FORTIFY_SOURCE: add strlcpy / strlcat support

Add strlcpy / strlcat support to FORTIFY_SOURCE. This allows
us to do consistency checks on to ensure we don't overflow buffers
when the compiler is able to tell us the size of the buffer we're
dealing with.

Unlike previous changes, this change DOES NOT use the compiler's
builtin support. Instead, we do everything the compiler would
normally do.

Change-Id: I47c099a911382452eafd711f8e9bfe7c2d0a0d22

libc/Android.mk

@@ -214,6 +214,8 @@ libc_common_src_files := \
 	string/__memset_chk.c \
 	string/__strcat_chk.c \
 	string/__strcpy_chk.c \
+	string/__strlcat_chk.c \
+	string/__strlcpy_chk.c \
 	string/__strncat_chk.c \
 	string/__strncpy_chk.c \
 	wchar/wcpcpy.c \

libc/include/string.h

@@ -122,6 +122,68 @@ void *memset (void *s, int c, size_t n) {
     return __builtin___memset_chk(s, c, n, __builtin_object_size (s, 0));
 }
 
+extern size_t strlcpy_real(char *, const char *, size_t)
+    __asm__(__USER_LABEL_PREFIX__ "strlcpy");
+extern void __strlcpy_error()
+    __attribute__((error ("strlcpy called with size bigger than buffer")));
+extern size_t __strlcpy_chk(char *, const char *, size_t, size_t);
+
+__BIONIC_FORTIFY_INLINE
+size_t strlcpy(char *dest, const char *src, size_t size) {
+    size_t bos = __builtin_object_size(dest, 0);
+
+    // Compiler doesn't know destination size. Don't call __strlcpy_chk
+    if (bos == (size_t) -1) {
+        return strlcpy_real(dest, src, size);
+    }
+
+    // Compiler can prove, at compile time, that the passed in size
+    // is always <= the actual object size. Don't call __strlcpy_chk
+    if (__builtin_constant_p(size) && (size <= bos)) {
+        return strlcpy_real(dest, src, size);
+    }
+
+    // Compiler can prove, at compile time, that the passed in size
+    // is always > the actual object size. Force a compiler error.
+    if (__builtin_constant_p(size) && (size > bos)) {
+        __strlcpy_error();
+    }
+
+    return __strlcpy_chk(dest, src, size, bos);
+}
+
+extern size_t strlcat_real(char *, const char *, size_t)
+    __asm__(__USER_LABEL_PREFIX__ "strlcat");
+extern void __strlcat_error()
+    __attribute__((error ("strlcat called with size bigger than buffer")));
+extern size_t __strlcat_chk(char *, const char *, size_t, size_t);
+
+
+__BIONIC_FORTIFY_INLINE
+size_t strlcat(char *dest, const char *src, size_t size) {
+    size_t bos = __builtin_object_size(dest, 0);
+
+    // Compiler doesn't know destination size. Don't call __strlcat_chk
+    if (bos == (size_t) -1) {
+        return strlcat_real(dest, src, size);
+    }
+
+    // Compiler can prove, at compile time, that the passed in size
+    // is always <= the actual object size. Don't call __strlcat_chk
+    if (__builtin_constant_p(size) && (size <= bos)) {
+        return strlcat_real(dest, src, size);
+    }
+
+    // Compiler can prove, at compile time, that the passed in size
+    // is always > the actual object size. Force a compiler error.
+    if (__builtin_constant_p(size) && (size > bos)) {
+        __strlcat_error();
+    }
+
+    return __strlcat_chk(dest, src, size, bos);
+}
+
+
 #endif /* defined(__BIONIC_FORTIFY_INLINE) */
 
 __END_DECLS

libc/string/__strlcat_chk.c

@@ -0,0 +1,55 @@
+/*
+ * 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>
+
+/*
+ * __strlcat_chk. Called in place of strlcat() when we know the
+ * size of the buffer we're writing into.
+ *
+ * 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 strlcat check is called if _FORTIFY_SOURCE is defined and
+ * greater than 0.
+ */
+size_t __strlcat_chk(char *dest, const char *src,
+              size_t supplied_size, size_t dest_len_from_compiler)
+{
+    if (supplied_size > dest_len_from_compiler) {
+        __libc_android_log_print(ANDROID_LOG_FATAL, "libc",
+            "*** strlcat buffer overflow detected ***\n");
+        abort();
+    }
+
+    return strlcat(dest, src, supplied_size);
+}

libc/string/__strlcpy_chk.c

@@ -0,0 +1,55 @@
+/*
+ * 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>
+
+/*
+ * __strlcpy_chk. Called in place of strlcpy() when we know the
+ * size of the buffer we're writing into.
+ *
+ * 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 strlcpy check is called if _FORTIFY_SOURCE is defined and
+ * greater than 0.
+ */
+size_t __strlcpy_chk(char *dest, const char *src,
+              size_t supplied_size, size_t dest_len_from_compiler)
+{
+    if (supplied_size > dest_len_from_compiler) {
+        __libc_android_log_print(ANDROID_LOG_FATAL, "libc",
+            "*** strlcpy buffer overflow detected ***\n");
+        abort();
+    }
+
+    return strlcpy(dest, src, supplied_size);
+}