[PATCH] [BZ #18433] Check file access/existence before forking.

[Joseph Myers]

On Sat, 12 Sep 2015, navid Rahimi wrote:

> On Sat, Sep 12, 2015 at 12:28 AM, Joseph Myers <joseph@codesourcery.com> wrote:
> > On Sat, 12 Sep 2015, navid Rahimi wrote:
> > You can't assume that pipe2 is supported unless __ASSUME_PIPE2 is defined.
> > It might be an ENOSYS stub, or it might be unsupported at runtime because
> > the kernel isn't recent enough.  In either case, an ENOSYS error from
> > pipe2 must not result in such an error from posix_spawn.
> > Joseph S. Myers
> > joseph@codesourcery.com
> 
> Freebsd uses vfork (and its blocking nature for parent process) for
> implementation of posix_spawn , but I have found cert article about
> not using vfork
> 
> https://www.securecoding.cert.org/confluence/pages/viewpage.action?pageId=1703954
> 
> pipes was more reliable in overall sight (in my opinion, because I
> have seen so much people complaining about vfork) , but I can

Well, you can use pipes provided you have a fallback from pipe2 to pipe in 
the case where __ASSUME_PIPE2 is not defined and pipe2 fails with ENOSYS 
at runtime.  (There would be a race if another thread forks and execs 
between the calls to pipe and fcntl FD_CLOEXEC, but that's unavoidable in 
the absence of pipe2.)

-- 
Joseph S. Myers
joseph@codesourcery.com