Re: Support for "pshared" POSIX semaphores

[Jason Thorpe <thorpej%me.com@localhost>]

> On Feb 4, 2019, at 4:30 AM, Joerg Sonnenberger <joerg%bec.de@localhost> wrote:
> 
> This seems to allow attaching to random semaphores by just knowing the
> right idea. This violates the definition of anonymous semaphores and I
> wouldn't be surprised if it creates some nasty security issues...

Well, the SUS says this about it:

<quote>
If the pshared argument has a non-zero value, then the semaphore is shared between processes; in this case, any process that can access the semaphore semcan use sem for performing sem_wait(), sem_timedwait(), sem_trywait(), sem_post(), and sem_destroy() operations.
</quote>

I supposed if we really wanted to, we could restrict to same-UID or something similar, but it seems like that might technically violate the standard.  I suppose we could wrap that behavior in a sysctl control.

It's unfortunate that POSIX semaphores are so poorly specified (and "pshared" especially), but there are real uses of them out in the wild.

I'm open to suggestions.

-- thorpej