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Re: [PATCH 00/26] Fixing wait, exit, ptrace, exec, and CLONE_THREAD

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Aleksa Sarai <asarai@suse.de> writes:

>> Another easy entry point is to see that a multi-threaded setuid won't
>> change the credentials on a zombie thread group leader.  Which can allow
>> sending signals to a process that the credential change should forbid.
>> This is in violation of posix and the semantics we attempt to enforce in
>> linux.
>
> I might be completely wrong on this point (and I haven't looked at the patches),
> but I was under the impression that multi-threaded set[ug]id was implemented in
> userspace (by glibc's nptl(7) library that uses RT signals internally to get
> each thread to update their credentials). And given that, I wouldn't be
> surprised (as a user) that zombie threads will have stale credentials (glibc
> isn't running in those threads anymore).
>
> Am I mistaken in that belief?

Would you be surprised if you learned that if your first thread
exits, it will become a zombie and persist for the lifetime of your
process?

Furthermore all non-thread specific signals will permission check
against that first zombie thread.

Which I think makes this surprising even if you know that setuid is
implemented in userspace.

Eric

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[PATCH 00/26] Fixing wait, exit, ptrace, exec, and CLONE_THREAD ebiederm@xmission.com (Eric W. Biederman) - 2017-06-06 21:10 +0200
  [PATCH 01/26] alpha: Remove unused TASK_GROUP_LEADER "Eric W. Biederman" <ebiederm@xmission.com> - 2017-06-06 21:20 +0200
    [PATCH 12/26] wait: Directly test for the two cases where wait_task_zombie is called "Eric W. Biederman" <ebiederm@xmission.com> - 2017-06-06 21:20 +0200
    [PATCH 15/26] wait: Don't delay !ptrace_reparented leaders "Eric W. Biederman" <ebiederm@xmission.com> - 2017-06-06 21:20 +0200
    [PATCH 13/26] wait: Remove unused delay_group_leader "Eric W. Biederman" <ebiederm@xmission.com> - 2017-06-06 21:20 +0200
    [PATCH 17/26] exit: Rework the exit states for ptracees "Eric W. Biederman" <ebiederm@xmission.com> - 2017-06-06 21:20 +0200
    [PATCH 20/26] wait: Don't pass the list to wait_consider_task "Eric W. Biederman" <ebiederm@xmission.com> - 2017-06-06 21:20 +0200
    [PATCH 26/26] pidns: Ensure zap_pid_ns_processes always terminates "Eric W. Biederman" <ebiederm@xmission.com> - 2017-06-06 21:20 +0200
    [PATCH 19/26] wait: Simpler code for clearing notask_error in wait_consider_task "Eric W. Biederman" <ebiederm@xmission.com> - 2017-06-06 21:20 +0200
    [PATCH 24/26] signal: In ptrace_stop improve identical signal detection "Eric W. Biederman" <ebiederm@xmission.com> - 2017-06-06 21:20 +0200
    [PATCH 09/26] signal: Don't allow sending SIGKILL or SIGSTOP to init "Eric W. Biederman" <ebiederm@xmission.com> - 2017-06-06 21:20 +0200
    [PATCH 03/26] signal: Do not perform permission checks when sending pdeath_signal "Eric W. Biederman" <ebiederm@xmission.com> - 2017-06-06 21:20 +0200
      Re: [PATCH 03/26] signal: Do not perform permission checks when  sending pdeath_signal Linus Torvalds <torvalds@linux-foundation.org> - 2017-06-06 22:10 +0200
        Re: [PATCH 03/26] signal: Do not perform permission checks when sending pdeath_signal ebiederm@xmission.com (Eric W. Biederman) - 2017-06-07 13:40 +0200
