2020-09-28 09:35:12

by Martin Schiller

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

This fixes a regression for blocking connects introduced by commit
4becb7ee5b3d ("net/x25: Fix x25_neigh refcnt leak when x25 disconnect").

The x25->neighbour is already set to "NULL" by x25_disconnect() now,
while a blocking connect is waiting in
x25_wait_for_connection_establishment(). Therefore x25->neighbour must
not be accessed here again and x25->state is also already set to
X25_STATE_0 by x25_disconnect().

Fixes: 4becb7ee5b3d ("net/x25: Fix x25_neigh refcnt leak when x25 disconnect")
Signed-off-by: Martin Schiller <[email protected]>
---
net/x25/af_x25.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

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;

sock->state = SS_CONNECTED;
rc = 0;
--
2.20.1

2020-09-29 01:47:44

by David Miller

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

From: Martin Schiller <[email protected]>
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.

2020-09-29 04:54:31

by Martin Schiller

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

On 2020-09-29 03:43, David Miller wrote:
> From: Martin Schiller <[email protected]>
> 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