linux-kernel - Re: [PATCH] mm/memcg: v1: account event registrations and drop world-writable cgroup.event

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Message-ID: <aLnbXSxyzhGYGjks@google.com>
Date: Thu, 4 Sep 2025 18:33:01 +0000
From: Roman Gushchin <roman.gushchin@...ux.dev>
To: Stanislav Fort <stanislav.fort@...le.com>
Cc: linux-mm@...ck.org, cgroups@...r.kernel.org,
	linux-kernel@...r.kernel.org, hannes@...xchg.org, mhocko@...nel.org,
	shakeel.butt@...ux.dev, muchun.song@...ux.dev,
	akpm@...ux-foundation.org, stable@...r.kernel.org,
	Stanislav Fort <disclosure@...le.com>
Subject: Re: [PATCH] mm/memcg: v1: account event registrations and drop
 world-writable cgroup.event_control

On Thu, Sep 04, 2025 at 09:12:48PM +0300, Stanislav Fort wrote:
> In cgroup v1, the legacy cgroup.event_control file is world-writable and allows unprivileged users to register unbounded events and thresholds. Each registration allocates kernel memory without capping or memcg charging, which can be abused to exhaust kernel memory in affected configurations.
> 
> Make the following minimal changes:
> - Account allocations with __GFP_ACCOUNT in event and threshold registration.
> - Remove CFTYPE_WORLD_WRITABLE from cgroup.event_control to make it owner-writable.
> 
> This does not affect cgroup v2. Allocations are still subject to kmem accounting being enabled, but this reduces unbounded global growth.
> 
> Reported-by: Stanislav Fort <disclosure@...le.com>
> Acked-by: Johannes Weiner <hannes@...xchg.org>
> Cc: stable@...r.kernel.org
> Signed-off-by: Stanislav Fort <disclosure@...le.com>

Acked-by: Roman Gushchin <roman.gushchin@...ux.dev>

Small nit: please, use GFP_KERNEL_ACCOUNT instead of
GFP_KERNEL | __GFP_ACCOUNT.

Thanks!