      Re: [PATCH 03/26] signal: Do not perform permission checks when  sending pdeath_signal Richard Weinberger <richard.weinberger@gmail.com> - 2017-06-06 23:50 +0200
    [PATCH 07/26] pidns: Improve the error handling in alloc_pid "Eric W. Biederman" <ebiederm@xmission.com> - 2017-06-06 21:20 +0200
    [PATCH 22/26] exit: Fix auto-wait of ptraced children "Eric W. Biederman" <ebiederm@xmission.com> - 2017-06-06 21:20 +0200
    [PATCH 02/26] cgroup: Don't open code tasklist_empty() "Eric W. Biederman" <ebiederm@xmission.com> - 2017-06-06 21:20 +0200
    [PATCH 04/26] signal: Make group_send_sig_info static "Eric W. Biederman" <ebiederm@xmission.com> - 2017-06-06 21:20 +0200
    [PATCH 23/26] signal:  Fix SIGCONT before group stop completes. "Eric W. Biederman" <ebiederm@xmission.com> - 2017-06-06 21:20 +0200
    [PATCH 18/26] wait: Fix WSTOPPED on a ptraced child "Eric W. Biederman" <ebiederm@xmission.com> - 2017-06-06 21:20 +0200
    [PATCH 10/26] ptrace: Simplify ptrace_detach & exit_ptrace "Eric W. Biederman" <ebiederm@xmission.com> - 2017-06-06 21:20 +0200
    [PATCH 21/26] wait: Optmize waitpid "Eric W. Biederman" <ebiederm@xmission.com> - 2017-06-06 21:20 +0200
    [PATCH 14/26] wait: Move changing of ptrace from wait_consider_task into wait_task_stopped "Eric W. Biederman" <ebiederm@xmission.com> - 2017-06-06 21:20 +0200
    [PATCH 08/26] exit: Make the runqueue rcu safe "Eric W. Biederman" <ebiederm@xmission.com> - 2017-06-06 21:20 +0200
      Re: [PATCH 08/26] exit: Make the runqueue rcu safe Oleg Nesterov <oleg@redhat.com> - 2017-06-07 15:20 +0200
    [PATCH 06/26] rlimit: Remove unnecessary grab of tasklist_lock "Eric W. Biederman" <ebiederm@xmission.com> - 2017-06-06 21:20 +0200
      Re: [PATCH 06/26] rlimit: Remove unnecessary grab of tasklist_lock Oleg Nesterov <oleg@redhat.com> - 2017-06-07 14:40 +0200
        Re: [PATCH 06/26] rlimit: Remove unnecessary grab of tasklist_lock ebiederm@xmission.com (Eric W. Biederman) - 2017-06-07 16:20 +0200
    [PATCH 16/26] exit: Fix reporting a ptraced !reparented leader has exited "Eric W. Biederman" <ebiederm@xmission.com> - 2017-06-06 21:20 +0200
    [PATCH 11/26] wait: Properly implement __WCLONE handling in the presence of exec and ptrace "Eric W. Biederman" <ebiederm@xmission.com> - 2017-06-06 21:20 +0200
    [PATCH 05/26] exit:  Remove the pointless clearing of SIGPENDING in __exit_signal "Eric W. Biederman" <ebiederm@xmission.com> - 2017-06-06 21:20 +0200
    [PATCH 25/26] signal: In ptrace_stop use CLD_TRAPPED in all ptrace signals "Eric W. Biederman" <ebiederm@xmission.com> - 2017-06-06 21:30 +0200
  Re: [PATCH 00/26] Fixing wait, exit, ptrace, exec, and CLONE_THREAD Aleksa Sarai <asarai@suse.de> - 2017-06-06 21:50 +0200
    Re: [PATCH 00/26] Fixing wait, exit, ptrace, exec, and CLONE_THREAD ebiederm@xmission.com (Eric W. Biederman) - 2017-06-07 13:50 +0200
      Re: [PATCH 00/26] Fixing wait, exit, ptrace, exec, and CLONE_THREAD Aleksa Sarai <asarai@suse.de> - 2017-06-07 14:30 +0200
  Re: [PATCH 00/26] Fixing wait, exit, ptrace, exec, and CLONE_THREAD Linus Torvalds <torvalds@linux-foundation.org> - 2017-06-06 22:10 +0200
    Re: [PATCH 00/26] Fixing wait, exit, ptrace, exec, and CLONE_THREAD ebiederm@xmission.com (Eric W. Biederman) - 2017-06-07 18:10 +0200

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