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

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Message-ID: <38dd70d77f8207395206564063b0a1a07dd1c6e7.camel@linux.dev>
Date: Mon, 05 Jan 2026 21:22:54 +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 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.

The original version not set xdp_buff->data_hard_start with xdp_frame, 
I set it with the correct position by adding the headroom, so there is no need 
for user to reduce the max input meta_len.

This patch is failed with the xdp_do_redirect test, I'll fix and send v2 if 
you're ok with that.
 
> 
> -Toke
> 

-- 
Thanks,
KaFai