Re: DoS with POSIX file locks?

Trond Myklebust
2006-03-21T18:17:03Z

On Tue, 2006-03-21 at 18:58 +0100, Miklos Szeredi wrote:
> > > Apps using LinuxThreads seem to be candidates:
> > >
> > > According to POSIX 1003.1c, a successful `exec*' in one of the
> > > threads should automatically terminate all other threads in the
> > > program. This behavior is not yet implemented in LinuxThreads.
> > > Calling `pthread_kill_other_threads_np' before `exec*' achieves
> > > much of the same behavior, except that if `exec*' ultimately
> > > fails, then all other threads are already killed.
> > >
> > > steal_locks() was probably added as a workaround for this case, no?
> >
> > Possibly, but LinuxThreads were never really POSIX thread compliant
> > anyway. Anyhow, the problem isn't really LinuxThreads, it is rather that
> > the existence of the standalone CLONE_FILES flag allows you to do a lot
> > of weird inheritance crap with 'posix locks' that the POSIX standards
> > committees never even had to consider.
>
> Yes. The execve-with-multiple-threads/posix-locks interaction is not
> documented for LinuxThreads but removing steal_locks() makes that
> implementation slighly differently incompatible to POSIX. Some
> application _might_ be relying on the current behavior.

That really doesn't matter: the current behaviour isn't ever going to
work for some of the most commonly used Linux filesystems out there.
IOW: Such an application isn't even going to be portable from one Linux
installation to another.

Cheers,
Trond