On Thu, Jun 11, 2026 at 10:18:49AM +0800, Xuan Zhuo wrote: > 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.
i don't get it, and then what? > > > > 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. I will be frank, I'm never sure where the confidential computing guys draw the line. Are speculative things of concern, for example? > > > > 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) { don't see why we would check page > > unsigned int frag_size = min((unsigned)PAGE_SIZE - offset, len); > > + > > + if (unlikely(skb_shinfo(skb)->nr_frags >= MAX_SKB_FRAGS)) > > + break; so do we want BUG_ON here maybe? > > skb_add_rx_frag(skb, skb_shinfo(skb)->nr_frags, page, offset, > > frag_size, truesize); > > len -= frag_size; > > -- > > 2.43.0 > >
