selftests/capabilities: Add tests for capability evolution

This test focuses on ambient capabilities. It requires either root or
the ability to create user namespaces. Some of the test cases will be
skipped for nonroot users.

Signed-off-by: Andy Lutomirski <[e-mail]>
Acked-by: Kees Cook <[e-mail]>
Cc: Christoph Lameter <[e-mail]> # Original author
Cc: Serge E. Hallyn <[e-mail]>
Cc: James Morris <[e-mail]>
Cc: Shuah Khan <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

tools/testing/selftests/capabilities/.gitignore

···
+test_execve
+validate_cap

tools/testing/selftests/capabilities/Makefile

···
+all:
+
+include ../lib.mk
+
+.PHONY: all clean
+
+TARGETS := validate_cap test_execve
+TEST_PROGS := test_execve
+
+CFLAGS := -O2 -g -std=gnu99 -Wall -lcap-ng
+
+all: $(TARGETS)
+
+clean:
+	$(RM) $(TARGETS)
+
+$(TARGETS): %: %.c
+	$(CC) -o $@ $(CFLAGS) $(EXTRA_CFLAGS) $^ -lrt -ldl

tools/testing/selftests/capabilities/test_execve.c

···
+#define _GNU_SOURCE
+
+#include <cap-ng.h>
+#include <err.h>
+#include <linux/capability.h>
+#include <stdbool.h>
+#include <string.h>
+#include <stdio.h>
+#include <fcntl.h>
+#include <errno.h>
+#include <stdarg.h>
+#include <sched.h>
+#include <sys/mount.h>
+#include <limits.h>
+#include <libgen.h>
+#include <malloc.h>
+#include <sys/wait.h>
+#include <sys/prctl.h>
+#include <sys/stat.h>
+
+#ifndef PR_CAP_AMBIENT
+#define PR_CAP_AMBIENT			47
+# define PR_CAP_AMBIENT_IS_SET		1
+# define PR_CAP_AMBIENT_RAISE		2
+# define PR_CAP_AMBIENT_LOWER		3
+# define PR_CAP_AMBIENT_CLEAR_ALL	4
+#endif
+
+static int nerrs;
+
+static void vmaybe_write_file(bool enoent_ok, char *filename, char *fmt, va_list ap)
+{
+	char buf[4096];
+	int fd;
+	ssize_t written;
+	int buf_len;
+
+	buf_len = vsnprintf(buf, sizeof(buf), fmt, ap);
+	if (buf_len < 0) {
+		err(1, "vsnprintf failed");
+	}
+	if (buf_len >= sizeof(buf)) {
+		errx(1, "vsnprintf output truncated");
+	}
+
+	fd = open(filename, O_WRONLY);
+	if (fd < 0) {
+		if ((errno == ENOENT) && enoent_ok)
+			return;
+		err(1, "open of %s failed", filename);
+	}
+	written = write(fd, buf, buf_len);
+	if (written != buf_len) {
+		if (written >= 0) {
+			errx(1, "short write to %s", filename);
+		} else {
+			err(1, "write to %s failed", filename);
+		}
+	}
+	if (close(fd) != 0) {
+		err(1, "close of %s failed", filename);
+	}
+}
+
+static void maybe_write_file(char *filename, char *fmt, ...)
+{
+	va_list ap;
+
+	va_start(ap, fmt);
+	vmaybe_write_file(true, filename, fmt, ap);
+	va_end(ap);
+}
+
+static void write_file(char *filename, char *fmt, ...)
+{
+	va_list ap;
+
+	va_start(ap, fmt);
+	vmaybe_write_file(false, filename, fmt, ap);
+	va_end(ap);
+}
+
+static bool create_and_enter_ns(uid_t inner_uid)
+{
+	uid_t outer_uid;
+	gid_t outer_gid;
+	int i;
+	bool have_outer_privilege;
+
+	outer_uid = getuid();
+	outer_gid = getgid();
+
+	/*
+	 * TODO: If we're already root, we could skip creating the userns.
+	 */
+
+	if (unshare(CLONE_NEWNS) == 0) {
+		printf("[NOTE]\tUsing global UIDs for tests\n");
+		if (prctl(PR_SET_KEEPCAPS, 1, 0, 0, 0) != 0)
+			err(1, "PR_SET_KEEPCAPS");
+		if (setresuid(inner_uid, inner_uid, -1) != 0)
