linux-kernel - Re: [ 08/31] use clamp

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Message-ID: <20121026001119.GA3028@elie.Belkin>
Date:	Thu, 25 Oct 2012 17:11:19 -0700
From:	Jonathan Nieder <jrnieder@...il.com>
To:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:	linux-kernel@...r.kernel.org, stable@...r.kernel.org,
	alan@...rguk.ukuu.org.uk, Fengguang Wu <fengguang.wu@...el.com>,
	Kees Cook <keescook@...omium.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [ 08/31] use clamp_t in UNAME26 fix

Hi,

Greg Kroah-Hartman wrote:

> commit 31fd84b95eb211d5db460a1dda85e004800a7b52 upstream.
>
> The min/max call needed to have explicit types on some architectures
> (e.g. mn10300). Use clamp_t instead to avoid the warning:
>
>   kernel/sys.c: In function 'override_release':
>   kernel/sys.c:1287:10: warning: comparison of distinct pointer types lacks a cast [enabled by default]
>
> Reported-by: Fengguang Wu <fengguang.wu@...el.com>
> Signed-off-by: Kees Cook <keescook@...omium.org>
> Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
> Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
[...]
> --- a/kernel/sys.c
> +++ b/kernel/sys.c
> @@ -1152,7 +1152,7 @@ static int override_release(char __user
>  			rest++;
>  		}
>  		v = ((LINUX_VERSION_CODE >> 8) & 0xff) + 40;
> -		copy = min(sizeof(buf), max_t(size_t, 1, len));
> +		copy = clamp_t(size_t, len, 1, sizeof(buf));
>  		copy = scnprintf(buf, copy, "2.6.%u%s", v, rest);

Does this have any effect at runtime?  If not, why is it needed for
stable kernels?
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