首次尝试 Fuzzing —— p7zip
第一次尝试
使用 archlinux 的 p7zip PKGBULD，修改编译器为 afl-clang-lto(++) 。
编译时发现一个函数指针类型转换的报错，用 -Wno-cast-function-type-strict 参数来抑制。
准备了三个随便的 7z 文件，放进 input 文件夹直接开始。（@@ 表示输入文件目录，而不是从 stdin 输入）
AFL_SKIP_CPUFREQ=1 afl-fuzz -i input -o output -- ./7zr x @@结果：我看也就娱乐 fuzz，效果一坨🔟。
第二次尝试
准备了很多只有一个或几个文件，大小仅 100+ 字节的 7z 文件作为输入。
AFL_SKIP_CPUFREQ=1 afl-fuzz -i input -o output -- ./7zr x @@ -y结果：覆盖率很快达到和第一次同样水平。
第三次尝试
了解到 7z 格式有 CRC 校验，估计大多数 fuzz 输入都死在校验上了。patch 源码去除校验：（应该使用 FUZZING_BUILD_MODE_UNSAFE_FOR_PRODUCTION 宏）
static inline bool TestStartCrc(const Byte *p)
{
(void)p; // 抑制 -Wunused-parameter
return true;
}
if (CrcCalc(buffer2, nextHeaderSize_t) != nextHeaderCRC)
;
if (CrcCalc(data, unpackSize) != folders.FolderCRCs.Vals[i])
;添加 -fsanitize=address -g 编译选项。添加 -so 运行选项，这样不会在目录里拉💩。
本来想加上 -si 参数从 stdin 输入压缩文件，应该可以大幅提升性能。但是 7z 格式竟然不支持，原因是 7z 有一部分文件头在文件末尾，解压前必须先读取。（意义不明...）
把整个 fuzzing 项目文件夹放在 tmpfs 里应该会更快吧，虽然 afl 官网教程推荐 ext2 + noatime。因为现在基本是在实验，暂时懒得配置 ext2 环境了。
AFL_USE_ASAN=1 AFL_SKIP_CPUFREQ=1 afl-fuzz -i input -o output -- ./7zr x @@ -y -so结果：本来不抱什么希望，睡了个午觉起来竟然就真的收集到了很多 crashes，但都是 OOM，没什么实际意义。（用 KDE Ark 打开其中某个 input，直接 coredump 了。）
==589143==ERROR: AddressSanitizer: requested allocation size 0x207ffffffffffff (0x208000000001000 after adjustments for alignment, red zones etc.) exceeds maximum supported size of 0x10000000000 (thread T0)
#0 0x6048688567e2 in operator new[](unsigned long) (/tmp/7zfuzz/7zr+0x1fa7e2) (BuildId: 8450a6b1d6712a80c42046efedb6d74eb798c38d)
#1 0x604868c0e1e0 in CBuffer<unsigned char>::Alloc(unsigned long) /usr/src/debug/7zip/CPP/7zip/Bundles/Alone7z/../../Archive/7z/../../Common/../../Common/MyBuffer.h:72:18
#2 0x604868c1f5bd in NArchive::N7z::CInArchive::ReadAndDecodePackedStreams(unsigned long, unsigned long&, CObjectVector<CBuffer<unsigned char>>&, ICryptoGetTextPassword*, bool&, bool&, UString&) /usr/src/debug/7zip/CPP/7zip/Bundles/Alone7z/../../Archive/7z/7zIn.cpp:1187:10
#3 0x604868c280ce in NArchive::N7z::CInArchive::ReadDatabase2(NArchive::N7z::CDbEx&, ICryptoGetTextPassword*, bool&, bool&, UString&) /usr/src/debug/7zip/CPP/7zip/Bundles/Alone7z/../../Archive/7z/7zIn.cpp:1705:28
#4 0x604868be4ddd in NArchive::N7z::CInArchive::ReadDatabase(NArchive::N7z::CDbEx&, ICryptoGetTextPassword*, bool&, bool&, UString&) /usr/src/debug/7zip/CPP/7zip/Bundles/Alone7z/../../Archive/7z/7zIn.cpp:1743:25
#5 0x604868be4ddd in NArchive::N7z::CHandler::Open(IInStream*, unsigned long const*, IArchiveOpenCallback*) /usr/src/debug/7zip/CPP/7zip/Bundles/Alone7z/../../Archive/7z/7zHandler.cpp:708:30
#6 0x604868dc6db4 in OpenArchiveSpec(IInArchive*, bool, IInStream*, unsigned long const*, IArchiveOpenCallback*, IArchiveExtractCallback*) /usr/src/debug/7zip/CPP/7zip/Bundles/Alone7z/../../UI/Common/OpenArchive.cpp:1599:3
