execveat.c

  1// SPDX-License-Identifier: GPL-2.0-only
  2/*
  3 * Copyright (c) 2014 Google, Inc.
  4 *
  5 * Selftests for execveat(2).
  6 */
  7
  8#ifndef _GNU_SOURCE
  9#define _GNU_SOURCE  /* to get O_PATH, AT_EMPTY_PATH */
 10#endif
 11#include <sys/sendfile.h>
 12#include <sys/stat.h>
 13#include <sys/syscall.h>
 14#include <sys/types.h>
 15#include <sys/wait.h>
 16#include <errno.h>
 17#include <fcntl.h>
 18#include <limits.h>
 19#include <stdio.h>
 20#include <stdlib.h>
 21#include <string.h>
 22#include <unistd.h>
 23
 24#include "kselftest.h"
 25
 26#define TESTS_EXPECTED 54
 27#define TEST_NAME_LEN (PATH_MAX * 4)
 28
 29#define CHECK_COMM "CHECK_COMM"
 30
 31static char longpath[2 * PATH_MAX] = "";
 32static char *envp[] = { "IN_TEST=yes", NULL, NULL };
 33static char *argv[] = { "execveat", "99", NULL };
 34
 35static int execveat_(int fd, const char *path, char **argv, char **envp,
 36		     int flags)
 37{
 38#ifdef __NR_execveat
 39	return syscall(__NR_execveat, fd, path, argv, envp, flags);
 40#else
 41	errno = ENOSYS;
 42	return -1;
 43#endif
 44}
 45
 46#define check_execveat_fail(fd, path, flags, errno)	\
 47	_check_execveat_fail(fd, path, flags, errno, #errno)
 48static int _check_execveat_fail(int fd, const char *path, int flags,
 49				int expected_errno, const char *errno_str)
 50{
 51	char test_name[TEST_NAME_LEN];
 52	int rc;
 53
 54	errno = 0;
 55	snprintf(test_name, sizeof(test_name),
 56		 "Check failure of execveat(%d, '%s', %d) with %s",
 57		 fd, path?:"(null)", flags, errno_str);
 58	rc = execveat_(fd, path, argv, envp, flags);
 59
 60	if (rc > 0) {
 61		ksft_print_msg("unexpected success from execveat(2)\n");
 62		ksft_test_result_fail("%s\n", test_name);
 63		return 1;
 64	}
 65	if (errno != expected_errno) {
 66		ksft_print_msg("expected errno %d (%s) not %d (%s)\n",
 67			       expected_errno, strerror(expected_errno),
 68			       errno, strerror(errno));
 69		ksft_test_result_fail("%s\n", test_name);
 70		return 1;
 71	}
 72	ksft_test_result_pass("%s\n", test_name);
 73	return 0;
 74}
 75
 76static int check_execveat_invoked_rc(int fd, const char *path, int flags,
 77				     int expected_rc, int expected_rc2)
 78{
 79	char test_name[TEST_NAME_LEN];
 80	int status;
 81	int rc;
 82	pid_t child;
 83	int pathlen = path ? strlen(path) : 0;
 84
 85	if (pathlen > 40)
 86		snprintf(test_name, sizeof(test_name),
 87			 "Check success of execveat(%d, '%.20s...%s', %d)... ",
 88			 fd, path, (path + pathlen - 20), flags);
 89	else
 90		snprintf(test_name, sizeof(test_name),
 91			 "Check success of execveat(%d, '%s', %d)... ",
 92			 fd, path?:"(null)", flags);
 93
 94	child = fork();
 95	if (child < 0) {
 96		ksft_perror("fork() failed");
 97		ksft_test_result_fail("%s\n", test_name);
 98		return 1;
 99	}
100	if (child == 0) {
101		/* Child: do execveat(). */
102		rc = execveat_(fd, path, argv, envp, flags);
103		ksft_print_msg("child execveat() failed, rc=%d errno=%d (%s)\n",
104			       rc, errno, strerror(errno));
105		exit(errno);
106	}
107	/* Parent: wait for & check child's exit status. */
108	rc = waitpid(child, &status, 0);
109	if (rc != child) {
110		ksft_print_msg("waitpid(%d,...) returned %d\n", child, rc);
111		ksft_test_result_fail("%s\n", test_name);
112		return 1;
113	}
114	if (!WIFEXITED(status)) {
115		ksft_print_msg("child %d did not exit cleanly, status=%08x\n",
116			       child, status);
