Re: [PATCH net] xdp: use multi-buff only if receive queue supports page pool

[Octavian Purdila <tavip@google.com>]

On Wed, Sep 24, 2025 at 5:09 PM Jakub Kicinski <kuba@kernel.org> wrote:
>
> On Wed, 24 Sep 2025 06:08:42 +0000 Octavian Purdila wrote:
> > When a BPF program that supports BPF_F_XDP_HAS_FRAGS is issuing
> > bpf_xdp_adjust_tail and a large packet is injected via /dev/net/tun a
> > crash occurs due to detecting a bad page state (page_pool leak).
> >
> > This is because xdp_buff does not record the type of memory and
> > instead relies on the netdev receive queue xdp info. Since the TUN/TAP
> > driver is using a MEM_TYPE_PAGE_SHARED memory model buffer, shrinking
> > will eventually call page_frag_free. But with current multi-buff
> > support for BPF_F_XDP_HAS_FRAGS programs buffers are allocated via the
> > page pool.
> >
> > To fix this issue check that the receive queue memory mode is of
> > MEM_TYPE_PAGE_POOL before using multi-buffs.
>
> This can also happen on veth, right? And veth re-stamps the Rx queues.

I am not sure if re-stamps will have ill effects.

The allocation and deallocation for this issue happens while
processing the same packet (receive skb -> skb_pp_cow_data ->
page_pool alloc ... __bpf_prog_run ->  bpf_xdp_adjust_tail).

IIUC, if the veth re-stamps the RX queue to MEM_TYPE_PAGE_POOL
skb_pp_cow_data will proceed to allocate from page_pool and
bpf_xdp_adjust_tail will correctly free from page_pool.