Subject: Re: [PATCH] block: Check ADMIN before NICE for IOPRIO_CLASS_RT
To:     Alistair Delva <adelva@google.com>, linux-kernel@vger.kernel.org
Cc:     Khazhismel Kumykov <khazhy@google.com>,
        Bart Van Assche <bvanassche@acm.org>,
        Serge Hallyn <serge@hallyn.com>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Paul Moore <paul@paul-moore.com>, selinux@vger.kernel.org,
        linux-security-module@vger.kernel.org, kernel-team@android.com,
        stable@vger.kernel.org
References: <20211115173850.3598768-1-adelva@google.com>
From:   Jens Axboe <axboe@kernel.dk>
Message-ID: <74179f08-3529-7502-db33-2ea18cab3f58@kernel.dk>
Date:   Mon, 15 Nov 2021 11:04:55 -0700
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101
 Thunderbird/68.10.0
MIME-Version: 1.0
In-Reply-To: <20211115173850.3598768-1-adelva@google.com>
Content-Type: text/plain; charset=utf-8
Content-Language: en-US
Content-Transfer-Encoding: 7bit
Precedence: bulk

On 11/15/21 10:38 AM, Alistair Delva wrote:
> Booting to Android userspace on 5.14 or newer triggers the following
> SELinux denial:
> 
> avc: denied { sys_nice } for comm="init" capability=23
>      scontext=u:r:init:s0 tcontext=u:r:init:s0 tclass=capability
>      permissive=0
> 
> Init is PID 0 running as root, so it already has CAP_SYS_ADMIN. For
> better compatibility with older SEPolicy, check ADMIN before NICE.

Seems a bit wonky to me, but the end result is the same. In any case,
this warrants a comment above it detailing why the ordering is
seemingly important.

-- 
Jens Axboe