linux-kernel - vmsplice exploits, stack protector and Makefiles

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Message-ID: <20080212090001.3fcc4ca0@laptopd505.fenrus.org>
Date:	Tue, 12 Feb 2008 09:00:01 -0800
From:	Arjan van de Ven <arjan@...radead.org>
To:	Sam Ravnborg <sam@...nborg.org>
Cc:	linux-kernel@...r.kernel.org, mingo@...e.hu,
	torvalds@...ux-foundation.org
Subject: vmsplice exploits, stack protector and Makefiles

Hi,

I just read the excellent LWN writeup of the vmsplice security thing, and that got me
wondering why this attack wasn't stopped by the CONFIG_CC_STACKPROTECTOR option... because
it plain should have been...

some analysis later.. it turns out that the following line in the top level Makefile,
added by you in October 2007, entirely disables CONFIG_CC_STACKPROTECTOR ;(
With this line removed the exploit will be nicely stopped.

# Force gcc to behave correct even for buggy distributions
CFLAGS          += $(call cc-option, -fno-stack-protector)

Now I realize that certain distros have patched gcc to compensate for their lack of distro
wide CFLAGS, and it's great to work around that... but would there be a way to NOT
disable this for CONFIG_CC_STACKPROTECTOR please? It would have made this
exploit not possible for those kernels that enable this feature (and that includes distros
like Fedora)

Greetings,
   Arjan van de Ven

-- 
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