virtio-net: fix len check in receive_big()

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 <bestswngs@gmail.com>
Signed-off-by: Xiang Mei <xmei5@asu.edu>
Reviewed-by: Xuan Zhuo <xuanzhuo@linux.alibaba.com>
Acked-by: Michael S. Tsirkin <mst@redhat.com>
Reviewed-by: Bui Quang Minh <minhquangbui99@gmail.com>
Link: https://patch.msgid.link/20260616042837.2249468-1-xmei5@asu.edu
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

0 files changed, 0 insertions, 0 deletions