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SubjectRe: [PATCH v10 1/2] fork: extend clone3() to support setting a PID
On Fri, Nov 15, 2019 at 10:34:20AM +0100, Oleg Nesterov wrote:
> On 11/14, Andrei Vagin wrote:
> >
> > On Thu, Nov 14, 2019 at 03:27:06PM +0100, Adrian Reber wrote:
> > ...
> > > diff --git a/include/uapi/linux/sched.h b/include/uapi/linux/sched.h
> > > index 1d500ed03c63..2e649cfa07f4 100644
> > > --- a/include/uapi/linux/sched.h
> > > +++ b/include/uapi/linux/sched.h
> > ...
> > > @@ -174,24 +186,51 @@ struct pid *alloc_pid(struct pid_namespace *ns)
> > > pid->level = ns->level;
> > >
> > > for (i = ns->level; i >= 0; i--) {
> > > - int pid_min = 1;
> > > + int tid = 0;
> > > +
> > > + if (set_tid_size) {
> > > + tid = set_tid[ns->level - i];
> > > + if (tid < 1 || tid >= pid_max)
> > > + return ERR_PTR(-EINVAL);
> >
> > do we need to release pids what have been allocated on previous levels?
>
> Heh ;) it is really amazing that nobody noticed this! Thanks Andrei.
>
> > nr = -EINVAL;
>
> retval = -EINVAL;
>
> > goto out_free;

How do we feel about moving this into a separate helper like below?
Keeps the ugliness out of alloc_pid() itself.

Christian

diff --git a/kernel/pid.c b/kernel/pid.c
index eb32668997c6..d3dfd1bbebaf 100644
--- a/kernel/pid.c
+++ b/kernel/pid.c
@@ -157,6 +157,31 @@ void free_pid(struct pid *pid)
call_rcu(&pid->rcu, delayed_put_pid);
}

+static int set_tid_next(pid_t *set_tid, size_t *size, int idx)
+{
+ int tid = 0;
+
+ if (*size) {
+ tid = set_tid[idx];
+ if (tid < 1 || tid >= pid_max)
+ return -EINVAL;
+
+ /*
+ * Also fail if a PID != 1 is requested and
+ * no PID 1 exists.
+ */
+ if (tid != 1 && !tmp->child_reaper)
+ return -EINVAL;
+
+ if (!ns_capable(tmp->user_ns, CAP_SYS_ADMIN))
+ return -EPERM;
+
+ (*size)--;
+ }
+
+ return tid;
+}
+
struct pid *alloc_pid(struct pid_namespace *ns, pid_t *set_tid,
size_t set_tid_size)
{
@@ -188,20 +213,10 @@ struct pid *alloc_pid(struct pid_namespace *ns, pid_t *set_tid,
for (i = ns->level; i >= 0; i--) {
int tid = 0;

- if (set_tid_size) {
- tid = set_tid[ns->level - i];
- if (tid < 1 || tid >= pid_max)
- return ERR_PTR(-EINVAL);
- /*
- * Also fail if a PID != 1 is requested and
- * no PID 1 exists.
- */
- if (tid != 1 && !tmp->child_reaper)
- return ERR_PTR(-EINVAL);
- if (!ns_capable(tmp->user_ns, CAP_SYS_ADMIN))
- return ERR_PTR(-EPERM);
- set_tid_size--;
- }
+ retval = set_tid_next(set_tid, &set_tid_size, ns->level - i);
+ if (retval < 0)
+ goto out_free;
+ tid = retval;

idr_preload(GFP_KERNEL);
spin_lock_irq(&pidmap_lock);
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