Message-ID: <c8edba64-9b4b-1ef8-f0b3-1b4beacf1551@colorfullife.com>
Date:   Tue, 4 Jan 2022 19:13:40 +0100
MIME-Version: 1.0
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101
 Thunderbird/91.4.0
Subject: Re: [PATCH v2] ipc: Store mqueue sysctls in the ipc namespace
Content-Language: en-US
To:     Alexey Gladkov <legion@kernel.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Linux Containers <containers@lists.linux.dev>
Cc:     Alexander Mikhalitsyn <alexander.mikhalitsyn@virtuozzo.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Christian Brauner <christian.brauner@ubuntu.com>,
        Daniel Walsh <dwalsh@redhat.com>,
        Davidlohr Bueso <dbueso@suse.de>,
        "Eric W . Biederman" <ebiederm@xmission.com>,
        Kirill Tkhai <ktkhai@virtuozzo.com>,
        Serge Hallyn <serge@hallyn.com>,
        Varad Gautam <varad.gautam@suse.com>,
        Vasily Averin <vvs@virtuozzo.com>,
        kernel test robot <lkp@intel.com>
References: <0f0408bb7fbf3187966a9bf19a98642a5d9669fe.1641225760.git.legion@kernel.org>
 <792dcae82bc228cd0bec1fa80ed4d2c9340b0f8f.1641296947.git.legion@kernel.org>
From:   Manfred Spraul <manfred@colorfullife.com>
In-Reply-To: <792dcae82bc228cd0bec1fa80ed4d2c9340b0f8f.1641296947.git.legion@kernel.org>
Content-Type: text/plain; charset=UTF-8; format=flowed
Content-Transfer-Encoding: 8bit
Precedence: bulk

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