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Subject: Re: [PATCH] mm: ksize() should silently accept a NULL pointer
To:     William Kucharski <william.kucharski@oracle.com>,
        linux-mm@kvack.org, linux-kernel@vger.kernel.org
Cc:     Christoph Lameter <cl@linux.com>,
        Pekka Enberg <penberg@kernel.org>,
        David Rientjes <rientjes@google.com>,
        Joonsoo Kim <iamjoonsoo.kim@lge.com>,
        Andrew Morton <akpm@linux-foundation.org>
References: <20200616225409.4670-1-william.kucharski@oracle.com>
From:   David Hildenbrand <david@redhat.com>
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Organization: Red Hat GmbH
Message-ID: <bee16e8c-2ec9-7a17-1f5d-82cc4891603b@redhat.com>
Date:   Wed, 17 Jun 2020 09:09:24 +0200
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Sender: linux-kernel-owner@vger.kernel.org
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On 17.06.20 00:54, William Kucharski wrote:
> Other mm routines such as kfree() and kzfree() silently do the right
> thing if passed a NULL pointer, so ksize() should do the same.
> 
> Signed-off-by: William Kucharski <william.kucharski@oracle.com>
> ---
>  mm/slab_common.c | 14 +++++---------
>  1 file changed, 5 insertions(+), 9 deletions(-)
> 
> diff --git a/mm/slab_common.c b/mm/slab_common.c
> index 9e72ba224175..2bff01ad94d8 100644
> --- a/mm/slab_common.c
> +++ b/mm/slab_common.c
> @@ -1660,10 +1660,9 @@ static __always_inline void *__do_krealloc(const void *p, size_t new_size,
>  					   gfp_t flags)
>  {
>  	void *ret;
> -	size_t ks = 0;
> +	size_t ks;
>  
> -	if (p)
> -		ks = ksize(p);
> +	ks = ksize(p);
>  
>  	if (ks >= new_size) {
>  		p = kasan_krealloc((void *)p, new_size, flags);
> @@ -1723,10 +1722,9 @@ void kzfree(const void *p)
>  	size_t ks;
>  	void *mem = (void *)p;
>  
> -	if (unlikely(ZERO_OR_NULL_PTR(mem)))
> -		return;
>  	ks = ksize(mem);
> -	memset(mem, 0, ks);
> +	if (ks)
> +		memset(mem, 0, ks);
>  	kfree(mem);
>  }
>  EXPORT_SYMBOL(kzfree);
> @@ -1749,8 +1747,6 @@ size_t ksize(const void *objp)
>  {
>  	size_t size;
>  
> -	if (WARN_ON_ONCE(!objp))
> -		return 0;
>  	/*
>  	 * We need to check that the pointed to object is valid, and only then
>  	 * unpoison the shadow memory below. We use __kasan_check_read(), to
> @@ -1764,7 +1760,7 @@ size_t ksize(const void *objp)
>  	 * We want to perform the check before __ksize(), to avoid potentially
>  	 * crashing in __ksize() due to accessing invalid metadata.
>  	 */
> -	if (unlikely(objp == ZERO_SIZE_PTR) || !__kasan_check_read(objp, 1))
> +	if (unlikely(ZERO_OR_NULL_PTR(objp)) || !__kasan_check_read(objp, 1))
>  		return 0;
>  
>  	size = __ksize(objp);
> 

Reviewed-by: David Hildenbrand <david@redhat.com>

-- 
Thanks,

David / dhildenb