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

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Message-ID: <ZW+Yv6TR+EMBp03f@orbyte.nwl.cc>
Date:   Tue, 5 Dec 2023 22:40:15 +0100
From:   Phil Sutter <phil@....cc>
To:     Jann Horn <jannh@...gle.com>
Cc:     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, 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?]

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@...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?

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

View attachment "0001-netfilter-xt_owner-Fix-for-unsafe-access-of-sk-sk_so.patch" of type "text/x-diff" (1979 bytes)