util/mkhtemp: new utility (hardened mktemp)

part of the same code library as nvmutil.

as part of this, i renamed util/nvmutil
to util/libreboot-utils/ because it is
now a multi-utility codebase.

this is more efficient, since i also wish
to use mkhtemp (function) in nvmutil.

Signed-off-by: Leah Rowe <leah@libreboot.org>

include/inject.sh

@@ -6,7 +6,7 @@
 
 cbcfgsdir="config/coreboot"
 tmpromdel="$XBMK_CACHE/DO_NOT_FLASH"
-nvmutil="util/nvmutil/nvmutil"
+nvmutil="util/libreboot-utils/nvmutil"
 ifdtool="elf/coreboot/default/ifdtool"
 
 checkvars="CONFIG_GBE_BIN_PATH"
@@ -197,8 +197,8 @@ modify_mac()
 	x_ cp "${CONFIG_GBE_BIN_PATH##*../}" "$xbtmp/gbe"
 
 	if [ -n "$new_mac" ] && [ "$new_mac" != "restore" ]; then
-		x_ make -C util/nvmutil clean
-		x_ make -C util/nvmutil
+		x_ make -C util/libreboot-utils clean
+		x_ make -C util/libreboot-utils
 
 		x_ "$nvmutil" "$xbtmp/gbe" setmac "$new_mac"
 	fi

util/libreboot-utils/.gitignore

@@ -1,5 +1,6 @@
 /nvm
 /nvmutil
+/mkhtemp
 *.bin
 *.o
 *.d

util/libreboot-utils/Makefile

@@ -24,8 +24,9 @@ STRICT = $(WARN) -std=c90 -pedantic -Werror
 HELLFLAGS = $(STRICT) -Weverything
 
 PROG = nvmutil
+PROGMKH = mkhtemp
 
-OBJS = \
+OBJS_NVMUTIL = \
 	obj/nvmutil.o \
 	obj/lib/state.o \
 	obj/lib/file.o \
@@ -38,17 +39,28 @@ OBJS = \
 	obj/lib/word.o \
 	obj/lib/mkhtemp.o
 
+OBJS_MKHTEMP = \
+	obj/mkhtemp.o \
+	obj/lib/file.o \
+	obj/lib/string.o \
+	obj/lib/num.o \
+	obj/lib/mkhtemp.o
+
 # default mode
 CFLAGS_MODE = $(PORTABLE)
 CC_MODE = $(CC)
 
-all: $(PROG)
+all: $(PROG) $(PROGMKH)
 
-$(PROG): $(OBJS)
-	$(CC_MODE) $(OBJS) -o $(PROG) $(LDFLAGS)
+$(PROG): $(OBJS_NVMUTIL)
+	$(CC_MODE) $(OBJS_NVMUTIL) -o $(PROG) $(LDFLAGS)
+
+$(PROGMKH): $(OBJS_MKHTEMP)
+	$(CC_MODE) $(OBJS_MKHTEMP) -o $(PROGMKH) $(LDFLAGS)
 
 # ensure obj directory exists
-$(OBJS): obj
+$(OBJS_NVMUTIL): obj
+$(OBJS_MKHTEMP): obj
 
 obj:
 	mkdir obj || true
@@ -59,6 +71,9 @@ obj:
 obj/nvmutil.o: nvmutil.c
 	$(CC_MODE) $(CFLAGS_MODE) -c nvmutil.c -o obj/nvmutil.o
 
+obj/mkhtemp.o: mkhtemp.c
+	$(CC_MODE) $(CFLAGS_MODE) -c mkhtemp.c -o obj/mkhtemp.o
+
 # library/helper objects
 
 obj/lib/state.o: lib/state.c
@@ -93,16 +108,19 @@ obj/lib/mkhtemp.o: lib/mkhtemp.c
 
 # install
 
-install: $(PROG)
+install: $(PROG) $(PROGMKH)
 	$(INSTALL) -d $(DESTDIR)$(PREFIX)/bin
 	$(INSTALL) $(PROG) $(DESTDIR)$(PREFIX)/bin/$(PROG)
 	chmod 755 $(DESTDIR)$(PREFIX)/bin/$(PROG)
+	$(INSTALL) $(PROGMKH) $(DESTDIR)$(PREFIX)/bin/$(PROGMKH)
+	chmod 755 $(DESTDIR)$(PREFIX)/bin/$(PROGMKH)
 
 uninstall:
 	rm -f $(DESTDIR)$(PREFIX)/bin/$(PROG)
+	rm -f $(DESTDIR)$(PREFIX)/bin/$(PROGMKH)
 
 clean:
-	rm -f $(PROG) $(OBJS)
+	rm -f $(PROG) $(PROGMKH) $(OBJS_NVMUTIL) $(OBJS_MKHTEMP)
 
 distclean: clean
 

util/libreboot-utils/include/common.h

@@ -1,5 +1,9 @@
 /* SPDX-License-Identifier: MIT
  * Copyright (c) 2022-2026 Leah Rowe <leah@libreboot.org>
+
+ TODO: this file should be split, into headers for each
+       C source file specifically. it was originally just
+       for nvmutil, until i added mkhtemp to the mix
  */
 
