linux-kernel - Re: [Security] [PATCH 2/2] taskstats: restrict access to user

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Message-ID: <CA+55aFymwBJ9CxOpnjnNxOxncHLkwfeFQ4Mm=ZhWBZDEAfAd1Q@mail.gmail.com>
Date:	Mon, 19 Sep 2011 11:32:24 -0700
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Andi Kleen <andi@...stfloor.org>
Cc:	Balbir Singh <bsingharora@...il.com>,
	Vasiliy Kulikov <segoon@...nwall.com>,
	Shailabh Nagar <nagar@...ibm.com>,
	linux-kernel@...r.kernel.org, security@...nel.org,
	Eric Paris <eparis@...hat.com>,
	Stephen Wilson <wilsons@...rt.ca>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	David Rientjes <rientjes@...gle.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Balbir Singh <balbir@...ux.vnet.ibm.com>,
	kernel-hardening@...ts.openwall.com
Subject: Re: [Security] [PATCH 2/2] taskstats: restrict access to user

On Mon, Sep 19, 2011 at 11:29 AM, Andi Kleen <andi@...stfloor.org> wrote:
>>
>>  #define KB 1024
>
> Needs to be 1024ULL, because the counters are 64bit.
>
>>  #define MB (1024*KB)
>> +#define KB_MASK (~(KB-1))
>
> Otherwise you lose the upper 32bits here.

No, it's an "int" constant, so it will sign-extend properly when it
gets extended to 64 bits.

It's "unsigned int" etc that can be dangerous in these kinds of situations.

(Of course, in other contexts, sign-extensions of masks is *bad*. So
it depends on what you do)

                     Linus
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