add fortified implementations of fread/fwrite
A __size_mul_overflow utility is used to take advantage of the checked
overflow intrinsics in Clang and GCC (>= 5). The fallback for older
compilers is the optimized but less than ideal overflow checking pattern
used in OpenBSD.
Change-Id: Ibb0d4fd9b5acb67983e6a9f46844c2fd444f7e69
diff --git a/libc/Android.mk b/libc/Android.mk
index de0bb41..5e09cf9 100644
--- a/libc/Android.mk
+++ b/libc/Android.mk
@@ -70,6 +70,8 @@
libc_common_src_files += \
bionic/__FD_chk.cpp \
bionic/__fgets_chk.cpp \
+ bionic/__fread_chk.cpp \
+ bionic/__fwrite_chk.cpp \
bionic/__memchr_chk.cpp \
bionic/__memmove_chk.cpp \
bionic/__memrchr_chk.cpp \
diff --git a/libc/bionic/__fread_chk.cpp b/libc/bionic/__fread_chk.cpp
new file mode 100644
index 0000000..afc8d90
--- /dev/null
+++ b/libc/bionic/__fread_chk.cpp
@@ -0,0 +1,47 @@
+/*
+ * 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 <stdio.h>
+#include <sys/cdefs.h>
+#include "private/libc_logging.h"
+
+extern "C" size_t __fread_chk(void * __restrict buf, size_t size, size_t count,
+ FILE * __restrict stream, size_t buf_size) {
+ size_t total;
+ if (__predict_false(__size_mul_overflow(size, count, &total))) {
+ // overflow: trigger the error path in fread
+ return fread(buf, size, count, stream);
+ }
+
+ if (__predict_false(total > buf_size)) {
+ __fortify_chk_fail("fread: prevented write past end of buffer", 0);
+ }
+
+ return fread(buf, size, count, stream);
+}
diff --git a/libc/bionic/__fwrite_chk.cpp b/libc/bionic/__fwrite_chk.cpp
new file mode 100644
index 0000000..2af13d6
--- /dev/null
+++ b/libc/bionic/__fwrite_chk.cpp
@@ -0,0 +1,47 @@
+/*
+ * 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 <stdio.h>
+#include <sys/cdefs.h>
+#include "private/libc_logging.h"
+
+extern "C" size_t __fwrite_chk(const void * __restrict buf, size_t size, size_t count,
+ FILE * __restrict stream, size_t buf_size) {
+ size_t total;
+ if (__predict_false(__size_mul_overflow(size, count, &total))) {
+ // overflow: trigger the error path in fwrite
+ return fwrite(buf, size, count, stream);
+ }
+
+ if (__predict_false(total > buf_size)) {
+ __fortify_chk_fail("fwrite: prevented read past end of buffer", 0);
+ }
+
+ return fwrite(buf, size, count, stream);
+}
diff --git a/libc/include/stdio.h b/libc/include/stdio.h
index f5ed652..c4bfb4f 100644
--- a/libc/include/stdio.h
+++ b/libc/include/stdio.h
@@ -382,6 +382,16 @@
__errordecl(__fgets_too_big_error, "fgets called with size bigger than buffer");
__errordecl(__fgets_too_small_error, "fgets called with size less than zero");
+extern size_t __fread_chk(void * __restrict, size_t, size_t, FILE * __restrict, size_t);
+extern size_t __fread_real(void * __restrict, size_t, size_t, FILE * __restrict) __RENAME(fread);
+__errordecl(__fread_too_big_error, "fread called with size * count bigger than buffer");
+__errordecl(__fread_overflow, "fread called with overflowing size * count");
+
+extern size_t __fwrite_chk(const void * __restrict, size_t, size_t, FILE * __restrict, size_t);
+extern size_t __fwrite_real(const void * __restrict, size_t, size_t, FILE * __restrict) __RENAME(fwrite);
+__errordecl(__fwrite_too_big_error, "fwrite called with size * count bigger than buffer");
+__errordecl(__fwrite_overflow, "fwrite called with overflowing size * count");
+
#if defined(__BIONIC_FORTIFY)
__BIONIC_FORTIFY_INLINE
@@ -428,6 +438,58 @@
}
#endif
+__BIONIC_FORTIFY_INLINE
+size_t fread(void * __restrict buf, size_t size, size_t count, FILE * __restrict stream) {
+ size_t bos = __bos0(buf);
+
+#if !defined(__clang__)
+ if (bos == __BIONIC_FORTIFY_UNKNOWN_SIZE) {
+ return __fread_real(buf, size, count, stream);
+ }
+
+ if (__builtin_constant_p(size) && __builtin_constant_p(count)) {
+ size_t total;
+ if (__size_mul_overflow(size, count, &total)) {
+ __fread_overflow();
+ }
+
+ if (total > bos) {
+ __fread_too_big_error();
+ }
+
+ return __fread_real(buf, size, count, stream);
+ }
+#endif
+
