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

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Message-Id: <201210252103.BJG56875.OtHFLOOVSFFQMJ@I-love.SAKURA.ne.jp>
Date:	Thu, 25 Oct 2012 21:03:14 +0900
From:	Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
To:	ppandit@...hat.com, keescook@...omium.org
Cc:	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

P J P wrote:
> 
>   Hello Kees,
> 
> +-- On Wed, 24 Oct 2012, Kees Cook wrote --+
> | What should the code here _actually_ be doing? The _script and _misc 
> | handlers expect to rewrite the bprm contents and recurse, but the module 
> | loader want to try again. It's not clear to me what the binfmt module 
> | handler is even there for; I don't see any binfmt-XXXX aliases in the tree. 
> | If nothing uses it, should we just rip it out? That would solve it too.
> 
> I've been following this issue and updated versions of HDs patch. Below is a 
> small patch to search_binary_handler() routine, which attempts to make the 
> request_module call before calling load_script routine.
> 
> Besides fixing the stack disclosure issue it also helps to *simplify* the 
> search_binary_handler routine by removing the -for (try=0;try<2;try++)- loop.
> 
> I'd really appreciate any comments/suggestions you may have.

Excuse me, but why do you change definition of printable(c) ?
Looks like a regression.

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

And if you meant

if (!(printable(bprm->buf[0]) && printable(bprm->buf[1])
	&& printable(bprm->buf[2]) && printable(bprm->buf[3])))

then, wouldn't that trigger request_module() recursion?
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