linux-kernel - Re: [PATCH] core: Catch overflows in do

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Date:	Tue, 08 Oct 2013 10:15:47 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Anatol Pomozov <anatol.pomozov@...il.com>
Cc:	linux-kernel@...r.kernel.org, joe@...ches.com,
	rdunlap@...radead.org
Subject: Re: [PATCH] core: Catch overflows in do_div() function

On Tue, 2013-10-08 at 09:10 -0700, Anatol Pomozov wrote:
> If second parameter passed to this function was 64 then it silently
> truncates to 32 bits. Catch such situation.
> 
> Signed-off-by: Anatol Pomozov <anatol.pomozov@...il.com>
> ---
>  include/asm-generic/div64.h | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/include/asm-generic/div64.h b/include/asm-generic/div64.h
> index 8f4e319..84339a0 100644
> --- a/include/asm-generic/div64.h
> +++ b/include/asm-generic/div64.h
> @@ -17,6 +17,7 @@
>   *       beware of side effects!
>   */
>  
> +#include <linux/bug.h>
>  #include <linux/types.h>
>  #include <linux/compiler.h>
>  
> @@ -25,6 +26,7 @@
>  # define do_div(n,base) ({					\
>  	uint32_t __base = (base);				\
>  	uint32_t __rem;						\
> +	BUG_ON(sizeof(base) > 4 && base >= (1UL<<32));		\

Problem is about

uint32_t __base = (base);

This was designed to avoid "base" being evaluated twice, as in

do_div(X, ++Y);

So I guess you need something to keep this in place.

 


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