linux-kernel - Re: [PATCH bpf-next 1/2] bpf, test_run: Fix user-memory-access vulnerability for LIVE

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Message-ID: <0cb5a1103b1bac18fb0b35c6a5d4fd2ac537dddc.camel@linux.dev>
Date: Tue, 06 Jan 2026 21:53:57 +0800
From: KaFai Wan <kafai.wan@...ux.dev>
To: Toke Høiland-Jørgensen <toke@...hat.com>, 
 ast@...nel.org, daniel@...earbox.net, andrii@...nel.org,
 martin.lau@...ux.dev,  eddyz87@...il.com, song@...nel.org,
 yonghong.song@...ux.dev,  john.fastabend@...il.com, kpsingh@...nel.org,
 sdf@...ichev.me, haoluo@...gle.com,  jolsa@...nel.org, davem@...emloft.net,
 edumazet@...gle.com, kuba@...nel.org,  pabeni@...hat.com, horms@...nel.org,
 hawk@...nel.org, shuah@...nel.org,  aleksander.lobakin@...el.com,
 bpf@...r.kernel.org, netdev@...r.kernel.org,  linux-kernel@...r.kernel.org,
 linux-kselftest@...r.kernel.org
Cc: Yinhao Hu <dddddd@...t.edu.cn>, Kaiyan Mei <M202472210@...t.edu.cn>, 
 Dongliang Mu <dzm91@...t.edu.cn>
Subject: Re: [PATCH bpf-next 1/2] bpf, test_run: Fix user-memory-access
 vulnerability for LIVE_FRAMES

On Mon, 2026-01-05 at 17:43 +0100, Toke Høiland-Jørgensen wrote:
> KaFai Wan <kafai.wan@...ux.dev> writes:
> 
> > On Mon, 2026-01-05 at 11:46 +0100, Toke Høiland-Jørgensen wrote:
> > > KaFai Wan <kafai.wan@...ux.dev> writes:
> > > 
> > > > This fix reverts to the original version and ensures data_hard_start
> > > > correctly points to the xdp_frame structure, eliminating the security
> > > > risk.
> > > 
> > > This is wrong. We should just be checking the meta_len on input to
> > > account for the size of xdp_frame. I'll send a patch.
> > 
> > Current version the actual limit of the max input meta_len for live frames is 
> > XDP_PACKET_HEADROOM - sizeof(struct xdp_frame), not
> > XDP_PACKET_HEADROOM.
> 
> By "current version", you mean the patch I sent[0], right?
> 
> If so, that was deliberate: the stack limits the maximum data_meta size
> to XDP_PACKET_HEADROOM - sizeof(struct xdp_frame), so there's no reason
> not to do the same for bpf_prog_run(). And some chance that diverging
> here will end up surfacing other bugs down the line.
> 
Oh, I see. Thank you for your explanation.
> -Toke
> 
> [0] https://lore.kernel.org/r/20260105114747.1358750-1-toke@redhat.com
> 

-- 
Thanks,
KaFai