+			err(1, "setresuid");
+
+		// Re-enable effective caps
+		capng_get_caps_process();
+		for (i = 0; i < CAP_LAST_CAP; i++)
+			if (capng_have_capability(CAPNG_PERMITTED, i))
+				capng_update(CAPNG_ADD, CAPNG_EFFECTIVE, i);
+		if (capng_apply(CAPNG_SELECT_CAPS) != 0)
+			err(1, "capng_apply");
+
+		have_outer_privilege = true;
+	} else if (unshare(CLONE_NEWUSER | CLONE_NEWNS) == 0) {
+		printf("[NOTE]\tUsing a user namespace for tests\n");
+		maybe_write_file("/proc/self/setgroups", "deny");
+		write_file("/proc/self/uid_map", "%d %d 1", inner_uid, outer_uid);
+		write_file("/proc/self/gid_map", "0 %d 1", outer_gid);
+
+		have_outer_privilege = false;
+	} else {
+		errx(1, "must be root or be able to create a userns");
+	}
+
+	if (mount("none", "/", NULL, MS_REC | MS_PRIVATE, NULL) != 0)
+		err(1, "remount everything private");
+
+	return have_outer_privilege;
+}
+
+static void chdir_to_tmpfs(void)
+{
+	char cwd[PATH_MAX];
+	if (getcwd(cwd, sizeof(cwd)) != cwd)
+		err(1, "getcwd");
+
+	if (mount("private_tmp", ".", "tmpfs", 0, "mode=0777") != 0)
+		err(1, "mount private tmpfs");
+
+	if (chdir(cwd) != 0)
+		err(1, "chdir to private tmpfs");
+
+	if (umount2(".", MNT_DETACH) != 0)
+		err(1, "detach private tmpfs");
+}
+
+static void copy_fromat_to(int fromfd, const char *fromname, const char *toname)
+{
+	int from = openat(fromfd, fromname, O_RDONLY);
+	if (from == -1)
+		err(1, "open copy source");
+
+	int to = open(toname, O_CREAT | O_WRONLY | O_EXCL, 0700);
+
+	while (true) {
+		char buf[4096];
+		ssize_t sz = read(from, buf, sizeof(buf));
+		if (sz == 0)
+			break;
+		if (sz < 0)
+			err(1, "read");
+
+		if (write(to, buf, sz) != sz)
+			err(1, "write");	/* no short writes on tmpfs */
+	}
+
+	close(from);
+	close(to);
+}
+
+static bool fork_wait(void)
+{
+	pid_t child = fork();
+	if (child == 0) {
+		nerrs = 0;
+		return true;
+	} else if (child > 0) {
+		int status;
+		if (waitpid(child, &status, 0) != child ||
+		    !WIFEXITED(status)) {
+			printf("[FAIL]\tChild died\n");
+			nerrs++;
+		} else if (WEXITSTATUS(status) != 0) {
+			printf("[FAIL]\tChild failed\n");
+			nerrs++;
+		} else {
+			printf("[OK]\tChild succeeded\n");
+		}
+
+		return false;
+	} else {
+		err(1, "fork");
+	}
+}
+
+static void exec_other_validate_cap(const char *name,
+				    bool eff, bool perm, bool inh, bool ambient)
+{
+	execl(name, name, (eff ? "1" : "0"),
+	      (perm ? "1" : "0"), (inh ? "1" : "0"), (ambient ? "1" : "0"),
+	      NULL);
+	err(1, "execl");
+}
+
+static void exec_validate_cap(bool eff, bool perm, bool inh, bool ambient)
+{
+	exec_other_validate_cap("./validate_cap", eff, perm, inh, ambient);
+}
+
+static int do_tests(int uid, const char *our_path)
+{
+	bool have_outer_privilege = create_and_enter_ns(uid);
+
+	int ourpath_fd = open(our_path, O_RDONLY | O_DIRECTORY);
+	if (ourpath_fd == -1)
+		err(1, "open '%s'", our_path);
+
+	chdir_to_tmpfs();
+
+	copy_fromat_to(ourpath_fd, "validate_cap", "validate_cap");
+
+	if (have_outer_privilege) {
+		uid_t gid = getegid();
+
+		copy_fromat_to(ourpath_fd, "validate_cap",
+			       "validate_cap_suidroot");
+		if (chown("validate_cap_suidroot", 0, -1) != 0)