 
@@ -495,8 +499,8 @@ const char *getnvmprogname(void);
 
 int new_tmpfile(int *fd, char **path);
 int new_tmpdir(int *fd, char **path);
-static int new_tmp_common(int *fd, char **path, int type);
-static int mkhtemp_try_create(int dirfd,
+int new_tmp_common(int *fd, char **path, int type);
+int mkhtemp_try_create(int dirfd,
     struct stat *st_dir_initial,
     char *fname_copy,
     char *p,

util/libreboot-utils/lib/mkhtemp.c

@@ -39,7 +39,7 @@ new_tmpdir(int *fd, char **path)
 	return new_tmp_common(fd, path, MKHTEMP_DIR);
 }
 
-static int
+int
 new_tmp_common(int *fd, char **path, int type)
 {
 #if defined(PATH_LEN) && \
@@ -466,13 +466,13 @@ sticky_hell:
 /* mk(h)temp - hardened mktemp.
  * like mkstemp, but (MUCH) harder.
  *
- * designed to resist TOCTOU attacsk
+ * designed to resist TOCTOU attacks
  * e.g. directory race / symlink attack
  * 
  * extremely strict and even implements
  * some limited userspace-level sandboxing,
- * similar to openbsd unveil (which you
- * can also use with this in your program)
+ * similar in spirit to openbsd unveil,
+ * though unveil is from kernel space.
  *
  * supports both files and directories.
  * file: type = MKHTEMP_FILE (0)
@@ -661,7 +661,7 @@ success:
 	return (*fd >= 0) ? *fd : -1;
 }
 
-static int
+int
 mkhtemp_try_create(int dirfd,
     struct stat *st_dir_initial,
     char *fname_copy,

util/libreboot-utils/lib/state.c

@@ -152,33 +152,6 @@ xstatus(void)
 	return x;
 }
 
-/* early init functions that
-   should not access state
-   WARNING:
-   does not do cleanup. only
-   call this during pre-init
- */
-void
-err_no_cleanup(int nvm_errval, const char *msg, ...)
-{
-	va_list args;
-
-	if (errno == 0)
-		errno = nvm_errval;
-	if (!errno)
-		errno = ECANCELED;
-
-	fprintf(stderr, "nvmutil: ");
-
-	va_start(args, msg);
-	vfprintf(stderr, msg, args);
-	va_end(args);
-
-	fprintf(stderr, ": %s\n", strerror(errno));
-
-	exit(EXIT_FAILURE);
-}
-
 void
 err(int nvm_errval, const char *msg, ...)
 {

util/libreboot-utils/lib/string.c

@@ -8,8 +8,11 @@
 #include <sys/stat.h>
 
 #include <errno.h>
+#include <stdarg.h>
 #include <stddef.h>
+#include <stdio.h>
 #include <string.h>
+#include <stdlib.h>
 #include <unistd.h>
 
 #include "../include/common.h"
@@ -112,3 +115,32 @@ slen(const char *s,
 	*rval = ch;
 	return 0;
 }
+
+/* the one for nvmutil state is in state.c */
+/* this one just exits */
+void
+err_no_cleanup(int nvm_errval, const char *msg, ...)
+{
+	va_list args;
+
+#if defined(__OpenBSD__) && defined(OpenBSD)
+#if (OpenBSD) >= 509
+	if (pledge("stdio", NULL) == -1)
+		fprintf(stderr, "pledge failure during exit");
+#endif
+#endif
+
+	if (!errno)
+		errno = ECANCELED;
+
+	fprintf(stderr, "nvmutil: ");
+
+	va_start(args, msg);
+	vfprintf(stderr, msg, args);
+	va_end(args);
+
+	fprintf(stderr, ": %s\n", strerror(errno));
+
+	exit(EXIT_FAILURE);
+}
+

