netdev - [PATCH] net/x25: fix nonblocking connect

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Date:   Thu,  9 Jan 2020 07:31:14 +0100
From:   Martin Schiller <ms@....tdt.de>
To:     arnd@...db.de, davem@...emloft.net
Cc:     andrew.hendry@...il.com, edumazet@...gle.com,
        gregkh@...uxfoundation.org, tglx@...utronix.de,
        linux-x25@...r.kernel.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, syzkaller-bugs@...glegroups.com,
        Martin Schiller <ms@....tdt.de>,
        syzbot+429c200ffc8772bfe070@...kaller.appspotmail.com,
        syzbot+eec0c87f31a7c3b66f7b@...kaller.appspotmail.com
Subject: [PATCH] net/x25: fix nonblocking connect

This patch fixes 2 issues in x25_connect():

1. It makes absolutely no sense to reset the neighbour and the
connection state after a (successful) nonblocking call of x25_connect.
This prevents any connection from being established, since the response
(call accept) cannot be processed.

2. Any further calls to x25_connect() while a call is pending should
simply return, instead of creating new Call Request (on different
logical channels).

This patch should also fix the "KASAN: null-ptr-deref Write in
x25_connect" and "BUG: unable to handle kernel NULL pointer dereference
in x25_connect" bugs reported by syzbot.

Signed-off-by: Martin Schiller <ms@....tdt.de>
Reported-by: syzbot+429c200ffc8772bfe070@...kaller.appspotmail.com
Reported-by: syzbot+eec0c87f31a7c3b66f7b@...kaller.appspotmail.com
---
 net/x25/af_x25.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/net/x25/af_x25.c b/net/x25/af_x25.c
index 2efe44a34644..d5b09bbff375 100644
--- a/net/x25/af_x25.c
+++ b/net/x25/af_x25.c
@@ -766,6 +766,10 @@ static int x25_connect(struct socket *sock, struct sockaddr *uaddr,
 	if (sk->sk_state == TCP_ESTABLISHED)
 		goto out;
 
+	rc = -EALREADY;	/* Do nothing if call is already in progress */
+	if (sk->sk_state == TCP_SYN_SENT)
+		goto out;
+
 	sk->sk_state   = TCP_CLOSE;
 	sock->state = SS_UNCONNECTED;
 
@@ -812,7 +816,7 @@ static int x25_connect(struct socket *sock, struct sockaddr *uaddr,
 	/* Now the loop */
 	rc = -EINPROGRESS;
 	if (sk->sk_state != TCP_ESTABLISHED && (flags & O_NONBLOCK))
-		goto out_put_neigh;
+		goto out;
 
 	rc = x25_wait_for_connection_establishment(sk);
 	if (rc)
-- 
2.20.1