linux-kernel - Re: [PATCH 0/3] extend get/setrlimit to support setting rlimits external to a process (v7)

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Message-ID: <20091102185137.GA28803@elte.hu>
Date:	Mon, 2 Nov 2009 19:51:37 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Neil Horman <nhorman@...driver.com>
Cc:	linux-kernel@...r.kernel.org, akpm@...ux-foundation.org,
	marcin.slusarz@...il.com, tglx@...utronix.de, mingo@...hat.com,
	hpa@...or.com, Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH 0/3] extend get/setrlimit to support setting rlimits
	external to a process (v7)

* Neil Horman <nhorman@...driver.com> wrote:

> > Have you ensured that no rlimit gets propagated during task init 
> > into some other value - under the previously correct assumption that 
> > rlimits dont change asynchronously under the feet of tasks?
> 
> I've looked, and the only place that I see the rlim array getting 
> copied is via copy_signal when we're in the clone path.  The entire 
> rlim array is copied from old task_struct to new task_struct under the 
> protection of the current->group_leader task lock, which I also hold 
> when updating via sys_setprlimit, so I think we're safe in this case.

I mean - do we set up any data structure based on a particular rlimit, 
that can get out of sync with the rlimit being updated?

A prominent example would be the stack limit - we base address layout 
decisions on it. Check arch/x86/mm/mmap.c. RLIM_INFINITY has a special 
meaning plus we also set mmap_base() based on the rlim.

Also, there appears to be almost no security checks in the new syscall! 
We look up a PID but that's it - this code will allow unprivileged users 
to lower various rlimits of system daemons - as if it were their own 
limit. That's a rather big security hole.

	Ingo
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