Linux Virtualization - Mar 2014 - [PATCH net] vhost: fix total length when packets are too short

When mergeable buffers are disabled, and the
incoming packet is too large for the rx buffer,
get_rx_bufs returns success.

This was intentional in order for make recvmsg
truncate the packet and then handle_rx would
detect err != sock_len and drop it.

Unfortunately we pass the original sock_len to
recvmsg - which means we use parts of iov not fully
validated.

Fix this up by detecting this overrun and doing packet drop
immediately.

CVE-2014-0055

Signed-off-by: Michael S. Tsirkin <mst at redhat.com>
---

Note: this is needed for -stable.

I wonder if this can still make the release.

 drivers/vhost/net.c | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
index a0fa5de..026be58 100644
--- a/drivers/vhost/net.c
+++ b/drivers/vhost/net.c
@@ -532,6 +532,12 @@ static int get_rx_bufs(struct vhost_virtqueue *vq,
 	*iovcount = seg;
 	if (unlikely(log))
 		*log_num = nlogs;
+
+	/* Detect overrun */
+	if (unlikely(datalen > 0)) {
+		r = UIO_MAXIOV + 1;
+		goto err;
+	}
 	return headcount;
 err:
 	vhost_discard_vq_desc(vq, headcount);
@@ -587,6 +593,14 @@ static void handle_rx(struct vhost_net *net)
 		/* On error, stop handling until the next kick. */
 		if (unlikely(headcount < 0))
 			break;
+		/* On overrun, truncate and discard */
+		if (unlikely(headcount > UIO_MAXIOV)) {
+			msg.msg_iovlen = 1;
+			err = sock->ops->recvmsg(NULL, sock, &msg,
+						 1, MSG_DONTWAIT | MSG_TRUNC);
+			pr_debug("Discarded rx packet: len %zd\n", sock_len);
+			continue;
+		}
 		/* OK, now we need to know about added descriptors. */
 		if (!headcount) {
 			if (unlikely(vhost_enable_notify(&net->dev, vq))) {
-- 
MST

On Thu, Mar 27, 2014 at 11:38:41AM +0200, Michael S. Tsirkin
wrote:
> When mergeable buffers are disabled, and the
> incoming packet is too large for the rx buffer,
> get_rx_bufs returns success.
> 
> This was intentional in order for make recvmsg
> truncate the packet and then handle_rx would
> detect err != sock_len and drop it.
> 
> Unfortunately we pass the original sock_len to
> recvmsg - which means we use parts of iov not fully
> validated.
> 
> Fix this up by detecting this overrun and doing packet drop
> immediately.
> 
> CVE-2014-0055
Ouch wrong CVE#. It's  CVE-2014-0077  actually.
Will resend V2 with the corrected commit log now.

> Signed-off-by: Michael S. Tsirkin <mst at redhat.com>
> ---
> 
> Note: this is needed for -stable.
> 
> I wonder if this can still make the release.
> 
>  drivers/vhost/net.c | 14 ++++++++++++++
>  1 file changed, 14 insertions(+)
> 
> diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
> index a0fa5de..026be58 100644
> --- a/drivers/vhost/net.c
> +++ b/drivers/vhost/net.c
> @@ -532,6 +532,12 @@ static int get_rx_bufs(struct vhost_virtqueue *vq,
>  	*iovcount = seg;
>  	if (unlikely(log))
>  		*log_num = nlogs;
> +
> +	/* Detect overrun */
> +	if (unlikely(datalen > 0)) {
> +		r = UIO_MAXIOV + 1;
> +		goto err;
> +	}
>  	return headcount;
>  err:
>  	vhost_discard_vq_desc(vq, headcount);
> @@ -587,6 +593,14 @@ static void handle_rx(struct vhost_net *net)
>  		/* On error, stop handling until the next kick. */
>  		if (unlikely(headcount < 0))
>  			break;
> +		/* On overrun, truncate and discard */
> +		if (unlikely(headcount > UIO_MAXIOV)) {
> +			msg.msg_iovlen = 1;
> +			err = sock->ops->recvmsg(NULL, sock, &msg,
> +						 1, MSG_DONTWAIT | MSG_TRUNC);
> +			pr_debug("Discarded rx packet: len %zd\n", sock_len);
> +			continue;
> +		}
>  		/* OK, now we need to know about added descriptors. */
>  		if (!headcount) {
>  			if (unlikely(vhost_enable_notify(&net->dev, vq))) {
> -- 
> MST