linux-kernel - Re: [PATCH] exec: do not leave bprm->interp on stack

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Date:	Fri, 23 Nov 2012 01:36:18 +0530 (IST)
From:	P J P <ppandit@...hat.com>
To:	unlisted-recipients:; (no To-header on input)
cc:	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] exec: do not leave bprm->interp on stack

+-- On Mon, 19 Nov 2012, Kees Cook wrote --+
| I think to avoid the explosion of request_module calls in the abusive
| case, we could simply return ELOOP instead of ENOEXEC on max
| recursion.

 -> http://www.spinics.net/lists/mm-commits/msg92433.html

1. returning -ELOOP has a side effect of not reaching to request_module()
   ever, for:
==
#ifdef CONFIG_MODULES
1415                 if (retval != -ENOEXEC || bprm->mm == NULL) {
1416                         break;
1417                 } else {
                        ...
==

2. above patch does not seem to fix the 2^6(64) recursions issue, for:
==
+                       bprm->recursion_depth = depth + 1;
                        retval = fn(bprm);
                        bprm->recursion_depth = depth;
==

setting - recursion_dept = depth - again and the outer for(try=0;try<2...) 
loop seems to be causing the 2^6 recursions.

Thank you.
--
Prasad J Pandit / Red Hat Security Response Team
DB7A 84C5 D3F9 7CD1 B5EB  C939 D048 7860 3655 602B
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