Re: [PATCH v2] locks: change POSIX lock ownership on execve when files_struct is displaced

[Al Viro]

On Thu, Mar 22, 2018 at 12:19:59AM -0500, Eric W. Biederman wrote:
> Jeff Layton <jlayton@xxxxxxxxxx> writes:
> 
> > From: Jeff Layton <jlayton@xxxxxxxxxx>
> >
> > POSIX mandates that open fds and their associated file locks should be
> > preserved across an execve. This works, unless the process is
> > multithreaded at the time that execve is called.
> 
> Would this perhaps work better if we moved unshare_files to after or
> inside of de_thread.  That would remove any cases where fd->count is > 1
> simply because you are multi-threaded.  It would only leave the strange
> cases where files struct is shared between different processes.

So during the probing of binfmts, etc. the descriptor table would be modifiable
by other threads?

flush_old_exec() is far too late in execve()...