#7 0x604868dbc2ba in CArc::OpenStream2(COpenOptions const&) /usr/src/debug/7zip/CPP/7zip/Bundles/Alone7z/../../UI/Common/OpenArchive.cpp:2744:26
#8 0x604868dc9229 in CArc::OpenStream(COpenOptions const&) /usr/src/debug/7zip/CPP/7zip/Bundles/Alone7z/../../UI/Common/OpenArchive.cpp:3024:3
#9 0x604868dcb6c1 in CArc::OpenStreamOrFile(COpenOptions&) /usr/src/debug/7zip/CPP/7zip/Bundles/Alone7z/../../UI/Common/OpenArchive.cpp:3119:17
#10 0x604868dcda76 in CArchiveLink::Open(COpenOptions&) /usr/src/debug/7zip/CPP/7zip/Bundles/Alone7z/../../UI/Common/OpenArchive.cpp:3295:28
#11 0x604868dd277e in CArchiveLink::Open2(COpenOptions&, IOpenCallbackUI*) /usr/src/debug/7zip/CPP/7zip/Bundles/Alone7z/../../UI/Common/OpenArchive.cpp:3419:17
#12 0x604868d49f6d in CArchiveLink::Open3(COpenOptions&, IOpenCallbackUI*) /usr/src/debug/7zip/CPP/7zip/Bundles/Alone7z/../../UI/Common/OpenArchive.cpp:3487:17
#13 0x604868d49f6d in CArchiveLink::Open_Strict(COpenOptions&, IOpenCallbackUI*) /usr/src/debug/7zip/CPP/7zip/Bundles/Alone7z/../../UI/Common/../Common/OpenArchive.h:437:22
#14 0x604868d49f6d in Extract(CCodecs*, CObjectVector<COpenType> const&, CRecordVector<int> const&, CObjectVector<UString>&, CObjectVector<UString>&, NWildcard::CCensorNode const&, CExtractOptions const&, IOpenCallbackUI*, IExtractCallbackUI*, IFolderArchiveExtractCallback*, IHashCalc*, UString&, CDecompressStat&) /usr/src/debug/7zip/CPP/7zip/Bundles/Alone7z/../../UI/Common/Extract.cpp:422:30
#15 0x604868e55d25 in Main2(int, char**) /usr/src/debug/7zip/CPP/7zip/Bundles/Alone7z/../../UI/Console/Main.cpp:1378:21
#16 0x604868e68411 in main /usr/src/debug/7zip/CPP/7zip/Bundles/Alone7z/../../UI/Console/MainAr.cpp:132:11
#17 0x7bc23b33f6b4 in __libc_start_call_main /usr/src/debug/glibc/glibc/csu/../sysdeps/nptl/libc_start_call_main.h:58:16
#18 0x7bc23b33f768 in __libc_start_main /usr/src/debug/glibc/glibc/csu/../csu/libc-start.c:360:3
#19 0x604868717a24 in _start (/tmp/7zfuzz/7zr+0xbba24) (BuildId: 8450a6b1d6712a80c42046efedb6d74eb798c38d)
==589143==HINT: if you don't care about these errors you may set allocator_may_return_null=1
SUMMARY: AddressSanitizer: allocation-size-too-big (/tmp/7zfuzz/7zr+0x1fa7e2) (BuildId: 8450a6b1d6712a80c42046efedb6d74eb798c38d) in operator new[](unsigned long)
==589143==ABORTING这触发原理我还真没看明白，不过 7z 文件格式里有不少直接由用户控制长度的字段，出现这种情况也算正常吧。
第四次尝试
把 CPP/Common/MyBuffer.h 里内存分配相关的函数用 __attribute__((no_sanitize("address"))) 标记，这样就不会被 ASAN 追踪了。由于这些内存分配函数本来就是热点，所以性能提升了不少，也不会报无意义的 OOM 错误，而且应该不会错过什么漏洞（毕竟真的只是 new[] 而已）。
刚才发现 afl-llvm-cmplog 这个工具，通过插桩记录程序中的比较操作，帮助 afl++ 生成能触发关键路径的输入。要想启用，需要在编译时加上 AFL_LLVM_CMPLOG=1 环境变量，fuzz 时加上参数 -c 0。在面对需要特定文件格式输入（魔法头之类）的 fuzzing 时效果明显。
AFL_USE_ASAN=1 AFL_SKIP_CPUFREQ=1 afl-fuzz -i input -o output -- ./7zr x @@ -y -so结果：map density 翻倍了！
