linux-kernel - Re: [PATCH] mm: fix arithmetic overflow in __vm_enough

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Date:	Fri, 30 Jan 2015 16:14:10 +0300
From:	Roman Gushchin <klamm@...dex-team.ru>
To:	Andrew Shewmaker <agshew@...il.com>
Cc:	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Rik van Riel <riel@...hat.com>,
	Konstantin Khlebnikov <khlebnikov@...dex-team.ru>,
	"stable@...r.kernel.org" <stable@...r.kernel.org>
Subject: Re: [PATCH] mm: fix arithmetic overflow in __vm_enough_memory()

29.01.2015, 22:57, "Andrew Shewmaker" <agshew@...il.com>:
> On Thu, Jan 29, 2015 at 04:06:03PM +0300, Roman Gushchin wrote:
>>  I noticed, that "allowed" can easily overflow by falling below 0,
>>  because (total_vm / 32) can be larger than "allowed". The problem
>>  occurs in OVERCOMMIT_NONE mode.
>>

> Makes sense to me. Please fix mm/nommu.c also.

Thanks!
I sent a patch for nommu.c.

>
> If a caller passes in a big negative value for pages,
> then vm_acct_memory() would decrement vm_committed_as, possibly
> causing percpu_counter_read_positive(&vm_committed_as) and
> __vm_enough_memory to return 0. Maybe that's okay? Callers
> won't be passing in a negative pages anyway. Is there a reason
> to let them, though?

I think, it isn't a problem, since no one will commit negative values (I hope).

R.
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