117		ksft_test_result_fail("%s\n", test_name);
118		return 1;
119	}
120	if ((WEXITSTATUS(status) != expected_rc) &&
121	    (WEXITSTATUS(status) != expected_rc2)) {
122		ksft_print_msg("child %d exited with %d neither %d nor %d\n",
123			       child, WEXITSTATUS(status), expected_rc,
124			       expected_rc2);
125		ksft_test_result_fail("%s\n", test_name);
126		return 1;
127	}
128	ksft_test_result_pass("%s\n", test_name);
129	return 0;
130}
131
132static int check_execveat(int fd, const char *path, int flags)
133{
134	return check_execveat_invoked_rc(fd, path, flags, 99, 99);
135}
136
137static char *concat(const char *left, const char *right)
138{
139	char *result = malloc(strlen(left) + strlen(right) + 1);
140
141	strcpy(result, left);
142	strcat(result, right);
143	return result;
144}
145
146static int open_or_die(const char *filename, int flags)
147{
148	int fd = open(filename, flags);
149
150	if (fd < 0)
151		ksft_exit_fail_msg("Failed to open '%s'; "
152			"check prerequisites are available\n", filename);
153	return fd;
154}
155
156static void exe_cp(const char *src, const char *dest)
157{
158	int in_fd = open_or_die(src, O_RDONLY);
159	int out_fd = open(dest, O_RDWR|O_CREAT|O_TRUNC, 0755);
160	struct stat info;
161
162	fstat(in_fd, &info);
163	sendfile(out_fd, in_fd, NULL, info.st_size);
164	close(in_fd);
165	close(out_fd);
166}
167
168#define XX_DIR_LEN 200
169static int check_execveat_pathmax(int root_dfd, const char *src, int is_script)
170{
171	int fail = 0;
172	int ii, count, len;
173	char longname[XX_DIR_LEN + 1];
174	int fd;
175
176	if (*longpath == '\0') {
177		/* Create a filename close to PATH_MAX in length */
178		char *cwd = getcwd(NULL, 0);
179
180		if (!cwd) {
181			ksft_perror("Failed to getcwd()");
182			return 2;
183		}
184		strcpy(longpath, cwd);
185		strcat(longpath, "/");
186		memset(longname, 'x', XX_DIR_LEN - 1);
187		longname[XX_DIR_LEN - 1] = '/';
188		longname[XX_DIR_LEN] = '\0';
189		count = (PATH_MAX - 3 - strlen(cwd)) / XX_DIR_LEN;
190		for (ii = 0; ii < count; ii++) {
191			strcat(longpath, longname);
192			mkdir(longpath, 0755);
193		}
194		len = (PATH_MAX - 3 - strlen(cwd)) - (count * XX_DIR_LEN);
195		if (len <= 0)
196			len = 1;
197		memset(longname, 'y', len);
198		longname[len] = '\0';
199		strcat(longpath, longname);
200		free(cwd);
201	}
202	exe_cp(src, longpath);
203
204	/*
205	 * Execute as a pre-opened file descriptor, which works whether this is
206	 * a script or not (because the interpreter sees a filename like
207	 * "/dev/fd/20").
208	 */
209	fd = open(longpath, O_RDONLY);
210	if (fd > 0) {
211		ksft_print_msg("Invoke copy of '%s' via filename of length %zu:\n",
212			       src, strlen(longpath));
213		fail += check_execveat(fd, "", AT_EMPTY_PATH);
214	} else {
215		ksft_print_msg("Failed to open length %zu filename, errno=%d (%s)\n",
216			       strlen(longpath), errno, strerror(errno));
217		fail++;
218	}
219
220	/*
221	 * Execute as a long pathname relative to "/".  If this is a script,
222	 * the interpreter will launch but fail to open the script because its
223	 * name ("/dev/fd/5/xxx....") is bigger than PATH_MAX.
224	 *
225	 * The failure code is usually 127 (POSIX: "If a command is not found,
226	 * the exit status shall be 127."), but some systems give 126 (POSIX:
227	 * "If the command name is found, but it is not an executable utility,
228	 * the exit status shall be 126."), so allow either.
