netdev - Re: Is xt_owner's owner_mt() racy with sock_orphan()? [worse with new TYPESAFE_BY

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Date: Tue, 5 Dec 2023 18:08:29 +0100
From: Jann Horn <jannh@...gle.com>
To: Pablo Neira Ayuso <pablo@...filter.org>, Jozsef Kadlecsik <kadlec@...filter.org>, 
	Florian Westphal <fw@...len.de>, netfilter-devel <netfilter-devel@...r.kernel.org>, coreteam@...filter.org
Cc: Christian Brauner <brauner@...nel.org>, "David S. Miller" <davem@...emloft.net>, 
	Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, 
	Network Development <netdev@...r.kernel.org>, kernel list <linux-kernel@...r.kernel.org>
Subject: Re: Is xt_owner's owner_mt() racy with sock_orphan()? [worse with new
 TYPESAFE_BY_RCU file lifetime?]

On Tue, Dec 5, 2023 at 5:40 PM Jann Horn <jannh@...gle.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?