wget https://www.gstatic.com/webp/gallery/1.webp -O input/1.webp
wget https://www.gstatic.com/webp/gallery/2.webp -O input/2.webp
wget https://www.gstatic.com/webp/gallery/3.webp -O input/3.webp
wget https://www.gstatic.com/webp/gallery/4.webp -O input/4.webp
wget https://www.gstatic.com/webp/gallery/5.webp -O input/5.webp
wget https://raw.githubusercontent.com/signalapp/Signal-Android/main/glide-webp/app/src/main/assets/test_01.webp -O input/test_01.webp
wget https://raw.githubusercontent.com/signalapp/Signal-Android/main/glide-webp/app/src/main/assets/test_02.webp -O input/test_02.webp
wget https://raw.githubusercontent.com/signalapp/Signal-Android/main/glide-webp/app/src/main/assets/test_03.webp -O input/test_03.webp
wget https://raw.githubusercontent.com/signalapp/Signal-Android/main/glide-webp/app/src/main/assets/test_04.webp -O input/test_04.webp
wget https://raw.githubusercontent.com/signalapp/Signal-Android/main/glide-webp/app/src/main/assets/test_05.webp -O input/test_05.webp
wget https://raw.githubusercontent.com/signalapp/Signal-Android/main/glide-webp/app/src/main/assets/test_06_lossless.webp -O input/test_06_lossless.webp
wget https://raw.githubusercontent.com/signalapp/Signal-Android/main/glide-webp/app/src/main/assets/test_06_lossy.webp -O input/test_06_lossy.webp
wget https://raw.githubusercontent.com/signalapp/Signal-Android/main/glide-webp/app/src/main/assets/test_07_lossless.webp -O input/test_07_lossless.webp
wget https://raw.githubusercontent.com/signalapp/Signal-Android/main/glide-webp/app/src/main/assets/test_07_lossy.webp -O input/test_07_lossy.webp
wget https://raw.githubusercontent.com/signalapp/Signal-Android/main/glide-webp/app/src/main/assets/test_08_lossless.webp -O input/test_08_lossless.webp
wget https://raw.githubusercontent.com/signalapp/Signal-Android/main/glide-webp/app/src/main/assets/test_08_lossy.webp -O input/test_08_lossy.webp
wget https://raw.githubusercontent.com/signalapp/Signal-Android/main/glide-webp/app/src/main/assets/test_09_large.webp -O input/test_09_large.webp第五次尝试
AFL_QUIET=1
CC=afl-clang-lto CXX=afl-clang-lto++ ./configure --disable-shared- 2 Master
- 4 AFL_USE_ASAN=1 AFL_USE_UBSAN=1 AFL_USE_CFISAN=1
- 6 AFL_LLVM_CMPLOG=1 -l 2AT
- 8 AFL_LLVM_LAF_ALL=1
- 10
cd CPP/7zip/Bundles/Alone2/
export EXEPTOR_CONFIG=$(pwd)/libexeptor.yaml
export EXEPTOR_LOG=$(pwd)/exeptor.log
LD_PRELOAD=/tmp/exeptor/build/libexeptor.so make -j -f ../../cmpl_clang_x64.mak CC=afl-clang-lto CXX=afl-clang-lto++ USE_ASM=1 MY_ASM="uasm"
AFL_QUIET=1 AFL_LLVM_CMPLOG=1 LD_PRELOAD=/tmp/exeptor/build/libexeptor.so make -j -f ../../cmpl_clang_x64.mak CC=afl-clang-lto CXX=afl-clang-lto++ USE_ASM=1 MY_ASM="uasm"
