execveat.c

// SPDX-License-Identifier: GPL-2.0-only
/*
 * Copyright (c) 2014 Google, Inc.
 *
 * Selftests for execveat(2).
 */

#ifndef _GNU_SOURCE
#define _GNU_SOURCE  /* to get O_PATH, AT_EMPTY_PATH */
#endif
#include <sys/sendfile.h>
#include <sys/stat.h>
#include <sys/syscall.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <errno.h>
#include <fcntl.h>
#include <limits.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>

#include "../kselftest.h"

#define TESTS_EXPECTED 54
#define TEST_NAME_LEN (PATH_MAX * 4)

#define CHECK_COMM "CHECK_COMM"

static char longpath[2 * PATH_MAX] = "";
static char *envp[] = { "IN_TEST=yes", NULL, NULL };
static char *argv[] = { "execveat", "99", NULL };

static int execveat_(int fd, const char *path, char **argv, char **envp,
		     int flags)
{
#ifdef __NR_execveat
	return syscall(__NR_execveat, fd, path, argv, envp, flags);
#else
	errno = ENOSYS;
	return -1;
#endif
}

#define check_execveat_fail(fd, path, flags, errno)	\
	_check_execveat_fail(fd, path, flags, errno, #errno)
static int _check_execveat_fail(int fd, const char *path, int flags,
				int expected_errno, const char *errno_str)
{
	char test_name[TEST_NAME_LEN];
	int rc;

	errno = 0;
	snprintf(test_name, sizeof(test_name),
		 "Check failure of execveat(%d, '%s', %d) with %s",
		 fd, path?:"(null)", flags, errno_str);
	rc = execveat_(fd, path, argv, envp, flags);

	if (rc > 0) {
		ksft_print_msg("unexpected success from execveat(2)\n");
		ksft_test_result_fail("%s\n", test_name);
		return 1;
	}
	if (errno != expected_errno) {
		ksft_print_msg("expected errno %d (%s) not %d (%s)\n",
			       expected_errno, strerror(expected_errno),
			       errno, strerror(errno));
		ksft_test_result_fail("%s\n", test_name);
		return 1;
	}
	ksft_test_result_pass("%s\n", test_name);
	return 0;
}

static int check_execveat_invoked_rc(int fd, const char *path, int flags,
				     int expected_rc, int expected_rc2)
{
	char test_name[TEST_NAME_LEN];
	int status;
	int rc;
	pid_t child;
	int pathlen = path ? strlen(path) : 0;

	if (pathlen > 40)
		snprintf(test_name, sizeof(test_name),
			 "Check success of execveat(%d, '%.20s...%s', %d)... ",
			 fd, path, (path + pathlen - 20), flags);
	else
		snprintf(test_name, sizeof(test_name),
			 "Check success of execveat(%d, '%s', %d)... ",
			 fd, path?:"(null)", flags);

	child = fork();
	if (child < 0) {
		ksft_perror("fork() failed");
		ksft_test_result_fail("%s\n", test_name);
		return 1;
	}
	if (child == 0) {
		/* Child: do execveat(). */
		rc = execveat_(fd, path, argv, envp, flags);
		ksft_print_msg("child execveat() failed, rc=%d errno=%d (%s)\n",
			       rc, errno, strerror(errno));
		exit(errno);
	}
	/* Parent: wait for & check child's exit status. */
	rc = waitpid(child, &status, 0);
	if (rc != child) {
		ksft_print_msg("waitpid(%d,...) returned %d\n", child, rc);
		ksft_test_result_fail("%s\n", test_name);
		return 1;
	}
	if (!WIFEXITED(status)) {
		ksft_print_msg("child %d did not exit cleanly, status=%08x\n",
			       child, status);
		ksft_test_result_fail("%s\n", test_name);
		return 1;
	}
	if ((WEXITSTATUS(status) != expected_rc) &&
	    (WEXITSTATUS(status) != expected_rc2)) {
		ksft_print_msg("child %d exited with %d neither %d nor %d\n",
			       child, WEXITSTATUS(status), expected_rc,
			       expected_rc2);
		ksft_test_result_fail("%s\n", test_name);
		return 1;
	}
	ksft_test_result_pass("%s\n", test_name);
	return 0;
}

