Message-ID: <960f74ac4a4b67ebb0c1c4311302798c1a9afc53.camel@ibm.com>
Date: Fri, 21 Nov 2025 22:28:13 +0000
From: Viacheslav Dubeyko <Slava.Dubeyko@....com>
To: "jack@...e.cz" <jack@...e.cz>,
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	<mehdi.benhadjkhelifa@...il.com>,
        "brauner@...nel.org" <brauner@...nel.org>,
        "viro@...iv.linux.org.uk" <viro@...iv.linux.org.uk>
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	<syzbot+ad45f827c88778ff7df6@...kaller.appspotmail.com>
Subject: RE: [PATCH v2] fs/hfs: fix s_fs_info leak on setup_bdev_super()
 failure

On Sat, 2025-11-22 at 00:16 +0100, Mehdi Ben Hadj Khelifa wrote:
> On 11/21/25 11:04 PM, Viacheslav Dubeyko wrote:
> > On Fri, 2025-11-21 at 23:48 +0100, Mehdi Ben Hadj Khelifa wrote:
> > > On 11/21/25 10:15 PM, Viacheslav Dubeyko wrote:
> > > > On Fri, 2025-11-21 at 20:44 +0100, Mehdi Ben Hadj Khelifa wrote:
> > > > > 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 have tried to run the xfstests with a kernel built with my patch and
> > > > > also without my patch for TEST and SCRATCH devices and in both cases my
> > > > > system crashes in running the generic/631 test.Still unsure of the
> > > > > cause. For more context, I'm running the tests on the 6.18-rc5 version
> > > > > of the kernel and the devices and the environment setup is as follows:
> > > > > 
> > > > > For device creation and mounting(also tried it with dd and had same
> > > > > results):
> > > > > fallocate -l 10G test.img
> > > > > fallocate -l 10G scratch.img
> > > > > sudo mkfs.hfs test.img
> > > > > sudo losetup /dev/loop0 ./test.img
> > > > > sudo losetup /dev/loop1 ./scratch.img
> > > > > sudo mkdir -p /mnt/test /mnt/scratch
> > > > > sudo mount /dev/loop0 /mnt/test
> > > > > 
> > > > > For environment setup(local.config):
> > > > > export TEST_DEV=/dev/loop0
> > > > > export TEST_DIR=/mnt/test
> > > > > export SCRATCH_DEV=/dev/loop1
> > > > > export SCRATCH_MNT=/mnt/scratch
> > > > 
> > > > This is my configuration:
> > > > 
> > > > export TEST_DEV=/dev/loop50
> > > > export TEST_DIR=/mnt/test
> > > > export SCRATCH_DEV=/dev/loop51
> > > > export SCRATCH_MNT=/mnt/scratch
> > > > 
> > > > export FSTYP=hfs
> > > > 
> > > Ah, Missed that option. I will try with that in my next testing.
> > > > Probably, you've missed FSTYP. Did you tried to run other file system at first
> > > > (for example, ext4) to be sure that everything is good?
> > > > 
> > > No, I barely squeezed in time today to the testing for the HFS so I
> > > didn't do any preliminary testing but I will check that too my next run
> > > before trying to test HFS.
> > > > > 
> > > > > Ran the tests using:sudo ./check -g auto
> > > > > 
> > > > 
> > > > You are brave guy. :) Currently, I am trying to fix the issues for quick group:
> > > > 
> > > > sudo ./check -g quick
> > > > 
> > > I thought I needed to do a more exhaustive testing so I went with auto.
> > > I will try to experiment with quick my next round of testing. Thanks for
> > > the heads up!
> > > > > If more context is needed to know the point of failure or if I have made
> > > > > a mistake during setup I'm happy to receive your comments since this is
> > > > > my first time trying to run xfstests.
> > > > > 
> > > > 
> > > > I don't see the crash on my side.
> > > > 
> > > > sudo ./check generic/631
> > > > FSTYP         -- hfs
> > > > PLATFORM      -- Linux/x86_64 hfsplus-testing-0001 6.18.0-rc3+ #96 SMP
> > > > PREEMPT_DYNAMIC Wed Nov 19 12:47:37 PST 2025
> > > > MKFS_OPTIONS  -- /dev/loop51
> > > > MOUNT_OPTIONS -- /dev/loop51 /mnt/scratch
> > > > 
> > > > generic/631       [not run] attr namespace trusted not supported by this
> > > > filesystem type: hfs
> > > > Ran: generic/631
> > > > Not run: generic/631
> > > > Passed all 1 tests
> > > > 
> > > > This test simply is not running for HFS case.
