On Wed, 10 Jun 2026 16:29:36 -0700, Xiang Mei <[email protected]> wrote: > This is a robustness hardening patch. The slow-path frag loop in > page_to_skb() walks the page chain via page->private until the > device-reported len is consumed, implicitly trusting that len fits the > chain. It does not stop when the chain is exhausted (page becomes NULL > at the tail), nor when nr_frags reaches the end of the static > skb_shinfo()->frags[MAX_SKB_FRAGS] array. > > Both bounds are needed: the chain length is big_packets_num_skbfrags + 1 > pages, which for an MTU-driven configuration can be well below > MAX_SKB_FRAGS, so neither guard implies the other. > > Make the loop self-defending so it no longer relies on the caller having > validated len: stop once the chain is exhausted, and never index past > MAX_SKB_FRAGS. No functional change for well-formed input.
At this point, we are assuming that len represents the correct packet length. If there is a bug in the validation, it can be fixed, just like in your previous patch. Indeed, not checking nr_frags is also based on the overall design. However, I do not recommend adding this kind of enhancement. If we follow this logic, we would end up adding similar code in many other places, which doesn't make much sense. Thanks. > > Signed-off-by: Xiang Mei <[email protected]> > --- > v2: robustness patch > > drivers/net/virtio_net.c | 5 ++++- > 1 file changed, 4 insertions(+), 1 deletion(-) > > diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c > index afe73eda1491..518c22fa1b68 100644 > --- a/drivers/net/virtio_net.c > +++ b/drivers/net/virtio_net.c > @@ -906,8 +906,11 @@ static struct sk_buff *page_to_skb(struct virtnet_info > *vi, > } > > BUG_ON(offset >= PAGE_SIZE); > - while (len) { > + while (len && page) { > unsigned int frag_size = min((unsigned)PAGE_SIZE - offset, len); > + > + if (unlikely(skb_shinfo(skb)->nr_frags >= MAX_SKB_FRAGS)) > + break; > skb_add_rx_frag(skb, skb_shinfo(skb)->nr_frags, page, offset, > frag_size, truesize); > len -= frag_size; > -- > 2.43.0 >
