Since commit 4959aebba8c0 ("virtio-net: use mtu size as buffer length for big packets"), when guest gso is off, 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.

Because the host announced buffer length can be malicious (e.g. the host vhost_net driver's get_rx_bufs is modified to announce incorrect length), we need a check in virtio_net receive path. Currently, the check is not adapted to the new change which can lead to NULL page pointer dereference in the below while loop when receiving length that is larger than the allocated one.

This commit fixes the received length check corresponding to the new change.

Fixes: 4959aebba8c0 ("virtio-net: use mtu size as buffer length for big packets") Cc: stable@vger.kernel.org Signed-off-by: Bui Quang Minh minhquangbui99@gmail.com --- Changes in v7: - Fix typos - Link to v6: https://lore.kernel.org/netdev/20251028143116.4532-1-minhquangbui99@gmail.co... Changes in v6: - Fix the length check - Link to v5: https://lore.kernel.org/netdev/20251024150649.22906-1-minhquangbui99@gmail.c... Changes in v5: - Move the length check to receive_big - Link to v4: https://lore.kernel.org/netdev/20251022160623.51191-1-minhquangbui99@gmail.c... Changes in v4: - Remove unrelated changes, add more comments - Link to v3: https://lore.kernel.org/netdev/20251021154534.53045-1-minhquangbui99@gmail.c... Changes in v3: - Convert BUG_ON to WARN_ON_ONCE - Link to v2: https://lore.kernel.org/netdev/20250708144206.95091-1-minhquangbui99@gmail.c... Changes in v2: - Remove incorrect give_pages call - Link to v1: https://lore.kernel.org/netdev/20250706141150.25344-1-minhquangbui99@gmail.c... --- drivers/net/virtio_net.c | 25 ++++++++++++------------- 1 file changed, 12 insertions(+), 13 deletions(-)

diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c index a757cbcab87f..421b9aa190a0 100644 --- a/drivers/net/virtio_net.c +++ b/drivers/net/virtio_net.c @@ -910,17 +910,6 @@ static struct sk_buff *page_to_skb(struct virtnet_info *vi, goto ok; }

- /* - * Verify that we can indeed put this data into a skb. - * This is here to handle cases when the device erroneously - * tries to receive more than is possible. This is usually - * the case of a broken device. - */ - if (unlikely(len > MAX_SKB_FRAGS * PAGE_SIZE)) { - net_dbg_ratelimited("%s: too much data\n", skb->dev->name); - dev_kfree_skb(skb); - return NULL; - } BUG_ON(offset >= PAGE_SIZE); while (len) { unsigned int frag_size = min((unsigned)PAGE_SIZE - offset, len); @@ -2107,9 +2096,19 @@ static struct sk_buff *receive_big(struct net_device *dev, struct virtnet_rq_stats *stats) { struct page *page = buf; - struct sk_buff *skb = - page_to_skb(vi, rq, page, 0, len, PAGE_SIZE, 0); + 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)) { + pr_debug("%s: rx error: len %u exceeds allocated size %lu\n", + dev->name, len, + (vi->big_packets_num_skbfrags + 1) * PAGE_SIZE); + goto err; + }

+ skb = page_to_skb(vi, rq, page, 0, len, PAGE_SIZE, 0); u64_stats_add(&stats->bytes, len - vi->hdr_len); if (unlikely(!skb)) goto err;