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    SubjectRe: [PATCH v3 1/2] fork: extend clone3() to support CLONE_SET_TID
    On Wed, Aug 07, 2019 at 06:08:56PM +0200, Oleg Nesterov wrote:
    > On 08/06, Adrian Reber wrote:
    > >
    > > @@ -2573,6 +2575,14 @@ noinline static int copy_clone_args_from_user(struct kernel_clone_args *kargs,
    > > .tls = args.tls,
    > > };
    > >
    > > + if (size == sizeof(struct clone_args)) {
    > > + /* Only check permissions if set_tid is actually set. */
    > > + if (args.set_tid &&
    > > + !ns_capable(pid_ns->user_ns, CAP_SYS_ADMIN))
    >
    > and I just noticed this uses pid_ns = task_active_pid_ns() ...
    >
    > is it correct?
    >
    > I feel I am totally confused, but should we use the same
    > p->nsproxy->pid_ns_for_children passed to alloc_pid?

    We need to have CAP_SYS_ADMIN in the owning user namespace of the target
    pidns for the pidns in which we spawn the new process. The value for
    pid_ns_for_children could've been altered by either passing CLONE_NEWPID
    or by having called unshare(CLONE_NEWPID) before. So yes,
    pid_ns_for_children is what we want.

    Sorry again for the delay in my responses. On vacation atm.

    Christian

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