linux-kernel - Re: [PATCH] Smackv10: Smack rules grammar + their stateful parser

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Message-Id: <200711060656.ADF87510.tJLVFOHOFSOFMQ@I-love.SAKURA.ne.jp>
Date:	Tue, 6 Nov 2007 06:56:43 +0900
From:	Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
To:	pavel@....cz, torvalds@...ux-foundation.org
Cc:	darwish.07@...il.com, casey@...aufler-ca.com,
	akpm@...ux-foundation.org, linux-security-module@...r.kernel.org,
	linux-kernel@...r.kernel.org, viro@....linux.org.uk
Subject: Re: [PATCH] Smackv10: Smack rules grammar + their stateful parser


Linus Torvalds wrote:
> I personally think string parsers are *much* better than the alternatives 
> (which basically boil down to nasty binary interfaces)
Me too.

> Binary structures and ioctl's are *much* worse. They are totally 
> undebuggable with generic tools (think "echo" or "strace"), and they are a 
> total nightmare to parse across architectures and pointer sizes.
Not only pointer sizes bugs, but also checking pointer address costs.
For binary policy, we have to examine ->next pointer is valid or not.
We can't blindly use address supplied from userland.

I have encountered mismatch of kernel version and AppArmor's policy parser version
when I just updated only kernel. As a result, the segmentation faults rushed toward me.
 From this experience, TOMOYO still uses string parser in the kernel.
If a parser doesn't consume much stack (i.e. call functions recursively), I think it is no problem.

Thanks.

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