[PATCH] btrfs: ioctl: Fix memory leak on duplicated memory

["Miquel Sabaté Solà" <mssola@mssola.com>]

On 'btrfs_ioctl_qgroup_assign' we first duplicate the argument as
provided by the user, which is kfree'd in the end. But this was not the
case when allocating memory for 'prealloc'. In this case, if it somehow
failed, then the previous code would go directly into calling
'mnt_drop_write_file', without freeing the string duplicated from the
user space.

Signed-off-by: Miquel Sabaté Solà <mssola@mssola.com>
---
 fs/btrfs/ioctl.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
index 185bef0df1c2..00381fdbff9d 100644
--- a/fs/btrfs/ioctl.c
+++ b/fs/btrfs/ioctl.c
@@ -3740,7 +3740,7 @@ static long btrfs_ioctl_qgroup_assign(struct file *file, void __user *arg)
 		prealloc = kzalloc(sizeof(*prealloc), GFP_KERNEL);
 		if (!prealloc) {
 			ret = -ENOMEM;
-			goto drop_write;
+			goto out_sa_drop_write;
 		}
 	}
 
@@ -3775,6 +3775,7 @@ static long btrfs_ioctl_qgroup_assign(struct file *file, void __user *arg)
 
 out:
 	kfree(prealloc);
+out_sa_drop_write:
 	kfree(sa);
 drop_write:
 	mnt_drop_write_file(file);
-- 
2.51.0