LSM: SafeSetID: selftest cleanup and prepare for GIDs

Add some notes on how to run the test, update the policy file paths to
reflect recent upstream changes, prepare test for adding GID testing.
Signed-off-by: Micah Morton <mortonm@chromium.org>

tools/testing/selftests/safesetid/Makefile

 # SPDX-License-Identifier: GPL-2.0
-# Makefile for mount selftests.
+# Makefile for SafeSetID selftest.
 CFLAGS = -Wall -O2
 LDLIBS = -lcap
 

tools/testing/selftests/safesetid/safesetid-test.c

@@ -16,17 +16,28 @@
 #include <stdbool.h>
 #include <stdarg.h>
 
+/*
+ * NOTES about this test:
+ * - requries libcap-dev to be installed on test system
+ * - requires securityfs to me mounted at /sys/kernel/security, e.g.:
+ * mount -n -t securityfs -o nodev,noexec,nosuid securityfs /sys/kernel/security
+ * - needs CONFIG_SECURITYFS and CONFIG_SAFESETID to be enabled
+ */
+
 #ifndef CLONE_NEWUSER
 # define CLONE_NEWUSER 0x10000000
 #endif
 
-#define ROOT_USER 0
-#define RESTRICTED_PARENT 1
-#define ALLOWED_CHILD1 2
-#define ALLOWED_CHILD2 3
-#define NO_POLICY_USER 4
+#define ROOT_UGID 0
+#define RESTRICTED_PARENT_UGID 1
+#define ALLOWED_CHILD1_UGID 2
+#define ALLOWED_CHILD2_UGID 3
+#define NO_POLICY_UGID 4
+
+#define UGID_POLICY_STRING "1:2\n1:3\n2:2\n3:3\n"
 
-char* add_whitelist_policy_file = "/sys/kernel/security/safesetid/add_whitelist_policy";
+char* add_uid_whitelist_policy_file = "/sys/kernel/security/safesetid/uid_allowlist_policy";
+char* add_gid_whitelist_policy_file = "/sys/kernel/security/safesetid/gid_allowlist_policy";
 
 static void die(char *fmt, ...)
 {
@@ -106,7 +117,7 @@ static void ensure_user_exists(uid_t uid)
 			die("couldn't open file\n");
 		if (fseek(fd, 0, SEEK_END))
 			die("couldn't fseek\n");
-		snprintf(name_str, 10, "%d", uid);
+		snprintf(name_str, 10, "user %d", uid);
 		p.pw_name=name_str;
 		p.pw_uid=uid;
 		p.pw_gecos="Test account";
@@ -122,7 +133,7 @@ static void ensure_user_exists(uid_t uid)
 
 static void ensure_securityfs_mounted(void)
 {
-	int fd = open(add_whitelist_policy_file, O_WRONLY);
+	int fd = open(add_uid_whitelist_policy_file, O_WRONLY);
 	if (fd < 0) {
 		if (errno == ENOENT) {
 			// Need to mount securityfs
@@ -135,36 +146,32 @@ static void ensure_securityfs_mounted(void)
 	} else {
 		if (close(fd) != 0) {
 			die("close of %s failed: %s\n",
-				add_whitelist_policy_file, strerror(errno));
+				add_uid_whitelist_policy_file, strerror(errno));
 		}
 	}
 }
 
-static void write_policies(void)
+static void write_uid_policies()
 {
-	static char *policy_str =
-		"1:2\n"
-		"1:3\n"
-		"2:2\n"
-		"3:3\n";
+	static char *policy_str = UGID_POLICY_STRING;
 	ssize_t written;
 	int fd;
 
-	fd = open(add_whitelist_policy_file, O_WRONLY);
+	fd = open(add_uid_whitelist_policy_file, O_WRONLY);
 	if (fd < 0)
-		die("can't open add_whitelist_policy file\n");
+		die("can't open add_uid_whitelist_policy file\n");
 	written = write(fd, policy_str, strlen(policy_str));
 	if (written != strlen(policy_str)) {
 		if (written >= 0) {
-			die("short write to %s\n", add_whitelist_policy_file);
+			die("short write to %s\n", add_uid_whitelist_policy_file);
 		} else {
 			die("write to %s failed: %s\n",
-				add_whitelist_policy_file, strerror(errno));
+				add_uid_whitelist_policy_file, strerror(errno));
 		}
 	}
 	if (close(fd) != 0) {
 		die("close of %s failed: %s\n",
-			add_whitelist_policy_file, strerror(errno));
+			add_uid_whitelist_policy_file, strerror(errno));
 	}
 }
 
