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btrfs: Fix use-after-free when cleaning up fs_devs with a single stale device

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Commit 4fde46f0cc ("Btrfs: free the stale device") introduced
btrfs_free_stale_device which iterates the device lists for all
registered btrfs filesystems and deletes those devices which aren't
mounted. In a btrfs_devices structure has only 1 device attached to it
and it is unused then btrfs_free_stale_devices will proceed to also free
the btrfs_fs_devices struct itself. Currently this leads to a use after
free since list_for_each_entry will try to perform a check on the
already freed memory to see if it has to terminate the loop.

The fix is to use 'break' when we know we are freeing the current
fs_devs.

Fixes: 4fde46f0cc ("Btrfs: free the stale device")
Signed-off-by: Nikolay Borisov <nborisov@suse.com>
Reviewed-by: Anand Jain <anand.jain@oracle.com>
Signed-off-by: David Sterba <dsterba@suse.com>
This commit is contained in:
Nikolay Borisov 2018-01-30 16:07:37 +02:00 committed by David Sterba
parent 627e08738e
commit fd649f10c3
1 changed files with 1 additions and 0 deletions
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fs/btrfs/volumes.c
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@ -645,6 +645,7 @@ static void btrfs_free_stale_devices(const char *path,
btrfs_sysfs_remove_fsid(fs_devs);
list_del(&fs_devs->list);
free_fs_devices(fs_devs);
break;
} else {
fs_devs->num_devices--;
list_del(&dev->dev_list);