From 4d12729aa4026229e4e118b924cc3b1c75ca214b Mon Sep 17 00:00:00 2001
From: Luke Shumaker <lukeshu@sbcglobal.net>
Date: Fri, 17 Jun 2016 20:09:33 -0400
Subject: write setuid, move things around

---
 bin/setuid.c | 108 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 108 insertions(+)
 create mode 100644 bin/setuid.c

(limited to 'bin/setuid.c')

diff --git a/bin/setuid.c b/bin/setuid.c
new file mode 100644
index 0000000..7ae1105
--- /dev/null
+++ b/bin/setuid.c
@@ -0,0 +1,108 @@
+/*
+  Copyright (C) 2006 West Consulting
+  Copyright (C) 2006-2015 Arthur de Jong
+  Copyright (C) 2015-2016 Luke Shumaker <lukeshu@sbcglobal.net>
+
+  This library is free software; you can redistribute it and/or
+  modify it under the terms of the GNU Lesser General Public
+  License as published by the Free Software Foundation; either
+  version 2.1 of the License, or (at your option) any later version.
+
+  This library is distributed in the hope that it will be useful,
+  but WITHOUT ANY WARRANTY; without even the implied warranty of
+  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+  Lesser General Public License for more details.
+
+  You should have received a copy of the GNU Lesser General Public
+  License along with this library; if not, write to the Free Software
+  Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
+  02110-1301 USA
+*/
+
+#include <dlfcn.h>             /* for dlopen(3), dlsym(3), and dlerror(3) */
+#include <errno.h>             /* for errno */
+#include <pwd.h>               /* for getpwnam(3) */
+#include <stdio.h>             /* for printf(3) and fprintf(3) */
+#include <string.h>            /* for strerror(3) */
+#include <sys/types.h>         /* for 'struct passwd' and 'struct group' */
+#include <systemd/sd-daemon.h> /* for SD_{WARNING,DEBUG} */
+#include <unistd.h>            /* for setuid(3), setgid(3), and dup2(3) */
+
+#define EXIT_SUCCESS         0
+#define EXIT_FAILURE         1
+#define EXIT_INVALIDARGUMENT 2
+#define EXIT_NOPERMISSION    4
+
+const char *nss_module_soname            = "libnss_ldap.so.2";
+const char *nss_module_sym_version       = "_nss_ldap_version";
+const char *nss_module_sym_enablelookups = "_nss_ldap_enablelookups";
+
+static void disable_nss_module(void) {
+	char *err;
+
+	dlerror();
+	void *handle = dlopen(nss_module_soname, RTLD_LAZY | RTLD_NODELETE);
+	err = dlerror();
+	if (handle == NULL) {
+		fprintf(stderr, SD_WARNING "NSS module %s not loaded: %s", nss_module_soname, err);
+		return;
+	}
+
+	dlerror();
+	char **version_info = dlsym(handle, nss_module_sym_version);
+	err = dlerror();
+	if ((version_info != NULL) && (err == NULL)) {
+		fprintf(stderr, SD_DEBUG "NSS module %s version %s %s", nss_module_soname,
+		        version_info[0],
+		        version_info[1]);
+	} else {
+		fprintf(stderr, SD_WARNING "NSS module %s version missing: %s", nss_module_soname, err);
+	}
+
+	dlerror();
+	int *enable_flag = dlsym(handle, nss_module_sym_enablelookups);
+	err = dlerror();
+	if ((enable_flag == NULL) || (err != NULL)) {
+		fprintf(stderr, SD_WARNING "Unable to disable NSS ldap module for nslcd process: %s", err);
+		dlclose(handle);
+		return;
+	}
+	*enable_flag = 0;
+	dlclose(handle);
+}
+
+void usage(char *cmd) {
+	printf("Usage: %s USERNAME COMMAND...\n", cmd);
+	printf("A simple setuid(3) wrapper that runs with the `ldap' NSS module disabled\n");
+}
+
+int main(int argc, char *argv[]) {
+	if (argc < 3) {
+		dup2(2, 1);
+		usage(argv[0]);
+		return EXIT_INVALIDARGUMENT;
+	}
+
+	disable_nss_module();
+
+	struct passwd *passwd = getpwnam(argv[1]);
+	if (passwd == NULL) {
+		fprintf(stderr, SD_ERR "Could not look up user: %s", argv[1]);
+		return EXIT_FAILURE;
+	}
+
+	if (setgid(passwd->pw_gid) != 0) {
+		fprintf(stderr, SD_ERR "Could not setgid(%lu): %s",
+		        (unsigned long int)passwd->pw_gid, strerror(errno));
+		return EXIT_NOPERMISSION;
+	}
+	if (setuid(passwd->pw_uid) != 0) {
+		fprintf(stderr, SD_ERR "Could not setuid(%lu): %s",
+		        (unsigned long int)passwd->pw_gid, strerror(errno));
+		return EXIT_NOPERMISSION;
+	}
+
+	execvp(argv[2], &argv[2]);
+	fprintf(stderr, SD_ERR "Could not exec: %s", strerror(errno));
+	return EXIT_FAILURE;
+}
-- 
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