Subject: Re: [PATCH bpf-next 1/2] bpf, test_run: Fix user-memory-access vulnerability for LIVE_FRAMES

From: Toke Høiland-Jørgensen <[email-masked]>
Date: Mon, 05 Jan 2026 17:43:50 +0100

KaFai Wan <[email-masked]> writes:

> On Mon, 2026-01-05 at 11:46 +0100, Toke Høiland-Jørgensen wrote:
>> KaFai Wan <[email-masked]> 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.

-Toke

[0] https://lore.kernel.org/r/[email-masked]