Virtualization - Jan 2015 - [PATCH] vhost/net: length miscalculation

commit 8b38694a2dc8b18374310df50174f1e4376d6824
    vhost/net: virtio 1.0 byte swap
had this chunk:
-       heads[headcount - 1].len += datalen;
+       heads[headcount - 1].len = cpu_to_vhost32(vq, len - datalen);

This adds datalen with the wrong sign, causing guest panics.

Fixes: 8b38694a2dc8b18374310df50174f1e4376d6824
Reported-by: Alex Williamson <alex.williamson at redhat.com>
Suggested-by: Greg Kurz <gkurz at linux.vnet.ibm.com>
Signed-off-by: Michael S. Tsirkin <mst at redhat.com>
---

Alex, could you please confirm this fixes the crash for you?

 drivers/vhost/net.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
index 14419a8..d415d69 100644
--- a/drivers/vhost/net.c
+++ b/drivers/vhost/net.c
@@ -538,7 +538,7 @@ static int get_rx_bufs(struct vhost_virtqueue *vq,
 		++headcount;
 		seg += in;
 	}
-	heads[headcount - 1].len = cpu_to_vhost32(vq, len - datalen);
+	heads[headcount - 1].len = cpu_to_vhost32(vq, len + datalen);
 	*iovcount = seg;
 	if (unlikely(log))
 		*log_num = nlogs;
-- 
MST

On Wed, 2015-01-07 at 10:55 +0200, Michael S. Tsirkin
wrote:
> commit 8b38694a2dc8b18374310df50174f1e4376d6824
>     vhost/net: virtio 1.0 byte swap
> had this chunk:
> -       heads[headcount - 1].len += datalen;
> +       heads[headcount - 1].len = cpu_to_vhost32(vq, len - datalen);
> 
> This adds datalen with the wrong sign, causing guest panics.
> 
> Fixes: 8b38694a2dc8b18374310df50174f1e4376d6824
> Reported-by: Alex Williamson <alex.williamson at redhat.com>
> Suggested-by: Greg Kurz <gkurz at linux.vnet.ibm.com>
> Signed-off-by: Michael S. Tsirkin <mst at redhat.com>
> ---
> 
> Alex, could you please confirm this fixes the crash for you?
Confirmed, this works.  Thanks,

Alex
>  drivers/vhost/net.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
> index 14419a8..d415d69 100644
> --- a/drivers/vhost/net.c
> +++ b/drivers/vhost/net.c
> @@ -538,7 +538,7 @@ static int get_rx_bufs(struct vhost_virtqueue *vq,
>  		++headcount;
>  		seg += in;
>  	}
> -	heads[headcount - 1].len = cpu_to_vhost32(vq, len - datalen);
> +	heads[headcount - 1].len = cpu_to_vhost32(vq, len + datalen);
>  	*iovcount = seg;
>  	if (unlikely(log))
>  		*log_num = nlogs;

Hello.

On 01/07/2015 11:55 AM, Michael S. Tsirkin wrote:
> commit 8b38694a2dc8b18374310df50174f1e4376d6824
>      vhost/net: virtio 1.0 byte swap
> had this chunk:
> -       heads[headcount - 1].len += datalen;
> +       heads[headcount - 1].len = cpu_to_vhost32(vq, len - datalen);
> This adds datalen with the wrong sign, causing guest panics.
> Fixes: 8b38694a2dc8b18374310df50174f1e4376d6824
    The format of this tag assumes 12-digit SHA1 hash and the commit 
description enclosed in parens and double quotes. See 
Documentation/SubmittingPatches.
> Reported-by: Alex Williamson <alex.williamson at redhat.com>
> Suggested-by: Greg Kurz <gkurz at linux.vnet.ibm.com>
> Signed-off-by: Michael S. Tsirkin <mst at redhat.com>
WBR, Sergei

On Wed, Jan 07, 2015 at 11:58:00PM +0300, Sergei Shtylyov
wrote:
> Hello.
> 
> On 01/07/2015 11:55 AM, Michael S. Tsirkin wrote:
> 
> >commit 8b38694a2dc8b18374310df50174f1e4376d6824
> >     vhost/net: virtio 1.0 byte swap
> >had this chunk:
> >-       heads[headcount - 1].len += datalen;
> >+       heads[headcount - 1].len = cpu_to_vhost32(vq, len - datalen);
> 
> >This adds datalen with the wrong sign, causing guest panics.
> 
> >Fixes: 8b38694a2dc8b18374310df50174f1e4376d6824
> 
>    The format of this tag assumes 12-digit SHA1 hash and the commit
> description enclosed in parens and double quotes. See
> Documentation/SubmittingPatches.
> 
> >Reported-by: Alex Williamson <alex.williamson at redhat.com>
> >Suggested-by: Greg Kurz <gkurz at linux.vnet.ibm.com>
> >Signed-off-by: Michael S. Tsirkin <mst at redhat.com>
> 
> WBR, Sergei
I pushed the patches to Linus unfortunately - there's
some urgency since many people are hitting the bug.
Will do my best to do it right next time.

-- 
MST