On Wed, Dec 06, 2023 at 05:28:44PM +0100, Jann Horn wrote: > On Tue, Dec 5, 2023 at 10:40 PM Phil Sutter <phil@xxxxxx> 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 <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. > > 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. It should be possible to split it into two static inlin helpers: owner_mt_fast() owner_mt_slow() And then abstract the lockless and locked fetches into the two helpers.
