock, struct sockaddr *uaddr,
 
 	/* Check if socket is already active */
 	rc = -EINVAL;
-	if (sk->sk_state != SMC_INIT)
+	if (sk->sk_state != SMC_INIT || smc->connect_nonblock)
 		goto out_rel;
 
 	smc->clcsock->sk->sk_reuse = sk->sk_reuse;
@@ -1390,7 +1390,8 @@ static int smc_listen(struct socket *sock, int backlog)
 	lock_sock(sk);
 
 	rc = -EINVAL;
-	if ((sk->sk_state != SMC_INIT) && (sk->sk_state != SMC_LISTEN))
+	if ((sk->sk_state != SMC_INIT && sk->sk_state != SMC_LISTEN) ||
+	    smc->connect_nonblock)
 		goto out;
 
 	rc = 0;
@@ -1518,7 +1519,7 @@ static int smc_sendmsg(struct socket *sock, struct msghdr *msg, size_t len)
 		goto out;
 
 	if (msg->msg_flags & MSG_FASTOPEN) {
-		if (sk->sk_state == SMC_INIT) {
+		if (sk->sk_state == SMC_INIT && !smc->connect_nonblock) {
 			smc_switch_to_fallback(smc);
 			smc->fallback_rsn = SMC_CLC_DECL_OPTUNSUPP;
 		} else {
-- 
2.21.0

Re: [PATCH net] net/smc: avoid fallback in case of non-blocking connect

[David Miller]

From: Karsten Graul <kgraul@linux.ibm.com>
Date: Fri,  2 Aug 2019 10:47:50 +0200

> From: Ursula Braun <ubraun@linux.ibm.com>
> 
> FASTOPEN is not possible with SMC. sendmsg() with msg_flag MSG_FASTOPEN
> triggers a fallback to TCP if the socket is in state SMC_INIT.
> But if a nonblocking connect is already started, fallback to TCP
> is no longer possible, even though the socket may still be in state
> SMC_INIT.
> And if a nonblocking connect is already started, a listen() call
> does not make sense.
> 
> Reported-by: syzbot+bd8cc73d665590a1fcad@syzkaller.appspotmail.com
> Fixes: 50717a37db032 ("net/smc: nonblocking connect rework")
> Signed-off-by: Ursula Braun <ubraun@linux.ibm.com>
> Signed-off-by: Karsten Graul <kgraul@linux.ibm.com>

Applied and queued up for -stable.