[PATCH RFC 10/28] hfsplus: don't set SB_RDONLY when creating the attributes tree

[Christian Brauner]

hfs_btree_open() sets SB_RDONLY when the map record of a b-tree doesn't
mark the header node as used. That's fine while mounting where the
mounter holds sb->s_umount. But hfsplus_create_attributes_file() calls
it too when the first extended attribute gets set on a filesystem that
doesn't have an attributes file yet. That runs on the live filesystem
without s_umount and a filesystem must not change SB_RDONLY behind the
VFS' back.

hfsplus_create_attributes_file() opens a tree it has just created
itself, with the header node marked as used. So there's nothing to
check there. Only do the check while the filesystem is being mounted.

No functional changes.

Signed-off-by: Christian Brauner (Amutable) <brauner at kernel.org>
---
 fs/hfsplus/btree.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/fs/hfsplus/btree.c b/fs/hfsplus/btree.c
index 2ea8cd5658e1..967c457d843d 100644
--- a/fs/hfsplus/btree.c
+++ b/fs/hfsplus/btree.c
@@ -385,7 +385,12 @@ struct hfs_btree *hfs_btree_open(struct super_block *sb, u32 id)
 	if (IS_ERR(node))
 		goto free_inode;
 
-	if (!hfs_bmap_test_bit(node, 0)) {
+	/*
+	 * Only a mount may set SB_RDONLY, later that needs s_umount. After the
+	 * mount this only opens the attributes tree that
+	 * hfsplus_create_attributes_file() just created with the bit set.
+	 */
+	if (!(sb->s_flags & SB_BORN) && !hfs_bmap_test_bit(node, 0)) {
 		pr_warn("(%s): %s (cnid 0x%x) map record invalid or bitmap corruption detected, forcing read-only.\n",
 				sb->s_id, hfs_btree_name(id), id);
 		pr_warn("Run fsck.hfsplus to repair.\n");

-- 
2.53.0