static int check_execveat(int fd, const char *path, int flags)
{
	return check_execveat_invoked_rc(fd, path, flags, 99, 99);
}

static char *concat(const char *left, const char *right)
{
	char *result = malloc(strlen(left) + strlen(right) + 1);

	strcpy(result, left);
	strcat(result, right);
	return result;
}

static int open_or_die(const char *filename, int flags)
{
	int fd = open(filename, flags);

	if (fd < 0)
		ksft_exit_fail_msg("Failed to open '%s'; "
			"check prerequisites are available\n", filename);
	return fd;
}

static void exe_cp(const char *src, const char *dest)
{
	int in_fd = open_or_die(src, O_RDONLY);
	int out_fd = open(dest, O_RDWR|O_CREAT|O_TRUNC, 0755);
	struct stat info;

	fstat(in_fd, &info);
	sendfile(out_fd, in_fd, NULL, info.st_size);
	close(in_fd);
	close(out_fd);
}

#define XX_DIR_LEN 200
static int check_execveat_pathmax(int root_dfd, const char *src, int is_script)
{
	int fail = 0;
	int ii, count, len;
	char longname[XX_DIR_LEN + 1];
	int fd;

	if (*longpath == '\0') {
		/* Create a filename close to PATH_MAX in length */
		char *cwd = getcwd(NULL, 0);

		if (!cwd) {
			ksft_perror("Failed to getcwd()");
			return 2;
		}
		strcpy(longpath, cwd);
		strcat(longpath, "/");
		memset(longname, 'x', XX_DIR_LEN - 1);
		longname[XX_DIR_LEN - 1] = '/';
		longname[XX_DIR_LEN] = '\0';
		count = (PATH_MAX - 3 - strlen(cwd)) / XX_DIR_LEN;
		for (ii = 0; ii < count; ii++) {
			strcat(longpath, longname);
			mkdir(longpath, 0755);
		}
		len = (PATH_MAX - 3 - strlen(cwd)) - (count * XX_DIR_LEN);
		if (len <= 0)
			len = 1;
		memset(longname, 'y', len);
		longname[len] = '\0';
		strcat(longpath, longname);
		free(cwd);
	}
	exe_cp(src, longpath);

	/*
	 * Execute as a pre-opened file descriptor, which works whether this is
	 * a script or not (because the interpreter sees a filename like
	 * "/dev/fd/20").
	 */
	fd = open(longpath, O_RDONLY);
	if (fd > 0) {
		ksft_print_msg("Invoke copy of '%s' via filename of length %zu:\n",
			       src, strlen(longpath));
		fail += check_execveat(fd, "", AT_EMPTY_PATH);
	} else {
		ksft_print_msg("Failed to open length %zu filename, errno=%d (%s)\n",
			       strlen(longpath), errno, strerror(errno));
		fail++;
	}

	/*
	 * Execute as a long pathname relative to "/".  If this is a script,
	 * the interpreter will launch but fail to open the script because its
	 * name ("/dev/fd/5/xxx....") is bigger than PATH_MAX.
	 *
	 * The failure code is usually 127 (POSIX: "If a command is not found,
	 * the exit status shall be 127."), but some systems give 126 (POSIX:
	 * "If the command name is found, but it is not an executable utility,
	 * the exit status shall be 126."), so allow either.
	 */
	if (is_script) {
		ksft_print_msg("Invoke script via root_dfd and relative filename\n");
		fail += check_execveat_invoked_rc(root_dfd, longpath + 1, 0,
						  127, 126);
	} else {
		ksft_print_msg("Invoke exec via root_dfd and relative filename\n");
		fail += check_execveat(root_dfd, longpath + 1, 0);
	}

	return fail;
}

static int check_execveat_comm(int fd, char *argv0, char *expected)
{
	char buf[128], *old_env, *old_argv0;
	int ret;

	snprintf(buf, sizeof(buf), CHECK_COMM "=%s", expected);

