Re: [PATCH] net/x25: Fix null-ptr-deref in x25_connect

[Martin Schiller]

On 2020-09-29 03:43, David Miller wrote:
From: Martin Schiller <m...@dev.tdt.de>
Date: Mon, 28 Sep 2020 11:23:27 +0200
diff --git a/net/x25/af_x25.c b/net/x25/af_x25.c
index 0bbb283f23c9..0524a5530b91 100644
--- a/net/x25/af_x25.c
+++ b/net/x25/af_x25.c
@@ -820,7 +820,7 @@ static int x25_connect(struct socket *sock, struct 
sockaddr *uaddr,

        rc = x25_wait_for_connection_establishment(sk);
        if (rc)
-               goto out_put_neigh;
+               goto out;

If x25_wait_for_connection_establishment() returns because of an 
interrupting
signal, we are not going to call x25_disconnect().

The case you are fixing only applies _sometimes_ when
x25_wait_for_connection_establishment() returns.  But not always.

That neighbour has to be released at this spot otherwise.

OK, thanks for the hint. So I think the simplest solution would be to 
check
that x25->neighbour is != NULL like this:

diff --git a/net/x25/af_x25.c b/net/x25/af_x25.c
index 0bbb283f23c9..046d3fee66a9 100644
--- a/net/x25/af_x25.c
+++ b/net/x25/af_x25.c
@@ -825,7 +825,7 @@ static int x25_connect(struct socket *sock, struct 
sockaddr *uaddr,
        sock->state = SS_CONNECTED;
        rc = 0;
 out_put_neigh:
-       if (rc) {
+       if (rc && x25->neighbour) {
                read_lock_bh(&x25_list_lock);
                x25_neigh_put(x25->neighbour);
                x25->neighbour = NULL;
--

What do you think?
If that would be OK, I'll send a v2 of the Patch.

- Martin