radare2/libr/util/sandbox.c

/* radare - LGPL - Copyright 2012-2017 - pancake */

#include <r_util.h>
#include <signal.h>
#if _MSC_VER
#include <process.h> // to compile execl under msvc windows
#include <direct.h>  // to compile chdir under msvc windows
#endif

#if HAVE_CAPSICUM
#include <sys/capsicum.h>
#endif

static bool enabled = false;
static bool disabled = false;

static bool inHomeWww(const char *path) {
	bool ret = false;
	char *homeWww = r_str_home (R2_HOME_WWWROOT R_SYS_DIR);
	if (homeWww) {
		if (!strncmp (path, homeWww, strlen (homeWww))) {
			ret = true;
		}
		free (homeWww);
	}
	return ret;
}

/**
 * This function verifies that the given path is allowed. Paths are allowed only if they don't
 * contain .. components (which would indicate directory traversal) and they are relative.
 * Paths pointing into the webroot are an exception: For reaching the webroot, .. and absolute
 * path are ok.
 */
R_API bool r_sandbox_check_path (const char *path) {
	size_t root_len;
	char *p;
	/* XXX: the sandbox can be bypassed if a directory is symlink */

	if (!path) {
		return false;
	}
	root_len = strlen (R2_LIBDIR"/radare2");
	if (!strncmp (path, R2_LIBDIR"/radare2", root_len)) {
		return true;
	}
	root_len = strlen (R2_DATDIR"/radare2");
	if (!strncmp (path, R2_DATDIR"/radare2", root_len)) {
		return true;
	}
	if (inHomeWww (path)) {
		return true;
	}
	// Accessing stuff inside the webroot is ok even if we need .. or leading / for that
	root_len = strlen (R2_WWWROOT);
	if (R2_WWWROOT[0] && !strncmp (path, R2_WWWROOT, root_len) && (
			R2_WWWROOT[root_len-1] == '/' || path[root_len] == '/' || path[root_len] == '\0')) {
		path += strlen (R2_WWWROOT);
		while (*path == '/') {
			path++;
		}
	}

	// ./ path is not allowed
        if (path[0]=='.' && path[1]=='/') {
		return false;
	}
	// Properly check for directrory traversal using "..". First, does it start with a .. part?
	if (path[0] == '.' && path[1] == '.' && (path[2] == '\0' || path[2] == '/')) {
		return 0;
	}

	// Or does it have .. in some other position?
	for (p = strstr (path, "/.."); p; p = strstr(p, "/..")) {
		if (p[3] == '\0' || p[3] == '/') {
			return false;
		}
	}
	// Absolute paths are forbidden.
	if (*path == '/') {
		return false;
	}
#if __UNIX__
	char ch;
	if (readlink (path, &ch, 1) != -1) {
		return false;
	}
#endif
	return true;
}

R_API bool r_sandbox_disable (bool e) {
	if (e) {
#if LIBC_HAVE_PLEDGE
		if (enabled) {
			eprintf ("sandbox mode couldn't be disabled when pledged\n");
			return enabled;
		}
#endif
#if HAVE_CAPSICUM
		if (enabled) {
			eprintf ("sandbox mode couldn't be disabled in capability mode\n");
			return enabled;
		}
#endif
		disabled = enabled;
		enabled = false;
	} else {
		enabled = disabled;
	}
	return enabled;
}

R_API bool r_sandbox_enable (bool e) {
	if (enabled) {
		if (!e) {
			// eprintf ("Cant disable sandbox\n");
		}
		return true;
	}
	enabled = e;
#if LIBC_HAVE_PLEDGE
	if (enabled && pledge ("stdio rpath tty prot_exec inet", NULL) == -1) {
		eprintf ("sandbox: pledge call failed\n");
		return false;
	}
#endif
#if HAVE_CAPSICUM
	if (enabled && cap_enter () != 0) {
		eprintf ("sandbox: call_enter failed\n");
		return false;
	}
#endif
	return enabled;
}

R_API int r_sandbox_system (const char *x, int n) {
	if (enabled) {
		eprintf ("sandbox: system call disabled\n");
		return -1;
	}
#if LIBC_HAVE_FORK
#if LIBC_HAVE_SYSTEM
	if (n) {
#if APPLE_SDK_IPHONEOS
#include <dlfcn.h>
		int (*__system)(const char *cmd)
			= dlsym (NULL, "system");
		if (__system) {
			return __system (x);
		}
		return -1;
#else
		return system (x);
#endif
	}
	return execl ("/bin/sh", "sh", "-c", x, (const char*)NULL);
#else
	#include <spawn.h>
	if (n && !strchr (x, '|')) {
		char **argv, *cmd = strdup (x);
		int rc, pid, argc;
		char *isbg = strchr (cmd, '&');
		// XXX this is hacky
		if (isbg) {
			*isbg = 0;
		}
		argv = r_str_argv (cmd, &argc);
		if (argv) {
			char *argv0 = r_file_path (argv[0]);
			if (!argv0) {
				eprintf ("Cannot find '%s'\n", argv[0]);
				return -1;
			}
			pid = 0;
			posix_spawn (&pid, argv0, NULL, NULL, argv, NULL);
			if (isbg) {
				// XXX. wait for children
				rc = 0;
			} else {
				rc = waitpid (pid, NULL, 0);
			}
			r_str_argv_free (argv);
			free (argv0);
			return rc;
		}
		eprintf ("Error parsing command arguments\n");
		return -1;
	}
	int child = fork();
	if (child == -1) return -1;
	if (child) {
		return waitpid (child, NULL, 0);
	}
	execl ("/bin/sh", "sh", "-c", x, (const char*)NULL);
	exit (1);
#endif
#endif
	return -1;
}

