Received-SPF: pass (google.com: domain of linux-kernel+bounces-101605-linux.lists.archive=gmail.com@vger.kernel.org designates 139.178.88.99 as permitted sender) client-ip=139.178.88.99;
Precedence: bulk
MIME-Version: 1.0
References: <20240313132214.48716-1-m.lobanov@rosalinux.ru>
In-Reply-To: <20240313132214.48716-1-m.lobanov@rosalinux.ru>
From: Eric Dumazet <edumazet@google.com>
Date: Wed, 13 Mar 2024 15:13:25 +0100
Message-ID: <CANn89iLfExAa7T+0bjyBHdbwrF-77SF+QaMHpy-tg7dYEp0YKQ@mail.gmail.com>
Subject: Re: [PATCH] x_25: Adding a null pointer dereference check to the
 x25_accept() function
To: Mikhail Lobanov <m.lobanov@rosalinux.ru>
Cc: Martin Schiller <ms@dev.tdt.de>, "David S. Miller" <davem@davemloft.net>, Jakub Kicinski <kuba@kernel.org>, 
	linux-x25@vger.kernel.org, linux-kernel@vger.kernel.org
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable

On Wed, Mar 13, 2024 at 2:23=E2=80=AFPM Mikhail Lobanov <m.lobanov@rosalinu=
x.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@rosalinux.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 soc=
ket *newsock, int flags,
>                 goto out2;
>         skb =3D 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 =3D -EINVAL;
> -       if (!skb->sk)
> +       if (!skb || !skb->sk)
>                 goto out2;
>         newsk            =3D skb->sk;
>         sock_graft(newsk, newsock);
> --
> 2.43.0
>