	old_env = envp[1];
	envp[1] = buf;

	old_argv0 = argv[0];
	argv[0] = argv0;

	ksft_print_msg("Check execveat(AT_EMPTY_PATH)'s comm is %s\n",
		       expected);
	ret = check_execveat_invoked_rc(fd, "", AT_EMPTY_PATH, 0, 0);

	envp[1] = old_env;
	argv[0] = old_argv0;

	return ret;
}

static int run_tests(void)
{
	int fail = 0;
	char *fullname = realpath("execveat", NULL);
	char *fullname_script = realpath("script", NULL);
	char *fullname_symlink = concat(fullname, ".symlink");
	int subdir_dfd = open_or_die("subdir", O_DIRECTORY|O_RDONLY);
	int subdir_dfd_ephemeral = open_or_die("subdir.ephemeral",
					       O_DIRECTORY|O_RDONLY);
	int dot_dfd = open_or_die(".", O_DIRECTORY|O_RDONLY);
	int root_dfd = open_or_die("/", O_DIRECTORY|O_RDONLY);
	int dot_dfd_path = open_or_die(".", O_DIRECTORY|O_RDONLY|O_PATH);
	int dot_dfd_cloexec = open_or_die(".", O_DIRECTORY|O_RDONLY|O_CLOEXEC);
	int fd = open_or_die("execveat", O_RDONLY);
	int fd_path = open_or_die("execveat", O_RDONLY|O_PATH);
	int fd_symlink = open_or_die("execveat.symlink", O_RDONLY);
	int fd_denatured = open_or_die("execveat.denatured", O_RDONLY);
	int fd_denatured_path = open_or_die("execveat.denatured",
					    O_RDONLY|O_PATH);
	int fd_script = open_or_die("script", O_RDONLY);
	int fd_ephemeral = open_or_die("execveat.ephemeral", O_RDONLY);
	int fd_ephemeral_path = open_or_die("execveat.path.ephemeral",
					    O_RDONLY|O_PATH);
	int fd_script_ephemeral = open_or_die("script.ephemeral", O_RDONLY);
	int fd_cloexec = open_or_die("execveat", O_RDONLY|O_CLOEXEC);
	int fd_script_cloexec = open_or_die("script", O_RDONLY|O_CLOEXEC);

	/* Check if we have execveat at all, and bail early if not */
	errno = 0;
	execveat_(-1, NULL, NULL, NULL, 0);
	if (errno == ENOSYS) {
		ksft_exit_skip(
			"ENOSYS calling execveat - no kernel support?\n");
	}

	/* Change file position to confirm it doesn't affect anything */
	lseek(fd, 10, SEEK_SET);

	/* Normal executable file: */
	/*   dfd + path */
	fail += check_execveat(subdir_dfd, "../execveat", 0);
	fail += check_execveat(dot_dfd, "execveat", 0);
	fail += check_execveat(dot_dfd_path, "execveat", 0);
	/*   absolute path */
	fail += check_execveat(AT_FDCWD, fullname, 0);
	/*   absolute path with nonsense dfd */
	fail += check_execveat(99, fullname, 0);
	/*   fd + no path */
	fail += check_execveat(fd, "", AT_EMPTY_PATH);
	/*   O_CLOEXEC fd + no path */
	fail += check_execveat(fd_cloexec, "", AT_EMPTY_PATH);
	/*   O_PATH fd */
	fail += check_execveat(fd_path, "", AT_EMPTY_PATH);

	/* Mess with executable file that's already open: */
	/*   fd + no path to a file that's been renamed */
	rename("execveat.ephemeral", "execveat.moved");
	fail += check_execveat(fd_ephemeral, "", AT_EMPTY_PATH);
	/*   fd + no path to a file that's been deleted */
	unlink("execveat.moved"); /* remove the file now fd open */
	fail += check_execveat(fd_ephemeral, "", AT_EMPTY_PATH);

	/* Mess with executable file that's already open with O_PATH */
	/*   fd + no path to a file that's been deleted */
	unlink("execveat.path.ephemeral");
	fail += check_execveat(fd_ephemeral_path, "", AT_EMPTY_PATH);

