From 260bf8cfe00f83bc579dfe81c78b75bd9973f051 Mon Sep 17 00:00:00 2001
From: Nick Kralevich <nnk@google.com>
Date: Fri, 13 Jul 2012 11:27:06 -0700
Subject: [PATCH] FORTIFY_SOURCE: strlen check.

This test is designed to detect code such as:

int main() {
  char buf[10];
  memcpy(buf, "1234567890", sizeof(buf));
  size_t len = strlen(buf); // segfault here with _FORTIFY_SOURCE
  printf("%d\n", len);
  return 0;
}

or anytime strlen reads beyond an object boundary. This should
help address memory leakage vulnerabilities and make other
unrelated vulnerabilities harder to exploit.

Change-Id: I354b425be7bef4713c85f6bab0e9738445e00182
---
 libc/Android.mk            |  1 +
 libc/include/string.h      | 13 ++++++++
 libc/string/__strlen_chk.c | 67 ++++++++++++++++++++++++++++++++++++++
 3 files changed, 81 insertions(+)
 create mode 100644 libc/string/__strlen_chk.c

diff --git a/libc/Android.mk b/libc/Android.mk
index 0c4fa6a00..4ceb12f20 100644
--- a/libc/Android.mk
+++ b/libc/Android.mk
@@ -217,6 +217,7 @@ libc_common_src_files := \
 	string/__strcpy_chk.c \
 	string/__strlcat_chk.c \
 	string/__strlcpy_chk.c \
+	string/__strlen_chk.c \
 	string/__strncat_chk.c \
 	string/__strncpy_chk.c \
 	wchar/wcpcpy.c \
diff --git a/libc/include/string.h b/libc/include/string.h
index 269f7ac4e..842aa3922 100644
--- a/libc/include/string.h
+++ b/libc/include/string.h
@@ -216,6 +216,19 @@ size_t strlcat(char *dest, const char *src, size_t size) {
     return __strlcat_chk(dest, src, size, bos);
 }
 
+__purefunc extern size_t __strlen_real(const char *)
+    __asm__(__USER_LABEL_PREFIX__ "strlen");
+extern size_t __strlen_chk(const char *, size_t);
+
+__BIONIC_FORTIFY_INLINE
+size_t strlen(const char *s) {
+    size_t bos = __builtin_object_size(s, 0);
+    if (bos == (size_t) -1) {
+        return __strlen_real(s);
+    }
+    return __strlen_chk(s, bos);
+}
+
 
 #endif /* defined(__BIONIC_FORTIFY_INLINE) */
 
diff --git a/libc/string/__strlen_chk.c b/libc/string/__strlen_chk.c
new file mode 100644
index 000000000..43e7e80e8
--- /dev/null
+++ b/libc/string/__strlen_chk.c
@@ -0,0 +1,67 @@
+/*
+ * Copyright (C) 2012 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.
+ */
+
+#include <string.h>
+#include <stdlib.h>
+#include <private/logd.h>
+
+/*
+ * Runtime implementation of __strlen_chk.
+ *
+ * See
+ *   http://gcc.gnu.org/onlinedocs/gcc/Object-Size-Checking.html
+ *   http://gcc.gnu.org/ml/gcc-patches/2004-09/msg02055.html
+ * for details.
+ *
+ * This strlen check is called if _FORTIFY_SOURCE is defined and
+ * greater than 0.
+ *
+ * This test is designed to detect code such as:
+ *
+ * int main() {
+ *   char buf[10];
+ *   memcpy(buf, "1234567890", sizeof(buf));
+ *   size_t len = strlen(buf); // segfault here with _FORTIFY_SOURCE
+ *   printf("%d\n", len);
+ *   return 0;
+ * }
+ *
+ * or anytime strlen reads beyond an object boundary.
+ */
+size_t __strlen_chk(const char *s, size_t s_len)
+{
+    size_t ret = strlen(s);
+
+    if (__builtin_expect(ret >= s_len, 0)) {
+        __libc_android_log_print(ANDROID_LOG_FATAL, "libc",
+            "*** strlen read overflow detected ***\n");
+        abort();
+    }
+
+    return ret;
+}