[RESEND PATCH v9] Mutex: Add pthread mutex tunables

[Florian Weimer]

* Carlos O'Donell:

> On 11/29/18 9:41 AM, Florian Weimer wrote:
>> * Kemi Wang:
>> 
>>> +# 	     SXID_ERASE: (default) Don't read for AT_SECURE binaries and
>>> +# 	     		 removed so that child processes can't read it.
>> 
>> I think this will not work as intended for libpthread tunables because
>> if libpthread is not linked in, no code in nptl/nptl-init.c ever runs.
>> 
>> I think we need to move the tunable to elf/dl-tunables.list, parse it
>> there, and communicate the result to libpthread, possibly via
>> _rtld_global_ro.
>
> This is a fairly arcane issue with tunables, are we certain this is a
> problem?

My concern is about the quoted part, from a new file added in this
patch.  The security controls will not work reliably in this context
because libpthread may never be loaded and the promised removal never
happens.

Thanks,
Florian