> > > > 
> > > > I see that HFS+ is failing for generic/631, but I don't see the crash. I am
> > > > running 6.18.0-rc3+ but I am not sure that 6.18.0-rc5+ could change something
> > > > dramatically.
> > > > 
> > > > My guess that, maybe, xfstests suite is trying to run some other file system but
> > > > not HFS.
> > > > 
> > > I'm assuming that it's running HFSPLUS testing foir me because I just
> > > realised that the package that I downloaded to do mkfs.hfs is just a
> > > symlink to mkfs.hfsplus. Also I didn't find a package(in arch) for
> > > mkfs.hfs in my quick little search now. All refer to mkfs.hfsplus as if
> > > mkfs.hfs is deprecated somehow. I will probably build it from source if
> > > available with fsck.hfs... Eitherway, even if i was testing for HFSPLUS
> > > i don't think that a fail on generic/631 would crash my system multiple
> > > times with different kernels. I would have to test with ext4 before and
> > > play around more to find out why that happened..
> > 
> > The mkfs.hfs is symlink on mkfs.hfsplus and the same for fsck. The mkfs.hfsplus
> > can create HFS volume by using this option:
> > 
> > -h create an HFS format filesystem (HFS Plus is the default)
> > 
> > I don't have any special package installed for HFS on my side.
> > 
> In my case, -h option in mkfs.hfsplus doesn't create hfs format 
> filesystem. I checked kernel docs and found this[1] which refers to a 
> package called hfsutils which has hformat as a binary for creating HFS 
> filesystems. I just got it and used it successfully. I will be rerunning 
> all tests soon.
> [1]:https://docs.kernel.org/filesystems/hfs.html  
> > Thanks,
> > Slava.
> > 
> Also did you check my other comments on the code part of your last 
> reply? Just making sure. Thanks.
> 
> Best Regards,
> Mehdi Ben Hadj Khelifa
> > > > > > > 
> > > > > > >     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,
> > > > 
> > > > I've realized that if we are trying to solve the issue with pure call of
> > > > kill_block_super() for the case of HFS/HFS+, then we could have the same trouble
> > > > for other file systems. It make sense to check that we do not have likewise
> > > > trouble for: bfs, hpfs, fat, nilfs2, ext2, ufs, adfs, omfs, isofs, udf, minix,
> > > > jfs, squashfs, freevxfs, befs.
> > > While I was doing my original fix for hfs, I did notice that too. Many
> > > other filesystems(not all) don't have a "custom" super block destroyer
> > > and they just refer to the generic kill_block_super() function which
> > > might lead to the same problem as HFS and HFS+. That would more digging
> > > too. I will see what I can do next when we finish HFS and potentially
> > > HFS+ first.
> > > > 
> > > > > > 
> > > > > > 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?
> > > > > > 
> > > > > I have checked the same error path and it seems that hfsplus_sb_info is
> > > > > not freed in that path(I could provide the exact call stack which would
> > > > > cause such a memory leak) although I didn't create or run any
> > > > > reproducers for this particular filesystem type.
> > > > > If you would like a patch for this issue, would something like what is
> > > > > shown below be acceptable? :
> > > > > 
> > > > > +static void hfsplus_kill_super(struct super_block *sb)
> > > > > +{
> > > > > +       struct hfsplus_sb_info *sbi = HFSPLUS_SB(sb);
> > > > > +
> > > > > +       kill_block_super(sb);
> > > > > +       kfree(sbi);
> > > > > +}
> > > > > +
> > > > >     static struct file_system_type hfsplus_fs_type = {
> > > > >            .owner          = THIS_MODULE,
> > > > >            .name           = "hfsplus",
> > > > > -       .kill_sb        = kill_block_super,
> > > > > +       .kill_sb        = hfsplus_kill_super,
> > > > >            .fs_flags       = FS_REQUIRES_DEV,
> > > > >            .init_fs_context = hfsplus_init_fs_context,
> > > > >     };
> > > > > 
> > > > > If there is something to add, remove or adjust. Please let me know in
> > > > > the case of you willing accepting such a patch of course.
