linux-kernel - Re: [PATCH v2] ipc: Store mqueue sysctls in the ipc namespace

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Message-ID: <c8edba64-9b4b-1ef8-f0b3-1b4beacf1551@colorfullife.com>
Date:   Tue, 4 Jan 2022 19:13:40 +0100
From:   Manfred Spraul <manfred@...orfullife.com>
To:     Alexey Gladkov <legion@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Linux Containers <containers@...ts.linux.dev>
Cc:     Alexander Mikhalitsyn <alexander.mikhalitsyn@...tuozzo.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Christian Brauner <christian.brauner@...ntu.com>,
        Daniel Walsh <dwalsh@...hat.com>,
        Davidlohr Bueso <dbueso@...e.de>,
        "Eric W . Biederman" <ebiederm@...ssion.com>,
        Kirill Tkhai <ktkhai@...tuozzo.com>,
        Serge Hallyn <serge@...lyn.com>,
        Varad Gautam <varad.gautam@...e.com>,
        Vasily Averin <vvs@...tuozzo.com>,
        kernel test robot <lkp@...el.com>
Subject: Re: [PATCH v2] ipc: Store mqueue sysctls in the ipc namespace

Hi Alexey,

On 1/4/22 12:51, Alexey Gladkov wrote:
> Right now, the mqueue sysctls take ipc namespaces into account in a
> rather hacky way. This works in most cases, but does not respect the
> user namespace.
>
> Within the user namespace, the user cannot change the /proc/sys/fs/mqueue/*
> parametres. This poses a problem in the rootless containers.
>
> To solve this I changed the implementation of the mqueue sysctls just
> like some other sysctls.
>
> Before this change:
>
> $ echo 5 | unshare -r -U -i tee /proc/sys/fs/mqueue/msg_max
> tee: /proc/sys/fs/mqueue/msg_max: Permission denied
> 5

Could you crosscheck that all (relevant) allocations in ipc/mqueue.c use 
GFP_KERNEL_ACCOUNT?

We should not allow normal users to use up all memory.

Otherwise:
The idea is good, the limits do not really prevent using up all memory, 
_ACCOUNT is the better approach.
And with _ACCOUNT, it doesn't hurt that the namespace root is able to 
set limits.


--

     Manfred