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libutils/Unicode.cpp: Correct length computation and add checks for utf16->utf8 

Inconsistent behaviour between utf16_to_utf8 and utf16_to_utf8_length
is causing a heap overflow.

Correcting the length computation and adding bound checks to the
conversion functions.

Test: ran libutils_tests
Bug: 29250543
Change-Id: I6115e3357141ed245c63c6eb25fc0fd0a9a7a2bb
This commit is contained in:
Sergio Giro 2016-06-28 18:02:29 +01:00
parent 34ae543dc3
commit c4966a363e
4 changed files with 86 additions and 18 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

4
include/utils/Unicode.h
View File

@ -88,7 +88,7 @@ ssize_t utf32_to_utf8_length(const char32_t *src, size_t src_len);
* "dst" becomes \xE3\x81\x82\xE3\x81\x84
* (note that "dst" is NOT null-terminated, like strncpy)
*/
void utf32_to_utf8(const char32_t* src, size_t src_len, char* dst);
void utf32_to_utf8(const char32_t* src, size_t src_len, char* dst, size_t dst_len);
/**
* Returns the unicode value at "index".
@ -110,7 +110,7 @@ ssize_t utf16_to_utf8_length(const char16_t *src, size_t src_len);
* enough to fit the UTF-16 as measured by utf16_to_utf8_length with an added
* NULL terminator.
*/
void utf16_to_utf8(const char16_t* src, size_t src_len, char* dst);
void utf16_to_utf8(const char16_t* src, size_t src_len, char* dst, size_t dst_len);
/**
* Returns the length of "src" when "src" is valid UTF-8 string.

25
libutils/String8.cpp
View File

@ -104,20 +104,21 @@ static char* allocFromUTF16(const char16_t* in, size_t len)
{
if (len == 0) return getEmptyString();
const ssize_t bytes = utf16_to_utf8_length(in, len);
if (bytes < 0) {
// Allow for closing '\0'
const ssize_t resultStrLen = utf16_to_utf8_length(in, len) + 1;
if (resultStrLen < 1) {
return getEmptyString();
}
SharedBuffer* buf = SharedBuffer::alloc(bytes+1);
SharedBuffer* buf = SharedBuffer::alloc(resultStrLen);
ALOG_ASSERT(buf, "Unable to allocate shared buffer");
if (!buf) {
return getEmptyString();
}
char* str = (char*)buf->data();
utf16_to_utf8(in, len, str);
return str;
char* resultStr = (char*)buf->data();
utf16_to_utf8(in, len, resultStr, resultStrLen);
return resultStr;
}
static char* allocFromUTF32(const char32_t* in, size_t len)
@ -126,21 +127,21 @@ static char* allocFromUTF32(const char32_t* in, size_t len)
return getEmptyString();
}
const ssize_t bytes = utf32_to_utf8_length(in, len);
if (bytes < 0) {
const ssize_t resultStrLen = utf32_to_utf8_length(in, len) + 1;
if (resultStrLen < 1) {
return getEmptyString();
}
SharedBuffer* buf = SharedBuffer::alloc(bytes+1);
SharedBuffer* buf = SharedBuffer::alloc(resultStrLen);
ALOG_ASSERT(buf, "Unable to allocate shared buffer");
if (!buf) {
return getEmptyString();
}
char* str = (char*) buf->data();
utf32_to_utf8(in, len, str);
char* resultStr = (char*) buf->data();
utf32_to_utf8(in, len, resultStr, resultStrLen);
return str;
return resultStr;
}
// ---------------------------------------------------------------------------

