linux-kernel - Re: [PATCH net v2] virtio-net: fix received length check in big packets

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Message-ID: <CACGkMEs01gmjEa+WyWZ+MspuRBjGcj8N+4ZQs5XCp+rYqZqB6Q@mail.gmail.com>
Date: Thu, 10 Jul 2025 18:44:03 +0800
From: Jason Wang <jasowang@...hat.com>
To: Paolo Abeni <pabeni@...hat.com>
Cc: Bui Quang Minh <minhquangbui99@...il.com>, netdev@...r.kernel.org, 
	"Michael S. Tsirkin" <mst@...hat.com>, Xuan Zhuo <xuanzhuo@...ux.alibaba.com>, 
	Eugenio Pérez <eperezma@...hat.com>, 
	Andrew Lunn <andrew+netdev@...n.ch>, "David S. Miller" <davem@...emloft.net>, 
	Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>, Gavin Li <gavinl@...dia.com>, 
	Gavi Teitz <gavi@...dia.com>, Parav Pandit <parav@...dia.com>, virtualization@...ts.linux.dev, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH net v2] virtio-net: fix received length check in big packets

On Thu, Jul 10, 2025 at 5:57 PM Paolo Abeni <pabeni@...hat.com> wrote:
>
> On 7/8/25 4:42 PM, Bui Quang Minh wrote:
> > Since commit 4959aebba8c0 ("virtio-net: use mtu size as buffer length
> > for big packets"), the allocated size for big packets is not
> > MAX_SKB_FRAGS * PAGE_SIZE anymore but depends on negotiated MTU. The
> > number of allocated frags for big packets is stored in
> > vi->big_packets_num_skbfrags. This commit fixes the received length
> > check corresponding to that change. The current incorrect check can lead
> > to NULL page pointer dereference in the below while loop when erroneous
> > length is received.
> >
> > Fixes: 4959aebba8c0 ("virtio-net: use mtu size as buffer length for big packets")
> > Signed-off-by: Bui Quang Minh <minhquangbui99@...il.com>
> > ---
> > Changes in v2:
> > - Remove incorrect give_pages call
> > ---
> >  drivers/net/virtio_net.c | 9 ++++++---
> >  1 file changed, 6 insertions(+), 3 deletions(-)
> >
> > diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> > index 5d674eb9a0f2..3a7f435c95ae 100644
> > --- a/drivers/net/virtio_net.c
> > +++ b/drivers/net/virtio_net.c
> > @@ -823,7 +823,7 @@ static struct sk_buff *page_to_skb(struct virtnet_info *vi,
> >  {
> >       struct sk_buff *skb;
> >       struct virtio_net_common_hdr *hdr;
> > -     unsigned int copy, hdr_len, hdr_padded_len;
> > +     unsigned int copy, hdr_len, hdr_padded_len, max_remaining_len;
> >       struct page *page_to_free = NULL;
> >       int tailroom, shinfo_size;
> >       char *p, *hdr_p, *buf;
> > @@ -887,12 +887,15 @@ static struct sk_buff *page_to_skb(struct virtnet_info *vi,
> >        * tries to receive more than is possible. This is usually
> >        * the case of a broken device.
> >        */
> > -     if (unlikely(len > MAX_SKB_FRAGS * PAGE_SIZE)) {
> > +     BUG_ON(offset >= PAGE_SIZE);
>
> Minor nit (not intended to block this patch): since you are touching
> this, you could consider replacing the BUG_ON() with a:
>
>  if (WARN_ON_ONCE()) <goto error path>.

I'm not sure I get this, but using BUG_ON() can help to prevent bugs
from being explored.

Thanks

>
> /P
>