Re: EACCES errors using preload libs

[Jason Gunthorpe <jgunthorpe-ePGOBjL8dl3ta4EC/59zMFaTQe2KTcn/@public.gmane.org>]

On Fri, Sep 30, 2016 at 12:43:02PM -0500, Steve Wise wrote:

> The single case I see failing so far is trying to preload my library with
> netserver.  If I run netserver with '-D -f' which avoids fork() calls, it
> works fine.  If I omit the -f, then the forked process gets an EACCES error
> trying to do ibv_query_device().  Thoughts?

Hum, so I expect the patch to break things. Specifically if you change
the process credentials after opening verbs. However just forking()
shouldn't cause a problem. Can you confirm there is nothing that
changes uid,gid, etc during the fork?

Unfortunately it was designed by Linus and Andy to work this way, so
we cannot weaken the check.

I don't know how your preload library works, but after fork basically
everything related to verbs is garbage - so it should be safe to
close/reopen then uverbs fd which will avoid the problem. It is only
because the FD was passed across a credential change that you got
EACCESS.

The way forward to restore the lost functionality is to rework the
entire uAPI to use ioctl, which is what Matan/Sean/etc have been
doing. But that work seems to be going very slowly, I hoped we'd have
something by now.

Jason
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