Commit 5afe6ce7 authored by Filipe Manana's avatar Filipe Manana Committed by David Sterba

Btrfs: always copy scrub arguments back to user space

If scrub returns an error we are not copying back the scrub arguments
structure to user space. This prevents user space to know how much
progress scrub has done if an error happened - this includes -ECANCELED
which is returned when users ask for scrub to stop. A particular use
case, which is used in btrfs-progs, is to resume scrub after it is
canceled, in that case it relies on checking the progress from the scrub
arguments structure and then use that progress in a call to resume
scrub.

So fix this by always copying the scrub arguments structure to user
space, overwriting the value returned to user space with -EFAULT only if
copying the structure failed to let user space know that either that
copying did not happen, and therefore the structure is stale, or it
happened partially and the structure is probably not valid and corrupt
due to the partial copy.
Reported-by: default avatarGraham Cobb <g.btrfs@cobb.uk.net>
Link: https://lore.kernel.org/linux-btrfs/d0a97688-78be-08de-ca7d-bcb4c7fb397e@cobb.uk.net/
Fixes: 06fe39ab ("Btrfs: do not overwrite scrub error with fault error in scrub ioctl")
CC: stable@vger.kernel.org # 5.1+
Reviewed-by: default avatarJohannes Thumshirn <johannes.thumshirn@wdc.com>
Reviewed-by: default avatarQu Wenruo <wqu@suse.com>
Tested-by: default avatarGraham Cobb <g.btrfs@cobb.uk.net>
Signed-off-by: default avatarFilipe Manana <fdmanana@suse.com>
Reviewed-by: default avatarDavid Sterba <dsterba@suse.com>
Signed-off-by: default avatarDavid Sterba <dsterba@suse.com>
parent 6282675e
......@@ -4252,7 +4252,19 @@ static long btrfs_ioctl_scrub(struct file *file, void __user *arg)
&sa->progress, sa->flags & BTRFS_SCRUB_READONLY,
0);
if (ret == 0 && copy_to_user(arg, sa, sizeof(*sa)))
/*
* Copy scrub args to user space even if btrfs_scrub_dev() returned an
* error. This is important as it allows user space to know how much
* progress scrub has done. For example, if scrub is canceled we get
* -ECANCELED from btrfs_scrub_dev() and return that error back to user
* space. Later user space can inspect the progress from the structure
* btrfs_ioctl_scrub_args and resume scrub from where it left off
* previously (btrfs-progs does this).
* If we fail to copy the btrfs_ioctl_scrub_args structure to user space
* then return -EFAULT to signal the structure was not copied or it may
* be corrupt and unreliable due to a partial copy.
*/
if (copy_to_user(arg, sa, sizeof(*sa)))
ret = -EFAULT;
if (!(sa->flags & BTRFS_SCRUB_READONLY))
......
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