[PATCH] Btrfs: do not overwrite scrub error with fault error in scrub ioctl

[PATCH] Btrfs: do not overwrite scrub error with fault error in scrub ioctl

[fdmanana]

From: Filipe Manana <fdmanana@suse.com>

If scrub returned an error and then the copy_to_user() call did not
succeed, we would overwrite the error returned by scrub with -EFAULT.
Fix that by removing the call to copy_to_user() as there is no need
to do it at all.

Signed-off-by: Filipe Manana <fdmanana@suse.com>
---
 fs/btrfs/ioctl.c | 3 ---
 1 file changed, 3 deletions(-)

diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
index 3a27efa2b955..01d18e1a393e 100644
--- a/fs/btrfs/ioctl.c
+++ b/fs/btrfs/ioctl.c
@@ -4301,9 +4301,6 @@ static long btrfs_ioctl_scrub(struct file *file, void __user *arg)
 			      &sa->progress, sa->flags & BTRFS_SCRUB_READONLY,
 			      0);
 
-	if (copy_to_user(arg, sa, sizeof(*sa)))
-		ret = -EFAULT;
-
 	if (!(sa->flags & BTRFS_SCRUB_READONLY))
 		mnt_drop_write_file(file);
 out:
-- 
2.11.0

[PATCH v2] Btrfs: do not overwrite scrub error with fault error in scrub ioctl

[fdmanana]

From: Filipe Manana <fdmanana@suse.com>

If scrub returned an error and then the copy_to_user() call did not
succeed, we would overwrite the error returned by scrub with -EFAULT.
Fix that by removing the call to copy_to_user() as there is no need
to do it at all.

Signed-off-by: Filipe Manana <fdmanana@suse.com>
---

V2: Leave to copy_to_user() call since progress needs to be reported back
    to user space.

 fs/btrfs/ioctl.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
index 3a27efa2b955..4c05d9c4fe3d 100644
--- a/fs/btrfs/ioctl.c
+++ b/fs/btrfs/ioctl.c
@@ -4301,7 +4301,7 @@ static long btrfs_ioctl_scrub(struct file *file, void __user *arg)
 			      &sa->progress, sa->flags & BTRFS_SCRUB_READONLY,
 			      0);
 
-	if (copy_to_user(arg, sa, sizeof(*sa)))
+	if (ret == 0 && copy_to_user(arg, sa, sizeof(*sa)))
 		ret = -EFAULT;
 
 	if (!(sa->flags & BTRFS_SCRUB_READONLY))
-- 
2.11.0

Re: [PATCH v2] Btrfs: do not overwrite scrub error with fault error in scrub ioctl

[David Sterba]

On Fri, Dec 14, 2018 at 07:50:17PM +0000, fdmanana@kernel.org wrote:
> From: Filipe Manana <fdmanana@suse.com>
> 
> If scrub returned an error and then the copy_to_user() call did not
> succeed, we would overwrite the error returned by scrub with -EFAULT.
> Fix that by removing the call to copy_to_user() as there is no need
> to do it at all.
> 
> Signed-off-by: Filipe Manana <fdmanana@suse.com>
> ---
> 
> V2: Leave to copy_to_user() call since progress needs to be reported back
>     to user space.

The changelog does not reflect v2, I'll update the last sentence to

"Fix that by calling copy_to_user() only if btrfs_scrub_dev returned
success."

Thanks.

Reviewed-by: David Sterba <dsterba@suse.com>