Re: [PATCH v2 1/1] mm/slab_common: reject zero object_size before calculate_alignment

[Vlastimil Babka (SUSE)]

On 8/26/26 03:55, Longlong Xia wrote:
> From: Longlong Xia <xialonglong@xxxxxxxxxx>
> 
> 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. Add !size to the check so a 0-size kmem_cache_create() is
> caught on CONFIG_DEBUG_VM builds, where it can be diagnosed when it
> surfaces.
> 
> Suggested-by: Hao Li <hao.li@xxxxxxxxx>
> Assisted-by: Codex:gpt-5.6-sol
> Signed-off-by: Longlong Xia <xialonglong@xxxxxxxxxx>

Applied to mm/slab.git slab/for-next, thanks.

I however support Harry's suggestion wrt (not) adressing theoretical issues
like this going forward.

> ---
> Changes in v2:
> - Drop the !object_size check in __kmem_cache_create_args() that v1
>   added to the always-compiled path, and keep the guard only in the
>   debug-only kmem_cache_sanity_check(), as suggested by Hao Li.
> 
> Link: https://lore.kernel.org/all/20260824092454.1693745-1-xialonglong2025@xxxxxxx/
> ---
>  mm/slab_common.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/mm/slab_common.c b/mm/slab_common.c
> index 95ddbab290d4..e205a99d85cf 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;
>  	}