On Thu, 17 Jul 2025 at 11:10, Jason Wang jasowang@redhat.com wrote:

On Thu, Jul 17, 2025 at 5:01 PM Will Deacon will@kernel.org wrote:

...

vhost_vsock_alloc_skb() returns NULL for packets advertising a length larger than VIRTIO_VSOCK_MAX_PKT_BUF_SIZE in the packet header. However, this is only checked once the SKB has been allocated and, if the length in the packet header is zero, the SKB may not be freed immediately.

Can this be triggered from the guest? (I guess yes) Did we need to consider it as a security issue?

Yep, but then the packet would still be discarded later, and the memory released, so it can only increase the pressure on allocation, but the guest can still do so by sending packets for example on an unopened port.

Stefano

...

Hoist the size check before the SKB allocation so that an iovec larger than VIRTIO_VSOCK_MAX_PKT_BUF_SIZE + the header size is rejected outright. The subsequent check on the length field in the header can then simply check that the allocated SKB is indeed large enough to hold the packet.

Cc: stable@vger.kernel.org Fixes: 71dc9ec9ac7d ("virtio/vsock: replace virtio_vsock_pkt with sk_buff") Reviewed-by: Stefano Garzarella sgarzare@redhat.com Signed-off-by: Will Deacon will@kernel.org

---

drivers/vhost/vsock.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/drivers/vhost/vsock.c b/drivers/vhost/vsock.c index 802153e23073..66a0f060770e 100644 --- a/drivers/vhost/vsock.c +++ b/drivers/vhost/vsock.c @@ -344,6 +344,9 @@ vhost_vsock_alloc_skb(struct vhost_virtqueue *vq,

    len = iov_length(vq->iov, out);

•   if (len > VIRTIO_VSOCK_MAX_PKT_BUF_SIZE + VIRTIO_VSOCK_SKB_HEADROOM)
  

•           return NULL;
  

•   /* len contains both payload and hdr */
    skb = virtio_vsock_alloc_skb(len, GFP_KERNEL);
    if (!skb)
  

@@ -367,8 +370,7 @@ vhost_vsock_alloc_skb(struct vhost_virtqueue *vq, return skb;

    /* The pkt is too big or the length in the header is invalid */

•   if (payload_len > VIRTIO_VSOCK_MAX_PKT_BUF_SIZE ||
  

•       payload_len + sizeof(*hdr) > len) {
  

•   if (payload_len + sizeof(*hdr) > len) {
            kfree_skb(skb);
            return NULL;
    }
  

-- 2.50.0.727.gbf7dc18ff4-goog

Thanks