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

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Date:	Thu, 25 Oct 2012 19:28:03 -0700
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	Jonathan Nieder <jrnieder@...il.com>
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

On Thu, Oct 25, 2012 at 05:11:19PM -0700, Jonathan Nieder wrote:
> 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?

It's a bugfix for the previous patch in this area, fixing the build
warning.  I don't like adding stable patches that add new warnings :)

thanks,

greg k-h
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