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@xxxxxxxxxx> 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@xxxxxx> > 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.
