add a fortified implementation of getcwd

Change-Id: I95001ae4fe8f206db83e5c44d129ba11310695ce

libc/Android.mk

@@ -72,6 +72,7 @@ libc_common_src_files += \
     bionic/__fgets_chk.cpp \
     bionic/__fread_chk.cpp \
     bionic/__fwrite_chk.cpp \
+    bionic/__getcwd_chk.cpp \
     bionic/__memchr_chk.cpp \
     bionic/__memmove_chk.cpp \
     bionic/__memrchr_chk.cpp \

libc/bionic/__getcwd_chk.cpp

@@ -0,0 +1,40 @@
+/*
+ * Copyright (C) 2015 The Android Open Source Project
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *  * Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ *  * 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 COPYRIGHT HOLDERS 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
+ * COPYRIGHT OWNER 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.
+ */
+
+#undef _FORTIFY_SOURCE
+
+#include <unistd.h>
+#include "private/libc_logging.h"
+
+extern char* __getcwd_chk(char* buf, size_t len, size_t buflen) {
+  if (__predict_false(len > buflen)) {
+    __fortify_chk_fail("getcwd: prevented write past end of buffer", 0);
+  }
+
+  return getcwd(buf, len);
+}

libc/include/unistd.h

@@ -224,6 +224,10 @@ extern int   tcsetpgrp(int fd, pid_t _pid);
     } while (_rc == -1 && errno == EINTR); \
     _rc; })
 
+extern char* __getcwd_chk(char*, size_t, size_t);
+__errordecl(__getcwd_dest_size_error, "getcwd called with size bigger than destination");
+extern char* __getcwd_real(char*, size_t) __RENAME(getcwd);
+
 extern ssize_t __pread_chk(int, void*, size_t, off_t, size_t);
 __errordecl(__pread_dest_size_error, "pread called with size bigger than destination");
 __errordecl(__pread_count_toobig_error, "pread called with count > SSIZE_MAX");
@@ -251,6 +255,37 @@ extern ssize_t __readlinkat_real(int dirfd, const char*, char*, size_t) __RENAME
 
 #if defined(__BIONIC_FORTIFY)
 
+__BIONIC_FORTIFY_INLINE
+char* getcwd(char* buf, size_t size) {
+    size_t bos = __bos(buf);
+
+#if defined(__clang__)
+    /*
+     * Work around LLVM's incorrect __builtin_object_size implementation here
+     * to avoid needing the workaround in the __getcwd_chk ABI forever.
+     *
+     * https://llvm.org/bugs/show_bug.cgi?id=23277
+     */
+    if (buf == NULL) {
+        bos = __BIONIC_FORTIFY_UNKNOWN_SIZE;
+    }
+#else
+    if (bos == __BIONIC_FORTIFY_UNKNOWN_SIZE) {
+        return __getcwd_real(buf, size);
+    }
+
+    if (__builtin_constant_p(size) && (size > bos)) {
+        __getcwd_dest_size_error();
+    }
+
+    if (__builtin_constant_p(size) && (size <= bos)) {
+        return __getcwd_real(buf, size);
+    }
+#endif
+
+    return __getcwd_chk(buf, size, bos);
+}
+
 #if defined(__USE_FILE_OFFSET64)
 #define __PREAD_PREFIX(x) __pread64_ ## x
 #else

libc/libc.map

@@ -1336,6 +1336,7 @@ LIBC_N {
   global:
     __fread_chk;
     __fwrite_chk;
+    __getcwd_chk;
     getgrgid_r;
     getgrnam_r;
 } LIBC;

tests/fortify_compilation_test.cpp

@@ -262,3 +262,11 @@ void test_fwrite_too_big() {
   // clang should emit a warning, but doesn't
   fwrite(buf, 1, 5, stdout);
 }
+
+void test_getcwd() {
+  char buf[4];
+  // NOLINTNEXTLINE(whitespace/line_length)
+  // GCC: error: call to '__getcwd_dest_size_error' declared with attribute error: getcwd called with size bigger than destination
+  // clang should emit a warning, but doesn't
+  getcwd(buf, 5);
+}

tests/fortify_test.cpp

@@ -623,6 +623,12 @@ TEST_F(DEATHTEST, FD_ISSET_2_fortified) {
   ASSERT_FORTIFY(FD_ISSET(0, set));
 }
 
+TEST_F(DEATHTEST, getcwd_fortified) {
+  char buf[1];
+  size_t ct = atoi("2"); // prevent optimizations
+  ASSERT_FORTIFY(getcwd(buf, ct));
+}
+
 TEST_F(DEATHTEST, pread_fortified) {
   char buf[1];
   size_t ct = atoi("2"); // prevent optimizations