From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from ganesha.gnumonks.org (ganesha.gnumonks.org [IPv6:2001:780:45:1d:225:90ff:fe52:c662]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id F0E7ED4B; Wed, 6 Dec 2023 08:48:37 -0800 (PST) Received: from [78.30.43.141] (port=41630 helo=gnumonks.org) by ganesha.gnumonks.org with esmtpsa (TLS1.3) tls TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (Exim 4.94.2) (envelope-from ) id 1rAv4b-003yIw-SR; Wed, 06 Dec 2023 17:48:35 +0100 Date: Wed, 6 Dec 2023 17:48:32 +0100 From: Pablo Neira Ayuso To: Jann Horn Cc: Phil Sutter , Jozsef Kadlecsik , Florian Westphal , netfilter-devel , coreteam@netfilter.org, Christian Brauner , "David S. Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Network Development , kernel list Subject: Re: Is xt_owner's owner_mt() racy with sock_orphan()? [worse with new TYPESAFE_BY_RCU file lifetime?] Message-ID: References: Precedence: bulk X-Mailing-List: netfilter-devel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: X-Spam-Score: -1.9 (-) On Wed, Dec 06, 2023 at 05:28:44PM +0100, Jann Horn wrote: > On Tue, Dec 5, 2023 at 10:40 PM Phil Sutter wrote: > > On Tue, Dec 05, 2023 at 06:08:29PM +0100, Jann Horn wrote: > > > On Tue, Dec 5, 2023 at 5:40 PM Jann Horn 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. > > Looks mostly reasonable to me; though I guess it's a bit weird to have > two separate bailout paths for checking whether sk->sk_socket is NULL, > where the first check can race, and the second check uses different > logic for determining the return value; I don't know whether that > actually matters semantically. But I'm not sure how to make it look > nicer either. > I guess you could add a READ_ONCE() around the first read to signal > that that's a potentially racy read, but I don't feel strongly about > that. The lack of READ_ONCE() on sk->sk_socket also got me thinking here, given this sk_set_socket(sk, NULL) in sock_orphan is done under the lock. I am taking Phil's patch, I think it is leaving things in better shape.