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

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <CAADnVQLEQ35S0n+GN6wn1ybPW3=SJhidp=f1z5fmq08kQ4ndJA@mail.gmail.com>
Date: Tue, 7 Oct 2025 13:18:18 -0700
From: Alexei Starovoitov <alexei.starovoitov@...il.com>
To: Maciej Fijalkowski <maciej.fijalkowski@...el.com>
Cc: bpf <bpf@...r.kernel.org>, Alexei Starovoitov <ast@...nel.org>, 
	Daniel Borkmann <daniel@...earbox.net>, Jesper Dangaard Brouer <hawk@...nel.org>, 
	Ilias Apalodimas <ilias.apalodimas@...aro.org>, Toke Høiland-Jørgensen <toke@...hat.com>, 
	Lorenzo Bianconi <lorenzo@...nel.org>, Network Development <netdev@...r.kernel.org>, 
	"Karlsson, Magnus" <magnus.karlsson@...el.com>, Andrii Nakryiko <andrii@...nel.org>, 
	Stanislav Fomichev <stfomichev@...il.com>, Alexander Lobakin <aleksander.lobakin@...el.com>, 
	syzbot+ff145014d6b0ce64a173@...kaller.appspotmail.com, 
	Ihor Solodrai <ihor.solodrai@...ux.dev>, Octavian Purdila <tavip@...gle.com>
Subject: Re: [PATCH bpf 1/2] xdp: update xdp_rxq_info's mem type in XDP
 generic hook

On Tue, Oct 7, 2025 at 12:39 PM Maciej Fijalkowski
<maciej.fijalkowski@...el.com> wrote:
>
> On Fri, Oct 03, 2025 at 10:29:08AM -0700, Alexei Starovoitov wrote:
> > On Fri, Oct 3, 2025 at 7:03 AM Maciej Fijalkowski
> > <maciej.fijalkowski@...el.com> wrote:
> > >
> > > 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 that 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.
> > >
> > > For this purpose introduce a small helper, xdp_update_mem_type(), that
> > > could be used on other callsites such as veth which are open to this
> > > problem as well. Here we call it right before executing XDP program in
> > > generic XDP hook.
> > >
> > > 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
> > > ---
> > >  include/net/xdp.h | 7 +++++++
> > >  net/core/dev.c    | 2 ++
> > >  2 files changed, 9 insertions(+)
> > >
> > > diff --git a/include/net/xdp.h b/include/net/xdp.h
> > > index f288c348a6c1..5568e41cc191 100644
> > > --- a/include/net/xdp.h
> > > +++ b/include/net/xdp.h
> > > @@ -336,6 +336,13 @@ xdp_update_skb_shared_info(struct sk_buff *skb, u8 nr_frags,
> > >         skb->pfmemalloc |= pfmemalloc;
> > >  }
> > >
> > > +static inline void
> > > +xdp_update_mem_type(struct xdp_buff *xdp)
> > > +{
> > > +       xdp->rxq->mem.type = page_pool_page_is_pp(virt_to_page(xdp->data)) ?
> > > +               MEM_TYPE_PAGE_POOL : MEM_TYPE_PAGE_SHARED;
> > > +}
> >
> > AI says that it's racy and I think it's onto something.
> > See
> > https://github.com/kernel-patches/bpf/actions/runs/18224704286/job/51892959919
> > and
> > https://github.com/kernel-patches/bpf/actions/runs/18224704286/job/51892959937
>
> How do we respond to this in future?

The bot will start sending emails eventually, so developers can
respond directly with email to maintainers.

> On first one AI missed the fact we run under napi so two cpus won't play
> with same rx queue concurrently. The second is valid thing to be fixed.

Good point about napi.