	/* Invalid argument failures */
	fail += check_execveat_fail(fd, "", 0, ENOENT);
	fail += check_execveat_fail(fd, NULL, AT_EMPTY_PATH, EFAULT);

	/* Symlink to executable file: */
	/*   dfd + path */
	fail += check_execveat(dot_dfd, "execveat.symlink", 0);
	fail += check_execveat(dot_dfd_path, "execveat.symlink", 0);
	/*   absolute path */
	fail += check_execveat(AT_FDCWD, fullname_symlink, 0);
	/*   fd + no path, even with AT_SYMLINK_NOFOLLOW (already followed) */
	fail += check_execveat(fd_symlink, "", AT_EMPTY_PATH);
	fail += check_execveat(fd_symlink, "",
			       AT_EMPTY_PATH|AT_SYMLINK_NOFOLLOW);

	/* Symlink fails when AT_SYMLINK_NOFOLLOW set: */
	/*   dfd + path */
	fail += check_execveat_fail(dot_dfd, "execveat.symlink",
				    AT_SYMLINK_NOFOLLOW, ELOOP);
	fail += check_execveat_fail(dot_dfd_path, "execveat.symlink",
				    AT_SYMLINK_NOFOLLOW, ELOOP);
	/*   absolute path */
	fail += check_execveat_fail(AT_FDCWD, fullname_symlink,
				    AT_SYMLINK_NOFOLLOW, ELOOP);

	/*  Non-regular file failure */
	fail += check_execveat_fail(dot_dfd, "pipe", 0, EACCES);
	unlink("pipe");

	/* Shell script wrapping executable file: */
	/*   dfd + path */
	fail += check_execveat(subdir_dfd, "../script", 0);
	fail += check_execveat(dot_dfd, "script", 0);
	fail += check_execveat(dot_dfd_path, "script", 0);
	/*   absolute path */
	fail += check_execveat(AT_FDCWD, fullname_script, 0);
	/*   fd + no path */
	fail += check_execveat(fd_script, "", AT_EMPTY_PATH);
	fail += check_execveat(fd_script, "",
			       AT_EMPTY_PATH|AT_SYMLINK_NOFOLLOW);
	/*   O_CLOEXEC fd fails for a script (as script file inaccessible) */
	fail += check_execveat_fail(fd_script_cloexec, "", AT_EMPTY_PATH,
				    ENOENT);
	fail += check_execveat_fail(dot_dfd_cloexec, "script", 0, ENOENT);

	/* Mess with script file that's already open: */
	/*   fd + no path to a file that's been renamed */
	rename("script.ephemeral", "script.moved");
	fail += check_execveat(fd_script_ephemeral, "", AT_EMPTY_PATH);
	/*   fd + no path to a file that's been deleted */
	unlink("script.moved"); /* remove the file while fd open */
	fail += check_execveat(fd_script_ephemeral, "", AT_EMPTY_PATH);

	/* Rename a subdirectory in the path: */
	rename("subdir.ephemeral", "subdir.moved");
	fail += check_execveat(subdir_dfd_ephemeral, "../script", 0);
	fail += check_execveat(subdir_dfd_ephemeral, "script", 0);
	/* Remove the subdir and its contents */
	unlink("subdir.moved/script");
	unlink("subdir.moved");
	/* Shell loads via deleted subdir OK because name starts with .. */
	fail += check_execveat(subdir_dfd_ephemeral, "../script", 0);
	fail += check_execveat_fail(subdir_dfd_ephemeral, "script", 0, ENOENT);