229	 */
230	if (is_script) {
231		ksft_print_msg("Invoke script via root_dfd and relative filename\n");
232		fail += check_execveat_invoked_rc(root_dfd, longpath + 1, 0,
233						  127, 126);
234	} else {
235		ksft_print_msg("Invoke exec via root_dfd and relative filename\n");
236		fail += check_execveat(root_dfd, longpath + 1, 0);
237	}
238
239	return fail;
240}
241
242static int check_execveat_comm(int fd, char *argv0, char *expected)
243{
244	char buf[128], *old_env, *old_argv0;
245	int ret;
246
247	snprintf(buf, sizeof(buf), CHECK_COMM "=%s", expected);
248
249	old_env = envp[1];
250	envp[1] = buf;
251
252	old_argv0 = argv[0];
253	argv[0] = argv0;
254
255	ksft_print_msg("Check execveat(AT_EMPTY_PATH)'s comm is %s\n",
256		       expected);
257	ret = check_execveat_invoked_rc(fd, "", AT_EMPTY_PATH, 0, 0);
258
259	envp[1] = old_env;
260	argv[0] = old_argv0;
261
262	return ret;
263}
264
265static int run_tests(void)
266{
267	int fail = 0;
268	char *fullname = realpath("execveat", NULL);
269	char *fullname_script = realpath("script", NULL);
270	char *fullname_symlink = concat(fullname, ".symlink");
271	int subdir_dfd = open_or_die("subdir", O_DIRECTORY|O_RDONLY);
272	int subdir_dfd_ephemeral = open_or_die("subdir.ephemeral",
273					       O_DIRECTORY|O_RDONLY);
274	int dot_dfd = open_or_die(".", O_DIRECTORY|O_RDONLY);
275	int root_dfd = open_or_die("/", O_DIRECTORY|O_RDONLY);
276	int dot_dfd_path = open_or_die(".", O_DIRECTORY|O_RDONLY|O_PATH);
277	int dot_dfd_cloexec = open_or_die(".", O_DIRECTORY|O_RDONLY|O_CLOEXEC);
278	int fd = open_or_die("execveat", O_RDONLY);
279	int fd_path = open_or_die("execveat", O_RDONLY|O_PATH);
280	int fd_symlink = open_or_die("execveat.symlink", O_RDONLY);
281	int fd_denatured = open_or_die("execveat.denatured", O_RDONLY);
282	int fd_denatured_path = open_or_die("execveat.denatured",
283					    O_RDONLY|O_PATH);
284	int fd_script = open_or_die("script", O_RDONLY);
285	int fd_ephemeral = open_or_die("execveat.ephemeral", O_RDONLY);
286	int fd_ephemeral_path = open_or_die("execveat.path.ephemeral",
287					    O_RDONLY|O_PATH);
288	int fd_script_ephemeral = open_or_die("script.ephemeral", O_RDONLY);
289	int fd_cloexec = open_or_die("execveat", O_RDONLY|O_CLOEXEC);
290	int fd_script_cloexec = open_or_die("script", O_RDONLY|O_CLOEXEC);
291
292	/* Check if we have execveat at all, and bail early if not */
293	errno = 0;
294	execveat_(-1, NULL, NULL, NULL, 0);
295	if (errno == ENOSYS) {
296		ksft_exit_skip(
297			"ENOSYS calling execveat - no kernel support?\n");
298	}
299
300	/* Change file position to confirm it doesn't affect anything */
301	lseek(fd, 10, SEEK_SET);
302
303	/* Normal executable file: */
304	/*   dfd + path */
305	fail += check_execveat(subdir_dfd, "../execveat", 0);
306	fail += check_execveat(dot_dfd, "execveat", 0);
307	fail += check_execveat(dot_dfd_path, "execveat", 0);
308	/*   absolute path */
309	fail += check_execveat(AT_FDCWD, fullname, 0);
310	/*   absolute path with nonsense dfd */
311	fail += check_execveat(99, fullname, 0);
312	/*   fd + no path */
313	fail += check_execveat(fd, "", AT_EMPTY_PATH);
314	/*   O_CLOEXEC fd + no path */
315	fail += check_execveat(fd_cloexec, "", AT_EMPTY_PATH);
316	/*   O_PATH fd */
317	fail += check_execveat(fd_path, "", AT_EMPTY_PATH);
318
319	/* Mess with executable file that's already open: */
320	/*   fd + no path to a file that's been renamed */
321	rename("execveat.ephemeral", "execveat.moved");
322	fail += check_execveat(fd_ephemeral, "", AT_EMPTY_PATH);
323	/*   fd + no path to a file that's been deleted */
