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

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Date:	Thu, 25 Oct 2012 18:27:32 +0530 (IST)
From:	P J P <ppandit@...hat.com>
To:	Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
cc:	keescook@...omium.org, viro@...iv.linux.org.uk,
	linux-kernel@...r.kernel.org, akpm@...ux-foundation.org,
	josh@...htriplett.org, serge.hallyn@...onical.com,
	linux-fsdevel@...r.kernel.org, me@...fdog.net
Subject: Re: [PATCH] exec: do not leave bprm->interp on stack

   Hello Tetsuo,

+-- On Thu, 25 Oct 2012, Tetsuo Handa wrote --+
| Excuse me, but why do you change definition of printable(c) ?
| Looks like a regression.

#define printable(c) (((c)=='\t') || ((c)=='\n') || (0x20<=(c) && (c)<=0x7e))

 Earlier definition of printable() as above was used to - break; - out of the 
loop when (c) was either tab or new line or any printable character. Whereas, 
in the patch it is used to call the request_module routine if the (c) is 
printable character, and hence the change to - printable().

| Wouldn't your patch trigger call request_module() whenever a script
| starting with "#!/bin/sh" is executed?

 Yes, Petr(a colleague here) already pointed out about excessive call to 
request_module() routine, in case if the requested module is already loaded or 
is not required/available. I'm trying to find a possible fix for the same.

Is there a way to to see if the requested module 'binfmt-xxxx' is accessible 
or not? The call to - request_module - could be conditioned accordingly.

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