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Date: Fri, 24 May 2024 12:23:50 -0700
From: Andrew Morton <akpm@linux-foundation.org>
To: Kuan-Wei Chiu <visitorckw@gmail.com>
Cc: jserv@ccns.ncku.edu.tw, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] tools/lib/slab: Fix potential NULL pointer dereference
 in kmalloc()
Message-Id: <20240524122350.a22ca8dfe07a21f3eb862159@linux-foundation.org>
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On Sat, 25 May 2024 03:14:59 +0800 Kuan-Wei Chiu <visitorckw@gmail.com> wrote:

> In kmalloc(), add a check to ensure that the pointer 'ret' is not NULL
> before attempting to memset it when the __GFP_ZERO flag is set. This
> prevents a potential NULL pointer dereference.
> 
> ...
>
> --- a/tools/lib/slab.c
> +++ b/tools/lib/slab.c
> @@ -22,7 +22,7 @@ void *kmalloc(size_t size, gfp_t gfp)
>  	uatomic_inc(&kmalloc_nr_allocated);
>  	if (kmalloc_verbose)
>  		printf("Allocating %p from malloc\n", ret);
> -	if (gfp & __GFP_ZERO)
> +	if (gfp & __GFP_ZERO && ret)
>  		memset(ret, 0, size);
>  	return ret;
>  }

I suspect we have a lot of unchecked mallocs in our userspace code.  If
there's an argument for fixing them all(?) then it would be best to do
this in a wholesale fashion rather than patch-at-a-time piecemeal.