324	unlink("execveat.moved"); /* remove the file now fd open */
325	fail += check_execveat(fd_ephemeral, "", AT_EMPTY_PATH);
326
327	/* Mess with executable file that's already open with O_PATH */
328	/*   fd + no path to a file that's been deleted */
329	unlink("execveat.path.ephemeral");
330	fail += check_execveat(fd_ephemeral_path, "", AT_EMPTY_PATH);
331
332	/* Invalid argument failures */
333	fail += check_execveat_fail(fd, "", 0, ENOENT);
334	fail += check_execveat_fail(fd, NULL, AT_EMPTY_PATH, EFAULT);
335
336	/* Symlink to executable file: */
337	/*   dfd + path */
338	fail += check_execveat(dot_dfd, "execveat.symlink", 0);
339	fail += check_execveat(dot_dfd_path, "execveat.symlink", 0);
340	/*   absolute path */
341	fail += check_execveat(AT_FDCWD, fullname_symlink, 0);
342	/*   fd + no path, even with AT_SYMLINK_NOFOLLOW (already followed) */
343	fail += check_execveat(fd_symlink, "", AT_EMPTY_PATH);
344	fail += check_execveat(fd_symlink, "",
345			       AT_EMPTY_PATH|AT_SYMLINK_NOFOLLOW);
346
347	/* Symlink fails when AT_SYMLINK_NOFOLLOW set: */
348	/*   dfd + path */
349	fail += check_execveat_fail(dot_dfd, "execveat.symlink",
350				    AT_SYMLINK_NOFOLLOW, ELOOP);
351	fail += check_execveat_fail(dot_dfd_path, "execveat.symlink",
352				    AT_SYMLINK_NOFOLLOW, ELOOP);
353	/*   absolute path */
354	fail += check_execveat_fail(AT_FDCWD, fullname_symlink,
355				    AT_SYMLINK_NOFOLLOW, ELOOP);
356
357	/*  Non-regular file failure */
358	fail += check_execveat_fail(dot_dfd, "pipe", 0, EACCES);
359	unlink("pipe");
360
361	/* Shell script wrapping executable file: */
362	/*   dfd + path */
363	fail += check_execveat(subdir_dfd, "../script", 0);
364	fail += check_execveat(dot_dfd, "script", 0);
365	fail += check_execveat(dot_dfd_path, "script", 0);
366	/*   absolute path */
367	fail += check_execveat(AT_FDCWD, fullname_script, 0);
368	/*   fd + no path */
369	fail += check_execveat(fd_script, "", AT_EMPTY_PATH);
370	fail += check_execveat(fd_script, "",
371			       AT_EMPTY_PATH|AT_SYMLINK_NOFOLLOW);
372	/*   O_CLOEXEC fd fails for a script (as script file inaccessible) */
373	fail += check_execveat_fail(fd_script_cloexec, "", AT_EMPTY_PATH,
374				    ENOENT);
375	fail += check_execveat_fail(dot_dfd_cloexec, "script", 0, ENOENT);
376
377	/* Mess with script file that's already open: */
378	/*   fd + no path to a file that's been renamed */
379	rename("script.ephemeral", "script.moved");
380	fail += check_execveat(fd_script_ephemeral, "", AT_EMPTY_PATH);
381	/*   fd + no path to a file that's been deleted */
382	unlink("script.moved"); /* remove the file while fd open */
383	fail += check_execveat(fd_script_ephemeral, "", AT_EMPTY_PATH);
384
385	/* Rename a subdirectory in the path: */
386	rename("subdir.ephemeral", "subdir.moved");
387	fail += check_execveat(subdir_dfd_ephemeral, "../script", 0);
388	fail += check_execveat(subdir_dfd_ephemeral, "script", 0);
389	/* Remove the subdir and its contents */
390	unlink("subdir.moved/script");
391	unlink("subdir.moved");
392	/* Shell loads via deleted subdir OK because name starts with .. */
393	fail += check_execveat(subdir_dfd_ephemeral, "../script", 0);
394	fail += check_execveat_fail(subdir_dfd_ephemeral, "script", 0, ENOENT);
395
396	/* Flag values other than AT_SYMLINK_NOFOLLOW => EINVAL */
397	fail += check_execveat_fail(dot_dfd, "execveat", 0xFFFF, EINVAL);
398	/* Invalid path => ENOENT */
399	fail += check_execveat_fail(dot_dfd, "no-such-file", 0, ENOENT);
400	fail += check_execveat_fail(dot_dfd_path, "no-such-file", 0, ENOENT);
