Btrfs: fix memory leak in the extent_same ioctl

commit 497b4050 upstream.

We were allocating memory with memdup_user() but we were never releasing
that memory. This affected pretty much every call to the ioctl, whether
it deduplicated extents or not.

This issue was reported on IRC by Julian Taylor and on the mailing list
by Marcel Ritter, credit goes to them for finding the issue.
Reported-by: Julian Taylor <jtaylor.debian@googlemail.com>
Reported-by: Marcel Ritter <ritter.marcel@gmail.com>
Signed-off-by: Filipe Manana <fdmanana@suse.com>
Reviewed-by: Mark Fasheh <mfasheh@suse.de>
Signed-off-by: Jiri Slaby <jslaby@suse.cz>

fs/btrfs/ioctl.c

@@ -2707,7 +2707,7 @@ static long btrfs_ioctl_file_extent_same(struct file *file,
 					 void __user *argp)
 {
 	struct btrfs_ioctl_same_args tmp;
-	struct btrfs_ioctl_same_args *same;
+	struct btrfs_ioctl_same_args *same = NULL;
 	struct btrfs_ioctl_same_extent_info *info;
 	struct inode *src = file->f_dentry->d_inode;
 	struct file *dst_file = NULL;
@@ -2833,6 +2833,7 @@ static long btrfs_ioctl_file_extent_same(struct file *file,
 
 out:
 	mnt_drop_write_file(file);
+	kfree(same);
 	return ret;
 }