linux-kernel - Re: [PATCH RESEND] memcg: Free spare array to avoid memory leak

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:	Tue, 1 May 2012 14:03:14 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Sha Zhengju <handai.szj@...il.com>
Cc:	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	cgroups@...r.kernel.org, Sha Zhengju <handai.szj@...bao.com>
Subject: Re: [PATCH RESEND] memcg: Free spare array to avoid memory leak

On Thu, 19 Apr 2012 16:54:50 +0800
Sha Zhengju <handai.szj@...il.com> wrote:

> From: Sha Zhengju <handai.szj@...bao.com>
> 
> When the last event is unregistered, there is no need to keep the spare
> array anymore. So free it to avoid memory leak.

How serious is this leak?  Is there any way in which it can be used to
consume unbounded amounts of memory?

> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -4412,6 +4412,12 @@ static void mem_cgroup_usage_unregister_event(struct cgroup *cgrp,
>  swap_buffers:
>  	/* Swap primary and spare array */
>  	thresholds->spare = thresholds->primary;
> +	/* If all events are unregistered, free the spare array */
> +	if (!new) {
> +		kfree(thresholds->spare);
> +		thresholds->spare = NULL;
> +	}
> +
>  	rcu_assign_pointer(thresholds->primary, new);
>  

The resulting code is really quite convoluted.  Try to read through it
and follow the handling of ->primary and ->spare.  Head spins.

What is the protocol here?  If ->primary is NULL then ->spare must also
be NULL?


I'll apply the patch, although I don't (yet) have sufficient info to
know which kernels it should be applied to.  Perhaps someone could
revisit this code and see if it can be made more straightforward.

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/