401	fail += check_execveat_fail(AT_FDCWD, "no-such-file", 0, ENOENT);
402	/* Attempt to execute directory => EACCES */
403	fail += check_execveat_fail(dot_dfd, "", AT_EMPTY_PATH, EACCES);
404	/* Attempt to execute non-executable => EACCES */
405	fail += check_execveat_fail(dot_dfd, "Makefile", 0, EACCES);
406	fail += check_execveat_fail(fd_denatured, "", AT_EMPTY_PATH, EACCES);
407	fail += check_execveat_fail(fd_denatured_path, "", AT_EMPTY_PATH,
408				    EACCES);
409	/* Attempt to execute nonsense FD => EBADF */
410	fail += check_execveat_fail(99, "", AT_EMPTY_PATH, EBADF);
411	fail += check_execveat_fail(99, "execveat", 0, EBADF);
412	/* Attempt to execute relative to non-directory => ENOTDIR */
413	fail += check_execveat_fail(fd, "execveat", 0, ENOTDIR);
414
415	fail += check_execveat_pathmax(root_dfd, "execveat", 0);
416	fail += check_execveat_pathmax(root_dfd, "script", 1);
417
418	/* /proc/pid/comm gives filename by default */
419	fail += check_execveat_comm(fd, "sentinel", "execveat");
420	/* /proc/pid/comm gives argv[0] when invoked via link */
421	fail += check_execveat_comm(fd_symlink, "sentinel", "execveat");
422	/* /proc/pid/comm gives filename if NULL is passed */
423	fail += check_execveat_comm(fd, NULL, "execveat");
424
425	return fail;
426}
427
428static void prerequisites(void)
429{
430	int fd;
431	const char *script = "#!/bin/bash\nexit $*\n";
432
433	/* Create ephemeral copies of files */
434	exe_cp("execveat", "execveat.ephemeral");
435	exe_cp("execveat", "execveat.path.ephemeral");
436	exe_cp("script", "script.ephemeral");
437	mkdir("subdir.ephemeral", 0755);
438
439	fd = open("subdir.ephemeral/script", O_RDWR|O_CREAT|O_TRUNC, 0755);
440	write(fd, script, strlen(script));
441	close(fd);
442
443	mkfifo("pipe", 0755);
444}
445
446int main(int argc, char **argv)
447{
448	int ii;
449	int rc;
450	const char *verbose = getenv("VERBOSE");
451	const char *check_comm = getenv(CHECK_COMM);
452
453	if (argc >= 2 || check_comm) {
454		/*
455		 * If we are invoked with an argument, or no arguments but a
456		 * command to check, don't run tests.
457		 */
458		const char *in_test = getenv("IN_TEST");
459
460		if (verbose) {
461			ksft_print_msg("invoked with:\n");
462			for (ii = 0; ii < argc; ii++)
463				ksft_print_msg("\t[%d]='%s\n'", ii, argv[ii]);
464		}
465
466		/* If the tests wanted us to check the command, do so. */
467		if (check_comm) {
468			/* TASK_COMM_LEN == 16 */
469			char buf[32];
470			int fd, ret;
471
472			fd = open("/proc/self/comm", O_RDONLY);
473			if (fd < 0) {
474				ksft_perror("open() comm failed");
475				exit(1);
476			}
477
478			ret = read(fd, buf, sizeof(buf));
479			if (ret < 0) {
480				ksft_perror("read() comm failed");
481				close(fd);
482				exit(1);
483			}
484			close(fd);
485
486			// trim off the \n
487			buf[ret-1] = 0;
488
489			if (strcmp(buf, check_comm)) {
490				ksft_print_msg("bad comm, got: %s expected: %s\n",
491					       buf, check_comm);
492				exit(1);
493			}
494
495			exit(0);
496		}
497
498		/* Check expected environment transferred. */
499		if (!in_test || strcmp(in_test, "yes") != 0) {
500			ksft_print_msg("no IN_TEST=yes in env\n");
501			return 1;
502		}
503
504		/* Use the final argument as an exit code. */
505		rc = atoi(argv[argc - 1]);
506		exit(rc);
507	} else {
508		ksft_print_header();
509		ksft_set_plan(TESTS_EXPECTED);
510		prerequisites();
511		if (verbose)
512			envp[1] = "VERBOSE=1";
513		rc = run_tests();
514		if (rc > 0)
515			printf("%d tests failed\n", rc);
516		ksft_finished();
517	}
518
519	return rc;
520}