linux-kernel - Re: [PATCH] mm: gup: fix access

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Date:   Sun, 23 Apr 2017 11:20:21 +0200
From:   Ingo Molnar <mingo@...nel.org>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Michal Hocko <mhocko@...e.com>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Lorenzo Stoakes <lstoakes@...il.com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm: gup: fix access_ok() argument type


* Arnd Bergmann <arnd@...db.de> wrote:

> MIPS just got changed to only accept a pointer argument for access_ok(),
> causing one warning in drivers/scsi/pmcraid.c. I tried changing x86
> the same way and found the same warning in __get_user_pages_fast()
> and nowhere else in the kernel during randconfig testing:

Doing that for x86 access_ok() would definitely be a good idea.

> mm/gup.c: In function '__get_user_pages_fast':
> mm/gup.c:1578:6: error: passing argument 1 of '__chk_range_not_ok' makes pointer from integer without a cast [-Werror=int-conversion]
> 
> It would probably be a good idea to enforce type-safety in general,
> so let's change this file to not cause a warning if we do that.
> 
> I don't know why the warning did not appear on MIPS.
> 
> Fixes: 2667f50e8b81 ("mm: introduce a general RCU get_user_pages_fast()")
> Cc: Alexander Viro <viro@...iv.linux.org.uk>
> Signed-off-by: Arnd Bergmann <arnd@...db.de>
> ---
>  mm/gup.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/mm/gup.c b/mm/gup.c
> index 2559a3987de7..7f5bc26d9229 100644
> --- a/mm/gup.c
> +++ b/mm/gup.c
> @@ -1575,7 +1575,7 @@ int __get_user_pages_fast(unsigned long start, int nr_pages, int write,
>  	end = start + len;
>  
>  	if (unlikely(!access_ok(write ? VERIFY_WRITE : VERIFY_READ,
> -					start, len)))
> +					(void __user *)start, len)))
>  		return 0;

Acked-by: Ingo Molnar <mingo@...nel.org>

Thanks,

	Ingo