+			err(1, "chown");
+		if (chmod("validate_cap_suidroot", S_ISUID | 0700) != 0)
+			err(1, "chmod");
+
+		copy_fromat_to(ourpath_fd, "validate_cap",
+			       "validate_cap_suidnonroot");
+		if (chown("validate_cap_suidnonroot", uid + 1, -1) != 0)
+			err(1, "chown");
+		if (chmod("validate_cap_suidnonroot", S_ISUID | 0700) != 0)
+			err(1, "chmod");
+
+		copy_fromat_to(ourpath_fd, "validate_cap",
+			       "validate_cap_sgidroot");
+		if (chown("validate_cap_sgidroot", -1, 0) != 0)
+			err(1, "chown");
+		if (chmod("validate_cap_sgidroot", S_ISGID | 0710) != 0)
+			err(1, "chmod");
+
+		copy_fromat_to(ourpath_fd, "validate_cap",
+			       "validate_cap_sgidnonroot");
+		if (chown("validate_cap_sgidnonroot", -1, gid + 1) != 0)
+			err(1, "chown");
+		if (chmod("validate_cap_sgidnonroot", S_ISGID | 0710) != 0)
+			err(1, "chmod");
+}
+
+	capng_get_caps_process();
+
+	/* Make sure that i starts out clear */
+	capng_update(CAPNG_DROP, CAPNG_INHERITABLE, CAP_NET_BIND_SERVICE);
+	if (capng_apply(CAPNG_SELECT_CAPS) != 0)
+		err(1, "capng_apply");
+
+	if (uid == 0) {
+		printf("[RUN]\tRoot => ep\n");
+		if (fork_wait())
+			exec_validate_cap(true, true, false, false);
+	} else {
+		printf("[RUN]\tNon-root => no caps\n");
+		if (fork_wait())
+			exec_validate_cap(false, false, false, false);
+	}
+
+	printf("[OK]\tCheck cap_ambient manipulation rules\n");
+
+	/* We should not be able to add ambient caps yet. */
+	if (prctl(PR_CAP_AMBIENT, PR_CAP_AMBIENT_RAISE, CAP_NET_BIND_SERVICE, 0, 0, 0) != -1 || errno != EPERM) {
+		if (errno == EINVAL)
+			printf("[FAIL]\tPR_CAP_AMBIENT_RAISE isn't supported\n");
+		else
+			printf("[FAIL]\tPR_CAP_AMBIENT_RAISE should have failed eith EPERM on a non-inheritable cap\n");
+		return 1;
+	}
+	printf("[OK]\tPR_CAP_AMBIENT_RAISE failed on non-inheritable cap\n");
+
+	capng_update(CAPNG_ADD, CAPNG_INHERITABLE, CAP_NET_RAW);
+	capng_update(CAPNG_DROP, CAPNG_PERMITTED, CAP_NET_RAW);
+	capng_update(CAPNG_DROP, CAPNG_EFFECTIVE, CAP_NET_RAW);
+	if (capng_apply(CAPNG_SELECT_CAPS) != 0)
+		err(1, "capng_apply");
+	if (prctl(PR_CAP_AMBIENT, PR_CAP_AMBIENT_RAISE, CAP_NET_RAW, 0, 0, 0) != -1 || errno != EPERM) {
+		printf("[FAIL]\tPR_CAP_AMBIENT_RAISE should have failed on a non-permitted cap\n");
+		return 1;
+	}
+	printf("[OK]\tPR_CAP_AMBIENT_RAISE failed on non-permitted cap\n");
+
+	capng_update(CAPNG_ADD, CAPNG_INHERITABLE, CAP_NET_BIND_SERVICE);
+	if (capng_apply(CAPNG_SELECT_CAPS) != 0)
+		err(1, "capng_apply");
+	if (prctl(PR_CAP_AMBIENT, PR_CAP_AMBIENT_RAISE, CAP_NET_BIND_SERVICE, 0, 0, 0) != 0) {
+		printf("[FAIL]\tPR_CAP_AMBIENT_RAISE should have succeeded\n");
+		return 1;
+	}
+	printf("[OK]\tPR_CAP_AMBIENT_RAISE worked\n");
+
+	if (prctl(PR_CAP_AMBIENT, PR_CAP_AMBIENT_IS_SET, CAP_NET_BIND_SERVICE, 0, 0, 0) != 1) {
+		printf("[FAIL]\tPR_CAP_AMBIENT_IS_SET is broken\n");
+		return 1;
+	}
+
+	if (prctl(PR_CAP_AMBIENT, PR_CAP_AMBIENT_CLEAR_ALL, 0, 0, 0, 0) != 0)
+		err(1, "PR_CAP_AMBIENT_CLEAR_ALL");
+
+	if (prctl(PR_CAP_AMBIENT, PR_CAP_AMBIENT_IS_SET, CAP_NET_BIND_SERVICE, 0, 0, 0) != 0) {
+		printf("[FAIL]\tPR_CAP_AMBIENT_CLEAR_ALL didn't work\n");
