On 2020/10/23 下午11:34, Michael S. Tsirkin wrote:

On Fri, Oct 23, 2020 at 03:08:53PM +0300, Dan Carpenter wrote:

quoted

The copy_to/from_user() functions return the number of bytes which we
weren't able to copy but the ioctl should return -EFAULT if they fail.

Fixes: a127c5bbb6a8 ("vhost-vdpa: fix backend feature ioctls")
Signed-off-by: Dan Carpenter <redacted>

Acked-by: Michael S. Tsirkin <mst@redhat.com>
Needed for stable I guess.

Agree.

Acked-by: Jason Wang <redacted>

quoted

---
  drivers/vhost/vdpa.c | 10 +++++-----
  1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/drivers/vhost/vdpa.c b/drivers/vhost/vdpa.c
index 62a9bb0efc55..c94a97b6bd6d 100644
--- a/drivers/vhost/vdpa.c
+++ b/drivers/vhost/vdpa.c

@@ -428,12 +428,11 @@ static long vhost_vdpa_unlocked_ioctl(struct file *filep,
  	void __user *argp = (void __user *)arg;
  	u64 __user *featurep = argp;
  	u64 features;
-	long r;
+	long r = 0;
  
  	if (cmd == VHOST_SET_BACKEND_FEATURES) {
-		r = copy_from_user(&features, featurep, sizeof(features));
-		if (r)
-			return r;
+		if (copy_from_user(&features, featurep, sizeof(features)))
+			return -EFAULT;
  		if (features & ~VHOST_VDPA_BACKEND_FEATURES)
  			return -EOPNOTSUPP;
  		vhost_set_backend_features(&v->vdev, features);

@@ -476,7 +475,8 @@ static long vhost_vdpa_unlocked_ioctl(struct file *filep,
  		break;
  	case VHOST_GET_BACKEND_FEATURES:
  		features = VHOST_VDPA_BACKEND_FEATURES;
-		r = copy_to_user(featurep, &features, sizeof(features));
+		if (copy_to_user(featurep, &features, sizeof(features)))
+			r = -EFAULT;
  		break;
  	default:
  		r = vhost_dev_ioctl(&v->vdev, cmd, argp);