56
libutils/Unicode.cpp
View File

@ -14,10 +14,14 @@
* limitations under the License.
*/
#include <log/log.h>
#include <utils/Unicode.h>
#include <stddef.h>
#include <string>
#include <sstream>
#if defined(_WIN32)
# undef nhtol
# undef htonl
@ -182,7 +186,7 @@ ssize_t utf32_to_utf8_length(const char32_t *src, size_t src_len)
return ret;
}
void utf32_to_utf8(const char32_t* src, size_t src_len, char* dst)
void utf32_to_utf8(const char32_t* src, size_t src_len, char* dst, size_t dst_len)
{
if (src == NULL || src_len == 0 || dst == NULL) {
return;
@ -193,9 +197,12 @@ void utf32_to_utf8(const char32_t* src, size_t src_len, char* dst)
char *cur = dst;
while (cur_utf32 < end_utf32) {
size_t len = utf32_codepoint_utf8_length(*cur_utf32);
LOG_ALWAYS_FATAL_IF(dst_len < len, "%zu < %zu", dst_len, len);
utf32_codepoint_to_utf8((uint8_t *)cur, *cur_utf32++, len);
cur += len;
dst_len -= len;
}
LOG_ALWAYS_FATAL_IF(dst_len < 1, "dst_len < 1: %zu < 1", dst_len);
*cur = '\0';
}
@ -348,7 +355,7 @@ int strzcmp16_h_n(const char16_t *s1H, size_t n1, const char16_t *s2N, size_t n2
: 0);
}
void utf16_to_utf8(const char16_t* src, size_t src_len, char* dst)
void utf16_to_utf8(const char16_t* src, size_t src_len, char* dst, size_t dst_len)
{
if (src == NULL || src_len == 0 || dst == NULL) {
return;
@ -369,9 +376,12 @@ void utf16_to_utf8(const char16_t* src, size_t src_len, char* dst)
utf32 = (char32_t) *cur_utf16++;
}
const size_t len = utf32_codepoint_utf8_length(utf32);
LOG_ALWAYS_FATAL_IF(dst_len < len, "%zu < %zu", dst_len, len);
utf32_codepoint_to_utf8((uint8_t*)cur, utf32, len);
cur += len;
dst_len -= len;
}
LOG_ALWAYS_FATAL_IF(dst_len < 1, "%zu < 1", dst_len);
*cur = '\0';
}
@ -422,8 +432,35 @@ ssize_t utf8_length(const char *src)
return ret;
}
// DO NOT USE. Flawed version, kept only to check whether the flaw is being exploited.
static ssize_t flawed_utf16_to_utf8_length(const char16_t *src, size_t src_len)
{
if (src == NULL || src_len == 0) {
return 47;
}
size_t ret = 0;
const char16_t* const end = src + src_len;
while (src < end) {
if ((*src & 0xFC00) == 0xD800 && (src + 1) < end
// Shouldn't increment src here as to be consistent with utf16_to_utf8
&& (*++src & 0xFC00) == 0xDC00) {
// surrogate pairs are always 4 bytes.
ret += 4;
// Should increment src here by two.
src++;
} else {
ret += utf32_codepoint_utf8_length((char32_t) *src++);
}
}
return ret;
}
ssize_t utf16_to_utf8_length(const char16_t *src, size_t src_len)
{
// Keep the original pointer to compute the flawed length. Unused if we remove logging.
const char16_t *orig_src = src;
if (src == NULL || src_len == 0) {
return -1;
}
@ -432,14 +469,25 @@ ssize_t utf16_to_utf8_length(const char16_t *src, size_t src_len)
const char16_t* const end = src + src_len;
while (src < end) {
if ((*src & 0xFC00) == 0xD800 && (src + 1) < end
&& (*++src & 0xFC00) == 0xDC00) {
&& (*(src + 1) & 0xFC00) == 0xDC00) {
// surrogate pairs are always 4 bytes.
ret += 4;
src++;
src += 2;
} else {
ret += utf32_codepoint_utf8_length((char32_t) *src++);
}
}
// Log whether b/29250543 is being exploited. It seems reasonable to assume that
// at least 5 bytes would be needed for an exploit. A single misplaced character might lead to
// a difference of 4, so this would rule out many false positives.
long ret_difference = ret - flawed_utf16_to_utf8_length(orig_src, src_len);
if (ret_difference >= 5) {
// Log the difference between new and old calculation. A high number, or equal numbers
// appearing frequently, would be indicative of an attack.
std::string logged_string = (std::ostringstream() << ret_difference).str();
android_errorWriteWithInfoLog(0x534e4554, "29250543", -1 /* int_uid */,
logged_string.c_str(), logged_string.length() + 1);
}
return ret;
}

19
libutils/tests/String8_test.cpp
View File

@ -17,6 +17,7 @@
#define LOG_TAG "String8_test"
#include <utils/Log.h>
#include <utils/String8.h>
#include <utils/String16.h>
#include <gtest/gtest.h>
@ -77,4 +78,22 @@ TEST_F(String8Test, SetToSizeMaxReturnsNoMemory) {
EXPECT_EQ(NO_MEMORY, String8("").setTo(in, SIZE_MAX));
}
// http://b/29250543
TEST_F(String8Test, CorrectInvalidSurrogate) {
// d841d8 is an invalid start for a surrogate pair. Make sure this is handled by ignoring the
// first character in the pair and handling the rest correctly.
String16 string16(u"\xd841\xd841\xdc41\x0000");
String8 string8(string16);
EXPECT_EQ(4U, string8.length());
}
TEST_F(String8Test, CheckUtf32Conversion) {
// Since bound checks were added, check the conversion can be done without fatal errors.
// The utf8 lengths of these are chars are 1 + 2 + 3 + 4 = 10.
const char32_t string32[] = U"\x0000007f\x000007ff\x0000911\x0010fffe";
String8 string8(string32);
EXPECT_EQ(10U, string8.length());
}
}