Re: [PATCH v2] Implement close-on-fork

Ralph Corderoy
2022-06-18T11:49:29Z

Hi Nate,

> One manifestation of this is a race conditions in system(), which
> (depending on the implementation) is non-atomic in that it first calls
> a fork() and then an exec().

The need for O_CLOFORK might be made more clear by looking at a
long-standing Go issue, i.e. unrelated to system(3), which was started
in 2017 by Russ Cox when he summed up the current race-condition
behaviour of trying to execve(2) a newly created file:
https://github.com/golang/go/issues/22315. I raised it on linux-kernel
in 2017, https://marc.info/?l=linux-kernel&m=150834137201488, and linked
to a proposed patch from 2011, ‘[PATCH] fs: add FD_CLOFORK and
O_CLOFORK’ by Changli Gao. As I said, long-standing.

The Go issue is worth a read. Russ wondered ‘What would Java do’ only
to find that Java already had an issue open for the same problem since
2014.

I think the kernel is the place to fix the problem, just as with
FD_CLOEXEC/O_CLOEXEC. Ian Lance Taylor says on the Go issue that it
looks like ‘Solaris and macOS and OpenBSD have O_CLOFORK already.
Hopefully it will catch on further’.

--
Cheers, Ralph.