Re: [PATCH 1/1] mm/slab_common: reject zero object_size before calculate_alignment

[Hao Li <hao.li@linux.dev>]

On Mon, Aug 24, 2026 at 05:24:54PM +0800, Longlong Xia wrote:
> From: Longlong Xia <xialonglong@kylinos.cn>
> 
> calculate_alignment() with SLAB_HWCACHE_ALIGN halves ralign in a
> while (size <= ralign / 2) loop. When size is 0, ralign eventually
> reaches 0 and the condition stays true indefinitely, hanging the
> kernel.
> 
> kmem_cache_sanity_check() rejected size > KMALLOC_MAX_SIZE but not
> size == 0, and the sanity check is compiled out without
> CONFIG_DEBUG_VM. Add a !object_size check in
> __kmem_cache_create_args(), which is always compiled, and add !size
> to the DEBUG_VM sanity check for diagnostics.
> 
> Assisted-by: Codex:gpt-5.6-sol
> Signed-off-by: Longlong Xia <xialonglong@kylinos.cn>
> ---
>  mm/slab_common.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/mm/slab_common.c b/mm/slab_common.c
> index 657fd75776ea..209fe838fe71 100644
> --- a/mm/slab_common.c
> +++ b/mm/slab_common.c
> @@ -102,7 +102,7 @@ static bool kmem_cache_is_duplicate_name(const char *name)
>  
>  static int kmem_cache_sanity_check(const char *name, unsigned int size)
>  {
> -	if (!name || in_interrupt() || size > KMALLOC_MAX_SIZE) {
> +	if (!name || in_interrupt() || !size || size > KMALLOC_MAX_SIZE) {
>  		pr_err("kmem_cache_create(%s) integrity check failed\n", name);
>  		return -EINVAL;
>  	}
> @@ -354,7 +354,7 @@ struct kmem_cache *__kmem_cache_create_args(const char *name,
>  		goto out_unlock;
>  	}
>  
> -	if (flags & ~SLAB_FLAGS_PERMITTED) {
> +	if (!object_size || flags & ~SLAB_FLAGS_PERMITTED) {

under !CONFIG_DEBUG_VM, I think we ignore the sanity_check deliberately, so it
seems we don't need to add !object_size check here. right?

>  		err = -EINVAL;
>  		goto out_unlock;
>  	}
> -- 
> 2.43.0
>