Re: [PATCH] xfs: Fix UBSAN null-ptr-deref in xfs_sysfs_init

[Darrick J. Wong]

On Fri, Aug 07, 2020 at 12:05:27AM +0900, Eiichi Tsukata wrote:
> If xfs_sysfs_init is called with parent_kobj == NULL, UBSAN
> shows the following warning:

This needs to be sent to the xfs mailing list, per get_maintainers.pl.

--D

>   UBSAN: null-ptr-deref in ./fs/xfs/xfs_sysfs.h:37:23
>   member access within null pointer of type 'struct xfs_kobj'
>   Call Trace:
>    dump_stack+0x10e/0x195
>    ubsan_type_mismatch_common+0x241/0x280
>    __ubsan_handle_type_mismatch_v1+0x32/0x40
>    init_xfs_fs+0x12b/0x28f
>    do_one_initcall+0xdd/0x1d0
>    do_initcall_level+0x151/0x1b6
>    do_initcalls+0x50/0x8f
>    do_basic_setup+0x29/0x2b
>    kernel_init_freeable+0x19f/0x20b
>    kernel_init+0x11/0x1e0
>    ret_from_fork+0x22/0x30
> 
> Fix it by checking parent_kobj before the code accesses its member.
> 
> Signed-off-by: Eiichi Tsukata <devel@xxxxxxxxxxxx>
> ---
>  fs/xfs/xfs_sysfs.h | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/xfs/xfs_sysfs.h b/fs/xfs/xfs_sysfs.h
> index e9f810fc6731..aad67dc4ab5b 100644
> --- a/fs/xfs/xfs_sysfs.h
> +++ b/fs/xfs/xfs_sysfs.h
> @@ -32,9 +32,9 @@ xfs_sysfs_init(
>  	struct xfs_kobj		*parent_kobj,
>  	const char		*name)
>  {
> +	struct kobject *parent = parent_kobj ? &parent_kobj->kobject : NULL;
>  	init_completion(&kobj->complete);
> -	return kobject_init_and_add(&kobj->kobject, ktype,
> -				    &parent_kobj->kobject, "%s", name);
> +	return kobject_init_and_add(&kobj->kobject, ktype, parent, "%s", name);
>  }
>  
>  static inline void
> -- 
> 2.26.2
>