R_API bool r_sandbox_creat (const char *path, int mode) {
	if (enabled) {
		return false;
#if 0
		if (mode & O_CREAT) return -1;
		if (mode & O_RDWR) return -1;
		if (!r_sandbox_check_path (path))
			return -1;
#endif
	}
	int fd = open (path, O_CREAT | O_TRUNC | O_WRONLY, mode);
	if (fd != -1) {
		close (fd);
		return true;
	}
	return false;
}

static char *expand_home(const char *p) {
	if (*p == '~') {
		return r_str_home (p);
	}
	return strdup (p);
}

R_API int r_sandbox_lseek (int fd, ut64 addr, int whence) {
	if (enabled) {
		return -1;
	}
	return lseek (fd, (off_t)addr, whence);
}

R_API int r_sandbox_read (int fd, ut8* buf, int len) {
	return enabled? -1 : read (fd, buf, len);
}

R_API int r_sandbox_write (int fd, const ut8* buf, int len) {
	return enabled? -1 : write (fd, buf, len);
}

R_API int r_sandbox_close (int fd) {
	return enabled? -1 : close (fd);
}

/* perm <-> mode */
R_API int r_sandbox_open (const char *path, int mode, int perm) {
	if (!path) {
		return -1;
	}
	char *epath = expand_home (path);
	int ret = -1;
#if __WINDOWS__
	mode |= O_BINARY;
	if (!strcmp (path, "/dev/null")) {
		path = "NUL";
	}
#endif
	if (enabled) {
		if ((mode & O_CREAT)
			|| (mode & O_RDWR)
			|| (!r_sandbox_check_path (epath))) {
			free (epath);
			return -1;
		}
	}
#if __WINDOWS__
	{
		wchar_t *wepath = r_utf8_to_utf16 (epath);
		if (!wepath) {
			free (epath);
			return -1;
		}
		ret = _wopen (wepath, mode, perm);
		free (wepath);
	}
#else // __WINDOWS__
	ret = open (epath, mode, perm);
#endif // __WINDOWS__
	free (epath);
	return ret;
}

R_API FILE *r_sandbox_fopen (const char *path, const char *mode) {
	FILE *ret = NULL;
	char *epath = NULL;
	if (!path) {
		return NULL;
	}
	if (enabled) {
		if (strchr (mode, 'w') || strchr (mode, 'a') || strchr (mode, '+')) {
			return NULL;
		}
		epath = expand_home (path);
		if (!r_sandbox_check_path (epath)) {
			free (epath);
			return NULL;
		}
	}
	if (!epath) {
		epath = expand_home (path);
	}
	if ((strchr (mode, 'w') || r_file_is_regular (epath))) {
#if __WINDOWS__
		wchar_t *wepath = r_utf8_to_utf16 (epath);
		if (!wepath) {
			free (epath);
			return ret;
		}
		wchar_t *wmode = r_utf8_to_utf16 (mode);
		if (!wmode) {
			free (wepath);
			free (epath);
			return ret;
		}
		ret = _wfopen (wepath, wmode);
		free (wmode);
		free (wepath);
#else // __WINDOWS__
		ret = fopen (epath, mode);
#endif // __WINDOWS__
	}
	free (epath);
	return ret;
}

R_API int r_sandbox_chdir (const char *path) {
	if (enabled) {
		// TODO: check path
		if (strstr (path, "../")) {
			return -1;
		}
		if (*path == '/') {
			return -1;
		}
		return -1;
	}
	return chdir (path);
}

R_API int r_sandbox_kill(int pid, int sig) {
	// XXX: fine-tune. maybe we want to enable kill for child?
	if (enabled) {
		return -1;
	}
#if __UNIX__
	return kill (pid, sig);
#endif
	return -1;
}
#if __WINDOWS__ && !defined(__CYGWIN__)
R_API HANDLE r_sandbox_opendir (const char *path, WIN32_FIND_DATAW *entry) {
	wchar_t dir[MAX_PATH];
	wchar_t *wcpath = 0;
	if (!path) {
		return NULL;
	}
	if (r_sandbox_enable (0)) {
		if (path && !r_sandbox_check_path (path)) {
			return NULL;
		}
	}
	if (!(wcpath = r_utf8_to_utf16 (path))) {
		return NULL;
	}
#if __MINGW32__
	swprintf (dir, L"%ls\\*.*", wcpath);
#else
	swprintf (dir, MAX_PATH, L"%ls\\*.*", wcpath);
#endif
	free (wcpath);
	return FindFirstFileW (dir, entry);
}
#else
R_API DIR* r_sandbox_opendir (const char *path) {
	if (!path) {
		return NULL;
	}
	if (r_sandbox_enable (0)) {
		if (path && !r_sandbox_check_path (path)) {
			return NULL;
		}
	}
	return opendir (path);
}
#endif
R_API bool r_sys_stop () {
	if (enabled) {
		return false;
	}
#if __UNIX__
	return !r_sandbox_kill (0, SIGTSTP);
#else
	return false;
#endif
}