Thread (5 messages) 5 messages, 4 authors, 6h ago

Re: [PATCH net] vsock/virtio: fix skb overhead overflow on 32-bit builds

From: David Laight <hidden>
Date: 2026-05-21 17:13:52
Also in: kvm, lkml, stable, virtualization

On Thu, 21 May 2026 14:47:32 +0200
Stefano Garzarella [off-list ref] wrote:
quoted hunk ↗ jump to hunk
From: Stefano Garzarella <sgarzare@redhat.com>

On 32-bit architectures, both skb_queue_len() and SKB_TRUESIZE(0) evaluate
to 32-bit values. The multiplication can overflow before being assigned to
the u64 skb_overhead variable, making the skb overhead check ineffective.

Cast skb_queue_len() to u64 so the multiplication is always performed in
64-bit arithmetic.

This issue was reported by Sashiko while reviewing another patch.

Fixes: 059b7dbd20a6 ("vsock/virtio: fix potential unbounded skb queue")
Closes: https://sashiko.dev/#/patchset/20260518090656.134588-1-sgarzare%40redhat.com
Cc: stable@vger.kernel.org
Signed-off-by: Stefano Garzarella <sgarzare@redhat.com>
---
 net/vmw_vsock/virtio_transport_common.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/net/vmw_vsock/virtio_transport_common.c b/net/vmw_vsock/virtio_transport_common.c
index df3b418e0392..71198bf23fc4 100644
--- a/net/vmw_vsock/virtio_transport_common.c
+++ b/net/vmw_vsock/virtio_transport_common.c
@@ -417,7 +417,7 @@ static int virtio_transport_send_pkt_info(struct vsock_sock *vsk,
 static bool virtio_transport_inc_rx_pkt(struct virtio_vsock_sock *vvs,
 					u32 len)
 {
-	u64 skb_overhead = (skb_queue_len(&vvs->rx_queue) + 1) * SKB_TRUESIZE(0);
+	u64 skb_overhead = ((u64)skb_queue_len(&vvs->rx_queue) + 1) * SKB_TRUESIZE(0);
I was thinking this should use mul_u32_u32().
But that is all moot.
'skb_overhead' is a memory size in bytes, 'unsigned long' it more than big enough.
No need for 64bit maths on 32bit.

-- David
 
 	/* Allow at most buf_alloc * 2 total budget (payload + overhead),
 	 * similar to how SO_RCVBUF is doubled to reserve space for sk_buff
  
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