Messages in this thread | | | Date | Mon, 12 Aug 2019 18:37:10 +0200 | From | Oleg Nesterov <> | Subject | Re: [PATCH v5 1/2] fork: extend clone3() to support CLONE_SET_TID |
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On 08/11, Adrian Reber wrote: > > include/linux/pid.h | 2 +- > include/linux/sched/task.h | 1 + > include/uapi/linux/sched.h | 1 + > kernel/fork.c | 22 ++++++++++++++++++++-- > kernel/pid.c | 36 +++++++++++++++++++++++++++++------- > 5 files changed, 52 insertions(+), 10 deletions(-)
Looks good to me...
A couple of nits below, but I won't insist, feel free to ignore.
> +/* > + * Different sizes of struct clone_args > + */ > +#define CLONE3_ARGS_SIZE_V0 64
I don't really understand why do we want the "size < CLONE3_ARGS_SIZE_V0" check in copy_clone_args_from_user(), but I won't argue.
> +/* V1 includes set_tid */ > +#define CLONE3_ARGS_SIZE_V1 72
unused?
> @@ -2031,7 +2038,13 @@ static __latent_entropy struct task_struct *copy_process( > stackleak_task_init(p); > > if (pid != &init_struct_pid) { > - pid = alloc_pid(p->nsproxy->pid_ns_for_children); > + if (args->set_tid && !ns_capable( > + p->nsproxy->pid_ns_for_children->user_ns, > + CAP_SYS_ADMIN)) { > + retval = -EPERM; > + goto bad_fork_cleanup_thread; > + } > + pid = alloc_pid(p->nsproxy->pid_ns_for_children, args->set_tid);
copy_process() is already huge and complex, why not move this check into alloc_pid() ? Again, note that is accepts the same ->pid_ns_for_children.
> @@ -166,6 +166,9 @@ struct pid *alloc_pid(struct pid_namespace *ns) > struct upid *upid; > int retval = -ENOMEM; > > + if (set_tid < 0 || set_tid >= pid_max) > + return ERR_PTR(-EINVAL); > + > pid = kmem_cache_alloc(ns->pid_cachep, GFP_KERNEL); > if (!pid) > return ERR_PTR(retval); > @@ -186,12 +189,31 @@ struct pid *alloc_pid(struct pid_namespace *ns) > if (idr_get_cursor(&tmp->idr) > RESERVED_PIDS) > pid_min = RESERVED_PIDS; > > - /* > - * Store a null pointer so find_pid_ns does not find > - * a partially initialized PID (see below). > - */ > - nr = idr_alloc_cyclic(&tmp->idr, NULL, pid_min, > - pid_max, GFP_ATOMIC); > + if (set_tid) { > + /* > + * Also fail if a PID != 1 is requested > + * and no PID 1 exists. > + */ > + nr = -EINVAL; > + if (set_tid == 1 || !idr_is_empty(&tmp->idr))
On the second thought, I think we should check ns->child_reaper != NULL rather than !idr_is_empty(), this looks more robust and clean.
And this way alloc_pid() can do everything lockless at the start,
if (set_tid) { if (set_tid < 0 || set_tid >= pid_max) return ERR_PTR(-EINVAL); if (set_tid != 1 && !ns->child_reaper) return ERR_PTR(-EINVAL); if (!ns_capable(ns->user_ns, CAP_SYS_ADMIN)) return ERR_PTR(-EPERM); }
and just for record... this is off-topic and I need to recheck, but today "ns->pid_allocated = 0" in free_pid() doesn't look right to me... This logic predates unshare(CLONE_PIDNS).
Oleg.
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