> > > > 
> > > > We call hfs_mdb_put() for the case of HFS:
> > > > 
> > > > void hfs_mdb_put(struct super_block *sb)
> > > > {
> > > > 	if (!HFS_SB(sb))
> > > > 		return;
> > > > 	/* free the B-trees */
> > > > 	hfs_btree_close(HFS_SB(sb)->ext_tree);
> > > > 	hfs_btree_close(HFS_SB(sb)->cat_tree);
> > > > 
> > > > 	/* free the buffers holding the primary and alternate MDBs */
> > > > 	brelse(HFS_SB(sb)->mdb_bh);
> > > > 	brelse(HFS_SB(sb)->alt_mdb_bh);
> > > > 
> > > > 	unload_nls(HFS_SB(sb)->nls_io);
> > > > 	unload_nls(HFS_SB(sb)->nls_disk);
> > > > 
> > > > 	kfree(HFS_SB(sb)->bitmap);
> > > > 	kfree(HFS_SB(sb));
> > > > 	sb->s_fs_info = NULL;
> > > > }
> > > > 
> > > > So, we need likewise course of actions for HFS+ because we have multiple
> > > > pointers in superblock too:
> > > > 
> > > IIUC, hfs_mdb_put() isn't called in the case of hfs_kill_super() in
> > > christian's patch because fill_super() (for the each specific
> > > filesystem) is responsible for cleaning up the superblock in case of
> > > failure and you can reference christian's patch[1] which he explained
> > > the reasoning for here[2].And in the error path the we are trying to
> > > fix, fill_super() isn't even called yet. So such pointers shouldn't be
> > > pointing to anything allocated yet hence only freeing the pointer to the
> > > sb_info here is sufficient I think.

I was confused that your code with hfs_mdb_put() is still in this email. So,
yes, hfs_fill_super()/hfsplus_fill_super() try to free the memory in the case of
failure. It means that if something wasn't been freed, then it will be issue in
these methods. Then, I don't see what should else need to be added here. Some
file systems do sb->s_fs_info = NULL. But absence of this statement is not
critical, from my point of view.

Thanks,
Slava.

> > > [1]:https://github.com/brauner/linux/commit/058747cefb26196f3c192c76c631051581b29b27  
> > > [2]:https://lore.kernel.org/all/20251119-delfin-bioladen-6bf291941d4f@brauner/  
> > > > struct hfsplus_sb_info {
> > > > 	void *s_vhdr_buf;
> > > > 	struct hfsplus_vh *s_vhdr;
> > > > 	void *s_backup_vhdr_buf;
> > > > 	struct hfsplus_vh *s_backup_vhdr;
> > > > 	struct hfs_btree *ext_tree;
> > > > 	struct hfs_btree *cat_tree;
> > > > 	struct hfs_btree *attr_tree;
> > > > 	atomic_t attr_tree_state;
> > > > 	struct inode *alloc_file;
> > > > 	struct inode *hidden_dir;
> > > > 	struct nls_table *nls;
> > > > 
> > > > 	/* Runtime variables */
> > > > 	u32 blockoffset;
> > > > 	u32 min_io_size;
> > > > 	sector_t part_start;
> > > > 	sector_t sect_count;
> > > > 	int fs_shift;
> > > > 
> > > > 	/* immutable data from the volume header */
> > > > 	u32 alloc_blksz;
> > > > 	int alloc_blksz_shift;
> > > > 	u32 total_blocks;
> > > > 	u32 data_clump_blocks, rsrc_clump_blocks;
> > > > 
> > > > 	/* mutable data from the volume header, protected by alloc_mutex */
> > > > 	u32 free_blocks;
> > > > 	struct mutex alloc_mutex;
> > > > 
> > > > 	/* mutable data from the volume header, protected by vh_mutex */
> > > > 	u32 next_cnid;
> > > > 	u32 file_count;
> > > > 	u32 folder_count;
> > > > 	struct mutex vh_mutex;
> > > > 
> > > > 	/* Config options */
> > > > 	u32 creator;
> > > > 	u32 type;
> > > > 
> > > > 	umode_t umask;
> > > > 	kuid_t uid;
> > > > 	kgid_t gid;
> > > > 
> > > > 	int part, session;
> > > > 	unsigned long flags;
> > > > 
> > > > 	int work_queued;               /* non-zero delayed work is queued */
> > > > 	struct delayed_work sync_work; /* FS sync delayed work */
> > > > 	spinlock_t work_lock;          /* protects sync_work and work_queued */
> > > > 	struct rcu_head rcu;
> > > > };
> > > > 
> > > 
> > > 
> > > > Thanks,
> > > > 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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