util/libreboot-utils/mkhtemp.c

@@ -0,0 +1,139 @@
+/* SPDX-License-Identifier: MIT
+ * Copyright (c) 2026 Leah Rowe <leah@libreboot.org>
+ *
+ * WORK IN PROGRESS (proof of concept), or, v0.0000001
+ *
+ * Mkhtemp - Hardened mktemp. Create files and directories
+ * randomly as determined by user's TMPDIR, or fallback. It
+ * attemps to provide mitigation against several TOCTOU-based
+ * attacks e.g. directory rename / symlink attacks, and it
+ * generally provides much higher strictness than previous
+ * implementations such as mktemp, mkstemp or even mkdtemp.
+ *
+ * Many programs rely on mktemp, and they use TMPDIR in a way
+ * that is quite insecure. Mkhtemp intends to change that,
+ * quite dramatically, with: userspace sandbox (and use OS
+ * level options e.g. OBSD pledge where available), constant
+ * identity/ownership checks on files, MUCH stricter ownership
+ * restrictions (e.g. enforce sticky bit policy on world-
+ * writeable tmpdirs), preventing operation on other people's
+ * files (only your own files) - even root is restricted,
+ * depending on how the code is compiled. Please read the code.
+ *
+ * This is the utility version, which makes use of the also-
+ * included library. No docs yet - source code are the docs,
+ * and the (ever evolving, and hardening) specification.
+ *
+ * This was written from scratch, for use in nvmutil, and
+ * it is designed to be portable (BSD, Linux). Patches
+ * very much welcome.
+ *
+ * WARNING: This is MUCH stricter than every other mktemp
+ *          implementation, even more so than mkdtemp or
+ *          the OpenBSD version of mkstemp. It *will* break,
+ *	    or more specifically, reveal the flaws in, almost
+ *	    every major critical infrastructure, because most
+ *	    people already use mktemp extremely insecurely.
+ *
+ * This tool is written by me, for me, and also Libreboot, but
+ * it will be summitted for review to various Linux distros
+ * and BSD projects once it has reached maturity.
+ */
+
+#if defined(__linux__) && !defined(_GNU_SOURCE)
+/* for openat2 on linux */
+#define _GNU_SOURCE 1
+#endif
+
+#ifdef __OpenBSD__
+#include <sys/param.h> /* pledge(2) */
+#endif
+
+#include <sys/types.h>
+#include <sys/stat.h>
+
+#include <errno.h>
+#include <fcntl.h>
+#include <limits.h>
+#include <stdarg.h>
+#include <stddef.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+
+#include "include/common.h"
+
+int
+main(int argc, char *argv[])
+{
+	char *s = NULL;
+	int fd = -1;
+	char c;
+	int type = MKHTEMP_FILE;
+	size_t len;
+
+#if defined (PATH_LEN) && \
+    (PATH_LEN) >= 256
+	size_t maxlen = PATH_LEN;
+#else
+	size_t maxlen = 4096;
+#endif
+
+/* https://man.openbsd.org/pledge.2 */
+#if defined(__OpenBSD__) && defined(OpenBSD)
+#if (OpenBSD) >= 509
+	if (pledge("stdio flock rpath wpath cpath", NULL) == -1)
+		err_no_cleanup(errno, "pledge, main");
+#endif
+#endif
+
+	while ((c = 
+	    getopt(argc, argv, "d")) != -1) {
+
+		switch(c) {
+		case 'd':
+
+			type = MKHTEMP_DIR;
+			break;
+		default:
+
+			err_no_cleanup(EINVAL,
+			    "usage: mkhtemp [-d]\n");
+		}
+	}
+
+	if (new_tmp_common(&fd, &s, type) < 0)
+		err_no_cleanup(errno, NULL);
+
+#if defined(__OpenBSD__) && defined(OpenBSD)
+#if (OpenBSD) >= 509
+	if (pledge("stdio", NULL) == -1)
+		err_no_cleanup(errno, "pledge, exit");
+#endif
+#endif
+
+	if (s == NULL)
+		err_no_cleanup(EFAULT, "bad string initialisation");
+
+	if (*s == '\0')
+		err_no_cleanup(EFAULT, "empty string initialisation");
+
+	if (slen(s, maxlen, &len) < 0)
+		err_no_cleanup(EFAULT, "unterminated string initialisation");
+
+	printf("%s\n", s);
+
+	return EXIT_SUCCESS;
+}/* 
+
+
+  ( >:3 )    
+   /| |\
+    / \
+
+
+
+
+
+                                                                             */

util/libreboot-utils/nvmutil.c

@@ -35,16 +35,6 @@ main(int argc, char *argv[])
 
 	size_t c;
 
-	int rval;
-	char *test = NULL;
-	int fd = -1;
-	rval = new_tmpdir(&fd, &test);
-	if (rval < 0)
-		err_no_cleanup(errno, "TESTERR: ");
-
-	printf("TEST: %s\n", test);
-	exit(1);
-
 /* https://man.openbsd.org/pledge.2
    https://man.openbsd.org/unveil.2     */
 #if defined(__OpenBSD__) && defined(OpenBSD)