Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Date:   Mon, 11 Nov 2019 16:25:15 +0100
From:   Oleg Nesterov <oleg@redhat.com>
To:     Adrian Reber <areber@redhat.com>
Cc:     Christian Brauner <christian.brauner@ubuntu.com>,
        Eric Biederman <ebiederm@xmission.com>,
        Pavel Emelyanov <ovzxemul@gmail.com>,
        Jann Horn <jannh@google.com>,
        Dmitry Safonov <0x7f454c46@gmail.com>,
        linux-kernel@vger.kernel.org, Andrei Vagin <avagin@gmail.com>,
        Mike Rapoport <rppt@linux.ibm.com>,
        Radostin Stoyanov <rstoyanov1@gmail.com>
Subject: Re: [PATCH v7 1/2] fork: extend clone3() to support setting a PID
Message-ID: <20191111152514.GA11389@redhat.com>
References: <20191111131704.656169-1-areber@redhat.com>
MIME-Version: 1.0
In-Reply-To: <20191111131704.656169-1-areber@redhat.com>
User-Agent: Mutt/1.5.24 (2015-08-30)
Content-Type: text/plain; charset=WINDOWS-1252
Content-Transfer-Encoding: quoted-printable
Content-Disposition: inline
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On 11/11, Adrian Reber wrote:
>
> v7:
>  - changed set_tid to be an array to set the PID of a process
>    in multiple nested PID namespaces at the same time as discussed
>    at LPC 2019 (container MC)

cough... iirc you convinced me this is not needed when we discussed
the previous version ;) Nevermind, probably my memory fools me.

So far I only have some cosmetic nits,

> @@ -175,6 +187,18 @@ struct pid *alloc_pid(struct pid_namespace *ns)
>
>  =09for (i =3D ns->level; i >=3D 0; i--) {
>  =09=09int pid_min =3D 1;
> +=09=09int t_pos =3D 0;
                    ^^^^^

I won't insist, but I'd suggest to cache set_tid[t_pos] instead to make
the code a bit more simple.

> @@ -186,12 +210,24 @@ struct pid *alloc_pid(struct pid_namespace *ns)
>  =09=09if (idr_get_cursor(&tmp->idr) > RESERVED_PIDS)
>  =09=09=09pid_min =3D RESERVED_PIDS;

You can probably move this code into the "else" branch below.

IOW, something like


=09for (i =3D ns->level; i >=3D 0; i--) {
=09=09int xxx =3D 0;

=09=09if (set_tid_size) {
=09=09=09int pos =3D ns->level - i;

=09=09=09xxx =3D set_tid[pos];
=09=09=09if (xxx < 1 || xxx >=3D pid_max)
=09=09=09=09return ERR_PTR(-EINVAL);
=09=09=09/* Also fail if a PID !=3D 1 is requested and no PID 1 exists */
=09=09=09if (xxx !=3D 1 && !tmp->child_reaper)
=09=09=09=09return ERR_PTR(-EINVAL);
=09=09=09if (!ns_capable(tmp->user_ns, CAP_SYS_ADMIN))
=09=09=09=09return ERR_PTR(-EPERM);
=09=09=09set_tid_size--;
=09=09}

=09=09idr_preload(GFP_KERNEL);
=09=09spin_lock_irq(&pidmap_lock);

=09=09if (xxx) {
=09=09=09nr =3D idr_alloc(&tmp->idr, NULL, xxx, xxx + 1,
=09=09=09=09=09GFP_ATOMIC);
=09=09=09/*
=09=09=09 * If ENOSPC is returned it means that the PID is
=09=09=09 * alreay in use. Return EEXIST in that case.
=09=09=09 */
=09=09=09if (nr =3D=3D -ENOSPC)
=09=09=09=09nr =3D -EEXIST;
=09=09} else {
=09=09=09int pid_min =3D 1;
=09=09=09/*
=09=09=09 * init really needs pid 1, but after reaching the
=09=09=09 * maximum wrap back to RESERVED_PIDS
=09=09=09 */
=09=09=09if (idr_get_cursor(&tmp->idr) > RESERVED_PIDS)
=09=09=09=09pid_min =3D RESERVED_PIDS;
=09=09=09/*
=09=09=09 * Store a null pointer so find_pid_ns does not find
=09=09=09 * a partially initialized PID (see below).
=09=09=09 */
=09=09=09nr =3D idr_alloc_cyclic(&tmp->idr, NULL, pid_min,
=09=09=09=09=09      pid_max, GFP_ATOMIC);
=09=09}

=09=09...

This way only the "if (set_tid_size)" block has to play with set_tid_size/s=
et_tid.

note also that this way we can easily allow set_tid[some_level] =3D=3D 0, w=
e can
simply do

=09-=09if (xxx < 1 || xxx >=3D pid_max)
=09+=09if (xxx < 0 || xxx >=3D pid_max)

although I don't think this is really useful.

Oleg.