On 7/8/25 21:52, Parav Pandit wrote:

quoted

From: Bui Quang Minh <redacted>
Sent: 08 July 2025 08:12 PM

Since commit 4959aebba8c0 ("virtio-net: use mtu size as buffer length for big
packets"), 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. This commit fixes the received length
check corresponding to that change. The current incorrect check can lead to
NULL page pointer dereference in the below while loop when erroneous
length is received.

Do you mean a device has copied X bytes in receive buffer but device reports X+Y bytes in the ring?

Yes, that's what I mean. AFAIK, it's not checked in the ring level.


Thanks,
Quang Minh.

quoted

Fixes: 4959aebba8c0 ("virtio-net: use mtu size as buffer length for big
packets")
Signed-off-by: Bui Quang Minh <redacted>
---
Changes in v2:
- Remove incorrect give_pages call
---
  drivers/net/virtio_net.c | 9 ++++++---
  1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c index

5d674eb9a0f2..3a7f435c95ae 100644

--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c

@@ -823,7 +823,7 @@ static struct sk_buff *page_to_skb(struct virtnet_info

*vi,  {
  	struct sk_buff *skb;
  	struct virtio_net_common_hdr *hdr;
-	unsigned int copy, hdr_len, hdr_padded_len;
+	unsigned int copy, hdr_len, hdr_padded_len, max_remaining_len;
  	struct page *page_to_free = NULL;
  	int tailroom, shinfo_size;
  	char *p, *hdr_p, *buf;

@@ -887,12 +887,15 @@ static struct sk_buff *page_to_skb(struct

virtnet_info *vi,
  	 * tries to receive more than is possible. This is usually
  	 * the case of a broken device.
  	 */
-	if (unlikely(len > MAX_SKB_FRAGS * PAGE_SIZE)) {
+	BUG_ON(offset >= PAGE_SIZE);
+	max_remaining_len = (unsigned int)PAGE_SIZE - offset;
+	max_remaining_len += vi->big_packets_num_skbfrags * PAGE_SIZE;
+	if (unlikely(len > max_remaining_len)) {
  		net_dbg_ratelimited("%s: too much data\n", skb->dev-

quoted

name);

  		dev_kfree_skb(skb);
  		return NULL;
  	}
-	BUG_ON(offset >= PAGE_SIZE);
+
  	while (len) {
  		unsigned int frag_size = min((unsigned)PAGE_SIZE - offset,
len);
  		skb_add_rx_frag(skb, skb_shinfo(skb)->nr_frags, page, offset,
--
2.43.0