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Date:   Wed, 6 Dec 2023 17:42:42 +0100
From:   Pablo Neira Ayuso <pablo@netfilter.org>
To:     Phil Sutter <phil@nwl.cc>, Jann Horn <jannh@google.com>,
        Jozsef Kadlecsik <kadlec@netfilter.org>,
        Florian Westphal <fw@strlen.de>,
        netfilter-devel <netfilter-devel@vger.kernel.org>,
        coreteam@netfilter.org, 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>
Subject: Re: Is xt_owner's owner_mt() racy with sock_orphan()? [worse with
 new TYPESAFE_BY_RCU file lifetime?]
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On Tue, Dec 05, 2023 at 10:40:15PM +0100, Phil Sutter wrote:
> Hi,
> 
> On Tue, Dec 05, 2023 at 06:08:29PM +0100, Jann Horn wrote:
> > On Tue, Dec 5, 2023 at 5:40 PM 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?
> 
> Sounds reasonable, although I wonder how likely a socket is to
> orphan while netfilter is processing a packet it just sent.
> 
> How about the attached patch? Not sure what hash to put into a Fixes:
> tag given this is a day 1 bug and ipt_owner/ip6t_owner predate git.
> 
> Thanks, Phil

> From 3e28490e43b04d49e6e7f145a70fff7dd42c8cc5 Mon Sep 17 00:00:00 2001
> From: Phil Sutter <phil@nwl.cc>
> Date: Tue, 5 Dec 2023 21:58:12 +0100
> Subject: [nf PATCH] netfilter: xt_owner: Fix for unsafe access of sk->sk_socket
> 
> A concurrently running sock_orphan() may NULL the sk_socket pointer in
> between check and deref. Follow other users (like nft_meta.c for
> instance) and acquire sk_callback_lock before dereferencing sk_socket.

For the record, I have placed this patch in nf.git

Thanks.