	/* Flag values other than AT_SYMLINK_NOFOLLOW => EINVAL */
	fail += check_execveat_fail(dot_dfd, "execveat", 0xFFFF, EINVAL);
	/* Invalid path => ENOENT */
	fail += check_execveat_fail(dot_dfd, "no-such-file", 0, ENOENT);
	fail += check_execveat_fail(dot_dfd_path, "no-such-file", 0, ENOENT);
	fail += check_execveat_fail(AT_FDCWD, "no-such-file", 0, ENOENT);
	/* Attempt to execute directory => EACCES */
	fail += check_execveat_fail(dot_dfd, "", AT_EMPTY_PATH, EACCES);
	/* Attempt to execute non-executable => EACCES */
	fail += check_execveat_fail(dot_dfd, "Makefile", 0, EACCES);
	fail += check_execveat_fail(fd_denatured, "", AT_EMPTY_PATH, EACCES);
	fail += check_execveat_fail(fd_denatured_path, "", AT_EMPTY_PATH,
				    EACCES);
	/* Attempt to execute nonsense FD => EBADF */
	fail += check_execveat_fail(99, "", AT_EMPTY_PATH, EBADF);
	fail += check_execveat_fail(99, "execveat", 0, EBADF);
	/* Attempt to execute relative to non-directory => ENOTDIR */
	fail += check_execveat_fail(fd, "execveat", 0, ENOTDIR);

	fail += check_execveat_pathmax(root_dfd, "execveat", 0);
	fail += check_execveat_pathmax(root_dfd, "script", 1);

	/* /proc/pid/comm gives filename by default */
	fail += check_execveat_comm(fd, "sentinel", "execveat");
	/* /proc/pid/comm gives argv[0] when invoked via link */
	fail += check_execveat_comm(fd_symlink, "sentinel", "execveat");
	/* /proc/pid/comm gives filename if NULL is passed */
	fail += check_execveat_comm(fd, NULL, "execveat");

	return fail;
}

static void prerequisites(void)
{
	int fd;
	const char *script = "#!/bin/bash\nexit $*\n";

	/* Create ephemeral copies of files */
	exe_cp("execveat", "execveat.ephemeral");
	exe_cp("execveat", "execveat.path.ephemeral");
	exe_cp("script", "script.ephemeral");
	mkdir("subdir.ephemeral", 0755);

	fd = open("subdir.ephemeral/script", O_RDWR|O_CREAT|O_TRUNC, 0755);
	write(fd, script, strlen(script));
	close(fd);

	mkfifo("pipe", 0755);
}

int main(int argc, char **argv)
{
	int ii;
	int rc;
	const char *verbose = getenv("VERBOSE");
	const char *check_comm = getenv(CHECK_COMM);

	if (argc >= 2 || check_comm) {
		/*
		 * If we are invoked with an argument, or no arguments but a
		 * command to check, don't run tests.
		 */
		const char *in_test = getenv("IN_TEST");

		if (verbose) {
			ksft_print_msg("invoked with:\n");
			for (ii = 0; ii < argc; ii++)
				ksft_print_msg("\t[%d]='%s\n'", ii, argv[ii]);
		}

		/* If the tests wanted us to check the command, do so. */
		if (check_comm) {
			/* TASK_COMM_LEN == 16 */
			char buf[32];
			int fd, ret;

			fd = open("/proc/self/comm", O_RDONLY);
			if (fd < 0) {
				ksft_perror("open() comm failed");
				exit(1);
			}

			ret = read(fd, buf, sizeof(buf));
			if (ret < 0) {
				ksft_perror("read() comm failed");
				close(fd);
				exit(1);
			}
			close(fd);

			// trim off the \n
			buf[ret-1] = 0;

			if (strcmp(buf, check_comm)) {
				ksft_print_msg("bad comm, got: %s expected: %s\n",
					       buf, check_comm);
				exit(1);
			}

			exit(0);
		}

		/* Check expected environment transferred. */
		if (!in_test || strcmp(in_test, "yes") != 0) {
			ksft_print_msg("no IN_TEST=yes in env\n");
			return 1;
		}

		/* Use the final argument as an exit code. */
		rc = atoi(argv[argc - 1]);
		exit(rc);
	} else {
		ksft_print_header();
		ksft_set_plan(TESTS_EXPECTED);
		prerequisites();
		if (verbose)
			envp[1] = "VERBOSE=1";
		rc = run_tests();
		if (rc > 0)
			printf("%d tests failed\n", rc);
		ksft_finished();
	}

	return rc;
}