Function secure_relative_open_linux

syscall.c:1710–1748

}

static int secure_relative_open_linux(const char *basedir, const char *relpath, int flags, mode_t mode)
{
	struct open_how how;
	int dirfd, retfd;

	memset(&how, 0, sizeof how);
	how.flags = flags;
	how.mode = mode;
	how.resolve = RESOLVE_BENEATH | RESOLVE_NO_MAGICLINKS;

	if (basedir == NULL) {
		dirfd = AT_FDCWD;
	} else if (basedir[0] == '/') {
		/* Absolute basedir: operator-trusted (module_dir and the
		 * like). Plain openat. */
		dirfd = openat(AT_FDCWD, basedir, O_RDONLY | O_DIRECTORY);
		if (dirfd == -1)
			return -1;
	} else {
		/* Relative basedir: may be wire-influenced via
		 * --link-dest / --copy-dest / --compare-dest. Resolve it
		 * under the same RESOLVE_BENEATH guarantee as relpath, so
		 * a parent symlink on basedir cannot redirect the dirfd
		 * outside the CWD anchor. */
		struct open_how bhow;
		memset(&bhow, 0, sizeof bhow);
		bhow.flags = O_RDONLY | O_DIRECTORY;
		bhow.resolve = RESOLVE_BENEATH | RESOLVE_NO_MAGICLINKS;
		dirfd = openat2_beneath(AT_FDCWD, basedir, &bhow);
		if (dirfd == -1)
			return -1;
	}

	retfd = openat2_beneath(dirfd, relpath, &how);

	if (dirfd != AT_FDCWD)
		close(dirfd);
	return retfd;
}
#endif

#ifdef O_RESOLVE_BENEATH