On Wed, 10 Jun 2026 16:29:35 -0700, Xiang Mei <[email protected]> wrote: > receive_big() bounds the device-announced length by > (big_packets_num_skbfrags + 1) * PAGE_SIZE. That is still too loose: > add_recvbuf_big() sets sg[1] to start at offset > sizeof(struct padded_vnet_hdr) into the first page, so the chain > actually carries hdr_len + (PAGE_SIZE - sizeof(padded_vnet_hdr)) + > big_packets_num_skbfrags * PAGE_SIZE bytes -- 20 bytes less than the > check allows for the common hdr_len == 12 case. > > A malicious virtio backend can announce a len in that gap. page_to_skb() > then walks one frag past the page chain, storing a NULL page->private > into skb_shinfo()->frags[MAX_SKB_FRAGS], which is both an out-of-bounds > write past the static frag array and a NULL frag handed up the rx path. > > Bound len by the size add_recvbuf_big() actually advertised. > > Fixes: 0c716703965f ("virtio-net: fix received length check in big packets") > Reported-by: Weiming Shi <[email protected]> > Signed-off-by: Xiang Mei <[email protected]>
Reviewed-by: Xuan Zhuo <[email protected]> > --- > v2: add 2/2 for robustness > > drivers/net/virtio_net.c | 8 +++++--- > 1 file changed, 5 insertions(+), 3 deletions(-) > > diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c > index f4adcfee7a80..afe73eda1491 100644 > --- a/drivers/net/virtio_net.c > +++ b/drivers/net/virtio_net.c > @@ -1999,15 +1999,17 @@ static struct sk_buff *receive_big(struct net_device > *dev, > struct virtnet_rq_stats *stats) > { > struct page *page = buf; > + unsigned long max_len; > struct sk_buff *skb; > > /* Make sure that len does not exceed the size allocated in > * add_recvbuf_big. > */ > - if (unlikely(len > (vi->big_packets_num_skbfrags + 1) * PAGE_SIZE)) { > + max_len = vi->hdr_len + (PAGE_SIZE - sizeof(struct padded_vnet_hdr)) + > + vi->big_packets_num_skbfrags * PAGE_SIZE; > + if (unlikely(len > max_len)) { > pr_debug("%s: rx error: len %u exceeds allocated size %lu\n", > - dev->name, len, > - (vi->big_packets_num_skbfrags + 1) * PAGE_SIZE); > + dev->name, len, max_len); > goto err; > } > > -- > 2.43.0 >
