Implement the POSIX-2024 close-on-fork flag, but modified to be

reset on exec as preserving it across exec is not necessary for its
original purpose and has security and usability concerns.

Many thanks to Ricardo Branco (rbranco (at) suse.de) who did an
independent implementation, caught that /dev/fd/* needed to be
handled, and provided a port of the illumos test suite.  Thanks
to tb@ for assistance with that.

ok deraadt@

2 files changed, 10 insertions, 9 deletions

diff --git a/src/lib/libc/stdlib/mkstemp.c b/src/lib/libc/stdlib/mkstemp.c
index 75a9d27d1a..760575005f 100644
--- a/src/lib/libc/stdlib/mkstemp.c
+++ b/src/lib/libc/stdlib/mkstemp.c
@@ -1,4 +1,4 @@
-/*      $OpenBSD: mkstemp.c,v 1.1 2024/01/19 19:45:02 millert Exp $ */
+/*      $OpenBSD: mkstemp.c,v 1.2 2025/08/04 04:59:31 guenther Exp $ */
 /*
  * Copyright (c) 2024 Todd C. Miller
  *
@@ -20,7 +20,8 @@
 #include <fcntl.h>
 #include <stdlib.h>
 
-#define MKOSTEMP_FLAGS  (O_APPEND | O_CLOEXEC | O_DSYNC | O_RSYNC | O_SYNC)
+#define MKOSTEMP_FLAGS \
+        (O_APPEND | O_CLOEXEC | O_CLOFORK | O_DSYNC | O_RSYNC | O_SYNC)
 
 static int
 mkstemp_cb(const char *path, int flags)
diff --git a/src/lib/libc/stdlib/mktemp.3 b/src/lib/libc/stdlib/mktemp.3
index 83b7c9eb30..e57ac77717 100644
--- a/src/lib/libc/stdlib/mktemp.3
+++ b/src/lib/libc/stdlib/mktemp.3
@@ -1,4 +1,4 @@
-.\"     $OpenBSD: mktemp.3,v 1.2 2024/03/01 21:30:40 millert Exp $
+.\"     $OpenBSD: mktemp.3,v 1.3 2025/08/04 04:59:31 guenther Exp $
 .\"
 .\" Copyright (c) 1989, 1991, 1993
 .\"     The Regents of the University of California.  All rights reserved.
@@ -27,7 +27,7 @@
 .\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 .\" SUCH DAMAGE.
 .\"
-.Dd $Mdocdate: March 1 2024 $
+.Dd $Mdocdate: August 4 2025 $
 .Dt MKTEMP 3
 .Os
 .Sh NAME
@@ -119,6 +119,8 @@ system call:
 Append on each write.
 .It Dv O_CLOEXEC
 Set the close-on-exec flag on the new file descriptor.
+.It Dv O_CLOFORK
+Set the close-on-fork flag on the new file descriptor.
 .It Dv O_SYNC
 Perform synchronous I/O operations.
 .El
@@ -345,18 +347,16 @@ function.
 .Xr tmpnam 3
 .Sh STANDARDS
 The
-.Fn mkdtemp
+.Fn mkdtemp ,
+.Fn mkostemp ,
 and
 .Fn mkstemp
 functions conform to the
-.St -p1003.1-2008
+.St -p1003.1-2024
 specification.
 The ability to specify more than six
 .Em X Ns s
 is an extension to that standard.
-The
-.Fn mkostemp
-function is expected to conform to a future revision of that standard.
 .Pp
 The
 .Fn mktemp