netdev - Re: [PATCH v2 bpf 1/2] xdp: update xdp_rxq_info's mem type in XDP generic hook

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Message-ID: <875xcdiijc.fsf@toke.dk>
Date: Fri, 17 Oct 2025 18:45:27 +0200
From: Toke Høiland-Jørgensen <toke@...hat.com>
To: Maciej Fijalkowski <maciej.fijalkowski@...el.com>, bpf@...r.kernel.org,
 ast@...nel.org, daniel@...earbox.net, hawk@...nel.org,
 ilias.apalodimas@...aro.org, lorenzo@...nel.org, kuba@...nel.org
Cc: netdev@...r.kernel.org, magnus.karlsson@...el.com, andrii@...nel.org,
 stfomichev@...il.com, aleksander.lobakin@...el.com, Maciej Fijalkowski
 <maciej.fijalkowski@...el.com>,
 syzbot+ff145014d6b0ce64a173@...kaller.appspotmail.com, Ihor Solodrai
 <ihor.solodrai@...ux.dev>, Octavian Purdila <tavip@...gle.com>
Subject: Re: [PATCH v2 bpf 1/2] xdp: update xdp_rxq_info's mem type in XDP
 generic hook

Maciej Fijalkowski <maciej.fijalkowski@...el.com> writes:

> Currently, generic XDP hook uses xdp_rxq_info from netstack Rx queues
> which do not have its XDP memory model registered. There is a case when
> XDP program calls bpf_xdp_adjust_tail() BPF helper, which in turn
> releases underlying memory. This happens when it consumes enough amount
> of bytes and when XDP buffer has fragments. For this action the memory
> model knowledge passed to XDP program is crucial so that core can call
> suitable function for freeing/recycling the page.
>
> For netstack queues it defaults to MEM_TYPE_PAGE_SHARED (0) due to lack
> of mem model registration. The problem we're fixing here is when kernel
> copied the skb to new buffer backed by system's page_pool and XDP buffer
> is built around it. Then when bpf_xdp_adjust_tail() calls
> __xdp_return(), it acts incorrectly due to mem type not being set to
> MEM_TYPE_PAGE_POOL and causes a page leak.
>
> Pull out the existing code from bpf_prog_run_generic_xdp() that
> init/prepares xdp_buff onto new helper xdp_convert_skb_to_buff() and
> embed there rxq's mem_type initialization that is assigned to xdp_buff.
>
> This problem was triggered by syzbot as well as AF_XDP test suite which
> is about to be integrated to BPF CI.
>
> Reported-by: syzbot+ff145014d6b0ce64a173@...kaller.appspotmail.com
> Closes: https://lore.kernel.org/netdev/6756c37b.050a0220.a30f1.019a.GAE@google.com/
> Fixes: e6d5dbdd20aa ("xdp: add multi-buff support for xdp running in generic mode")
> Tested-by: Ihor Solodrai <ihor.solodrai@...ux.dev>
> Co-developed-by: Octavian Purdila <tavip@...gle.com>
> Signed-off-by: Octavian Purdila <tavip@...gle.com> # whole analysis, testing, initiating a fix
> Signed-off-by: Maciej Fijalkowski <maciej.fijalkowski@...el.com> # commit msg and proposed more robust fix

Reviewed-by: Toke Høiland-Jørgensen <toke@...hat.com>