+		return 1;
+	}
+
+	if (prctl(PR_CAP_AMBIENT, PR_CAP_AMBIENT_RAISE, CAP_NET_BIND_SERVICE, 0, 0, 0) != 0)
+		err(1, "PR_CAP_AMBIENT_RAISE");
+
+	capng_update(CAPNG_DROP, CAPNG_INHERITABLE, CAP_NET_BIND_SERVICE);
+	if (capng_apply(CAPNG_SELECT_CAPS) != 0)
+		err(1, "capng_apply");
+
+	if (prctl(PR_CAP_AMBIENT, PR_CAP_AMBIENT_IS_SET, CAP_NET_BIND_SERVICE, 0, 0, 0) != 0) {
+		printf("[FAIL]\tDropping I should have dropped A\n");
+		return 1;
+	}
+
+	printf("[OK]\tBasic manipulation appears to work\n");
+
+	capng_update(CAPNG_ADD, CAPNG_INHERITABLE, CAP_NET_BIND_SERVICE);
+	if (capng_apply(CAPNG_SELECT_CAPS) != 0)
+		err(1, "capng_apply");
+	if (uid == 0) {
+		printf("[RUN]\tRoot +i => eip\n");
+		if (fork_wait())
+			exec_validate_cap(true, true, true, false);
+	} else {
+		printf("[RUN]\tNon-root +i => i\n");
+		if (fork_wait())
+			exec_validate_cap(false, false, true, false);
+	}
+
+	if (prctl(PR_CAP_AMBIENT, PR_CAP_AMBIENT_RAISE, CAP_NET_BIND_SERVICE, 0, 0, 0) != 0)
+		err(1, "PR_CAP_AMBIENT_RAISE");
+
+	printf("[RUN]\tUID %d +ia => eipa\n", uid);
+	if (fork_wait())
+		exec_validate_cap(true, true, true, true);
+
+	/* The remaining tests need real privilege */
+
+	if (!have_outer_privilege) {
+		printf("[SKIP]\tSUID/SGID tests (needs privilege)\n");
+		goto done;
+	}
+
+	if (uid == 0) {
+		printf("[RUN]\tRoot +ia, suidroot => eipa\n");
+		if (fork_wait())
+			exec_other_validate_cap("./validate_cap_suidroot",
+						true, true, true, true);
+
+		printf("[RUN]\tRoot +ia, suidnonroot => ip\n");
+		if (fork_wait())
+			exec_other_validate_cap("./validate_cap_suidnonroot",
+						false, true, true, false);
+
+		printf("[RUN]\tRoot +ia, sgidroot => eipa\n");
+		if (fork_wait())
+			exec_other_validate_cap("./validate_cap_sgidroot",
+						true, true, true, true);
+
+		if (fork_wait()) {
+			printf("[RUN]\tRoot, gid != 0, +ia, sgidroot => eip\n");
+			if (setresgid(1, 1, 1) != 0)
+				err(1, "setresgid");
+			exec_other_validate_cap("./validate_cap_sgidroot",
+						true, true, true, false);
+		}
+
+		printf("[RUN]\tRoot +ia, sgidnonroot => eip\n");
+		if (fork_wait())
+			exec_other_validate_cap("./validate_cap_sgidnonroot",
+						true, true, true, false);
+	} else {
+		printf("[RUN]\tNon-root +ia, sgidnonroot => i\n");
+		exec_other_validate_cap("./validate_cap_sgidnonroot",
+						false, false, true, false);
+
+		if (fork_wait()) {
+			printf("[RUN]\tNon-root +ia, sgidroot => i\n");
+			if (setresgid(1, 1, 1) != 0)
+				err(1, "setresgid");
+			exec_other_validate_cap("./validate_cap_sgidroot",
+						false, false, true, false);
+		}
+	}
+
+done:
+	return nerrs ? 1 : 0;
+}
+
+int main(int argc, char **argv)
+{
+	char *tmp1, *tmp2, *our_path;
+
+	/* Find our path */
+	tmp1 = strdup(argv[0]);
+	if (!tmp1)
+		err(1, "strdup");
+	tmp2 = dirname(tmp1);
+	our_path = strdup(tmp2);
+	if (!our_path)
+		err(1, "strdup");
+	free(tmp1);
+
+	if (fork_wait()) {
+		printf("[RUN]\t+++ Tests with uid == 0 +++\n");
+		return do_tests(0, our_path);
+	}
+
+	if (fork_wait()) {
+		printf("[RUN]\t+++ Tests with uid != 0 +++\n");
+		return do_tests(1, our_path);
+	}
+
+	return nerrs ? 1 : 0;
+}

