linux-kernel - Re: [PATCH] kernel: arg2 is unsigned long which is never

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Date:	Wed, 06 Feb 2013 18:36:38 +0800
From:	Chen Gang <gang.chen@...anux.com>
To:	Cyrill Gorcunov <gorcunov@...nvz.org>
CC:	Chen Gang <gang.chen@...anux.com>, akpm@...ux-foundation.org,
	keescook@...omium.org, serge.hallyn@...onical.com,
	ebiederm@...ssion.com,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Alan Cox <alan@...rguk.ukuu.org.uk>, marcel@...tmann.org
Subject: Re: [PATCH] kernel: arg2 is unsigned long which is never < 0

于 2013年02月06日 16:56, Cyrill Gorcunov 写道:
> On Wed, Feb 06, 2013 at 04:44:35PM +0800, Chen Gang wrote:
>> > 
>> > diff --git a/kernel/sys.c b/kernel/sys.c
>> > index 24d1ef5..568b9ca 100644
>> > --- a/kernel/sys.c
>> > +++ b/kernel/sys.c
>> > @@ -2027,7 +2027,7 @@ SYSCALL_DEFINE5(prctl, int, option, unsigned long, arg2, unsigned long, arg3,
>> >  			error = get_dumpable(me->mm);
>> >  			break;
>> >  		case PR_SET_DUMPABLE:
>> > -			if (arg2 < 0 || arg2 > 1) {
>> > +			if (arg2 > 1) {
>> >  				error = -EINVAL;
>> >  				break;
>> >  			}
> I guess
> 
> 	if (arg2 != SUID_DUMPABLE_DISABLED &&
> 	    arg2 != SUID_DUMPABLE_ENABLED) {
> 		error = -EINVAL;
> 		break;
> 	}
> 
> would be better. Still, current patch looks good to me.

thank you for your suggestion, firstly.

and after read more, it seems a little more complex:
for me, I think it would be better:

 	if (arg2 != SUID_DUMP_DISABLE && arg2 != SUID_DUMP_USER) {
 		error = -EINVAL;
 		break;
 	}


the reason is below:

it has 2 branches:

  branch 1:

    #define SUID_DUMP_DISABLE      0       /* No setuid dumping */
    #define SUID_DUMP_USER         1       /* Dump as user of process */
    #define SUID_DUMP_ROOT         2       /* Dump as root */

    in patch d6e711448137ca3301512cec41a2c2ce852b3d0a
      Signed-of-by Alan Cox in 2005.
      define these constant for using.
      change 2 choices to 3 choices (add a new choice).

    in patch abf75a5033d4da7b8a7e92321d74021d1fcfb502
      Signed-of-by Marcel Holtmann in 2006.
      find and fix a security issue for it.


  branch 2:

    #define SUID_DUMPABLE_DISABLED  0
    #define SUID_DUMPABLE_ENABLED   1
    #define SUID_DUMPABLE_SAFE      2

    in patch 54b501992dd2a839e94e76aa392c392b55080ce8
      Signed-of-by Kees Cook in Jul 30 2012
      define the constants for using
      print warning when detect unsafe core_pattern settings

    in patch 0f4cfb2e4e7a7e4e97a3e90e2ba1062f07fb2cb1
      Signed-of-by Oleg Nesterov in Oct 4 2012
      use SUID_DUMPABLE_ENABLED rather than hardcoded 1

analysing:
  branch 1 and branch 2 have the same values with different macro names.
  branch 1 is much older than branch 2.
  for features:
    branch 1 is for functional feature and bug fix,
    branch 2 is for printing warning and beautifying code.

  it seems:
    branch 2 did not notice the branch 1, before it performs.
    if it noticed, it is meanless to define the new macros.

result:
  still use the macros of branch 1
  and use branch 1 macros instead of branch 2 macros (need an additional patch).

  :-)

  Regards.

-- 
Chen Gang

Asianux Corporation
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