netdev - Re: [External] Re: [PATCH bpf v2 1/2] bpf: syzkaller found null ptr deref in unix

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Message-ID: <CAONe227zBRfcadH22X1A=qRRqNszXFXT0N5Oqt692rcGbsrs9w@mail.gmail.com>
Date: Wed, 13 Dec 2023 15:23:12 -0800
From: Amery Hung <amery.hung@...edance.com>
To: Daniel Borkmann <daniel@...earbox.net>
Cc: Cong Wang <xiyou.wangcong@...il.com>, John Fastabend <john.fastabend@...il.com>, 
	Kuniyuki Iwashima <kuniyu@...zon.com>, bpf@...r.kernel.org, edumazet@...gle.com, 
	jakub@...udflare.com, martin.lau@...nel.org, netdev@...r.kernel.org
Subject: Re: [External] Re: [PATCH bpf v2 1/2] bpf: syzkaller found null ptr
 deref in unix_bpf proto add

On Mon, Dec 11, 2023 at 6:56 AM Daniel Borkmann <daniel@...earbox.net> wrote:
>
> On 12/8/23 5:19 AM, Cong Wang wrote:
> > On Mon, Dec 04, 2023 at 01:40:40PM -0800, John Fastabend wrote:
> >> Kuniyuki Iwashima wrote:
> >>> From: John Fastabend <john.fastabend@...il.com>
> >>> Date: Fri,  1 Dec 2023 10:01:38 -0800
> >>>> I added logic to track the sock pair for stream_unix sockets so that we
> >>>> ensure lifetime of the sock matches the time a sockmap could reference
> >>>> the sock (see fixes tag). I forgot though that we allow af_unix unconnected
> >>>> sockets into a sock{map|hash} map.
> >>>>
> >>>> This is problematic because previous fixed expected sk_pair() to exist
> >>>> and did not NULL check it. Because unconnected sockets have a NULL
> >>>> sk_pair this resulted in the NULL ptr dereference found by syzkaller.
> >>>>
> >>>> BUG: KASAN: null-ptr-deref in unix_stream_bpf_update_proto+0x72/0x430 net/unix/unix_bpf.c:171
> >>>> Write of size 4 at addr 0000000000000080 by task syz-executor360/5073
> >>>> Call Trace:
> >>>>   <TASK>
> >>>>   ...
> >>>>   sock_hold include/net/sock.h:777 [inline]
> >>>>   unix_stream_bpf_update_proto+0x72/0x430 net/unix/unix_bpf.c:171
> >>>>   sock_map_init_proto net/core/sock_map.c:190 [inline]
> >>>>   sock_map_link+0xb87/0x1100 net/core/sock_map.c:294
> >>>>   sock_map_update_common+0xf6/0x870 net/core/sock_map.c:483
> >>>>   sock_map_update_elem_sys+0x5b6/0x640 net/core/sock_map.c:577
> >>>>   bpf_map_update_value+0x3af/0x820 kernel/bpf/syscall.c:167
> >>>>
> >>>> We considered just checking for the null ptr and skipping taking a ref
> >>>> on the NULL peer sock. But, if the socket is then connected() after
> >>>> being added to the sockmap we can cause the original issue again. So
> >>>> instead this patch blocks adding af_unix sockets that are not in the
> >>>> ESTABLISHED state.
> >>>
> >>> I'm not sure if someone has the unconnected stream socket use case
> >>> though, can't we call additional sock_hold() in connect() by checking
> >>> sk_prot under sk_callback_lock ?
> >>
> >> Could be done I guess yes. I'm not sure the utility of it though. I
> >> thought above patch was the simplest solution and didn't require touching
> >> main af_unix code. I don't actually use the sockmap with af_unix
> >> sockets anywhere so maybe someone who is using this can comment if
> >> unconnected is needed?
> >
> > Our use case is also connected unix stream socket, as demonstrated in
> > the selftest unix_redir_to_connected().
>
> Great, is everyone good to move this fix forward then? Would be great if
> this receives at least one ack if the latter is indeed the case.
>
> Thanks,
> Daniel

I just want to ack that we are not inserting unconnected UDS to sockmap.