syscalls: add selftest for execveat(2)

Signed-off-by: David Drysdale <drysdale@google.com>
Cc: Meredydd Luff <meredydd@senatehouse.org>
Cc: Shuah Khan <shuah.kh@samsung.com>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Rich Felker <dalias@aerifal.cx>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Michael Kerrisk <mtk.manpages@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

tools/testing/selftests/Makefile

@@ -15,6 +15,7 @@ TARGETS += user
 TARGETS += sysctl
 TARGETS += firmware
 TARGETS += ftrace
+TARGETS += exec
 
 TARGETS_HOTPLUG = cpu-hotplug
 TARGETS_HOTPLUG += memory-hotplug

tools/testing/selftests/exec/.gitignore

+subdir*
+script*
+execveat
+execveat.symlink
+execveat.moved
+execveat.path.ephemeral
+execveat.ephemeral
+execveat.denatured
+xxxxxxxx*
\ No newline at end of file

tools/testing/selftests/exec/Makefile

+CC = $(CROSS_COMPILE)gcc
+CFLAGS = -Wall
+BINARIES = execveat
+DEPS = execveat.symlink execveat.denatured script subdir
+all: $(BINARIES) $(DEPS)
+
+subdir:
+	mkdir -p $@
+script:
+	echo '#!/bin/sh' > $@
+	echo 'exit $$*' >> $@
+	chmod +x $@
+execveat.symlink: execveat
+	ln -s -f $< $@
+execveat.denatured: execveat
+	cp $< $@
+	chmod -x $@
+%: %.c
+	$(CC) $(CFLAGS) -o $@ $^
+
+run_tests: all
+	./execveat
+
+clean:
+	rm -rf $(BINARIES) $(DEPS) subdir.moved execveat.moved xxxxx*

tools/testing/selftests/exec/execveat.c

+/*
+ * Copyright (c) 2014 Google, Inc.
+ *
+ * Licensed under the terms of the GNU GPL License version 2
+ *
+ * Selftests for execveat(2).
+ */
+
+#define _GNU_SOURCE  /* to get O_PATH, AT_EMPTY_PATH */
+#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>
+
+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)
+{
+	int rc;
+
+	errno = 0;
+	printf("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) {
+		printf("[FAIL] (unexpected success from execveat(2))\n");
+		return 1;
+	}
+	if (errno != expected_errno) {
+		printf("[FAIL] (expected errno %d (%s) not %d (%s)\n",
+			expected_errno, strerror(expected_errno),
+			errno, strerror(errno));
+		return 1;
+	}
+	printf("[OK]\n");
+	return 0;
+}
+
+static int check_execveat_invoked_rc(int fd, const char *path, int flags,
+				     int expected_rc)
+{
+	int status;
+	int rc;
+	pid_t child;
+	int pathlen = path ? strlen(path) : 0;
+
+	if (pathlen > 40)
+		printf("Check success of execveat(%d, '%.20s...%s', %d)... ",
+			fd, path, (path + pathlen - 20), flags);
+	else
+		printf("Check success of execveat(%d, '%s', %d)... ",
+			fd, path?:"(null)", flags);
+	child = fork();
+	if (child < 0) {
+		printf("[FAIL] (fork() failed)\n");
+		return 1;
+	}
+	if (child == 0) {
+		/* Child: do execveat(). */
+		rc = execveat_(fd, path, argv, envp, flags);
+		printf("[FAIL]: execveat() failed, rc=%d errno=%d (%s)\n",
+			rc, errno, strerror(errno));
+		exit(1);  /* should not reach here */
+	}
+	/* Parent: wait for & check child's exit status. */
+	rc = waitpid(child, &status, 0);
+	if (rc != child) {
+		printf("[FAIL] (waitpid(%d,...) returned %d)\n", child, rc);
+		return 1;
+	}
+	if (!WIFEXITED(status)) {
+		printf("[FAIL] (child %d did not exit cleanly, status=%08x)\n",
+			child, status);
+		return 1;
+	}
+	if (WEXITSTATUS(status) != expected_rc) {
+		printf("[FAIL] (child %d exited with %d not %d)\n",
+			child, WEXITSTATUS(status), expected_rc);
+		return 1;
+	}
+	printf("[OK]\n");
+	return 0;
+}
+
+static int check_execveat(int fd, const char *path, int flags)
+{
+	return check_execveat_invoked_rc(fd, path, flags, 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) {
+		printf("Failed to open '%s'; "
+			"check prerequisites are available\n", filename);
+		exit(1);
+	}
+	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 dot_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 */
+		memset(longname, 'x', XX_DIR_LEN - 1);
+		longname[XX_DIR_LEN - 1] = '/';
+		longname[XX_DIR_LEN] = '\0';
+		count = (PATH_MAX - 3) / XX_DIR_LEN;
+		for (ii = 0; ii < count; ii++) {
+			strcat(longpath, longname);
+			mkdir(longpath, 0755);
+		}
+		len = (PATH_MAX - 3) - (count * XX_DIR_LEN);
+		if (len <= 0)
+			len = 1;
+		memset(longname, 'y', len);
+		longname[len] = '\0';
+		strcat(longpath, longname);
+	}
+	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) {
+		printf("Invoke copy of '%s' via filename of length %lu:\n",
+			src, strlen(longpath));
+		fail += check_execveat(fd, "", AT_EMPTY_PATH);
+	} else {
+		printf("Failed to open length %lu 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.
+	 */
+	if (is_script)
+		fail += check_execveat_invoked_rc(dot_dfd, longpath, 0, 127);
+	else
+		fail += check_execveat(dot_dfd, longpath, 0);
+
+	return fail;
+}
+
+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 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);
+
+	/* 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);
+
+	/* 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(dot_dfd, "execveat", 0);
+	fail += check_execveat_pathmax(dot_dfd, "script", 1);
+	return fail;
+}
+
+static void prerequisites(void)
+{
+	int fd;
+	const char *script = "#!/bin/sh\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);
+}
+
+int main(int argc, char **argv)
+{
+	int ii;
+	int rc;
+	const char *verbose = getenv("VERBOSE");
+
+	if (argc >= 2) {
+		/* If we are invoked with an argument, don't run tests. */
+		const char *in_test = getenv("IN_TEST");
+
+		if (verbose) {
+			printf("  invoked with:");
+			for (ii = 0; ii < argc; ii++)
+				printf(" [%d]='%s'", ii, argv[ii]);
+			printf("\n");
+		}
+
+		/* Check expected environment transferred. */
+		if (!in_test || strcmp(in_test, "yes") != 0) {
+			printf("[FAIL] (no IN_TEST=yes in env)\n");
+			return 1;
+		}
+
+		/* Use the final argument as an exit code. */
+		rc = atoi(argv[argc - 1]);
+		fflush(stdout);
+	} else {
+		prerequisites();
+		if (verbose)
+			envp[1] = "VERBOSE=1";
+		rc = run_tests();
+		if (rc > 0)
+			printf("%d tests failed\n", rc);
+	}
+	return rc;
+}