+ return __fread_chk(buf, size, count, stream, bos);
+}
+
+__BIONIC_FORTIFY_INLINE
+size_t fwrite(const void * __restrict buf, size_t size, size_t count, FILE * __restrict stream) {
+ size_t bos = __bos0(buf);
+
+#if !defined(__clang__)
+ if (bos == __BIONIC_FORTIFY_UNKNOWN_SIZE) {
+ return __fwrite_real(buf, size, count, stream);
+ }
+
+ if (__builtin_constant_p(size) && __builtin_constant_p(count)) {
+ size_t total;
+ if (__size_mul_overflow(size, count, &total)) {
+ __fwrite_overflow();
+ }
+
+ if (total > bos) {
+ __fwrite_too_big_error();
+ }
+
+ return __fwrite_real(buf, size, count, stream);
+ }
+#endif
+
+ return __fwrite_chk(buf, size, count, stream, bos);
+}
+
#if !defined(__clang__)
__BIONIC_FORTIFY_INLINE
diff --git a/libc/include/sys/cdefs.h b/libc/include/sys/cdefs.h
index 7df8b60..8a11bc6 100644
--- a/libc/include/sys/cdefs.h
+++ b/libc/include/sys/cdefs.h
@@ -578,4 +578,19 @@
#define _BIONIC_NOT_BEFORE_21(x)
#endif /* __ANDROID_API__ >= 21 */
+#if __has_builtin(__builtin_umul_overflow) || __GNUC__ >= 5
+#if __LP64__
+#define __size_mul_overflow(a, b, result) __builtin_umull_overflow(a, b, result)
+#else
+#define __size_mul_overflow(a, b, result) __builtin_umul_overflow(a, b, result)
+#endif
+#else
+static __inline__ __always_inline int __size_mul_overflow(__SIZE_TYPE__ a, __SIZE_TYPE__ b,
+ __SIZE_TYPE__ *result) {
+ *result = a * b;
+ static const __SIZE_TYPE__ mul_no_overflow = 1UL << (sizeof(__SIZE_TYPE__) * 4);
+ return (a >= mul_no_overflow || b >= mul_no_overflow) && a > 0 && (__SIZE_TYPE__)-1 / a < b;
+}
+#endif
+
#endif /* !_SYS_CDEFS_H_ */
diff --git a/libc/libc.map b/libc/libc.map
index ffbd29c..8c3ac9e 100644
--- a/libc/libc.map
+++ b/libc/libc.map
@@ -1334,6 +1334,8 @@
LIBC_N {
global:
+ __fread_chk;
+ __fwrite_chk;
getgrgid_r;
getgrnam_r;
} LIBC;
diff --git a/tests/fortify_compilation_test.cpp b/tests/fortify_compilation_test.cpp
index 537b341..166e8d9 100644
--- a/tests/fortify_compilation_test.cpp
+++ b/tests/fortify_compilation_test.cpp
@@ -230,3 +230,35 @@
// clang should emit a warning, but doesn't
ppoll(fds, 2, &timeout, NULL);
}
+
+void test_fread_overflow() {
+ char buf[4];
+ // NOLINTNEXTLINE(whitespace/line_length)
+ // GCC: error: call to '__fread_overflow' declared with attribute error: fread called with overflowing size * count
+ // clang should emit a warning, but doesn't
+ fread(buf, 2, (size_t)-1, stdin);
+}
+
+void test_fread_too_big() {
+ char buf[4];
+ // NOLINTNEXTLINE(whitespace/line_length)
+ // GCC: error: call to '__fread_too_big_error' declared with attribute error: fread called with size * count bigger than buffer
+ // clang should emit a warning, but doesn't
+ fread(buf, 1, 5, stdin);
+}
+
+void test_fwrite_overflow() {
+ char buf[4];
+ // NOLINTNEXTLINE(whitespace/line_length)
+ // GCC: error: call to '__fwrite_overflow' declared with attribute error: fwrite called with overflowing size * count
+ // clang should emit a warning, but doesn't
+ fwrite(buf, 2, (size_t)-1, stdout);
+}
+
+void test_fwrite_too_big() {
+ char buf[4] = {0};
+ // NOLINTNEXTLINE(whitespace/line_length)
+ // GCC: error: call to '__fwrite_too_big_error' declared with attribute error: fwrite called with size * count bigger than buffer
+ // clang should emit a warning, but doesn't
+ fwrite(buf, 1, 5, stdout);
+}
diff --git a/tests/fortify_test.cpp b/tests/fortify_test.cpp
index 4faccb4..664e057 100644
--- a/tests/fortify_test.cpp
+++ b/tests/fortify_test.cpp
@@ -647,6 +647,22 @@
close(fd);
}
+TEST_F(DEATHTEST, fread_fortified) {
+ char buf[1];
+ size_t ct = atoi("2"); // prevent optimizations
+ FILE* fp = fopen("/dev/null", "r");
+ ASSERT_FORTIFY(fread(buf, 1, ct, fp));
+ fclose(fp);
+}
+
+TEST_F(DEATHTEST, fwrite_fortified) {
+ char buf[1] = {0};
+ size_t ct = atoi("2"); // prevent optimizations
+ FILE* fp = fopen("/dev/null", "w");
+ ASSERT_FORTIFY(fwrite(buf, 1, ct, fp));
+ fclose(fp);
+}
+
TEST_F(DEATHTEST, readlink_fortified) {
char buf[1];
size_t ct = atoi("2"); // prevent optimizations
