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Date:   Fri, 15 Nov 2019 11:49:10 +0100
From:   Oleg Nesterov <oleg@redhat.com>
To:     Christian Brauner <christian.brauner@ubuntu.com>
Cc:     Andrei Vagin <avagin@gmail.com>, Adrian Reber <areber@redhat.com>,
        Eric Biederman <ebiederm@xmission.com>,
        Pavel Emelyanov <ovzxemul@gmail.com>,
        Jann Horn <jannh@google.com>,
        Dmitry Safonov <0x7f454c46@gmail.com>,
        Rasmus Villemoes <linux@rasmusvillemoes.dk>,
        linux-kernel@vger.kernel.org, Mike Rapoport <rppt@linux.ibm.com>,
        Radostin Stoyanov <rstoyanov1@gmail.com>
Subject: Re: [PATCH v10 1/2] fork: extend clone3() to support setting a PID
Message-ID: <20191115104909.GB25528@redhat.com>
References: <20191114142707.1608679-1-areber@redhat.com>
 <20191114191538.GC171963@gmail.com>
 <20191115093419.GA25528@redhat.com>
 <20191115095854.4vr6bgfz6ny5zbpd@wittgenstein>
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In-Reply-To: <20191115095854.4vr6bgfz6ny5zbpd@wittgenstein>
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On 11/15, Christian Brauner wrote:
>
> +static int set_tid_next(pid_t *set_tid, size_t *size, int idx)
> +{
> +=09int tid =3D 0;
> +
> +=09if (*size) {
> +=09=09tid =3D set_tid[idx];
> +=09=09if (tid < 1 || tid >=3D pid_max)
> +=09=09=09return -EINVAL;
> +
> +=09=09/*
> +=09=09 * Also fail if a PID !=3D 1 is requested and
> +=09=09 * no PID 1 exists.
> +=09=09 */
> +=09=09if (tid !=3D 1 && !tmp->child_reaper)
> +=09=09=09return -EINVAL;
> +
> +=09=09if (!ns_capable(tmp->user_ns, CAP_SYS_ADMIN))
> +=09=09=09return -EPERM;
> +
> +=09=09(*size)--;
> +=09}

this needs more args, struct pid_namespace *tmp + pid_t pid_max

> +
> +=09return tid;
> +}
> +
>  struct pid *alloc_pid(struct pid_namespace *ns, pid_t *set_tid,
>  =09=09      size_t set_tid_size)
>  {
> @@ -188,20 +213,10 @@ struct pid *alloc_pid(struct pid_namespace *ns, pid=
_t *set_tid,
>  =09for (i =3D ns->level; i >=3D 0; i--) {
>  =09=09int tid =3D 0;
> =20
> -=09=09if (set_tid_size) {
> -=09=09=09tid =3D set_tid[ns->level - i];
> -=09=09=09if (tid < 1 || tid >=3D pid_max)
> -=09=09=09=09return ERR_PTR(-EINVAL);
> -=09=09=09/*
> -=09=09=09 * Also fail if a PID !=3D 1 is requested and
> -=09=09=09 * no PID 1 exists.
> -=09=09=09 */
> -=09=09=09if (tid !=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=09retval =3D set_tid_next(set_tid, &set_tid_size, ns->level - i);
> +=09=09if (retval < 0)
> +=09=09=09goto out_free;
> +=09=09tid =3D retval;

Well, if we add a helper then

=09static inline int check_tid(tid, max, ns)
=09{
=09=09if (tid < 1 || tid >=3D max)
=09=09=09return ERR_PTR(-EINVAL);
=09=09/*
=09=09 * Also fail if a PID !=3D 1 is requested and
=09=09 * no PID 1 exists.
=09=09 */
=09=09if (tid !=3D 1 && !ns->child_reaper)
=09=09=09return ERR_PTR(-EINVAL);
=09=09if (!ns_capable(ns->user_ns, CAP_SYS_ADMIN))
=09=09=09return ERR_PTR(-EPERM);
=09=09return 0;
=09}

=09... alloc_pid() ...

=09=09if (set_tid_size) {
=09=09=09tid =3D set_tid[ns->level - i];
=09=09=09retval =3D check_tid(tid, pid_max, tmp);
=09=09=09if (retval)
=09=09=09=09goto out_free;
=09=09=09set_tid_size--;
=09=09}

looks more clean to me. But still ugly. IMO,

=09=09if (set_tid_size) {
=09=09=09tid =3D set_tid[ns->level - i];

=09=09=09retval =3D -EINVAL;
=09=09=09if (tid < 1 || tid >=3D pid_max)
=09=09=09=09goto out_free;
=09=09=09/*
=09=09=09 * Also fail if a PID !=3D 1 is requested and
=09=09=09 * no PID 1 exists.
=09=09=09 */
=09=09=09if (tid !=3D 1 && !tmp->child_reaper)
=09=09=09=09goto out_free;
=09=09=09retval =3D -EPERM;
=09=09=09if (!ns_capable(tmp->user_ns, CAP_SYS_ADMIN))
=09=09=09=09goto out_free;
=09=09=09set_tid_size--;
=09=09}

makes more sense.

Oleg.