linux-kernel - Re: [PATCH] x_25: Adding a null pointer dereference check to the x25

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Date: Wed, 13 Mar 2024 15:13:25 +0100
From: Eric Dumazet <edumazet@...gle.com>
To: Mikhail Lobanov <m.lobanov@...alinux.ru>
Cc: Martin Schiller <ms@....tdt.de>, "David S. Miller" <davem@...emloft.net>, Jakub Kicinski <kuba@...nel.org>, 
	linux-x25@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] x_25: Adding a null pointer dereference check to the
 x25_accept() function

On Wed, Mar 13, 2024 at 2:23 PM Mikhail Lobanov <m.lobanov@...alinux.ru> wrote:
>
> To avoid the problem of dereferencing the null pointer in the x25_accept()
> function, you need to add an additional check that the pointer skb is
> not equal to NULL.
>
> Found by Linux Verification Center (linuxtesting.org) with SVACE.
>
> Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
> Signed-off-by: Mikhail Lobanov <m.lobanov@...alinux.ru>
> ---
>  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 f7a7c7798c3b..91bc5994cef6 100644
> --- a/net/x25/af_x25.c
> +++ b/net/x25/af_x25.c
> @@ -896,7 +896,7 @@ static int x25_accept(struct socket *sock, struct socket *newsock, int flags,
>                 goto out2;
>         skb = skb_dequeue(&sk->sk_receive_queue);

skb can not be NULL at this point, we hold the socket lock.

Otherwise the bug would be in x25_wait_for_data()

>         rc = -EINVAL;
> -       if (!skb->sk)
> +       if (!skb || !skb->sk)
>                 goto out2;
>         newsk            = skb->sk;
>         sock_graft(newsk, newsock);
> --
> 2.43.0
>