Subject: Re: [PATCH 2/2] mingw: ensure temporary file handles are not inherited by child processes

From: Eric Wong <[email-masked]>
Date: Thu, 18 Aug 2016 17:35:55 +0000

Johannes Schindelin <[email-masked]> wrote:
> +++ b/compat/mingw.h
> @@ -67,6 +67,10 @@ typedef int pid_t;
>  #define F_SETFD 2
>  #define FD_CLOEXEC 0x1
>  
> +#if !defined O_CLOEXEC && defined O_NOINHERIT
> +#define O_CLOEXEC	O_NOINHERIT
> +#endif

> +++ b/tempfile.c
> @@ -120,7 +120,7 @@ int create_tempfile(struct tempfile *tempfile, const char *path)
>  	prepare_tempfile_object(tempfile);
>  
>  	strbuf_add_absolute_path(&tempfile->filename, path);
> -	tempfile->fd = open(tempfile->filename.buf, O_RDWR | O_CREAT | O_EXCL, 0666);
> +	tempfile->fd = open(tempfile->filename.buf, O_RDWR | O_CREAT | O_EXCL | O_CLOEXEC, 0666);
>  	if (tempfile->fd < 0) {
>  		strbuf_reset(&tempfile->filename);
>  		return -1;

O_CLOEXEC only exists since Linux 2.6.23 and there are likely
still LTS (CentOS 5.x?) and non-Linux systems which do not have
it, as well as machines with could have it defined in userspace
headers but not have it in the kernel.

So I suggest something like the following: (untested)

#define GIT_O_TMP (O_RDWR | O_CREAT | O_EXCL)

#ifndef O_CLOEXEC
#  define O_CLOEXEC 0
#endif
	/* state: -1=unknown; 0=broken; 1=working */
	static int cloexec_state = O_CLOEXEC == 0 ? 0 : -1;
	static int GIT_O_ETMP = (GIT_O_TMP | O_CLOEXEC)

	int fd = open(filename, GIT_O_ETMP, 0666);

	if (fd < 0 && errno == EINVAL && cloexec_state == -1 &&
			GIT_O_ETMP != GIT_O_TMP) {
		GIT_O_ETMP = GIT_O_TMP;

		fd = open(filename, GIT_O_ETMP, 0666);
		if (fd >= 0)
			/* don't try O_CLOEXEC again */
			cloexec_state = 0;
	}

	/*
	 * This is racy in the presence of threads,
	 * but the best we can do for old *nix:
	 */
#if defined(F_GETFD) && defined(F_SETFD) && defined(FD_CLOEXEC)
	if (fd >= 0 && cloexec_state != 1) {
		int flags = fcntl(fd, F_GETFD);

		if (flags == -1)
			die_errno("F_GETFD failed");
		if (flags & O_CLOEXEC)
			cloexec_state = 1;
		else {
			flags = fcntl(fd, F_SETFD, flags | FD_CLOEXEC);
			if (flags == -1)
				die_errno("F_SETFD failed");
			cloexec_state = 0;

		}
	}
#endif
	...