Message-ID: <25434098-4bf0-4330-b7b1-527983d9c903@gmail.com>
Date: Wed, 19 Nov 2025 23:21:01 +0100
From: Mehdi Ben Hadj Khelifa <mehdi.benhadjkhelifa@...il.com>
To: Viacheslav Dubeyko <Slava.Dubeyko@....com>,
 "glaubitz@...sik.fu-berlin.de" <glaubitz@...sik.fu-berlin.de>,
 "frank.li@...o.com" <frank.li@...o.com>,
 "slava@...eyko.com" <slava@...eyko.com>,
 "brauner@...nel.org" <brauner@...nel.org>,
 "viro@...iv.linux.org.uk" <viro@...iv.linux.org.uk>,
 "jack@...e.cz" <jack@...e.cz>
Cc: "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 11/19/25 8:58 PM, 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. ;)
> 
I did not know of such tests. I will try to run them for both my patch 
and christian's patch[1] and report the results.
>>
>>   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?
> 
Yes, I will check it tomorrow in addition to running xfstests and report 
my findings in response to this email. But I'm not sure if my solution 
would be the attended fix or a similar solution to what christian did is 
preferred instead for HFS+. We'll discuss it when I send a response.
> Thanks,
> Slava.
> 
Thank you for your insights Slava!

Best Regards,
Mehdi Ben Hadj Khelifa
>> +	.kill_sb	= hfs_kill_sb,
>>   	.fs_flags	= FS_REQUIRES_DEV,
>>   	.init_fs_context = hfs_init_fs_context,
>>   };
> 
> [1] https://github.com/hfs-linux-kernel/hfs-linux-kernel/issues
> [2] https://elixir.bootlin.com/linux/v6.18-rc6/source/fs/hfsplus/super.c#L694

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