Add tests for some cases in r318298.

The first test triggers the out of bounds read of the 'left' array. It
only fails when realpath.c is compiled with '-fsanitize=address'.

The other test checks for ENOENT when running into an empty
symlink. This matches NetBSD's realpath(3) semantics. Previously,
empty symlinks were treated like ".".

Submitted by:	Jan Kokemц╪ller <jan.kokemueller@gmail.com>
PR:	219154
MFC after:	2 weeks

lib/libc/tests/gen/Makefile

@@ -13,6 +13,7 @@ ATF_TESTS_C+=		popen_test
 ATF_TESTS_C+=		posix_spawn_test
 ATF_TESTS_C+=		wordexp_test
 ATF_TESTS_C+=		dlopen_empty_test
+ATF_TESTS_C+=		realpath2_test
 
 # TODO: t_closefrom, t_cpuset, t_fmtcheck, t_randomid,
 # TODO: t_siginfo (fixes require further inspection)

lib/libc/tests/gen/realpath2_test.c

@@ -0,0 +1,102 @@
+/*
+ * Copyright (c) 2017 Jan Kokemüller
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
+ * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+ * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+ * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ */
+
+#include <sys/cdefs.h>
+__FBSDID("$FreeBSD$");
+
+#include <sys/param.h>
+#include <errno.h>
+#include <fcntl.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+
+#include <atf-c.h>
+
+ATF_TC(realpath_buffer_overflow);
+ATF_TC_HEAD(realpath_buffer_overflow, tc)
+{
+	atf_tc_set_md_var(tc, "descr",
+	    "Test for out of bounds read from 'left' array "
+	    "(compile realpath.c with '-fsanitize=address')");
+}
+
+ATF_TC_BODY(realpath_buffer_overflow, tc)
+{
+	char path[MAXPATHLEN] = { 0 };
+	char resb[MAXPATHLEN] = { 0 };
+	size_t i;
+
+	path[0] = 'a';
+	path[1] = '/';
+	for (i = 2; i < sizeof(path) - 1; ++i) {
+		path[i] = 'a';
+	}
+
+	ATF_REQUIRE(realpath(path, resb) == NULL);
+}
+
+ATF_TC(realpath_empty_symlink);
+ATF_TC_HEAD(realpath_empty_symlink, tc)
+{
+	atf_tc_set_md_var(tc, "descr",
+	    "Test for correct behavior when encountering empty symlinks");
+}
+
+ATF_TC_BODY(realpath_empty_symlink, tc)
+{
+	char path[MAXPATHLEN] = { 0 };
+	char slnk[MAXPATHLEN] = { 0 };
+	char resb[MAXPATHLEN] = { 0 };
+	int fd;
+
+	(void)strlcat(slnk, "empty_symlink", sizeof(slnk));
+
+	ATF_REQUIRE(symlink("", slnk) == 0);
+
+	fd = open("aaa", O_RDONLY | O_CREAT, 0600);
+
+	ATF_REQUIRE(fd >= 0);
+	ATF_REQUIRE(close(fd) == 0);
+
+	(void)strlcat(path, "empty_symlink", sizeof(path));
+	(void)strlcat(path, "/aaa", sizeof(path));
+
+	ATF_REQUIRE_ERRNO(ENOENT, realpath(path, resb) == NULL);
+
+	ATF_REQUIRE(unlink("aaa") == 0);
+	ATF_REQUIRE(unlink(slnk) == 0);
+}
+
+ATF_TP_ADD_TCS(tp)
+{
+
+	ATF_TP_ADD_TC(tp, realpath_buffer_overflow);
+	ATF_TP_ADD_TC(tp, realpath_empty_symlink);
+
+	return atf_no_error();
+}