On Thu, Oct 06, 2022 at 01:20:35PM -0700, Kees Cook wrote: > > So the question, then, is "why are they trying to exec while actively > spawning new threads?" That appears to be the core problem here, and as > far as I can tell, the kernel has behaved this way for a very long time. > I don't think the kernel should fix this, either, because it leads to a > very weird state for userspace, where the thread spawner may suddenly > die due to the exec happening in another thread. This really looks like > something userspace needs to handle correctly (i.e. don't try to exec > while actively spawning threads). One of the classic failure modes is when a threaded program calls a library, and that library might try to do a fork/exec (or call system(3) to run some command. e.g., such as running "lvm create ..." or to spawn some kind of helper daemon. There are a number of stack overflow questions about this, and there are some solutions to _some_ of the problems, such as using pthread_atfork(), and knowing that you are about to call fork/exec, and use some out of band mechanism to to make sure no threads get spawned until the fork/exec is completed --- but if you don't know that a library is going to do a fork/exec, well, life is tough. One technique even advocated by a stack overflow article is "avoid using threads whenver possible". :-/ - Ted