tools/testing/selftests/capabilities/validate_cap.c

···
+#include <cap-ng.h>
+#include <err.h>
+#include <linux/capability.h>
+#include <stdbool.h>
+#include <string.h>
+#include <stdio.h>
+#include <sys/prctl.h>
+#include <sys/auxv.h>
+
+#ifndef PR_CAP_AMBIENT
+#define PR_CAP_AMBIENT			47
+# define PR_CAP_AMBIENT_IS_SET		1
+# define PR_CAP_AMBIENT_RAISE		2
+# define PR_CAP_AMBIENT_LOWER		3
+# define PR_CAP_AMBIENT_CLEAR_ALL	4
+#endif
+
+#if __GLIBC__ > 2 || (__GLIBC__ == 2 && __GLIBC_MINOR__ >= 19)
+# define HAVE_GETAUXVAL
+#endif
+
+static bool bool_arg(char **argv, int i)
+{
+	if (!strcmp(argv[i], "0"))
+		return false;
+	else if (!strcmp(argv[i], "1"))
+		return true;
+	else
+		errx(1, "wrong argv[%d]", i);
+}
+
+int main(int argc, char **argv)
+{
+	const char *atsec = "";
+
+	/*
+	 * Be careful just in case a setgid or setcapped copy of this
+	 * helper gets out.
+	 */
+
+	if (argc != 5)
+		errx(1, "wrong argc");
+
+#ifdef HAVE_GETAUXVAL
+	if (getauxval(AT_SECURE))
+		atsec = " (AT_SECURE is set)";
+	else
+		atsec = " (AT_SECURE is not set)";
+#endif
+
+	capng_get_caps_process();
+
+	if (capng_have_capability(CAPNG_EFFECTIVE, CAP_NET_BIND_SERVICE) != bool_arg(argv, 1)) {
+		printf("[FAIL]\tWrong effective state%s\n", atsec);
+		return 1;
+	}
+	if (capng_have_capability(CAPNG_PERMITTED, CAP_NET_BIND_SERVICE) != bool_arg(argv, 2)) {
+		printf("[FAIL]\tWrong permitted state%s\n", atsec);
+		return 1;
+	}
+	if (capng_have_capability(CAPNG_INHERITABLE, CAP_NET_BIND_SERVICE) != bool_arg(argv, 3)) {
+		printf("[FAIL]\tWrong inheritable state%s\n", atsec);
+		return 1;
+	}
+
+	if (prctl(PR_CAP_AMBIENT, PR_CAP_AMBIENT_IS_SET, CAP_NET_BIND_SERVICE, 0, 0, 0) != bool_arg(argv, 4)) {
+		printf("[FAIL]\tWrong ambient state%s\n", atsec);
+		return 1;
+	}
+
+	printf("[OK]\tCapabilities after execve were correct\n");
+	return 0;
+}