linux-kernel - Re: [PATCH] module/decompress: Adjust module_extend_max

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Message-ID: <d7382c8a-cfb2-4389-b120-f01a17e248ab@suse.com>
Date: Mon, 28 Apr 2025 12:30:03 +0200
From: Petr Pavlu <petr.pavlu@...e.com>
To: Kees Cook <kees@...nel.org>
Cc: Luis Chamberlain <mcgrof@...nel.org>,
 Sami Tolvanen <samitolvanen@...gle.com>, Daniel Gomez
 <da.gomez@...sung.com>, linux-modules@...r.kernel.org,
 linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org
Subject: Re: [PATCH] module/decompress: Adjust module_extend_max_pages()
 allocation type

On 4/26/25 08:24, Kees Cook wrote:
> In preparation for making the kmalloc family of allocators type aware,
> we need to make sure that the returned type from the allocation matches
> the type of the variable being assigned. (Before, the allocator would
> always return "void *", which can be implicitly cast to any pointer type.)
> 
> The assigned type is "struct page **" but the returned type will be
> "struct page ***". These have the same allocation size (pointer size), but
> the types don't match. Adjust the allocation type to match the assignment.
> 
> Signed-off-by: Kees Cook <kees@...nel.org>
> ---
> Cc: Luis Chamberlain <mcgrof@...nel.org>
> Cc: Petr Pavlu <petr.pavlu@...e.com>
> Cc: Sami Tolvanen <samitolvanen@...gle.com>
> Cc: Daniel Gomez <da.gomez@...sung.com>
> Cc: <linux-modules@...r.kernel.org>
> ---
>  kernel/module/decompress.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/kernel/module/decompress.c b/kernel/module/decompress.c
> index 474e68f0f063..bbb2a55568cd 100644
> --- a/kernel/module/decompress.c
> +++ b/kernel/module/decompress.c
> @@ -19,7 +19,7 @@ static int module_extend_max_pages(struct load_info *info, unsigned int extent)
>  	struct page **new_pages;
>  
>  	new_pages = kvmalloc_array(info->max_pages + extent,
> -				   sizeof(info->pages), GFP_KERNEL);
> +				   sizeof(*new_pages), GFP_KERNEL);
>  	if (!new_pages)
>  		return -ENOMEM;
>  

The function has a similar type mismatch a few lines below:

memcpy(new_pages, info->pages, info->max_pages * sizeof(info->pages));

The sizeof operator is used on 'struct page **', but it should be really
on 'struct page *'.

Could you please fix this as well? For consistency with your patch,
I suggest changing it to 'sizeof(*new_pages)'.

-- 
Thanks,
Petr