Linux Virtualization - Jan 2018 - [PATCH net 1/2] vhost: use mutex_lock_nested() in vhost_dev_lock_vqs()

We used to call mutex_lock() in vhost_dev_lock_vqs() which tries to
hold mutexes of all virtqueues. This may confuse lockdep to report a
possible deadlock because of trying to hold locks belong to same
class. Switch to use mutex_lock_nested() to avoid false positive.

Fixes: 6b1e6cc7855b0 ("vhost: new device IOTLB API")
Reported-by: syzbot+dbb7c1161485e61b0241 at syzkaller.appspotmail.com
Signed-off-by: Jason Wang <jasowang at redhat.com>
---
 drivers/vhost/vhost.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
index 33ac2b1..549771a 100644
--- a/drivers/vhost/vhost.c
+++ b/drivers/vhost/vhost.c
@@ -904,7 +904,7 @@ static void vhost_dev_lock_vqs(struct vhost_dev *d)
 {
 	int i = 0;
 	for (i = 0; i < d->nvqs; ++i)
-		mutex_lock(&d->vqs[i]->mutex);
+		mutex_lock_nested(&d->vqs[i]->mutex, i);
 }
 
 static void vhost_dev_unlock_vqs(struct vhost_dev *d)
-- 
2.7.4

The code will try to access dev->iotlb when processing
VHOST_IOTLB_INVALIDATE even if it was not initialized which may lead
to NULL pointer dereference. Fixes this by check dev->iotlb before.

Fixes: 6b1e6cc7855b0 ("vhost: new device IOTLB API")
Signed-off-by: Jason Wang <jasowang at redhat.com>
---
 drivers/vhost/vhost.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
index 549771a..5727b18 100644
--- a/drivers/vhost/vhost.c
+++ b/drivers/vhost/vhost.c
@@ -1015,6 +1015,10 @@ static int vhost_process_iotlb_msg(struct vhost_dev *dev,
 		vhost_iotlb_notify_vq(dev, msg);
 		break;
 	case VHOST_IOTLB_INVALIDATE:
+		if (!dev->iotlb) {
+			ret = -EFAULT;
+			break;
+		}
 		vhost_vq_meta_reset(dev);
 		vhost_del_umem_range(dev->iotlb, msg->iova,
 				     msg->iova + msg->size - 1);
-- 
2.7.4

On Tue, Jan 23, 2018 at 05:27:25PM +0800, Jason Wang
wrote:
> We used to call mutex_lock() in vhost_dev_lock_vqs() which tries to
> hold mutexes of all virtqueues. This may confuse lockdep to report a
> possible deadlock because of trying to hold locks belong to same
> class. Switch to use mutex_lock_nested() to avoid false positive.
> 
> Fixes: 6b1e6cc7855b0 ("vhost: new device IOTLB API")
> Reported-by: syzbot+dbb7c1161485e61b0241 at syzkaller.appspotmail.com
> Signed-off-by: Jason Wang <jasowang at redhat.com>
Acked-by: Michael S. Tsirkin <mst at redhat.com>
> ---
>  drivers/vhost/vhost.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
> index 33ac2b1..549771a 100644
> --- a/drivers/vhost/vhost.c
> +++ b/drivers/vhost/vhost.c
> @@ -904,7 +904,7 @@ static void vhost_dev_lock_vqs(struct vhost_dev *d)
>  {
>  	int i = 0;
>  	for (i = 0; i < d->nvqs; ++i)
> -		mutex_lock(&d->vqs[i]->mutex);
> +		mutex_lock_nested(&d->vqs[i]->mutex, i);
>  }
>  
>  static void vhost_dev_unlock_vqs(struct vhost_dev *d)
> -- 
> 2.7.4

On Tue, Jan 23, 2018 at 05:27:26PM +0800, Jason Wang
wrote:
> The code will try to access dev->iotlb when processing
> VHOST_IOTLB_INVALIDATE even if it was not initialized which may lead
> to NULL pointer dereference. Fixes this by check dev->iotlb before.
> 
> Fixes: 6b1e6cc7855b0 ("vhost: new device IOTLB API")
> Signed-off-by: Jason Wang <jasowang at redhat.com>
Acked-by: Michael S. Tsirkin <mst at redhat.com>
> ---
>  drivers/vhost/vhost.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
> index 549771a..5727b18 100644
> --- a/drivers/vhost/vhost.c
> +++ b/drivers/vhost/vhost.c
> @@ -1015,6 +1015,10 @@ static int vhost_process_iotlb_msg(struct vhost_dev
*dev,
>  		vhost_iotlb_notify_vq(dev, msg);
>  		break;
>  	case VHOST_IOTLB_INVALIDATE:
> +		if (!dev->iotlb) {
> +			ret = -EFAULT;
> +			break;
> +		}
>  		vhost_vq_meta_reset(dev);
>  		vhost_del_umem_range(dev->iotlb, msg->iova,
>  				     msg->iova + msg->size - 1);
> -- 
> 2.7.4

From: Jason Wang <jasowang at redhat.com>
Date: Tue, 23 Jan 2018 17:27:25 +0800
> We used to call mutex_lock() in vhost_dev_lock_vqs() which tries to
> hold mutexes of all virtqueues. This may confuse lockdep to report a
> possible deadlock because of trying to hold locks belong to same
> class. Switch to use mutex_lock_nested() to avoid false positive.
> 
> Fixes: 6b1e6cc7855b0 ("vhost: new device IOTLB API")
> Reported-by: syzbot+dbb7c1161485e61b0241 at syzkaller.appspotmail.com
> Signed-off-by: Jason Wang <jasowang at redhat.com>
Michael, I see you ACK'd this, meaning that you're OK with these two
fixes going via my net tree?

Thanks.

On Wed, Jan 24, 2018 at 04:38:30PM -0500, David Miller
wrote:
> From: Jason Wang <jasowang at redhat.com>
> Date: Tue, 23 Jan 2018 17:27:25 +0800
> 
> > We used to call mutex_lock() in vhost_dev_lock_vqs() which tries to
> > hold mutexes of all virtqueues. This may confuse lockdep to report a
> > possible deadlock because of trying to hold locks belong to same
> > class. Switch to use mutex_lock_nested() to avoid false positive.
> > 
> > Fixes: 6b1e6cc7855b0 ("vhost: new device IOTLB API")
> > Reported-by: syzbot+dbb7c1161485e61b0241 at syzkaller.appspotmail.com
> > Signed-off-by: Jason Wang <jasowang at redhat.com>
> 
> Michael, I see you ACK'd this, meaning that you're OK with these
two
> fixes going via my net tree?
> 
> Thanks.
Yes - this seems to be what Jason wanted (judging by the net
tag in the subject) and I'm fine with it.
Thanks a lot.

-- 
MST