@@ -260,11 +267,11 @@ static void test_setuid(uid_t child_uid, bool expect_success)
 
 static void ensure_users_exist(void)
 {
-	ensure_user_exists(ROOT_USER);
-	ensure_user_exists(RESTRICTED_PARENT);
-	ensure_user_exists(ALLOWED_CHILD1);
-	ensure_user_exists(ALLOWED_CHILD2);
-	ensure_user_exists(NO_POLICY_USER);
+	ensure_user_exists(ROOT_UGID);
+	ensure_user_exists(RESTRICTED_PARENT_UGID);
+	ensure_user_exists(ALLOWED_CHILD1_UGID);
+	ensure_user_exists(ALLOWED_CHILD2_UGID);
+	ensure_user_exists(NO_POLICY_UGID);
 }
 
 static void drop_caps(bool setid_retained)
@@ -285,39 +292,38 @@ int main(int argc, char **argv)
 {
 	ensure_users_exist();
 	ensure_securityfs_mounted();
-	write_policies();
+	write_uid_policies();
 
 	if (prctl(PR_SET_KEEPCAPS, 1L))
 		die("Error with set keepcaps\n");
 
-	// First test to make sure we can write userns mappings from a user
-	// that doesn't have any restrictions (as long as it has CAP_SETUID);
-	if (setuid(NO_POLICY_USER) < 0)
-		die("Error with set uid(%d)\n", NO_POLICY_USER);
-	if (setgid(NO_POLICY_USER) < 0)
-		die("Error with set gid(%d)\n", NO_POLICY_USER);
-
+	// First test to make sure we can write userns mappings from a non-root
+	// user that doesn't have any restrictions (as long as it has
+	// CAP_SETUID);
+	if (setgid(NO_POLICY_UGID) < 0)
+		die("Error with set gid(%d)\n", NO_POLICY_UGID);
+	if (setuid(NO_POLICY_UGID) < 0)
+		die("Error with set uid(%d)\n", NO_POLICY_UGID);
 	// Take away all but setid caps
 	drop_caps(true);
-
 	// Need PR_SET_DUMPABLE flag set so we can write /proc/[pid]/uid_map
 	// from non-root parent process.
 	if (prctl(PR_SET_DUMPABLE, 1, 0, 0, 0))
 		die("Error with set dumpable\n");
-
 	if (!test_userns(true)) {
 		die("test_userns failed when it should work\n");
 	}
 
-	if (setuid(RESTRICTED_PARENT) < 0)
-		die("Error with set uid(%d)\n", RESTRICTED_PARENT);
-	if (setgid(RESTRICTED_PARENT) < 0)
-		die("Error with set gid(%d)\n", RESTRICTED_PARENT);
+	// Now switch to a user/group with restrictions
+	if (setgid(RESTRICTED_PARENT_UGID) < 0)
+		die("Error with set gid(%d)\n", RESTRICTED_PARENT_UGID);
+	if (setuid(RESTRICTED_PARENT_UGID) < 0)
+		die("Error with set uid(%d)\n", RESTRICTED_PARENT_UGID);
 
-	test_setuid(ROOT_USER, false);
-	test_setuid(ALLOWED_CHILD1, true);
-	test_setuid(ALLOWED_CHILD2, true);
-	test_setuid(NO_POLICY_USER, false);
+	test_setuid(ROOT_UGID, false);
+	test_setuid(ALLOWED_CHILD1_UGID, true);
+	test_setuid(ALLOWED_CHILD2_UGID, true);
+	test_setuid(NO_POLICY_UGID, false);
 
 	if (!test_userns(false)) {
 		die("test_userns worked when it should fail\n");
@@ -331,5 +337,6 @@ int main(int argc, char **argv)
 
 	// NOTE: this test doesn't clean up users that were created in
 	// /etc/passwd or flush policies that were added to the LSM.
+	printf("test successful!\n");
 	return EXIT_SUCCESS;
 }