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

Mehdi Ben Hadj Khelifa
2025-11-21T22:17:11Z

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@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.
>>>>>
>>>>> 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.
>> [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