linux-kernel - [PATCH 4.4 182/183] net/x25: fix nonblocking connect

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Message-Id: <20200128135847.894325353@linuxfoundation.org>
Date:   Tue, 28 Jan 2020 15:06:41 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Martin Schiller <ms@....tdt.de>,
        syzbot+429c200ffc8772bfe070@...kaller.appspotmail.com,
        syzbot+eec0c87f31a7c3b66f7b@...kaller.appspotmail.com,
        "David S. Miller" <davem@...emloft.net>
Subject: [PATCH 4.4 182/183] net/x25: fix nonblocking connect

From: Martin Schiller <ms@....tdt.de>

commit e21dba7a4df4d93da237da65a096084b4f2e87b4 upstream.

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
Signed-off-by: David S. Miller <davem@...emloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 net/x25/af_x25.c |    6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

--- a/net/x25/af_x25.c
+++ b/net/x25/af_x25.c
@@ -764,6 +764,10 @@ static int x25_connect(struct socket *so
 	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;

@@ -810,7 +814,7 @@ static int x25_connect(struct socket *so
 	/* 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)