btrfs: correctly escape subvol in btrfs_show_options()

Currently, displaying the btrfs subvol mount option doesn't escape ','.
This makes parsing /proc/self/mounts and /proc/self/mountinfo
ambiguous for subvolume names that contain commas. The text after the
comma could be mistaken for another option (think "subvol=foo,ro", where
ro is actually part of the subvolumes name).

Replace the manual escape characters list with a call to
seq_show_option(). Thanks to Calvin Walton for suggesting this approach.

Fixes: c8d3fe028f64 ("Btrfs: show subvol= and subvolid= in /proc/mounts")
CC: stable@vger.kernel.org # 5.4+
Suggested-by: Calvin Walton <calvin.walton@kepstin.ca>
Signed-off-by: Johannes Kimmel <kernel@bareminimum.eu>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

diff --git a/fs/btrfs/super.c b/fs/btrfs/super.c
index 40709e2a44fceca747b45fc219d6f87aa50d4d2b..7121d8c7a318ec2d4db959d5f69d06be2f75f974 100644 (file)
--- a/fs/btrfs/super.c
+++ b/fs/btrfs/super.c
@@ -1139,8 +1139,7 @@ static int btrfs_show_options(struct seq_file *seq, struct dentry *dentry)
        subvol_name = btrfs_get_subvol_name_from_objectid(info,
                        btrfs_root_id(BTRFS_I(d_inode(dentry))->root));
        if (!IS_ERR(subvol_name)) {
-               seq_puts(seq, ",subvol=");
-               seq_escape(seq, subvol_name, " \t\n\\");
+               seq_show_option(seq, "subvol", subvol_name);
                kfree(subvol_name);
        }
        return 0;