linux-kernel - [PATCH net v3] virtio-net: fix received length check in big packets

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Message-ID: <20251021154534.53045-1-minhquangbui99@gmail.com>
Date: Tue, 21 Oct 2025 22:45:34 +0700
From: Bui Quang Minh <minhquangbui99@...il.com>
To: netdev@...r.kernel.org
Cc: "Michael S. Tsirkin" <mst@...hat.com>,
	Jason Wang <jasowang@...hat.com>,
	Xuan Zhuo <xuanzhuo@...ux.alibaba.com>,
	Eugenio Pérez <eperezma@...hat.com>,
	Andrew Lunn <andrew+netdev@...n.ch>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>,
	Paolo Abeni <pabeni@...hat.com>,
	Gavin Li <gavinl@...dia.com>,
	Gavi Teitz <gavi@...dia.com>,
	Parav Pandit <parav@...dia.com>,
	virtualization@...ts.linux.dev,
	linux-kernel@...r.kernel.org,
	Bui Quang Minh <minhquangbui99@...il.com>
Subject: [PATCH net v3] virtio-net: fix received length check in big packets

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.

Fixes: 4959aebba8c0 ("virtio-net: use mtu size as buffer length for big packets")
Signed-off-by: Bui Quang Minh <minhquangbui99@...il.com>
---
Changes in v3:
- Convert BUG_ON to WARN_ON_ONCE
Changes in v2:
- Remove incorrect give_pages call
---
 drivers/net/virtio_net.c | 18 +++++++++++++-----
 1 file changed, 13 insertions(+), 5 deletions(-)

diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index a757cbcab87f..e7b33e40ea99 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -852,7 +852,7 @@ 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;
@@ -916,12 +916,16 @@ 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)) {
+	if (WARN_ON_ONCE(offset >= PAGE_SIZE))
+		goto err;
+
+	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->name);
-		dev_kfree_skb(skb);
-		return NULL;
+		goto err;
 	}
-	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,
@@ -941,6 +945,10 @@ static struct sk_buff *page_to_skb(struct virtnet_info *vi,
 		put_page(page_to_free);
 
 	return skb;
+
+err:
+	dev_kfree_skb(skb);
+	return NULL;
 }
 
 static void virtnet_rq_unmap(struct receive_queue *rq, void *buf, u32 len)
-- 
2.43.0