Re: [PATCH] ocfs2: Publish the filecheck owner before adding sysfs attributes

[Heming Zhao <heming.zhao@suse.com>]

On Fri, Oct 09, 2026 at 06:04:49PM +0800, Cen Zhang wrote:
> ocfs2_filecheck_create_sysfs() initializes the filecheck allocation
> before calling kobject_init_and_add(), but assigns entry->fs_fcheck
> only after that call returns. The default attribute group can already
> be visible while registration is in progress. A concurrent read can
> therefore enter ocfs2_filecheck_attr_show() with a NULL fs_fcheck and
> try to lock its fc_lock.
> 
> Assign the initialized owner before adding the kobject, so every
> activated attribute has valid state. Clear the pointer when addition
> fails, preserving the existing teardown guard and error cleanup.
> 
> A controlled probe-instrumented test kernel with the original OCFS2
> registration ordering produced this Oops during a concurrent sysfs read:
> 
>   KASAN: null-ptr-deref in range [0x0000000000000028-0x000000000000002f]
>   RIP: 0010:kasan_byte_accessible+0x15/0x30
>   Call Trace:
>    <TASK>
>    __kasan_check_byte+0x13/0x50
>    lock_acquire+0x113/0x300
>    _raw_spin_lock+0x31/0x40
>    ocfs2_filecheck_attr_show+0x138/0x5f0
>    ocfs2_filecheck_show+0x5d/0x90
>    sysfs_kf_seq_show+0x1d3/0x360
>    seq_read_iter+0x480/0x1110
>    kernfs_fop_read_iter+0x419/0x5a0
>    vfs_read+0x7d2/0xc20
>    ksys_read+0x111/0x200
>    do_syscall_64+0x114/0x620
>    entry_SYSCALL_64_after_hwframe+0x77/0x7f
>    </TASK>
>   Modules linked in:
> 
> Fixes: a860f6eb4c6a ("ocfs2: sysfile interfaces for online file check")
> Assisted-by: LLM
> Signed-off-by: Cen Zhang <zzzccc427@gmail.com>
> ---
>  fs/ocfs2/filecheck.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/ocfs2/filecheck.c b/fs/ocfs2/filecheck.c
> index be713d7d24a76b9aa8fcded3d83b3d91d124eb6e..862c1ee7099c943b2e3e57e31f887380c6dc8a88 100644
> --- a/fs/ocfs2/filecheck.c
> +++ b/fs/ocfs2/filecheck.c
> @@ -181,2 +181,4 @@ int ocfs2_filecheck_create_sysfs(struct ocfs2_super *osb)
>  
> +	/* Publish the initialized owner before activating its sysfs callbacks. */
> +	entry->fs_fcheck = fcheck;
>  	entry->fs_kobj.kset = osb->osb_dev_kset;
> @@ -186,2 +188,3 @@ int ocfs2_filecheck_create_sysfs(struct ocfs2_super *osb)
>  	if (ret) {
> +		entry->fs_fcheck = NULL;

setting to NULL is unnecessary, it becomes a harmless dangling pointer here.
Other code looks good to me.

Thanks,
Heming
>  		kobject_put(&entry->fs_kobj);
> @@ -191,3 +194,2 @@ int ocfs2_filecheck_create_sysfs(struct ocfs2_super *osb)
>  
> -	entry->fs_fcheck = fcheck;
>  	return 0;
>