linux-kernel - Re: [Patch] slub: Fix a missing-check bug in mm/slub.c file of Linux 5.1.1

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Date:   Sat, 18 May 2019 21:43:02 -0700 (PDT)
From:   David Rientjes <rientjes@...gle.com>
To:     Gen Zhang <blackgod016574@...il.com>
cc:     iamjoonsoo.kim@....com, linux-kernel@...r.kernel.org
Subject: Re: [Patch] slub: Fix a missing-check bug in mm/slub.c file of Linux
 5.1.1

On Wed, 15 May 2019, Gen Zhang wrote:

> Pointer s is allocated with kmem_cache_zalloc(). And s is used in the 
> follwoing codes. However, when kmem_cache_zalloc fails, using s will
> cause null pointer dereference and the kernel will go wrong. Thus we 
> check whether the kmem_cache_zalloc fails.
> 
> Signed-off-by: Gen Zhang <blackgod016574@...il.com>
> 

It's ok if we encounter a NULL pointer dereference here, if we are ENOMEM 
then there is no way to initialize the slub allocator to be able to 
perform any future memory allocation.  Returning an error code won't help.

> ---
> --- mm/slub.c
> +++ mm/slub.c
> @@ -4201,6 +4201,8 @@ static struct kmem_cache * __init bootst
>  {
>  	int node;
>  	struct kmem_cache *s = kmem_cache_zalloc(kmem_cache, GFP_NOWAIT);
> +	if (!s)
> +		return ERR_PTR(-ENOMEM);
>  	struct kmem_cache_node *n;
>  
>  	memcpy(s, static_cache, kmem_cache->object_size);

It's not legal to mix declarations within the C code here.