linux-kernel - Re: [PATCH v2] fs/hfs: fix s_fs_info leak on setup_bdev

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Message-ID: <20251126-gebaggert-anpacken-d0d9fb10b9bc@brauner>
Date: Wed, 26 Nov 2025 14:48:26 +0100
From: Christian Brauner <brauner@...nel.org>
To: Viacheslav Dubeyko <Slava.Dubeyko@....com>
Cc: "glaubitz@...sik.fu-berlin.de" <glaubitz@...sik.fu-berlin.de>, 
	"frank.li@...o.com" <frank.li@...o.com>, "slava@...eyko.com" <slava@...eyko.com>, 
	"mehdi.benhadjkhelifa@...il.com" <mehdi.benhadjkhelifa@...il.com>, "viro@...iv.linux.org.uk" <viro@...iv.linux.org.uk>, 
	"jack@...e.cz" <jack@...e.cz>, "khalid@...nel.org" <khalid@...nel.org>, 
	"linux-kernel-mentees@...ts.linuxfoundation.org" <linux-kernel-mentees@...ts.linuxfoundation.org>, "linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>, 
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, "skhan@...uxfoundation.org" <skhan@...uxfoundation.org>, 
	"david.hunter.linux@...il.com" <david.hunter.linux@...il.com>, 
	"syzbot+ad45f827c88778ff7df6@...kaller.appspotmail.com" <syzbot+ad45f827c88778ff7df6@...kaller.appspotmail.com>
Subject: Re: [PATCH v2] fs/hfs: fix s_fs_info leak on setup_bdev_super()
 failure

On Wed, Nov 19, 2025 at 07:58:21PM +0000, Viacheslav Dubeyko wrote:
> On Wed, 2025-11-19 at 08:38 +0100, Mehdi Ben Hadj Khelifa wrote:
> > 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@...kaller.appspotmail.com
> > Closes: https://syzkaller.appspot.com/bug?extid=ad45f827c88778ff7df6  
> > Tested-by: syzbot+ad45f827c88778ff7df6@...kaller.appspotmail.com
> > Suggested-by: Al Viro <viro@...iv.linux.org.uk>
> > Signed-off-by: Mehdi Ben Hadj Khelifa <mehdi.benhadjkhelifa@...il.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.
> 
> Have you run xfstests for the patch? Unfortunately, we have multiple xfstests
> failures for HFS now. And you can check the list of known issues here [1]. The
> main point of such run of xfstests is to check that maybe some issue(s) could be
> fixed by the patch. And, more important that you don't introduce new issues. ;)
> 
> > 
> >  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,
> 
> It looks like we have the same issue for the case of HFS+ [2]. Could you please
> double check that HFS+ should be fixed too?

There's no need to open-code this unless I'm missing something. All you
need is the following two patches - untested. Both issues were
introduced by the conversion to the new mount api.

View attachment "0001-hfs-ensure-sb-s_fs_info-is-always-cleaned-up.patch" of type "text/x-diff" (4594 bytes)

View attachment "0002-hfsplus-ensure-sb-s_fs_info-is-always-cleaned-up.patch" of type "text/x-diff" (2055 bytes)