Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.36 as permitted sender) client-ip=23.128.96.36;
MIME-Version: 1.0
References: <CAG48ez0TfTAkaRWFCTb44x=TWP_sDZVx-5U2hvfQSFOhghNrCA@mail.gmail.com>
In-Reply-To: <CAG48ez0TfTAkaRWFCTb44x=TWP_sDZVx-5U2hvfQSFOhghNrCA@mail.gmail.com>
From:   Jann Horn <jannh@google.com>
Date:   Tue, 5 Dec 2023 18:08:29 +0100
Message-ID: <CAG48ez1hXk_cffp3dy-bYMcoyCCj-EySYR5SzYrNiRHGD=hOUg@mail.gmail.com>
Subject: Re: Is xt_owner's owner_mt() racy with sock_orphan()? [worse with new
 TYPESAFE_BY_RCU file lifetime?]
To:     Pablo Neira Ayuso <pablo@netfilter.org>,
        Jozsef Kadlecsik <kadlec@netfilter.org>,
        Florian Westphal <fw@strlen.de>,
        netfilter-devel <netfilter-devel@vger.kernel.org>,
        coreteam@netfilter.org
Cc:     Christian Brauner <brauner@kernel.org>,
        "David S. Miller" <davem@davemloft.net>,
        Eric Dumazet <edumazet@google.com>,
        Jakub Kicinski <kuba@kernel.org>,
        Paolo Abeni <pabeni@redhat.com>,
        Network Development <netdev@vger.kernel.org>,
        kernel list <linux-kernel@vger.kernel.org>
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable
Precedence: bulk

On Tue, Dec 5, 2023 at 5:40=E2=80=AFPM Jann Horn <jannh@google.com> wrote:
>
> Hi!
>
> I think this code is racy, but testing that seems like a pain...
>
> owner_mt() in xt_owner runs in context of a NF_INET_LOCAL_OUT or
> NF_INET_POST_ROUTING hook. It first checks that sk->sk_socket is
> non-NULL, then checks that sk->sk_socket->file is non-NULL, then
> accesses the ->f_cred of that file.
>
> I don't see anything that protects this against a concurrent
> sock_orphan(), which NULLs out the sk->sk_socket pointer, if we're in

Ah, and all the other users of ->sk_socket in net/netfilter/ do it
under the sk_callback_lock... so I guess the fix would be to add the
same in owner_mt?