netdev - Re: [PATCH bpf-next] bpf: Make sure internal and UAPI bpf

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Message-ID: <87r08yq4us.fsf@toke.dk>
Date: Wed, 02 Oct 2024 10:35:55 +0200
From: Toke Høiland-Jørgensen <toke@...hat.com>
To: Daniel Borkmann <daniel@...earbox.net>, Alexei Starovoitov
 <ast@...nel.org>, Andrii Nakryiko <andrii@...nel.org>, Martin KaFai Lau
 <martin.lau@...ux.dev>, Eduard Zingerman <eddyz87@...il.com>, Song Liu
 <song@...nel.org>, Yonghong Song <yonghong.song@...ux.dev>, John Fastabend
 <john.fastabend@...il.com>, KP Singh <kpsingh@...nel.org>, Stanislav
 Fomichev <sdf@...ichev.me>, Hao Luo <haoluo@...gle.com>, Jiri Olsa
 <jolsa@...nel.org>, Hangbin Liu <liuhangbin@...il.com>, Jesper Dangaard
 Brouer <brouer@...hat.com>
Cc: syzbot+cca39e6e84a367a7e6f6@...kaller.appspotmail.com, "David S. Miller"
 <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski
 <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, bpf@...r.kernel.org,
 netdev@...r.kernel.org
Subject: Re: [PATCH bpf-next] bpf: Make sure internal and UAPI bpf_redirect
 flags don't overlap

Daniel Borkmann <daniel@...earbox.net> writes:

> On 9/20/24 2:56 PM, Toke Høiland-Jørgensen wrote:
>> The bpf_redirect_info is shared between the SKB and XDP redirect paths,
>> and the two paths use the same numeric flag values in the ri->flags
>> field (specifically, BPF_F_BROADCAST == BPF_F_NEXTHOP). This means that
>> if skb bpf_redirect_neigh() is used with a non-NULL params argument and,
>> subsequently, an XDP redirect is performed using the same
>> bpf_redirect_info struct, the XDP path will get confused and end up
>> crashing, which syzbot managed to trigger.
>>
>> With the stack-allocated bpf_redirect_info, the structure is no longer
>> shared between the SKB and XDP paths, so the crash doesn't happen
>> anymore. However, different code paths using identically-numbered flag
>> values in the same struct field still seems like a bit of a mess, so
>> this patch cleans that up by moving the flag definitions together and
>> redefining the three flags in BPF_F_REDIRECT_INTERNAL to not overlap
>> with the flags used for XDP. It also adds a BUILD_BUG_ON() check to make
>> sure the overlap is not re-introduced by mistake.
>>
>> Fixes: e624d4ed4aa8 ("xdp: Extend xdp_redirect_map with broadcast support")
>> Reported-by: syzbot+cca39e6e84a367a7e6f6@...kaller.appspotmail.com
>> Closes: https://syzkaller.appspot.com/bug?extid=cca39e6e84a367a7e6f6
>> Signed-off-by: Toke Høiland-Jørgensen <toke@...hat.com>
>> ---
>>   include/uapi/linux/bpf.h | 14 ++++++--------
>>   net/core/filter.c        |  8 +++++---
>>   2 files changed, 11 insertions(+), 11 deletions(-)
> Lgtm, applied, thanks! I also added a tools header sync.I took this into 
> bpf tree, so that stable can pick it up.

Great! Thanks for the fixups :)

-Toke