[PATCH v2] fs/hfs: fix s_fs_info leak on setup_bdev_super() failure

[Mehdi Ben Hadj Khelifa <mehdi.benhadjkhelifa@gmail.com>]

The regression introduced by commit aca740cecbe5 ("fs: open block device
after superblock creation") allows setup_bdev_super() to fail after a new
superblock has been allocated by sget_fc(), but before hfs_fill_super()
takes ownership of the filesystem-specific s_fs_info data.

In that case, hfs_put_super() and the failure paths of hfs_fill_super()
are never reached, leaving the HFS mdb structures attached to s->s_fs_info
unreleased.The default kill_block_super() teardown also does not free 
HFS-specific resources, resulting in a memory leak on early mount failure.

Fix this by moving all HFS-specific teardown (hfs_mdb_put()) from
hfs_put_super() and the hfs_fill_super() failure path into a dedicated
hfs_kill_sb() implementation. This ensures that both normal unmount and
early teardown paths (including setup_bdev_super() failure) correctly
release HFS metadata.

This also preserves the intended layering: generic_shutdown_super()
handles VFS-side cleanup, while HFS filesystem state is fully destroyed
afterwards.

Fixes: aca740cecbe5 ("fs: open block device after superblock creation")
Reported-by: syzbot+ad45f827c88778ff7df6@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=ad45f827c88778ff7df6
Tested-by: syzbot+ad45f827c88778ff7df6@syzkaller.appspotmail.com
Suggested-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Mehdi Ben Hadj Khelifa <mehdi.benhadjkhelifa@gmail.com>
---
ChangeLog:

Changes from v1:

-Changed the patch direction to focus on hfs changes specifically as 
suggested by al viro

Link:https://lore.kernel.org/all/20251114165255.101361-1-mehdi.benhadjkhelifa@gmail.com/

Note:This patch might need some more testing as I only did run selftests 
with no regression, check dmesg output for no regression, run reproducer 
with no bug and test it with syzbot as well.

 fs/hfs/super.c | 16 ++++++++++++----
 1 file changed, 12 insertions(+), 4 deletions(-)

diff --git a/fs/hfs/super.c b/fs/hfs/super.c
index 47f50fa555a4..06e1c25e47dc 100644
--- a/fs/hfs/super.c
+++ b/fs/hfs/super.c
@@ -49,8 +49,6 @@ static void hfs_put_super(struct super_block *sb)
 {
 	cancel_delayed_work_sync(&HFS_SB(sb)->mdb_work);
 	hfs_mdb_close(sb);
-	/* release the MDB's resources */
-	hfs_mdb_put(sb);
 }
 
 static void flush_mdb(struct work_struct *work)
@@ -383,7 +381,6 @@ static int hfs_fill_super(struct super_block *sb, struct fs_context *fc)
 bail_no_root:
 	pr_err("get root inode failed\n");
 bail:
-	hfs_mdb_put(sb);
 	return res;
 }
 
@@ -431,10 +428,21 @@ static int hfs_init_fs_context(struct fs_context *fc)
 	return 0;
 }
 
+static void hfs_kill_sb(struct super_block *sb)
+{
+	generic_shutdown_super(sb);
+	hfs_mdb_put(sb);
+	if (sb->s_bdev) {
+		sync_blockdev(sb->s_bdev);
+		bdev_fput(sb->s_bdev_file);
+	}
+
+}
+
 static struct file_system_type hfs_fs_type = {
 	.owner		= THIS_MODULE,
 	.name		= "hfs",
-	.kill_sb	= kill_block_super,
+	.kill_sb	= hfs_kill_sb,
 	.fs_flags	= FS_REQUIRES_DEV,
 	.init_fs_context = hfs_init_fs_context,
 };
-- 
2.52.0