[PATCH v3 1/9] vhost/vsock: Avoid allocating arbitrarily-sized SKBs

[PATCH v3 1/9] vhost/vsock: Avoid allocating arbitrarily-sized SKBs

[Will Deacon]

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.

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")
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

[PATCH v3 2/9] vsock/virtio: Validate length in packet header before skb_put()

[Will Deacon]

When receiving a vsock packet in the guest, only the virtqueue buffer
size is validated prior to virtio_vsock_skb_rx_put(). Unfortunately,
virtio_vsock_skb_rx_put() uses the length from the packet header as the
length argument to skb_put(), potentially resulting in SKB overflow if
the host has gone wonky.

Validate the length as advertised by the packet header before calling
virtio_vsock_skb_rx_put().

Cc: <stable@vger.kernel.org>
Fixes: 71dc9ec9ac7d ("virtio/vsock: replace virtio_vsock_pkt with sk_buff")
Signed-off-by: Will Deacon <will@kernel.org>
---
 net/vmw_vsock/virtio_transport.c | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/net/vmw_vsock/virtio_transport.c b/net/vmw_vsock/virtio_transport.c
index f0e48e6911fc..bd2c6aaa1a93 100644
--- a/net/vmw_vsock/virtio_transport.c
+++ b/net/vmw_vsock/virtio_transport.c
@@ -624,8 +624,9 @@ static void virtio_transport_rx_work(struct work_struct *work)
 	do {
 		virtqueue_disable_cb(vq);
 		for (;;) {
+			unsigned int len, payload_len;
+			struct virtio_vsock_hdr *hdr;
 			struct sk_buff *skb;
-			unsigned int len;
 
 			if (!virtio_transport_more_replies(vsock)) {
 				/* Stop rx until the device processes already
@@ -642,12 +643,19 @@ static void virtio_transport_rx_work(struct work_struct *work)
 			vsock->rx_buf_nr--;
 
 			/* Drop short/long packets */
-			if (unlikely(len < sizeof(struct virtio_vsock_hdr) ||
+			if (unlikely(len < sizeof(*hdr) ||
 				     len > virtio_vsock_skb_len(skb))) {
 				kfree_skb(skb);
 				continue;
 			}
 
+			hdr = virtio_vsock_hdr(skb);
+			payload_len = le32_to_cpu(hdr->len);
+			if (payload_len > len - sizeof(*hdr)) {
+				kfree_skb(skb);
+				continue;
+			}
+
 			virtio_vsock_skb_rx_put(skb);
 			virtio_transport_deliver_tap_pkt(skb);
 			virtio_transport_recv_pkt(&virtio_transport, skb);
-- 
2.50.0.727.gbf7dc18ff4-goog

Re: [PATCH v3 1/9] vhost/vsock: Avoid allocating arbitrarily-sized SKBs

[Stefano Garzarella]

On Mon, Jul 14, 2025 at 04:20:55PM +0100, Will Deacon 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.
>
>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")
>Signed-off-by: Will Deacon <will@kernel.org>
>---
> drivers/vhost/vsock.c | 6 ++++--
> 1 file changed, 4 insertions(+), 2 deletions(-)

Reviewed-by: Stefano Garzarella <sgarzare@redhat.com>

>
>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
>

Re: [PATCH v3 2/9] vsock/virtio: Validate length in packet header before skb_put()

[Stefano Garzarella]

On Mon, Jul 14, 2025 at 04:20:56PM +0100, Will Deacon wrote:
>When receiving a vsock packet in the guest, only the virtqueue buffer
>size is validated prior to virtio_vsock_skb_rx_put(). Unfortunately,
>virtio_vsock_skb_rx_put() uses the length from the packet header as the
>length argument to skb_put(), potentially resulting in SKB overflow if
>the host has gone wonky.
>
>Validate the length as advertised by the packet header before calling
>virtio_vsock_skb_rx_put().
>
>Cc: <stable@vger.kernel.org>
>Fixes: 71dc9ec9ac7d ("virtio/vsock: replace virtio_vsock_pkt with sk_buff")
>Signed-off-by: Will Deacon <will@kernel.org>
>---
> net/vmw_vsock/virtio_transport.c | 12 ++++++++++--
> 1 file changed, 10 insertions(+), 2 deletions(-)
>
>diff --git a/net/vmw_vsock/virtio_transport.c b/net/vmw_vsock/virtio_transport.c
>index f0e48e6911fc..bd2c6aaa1a93 100644
>--- a/net/vmw_vsock/virtio_transport.c
>+++ b/net/vmw_vsock/virtio_transport.c
>@@ -624,8 +624,9 @@ static void virtio_transport_rx_work(struct work_struct *work)
> 	do {
> 		virtqueue_disable_cb(vq);
> 		for (;;) {
>+			unsigned int len, payload_len;
>+			struct virtio_vsock_hdr *hdr;
> 			struct sk_buff *skb;
>-			unsigned int len;
>
> 			if (!virtio_transport_more_replies(vsock)) {
> 				/* Stop rx until the device processes already
>@@ -642,12 +643,19 @@ static void virtio_transport_rx_work(struct work_struct *work)
> 			vsock->rx_buf_nr--;
>
> 			/* Drop short/long packets */
>-			if (unlikely(len < sizeof(struct virtio_vsock_hdr) ||
>+			if (unlikely(len < sizeof(*hdr) ||

pre-existing: in some part we use sizeof(*hdr) in other 
VIRTIO_VSOCK_SKB_HEADROOM, I think we should try to uniform that, but of 
course not for this series!

> 				     len > virtio_vsock_skb_len(skb))) {
> 				kfree_skb(skb);
> 				continue;
> 			}
>
>+			hdr = virtio_vsock_hdr(skb);
>+			payload_len = le32_to_cpu(hdr->len);
>+			if (payload_len > len - sizeof(*hdr)) {

Since this is an hot path, should we use `unlikely`, like in the 
previous check, to instruct the branch predictor?

The rest LGTM!

Thanks,
Stefano

>+				kfree_skb(skb);
>+				continue;
>+			}
>+
> 			virtio_vsock_skb_rx_put(skb);
> 			virtio_transport_deliver_tap_pkt(skb);
> 			virtio_transport_recv_pkt(&virtio_transport, skb);
>-- 
>2.50.0.727.gbf7dc18ff4-goog
>