AFL_LLVM_LAF_ALL=1 LD_PRELOAD=/tmp/exeptor/build/libexeptor.so make -j -f ../../cmpl_clang_x64.mak CC=afl-clang-lto CXX=afl-clang-lto++ USE_ASM=1 MY_ASM="uasm"
-f
llvm-ar rcs 7z.a ./b/c_x64/*.o
docker build . -t fuzz-7zip
docker run --rm -it --tmpfs /ramdisk:exec fuzz-7zip
cp -r /root/fuzz/ /ramdisk/ && cd /ramdisk/fuzz
export AFL_TESTCACHE_SIZE=256
AFL_FINAL_SYNC=1 afl-fuzz -i input -o output -M master -a binary -G 1024 -b 2 -- ./7zz_normal x -so -tzip @@
AFL_USE_ASAN=1 afl-fuzz -i input -o output -S sanitizer -a binary -G 1024 -b 4 -- ./7zz_sanitizer x -so -tzip @@
afl-fuzz -i input -o output -S cmplog -a binary -G 1024 -b 6 -c 0 -l 2AT -- ./7zz_cmplog x -so -tzip @@
afl-fuzz -i input -o output -S compcov -a binary -G 1024 -b 8 -- ./7zz_cmpcov x -so -tzip @@#define Z7_ST
#include "../CPP/7zip/Archive/Common/DummyOutStream.h"
#include "../CPP/7zip/Common/CWrappers.h"
#include "7zAlloc.h"
#include "7zTypes.h"
#include "Alloc.h"
#include "Xz.h"
#include <string.h>
#include <unistd.h>
static const ISzAlloc alloc = {SzAlloc, SzFree};
static int isMT = False;
static CXzStatInfo stat;
class FakeOutStream : public ISequentialOutStream {
public:
// IUnknown
STDMETHOD(QueryInterface)(REFIID, void **) { return S_OK; }
STDMETHOD_(ULONG, AddRef)() { return 1; }
STDMETHOD_(ULONG, Release)() { return 1; }
// ISequentialOutStream
STDMETHOD(Write)(const void *, UInt32 size, UInt32 *processedSize) {
*processedSize = size;
return S_OK;
}
};
// Dummy input stream for fuzzing, construt with const uint8_t *Data, size_t
// Size
#include <algorithm>
class BufInStream : public ISequentialInStream {
private:
const uint8_t *_data;
size_t _size;
size_t _pos;
public:
BufInStream() : _data(nullptr), _size(0), _pos(0) {}
void SetData(const uint8_t *data, size_t size) {
_data = data;
_size = size;
_pos = 0;
}
// IUnknown
STDMETHOD(QueryInterface)(REFIID, void **) { return S_OK; }
STDMETHOD_(ULONG, AddRef)() { return 1; }
STDMETHOD_(ULONG, Release)() { return 1; }
// ISequentialInStream
STDMETHOD(Read)(void *data, UInt32 size, UInt32 *processedSize) {
if (_pos >= _size) {
if (processedSize)
*processedSize = 0;
return S_OK;
}
UInt32 toRead = (UInt32)std::min<size_t>(size, _size - _pos);
memcpy(data, _data + _pos, toRead);
_pos += toRead;
if (processedSize)
*processedSize = toRead;
return S_OK;
}
STDMETHOD(Seek)(Int64 offset, UInt32 seekOrigin, UInt64 *newPosition) {
if (seekOrigin == STREAM_SEEK_SET)
_pos = (UInt32)offset;
else if (seekOrigin == STREAM_SEEK_CUR)
_pos += (UInt32)offset;
else if (seekOrigin == STREAM_SEEK_END)
_pos = (UInt32)(_size + offset);
if (newPosition)
*newPosition = _pos;
return S_OK;
}
};
extern "C" int LLVMFuzzerTestOneInput(const uint8_t *Data, size_t Size) {
CXzDecMtHandle p = XzDecMt_Create(&alloc, &g_AlignedAlloc);
CXzDecMtProps props;
XzDecMtProps_Init(&props);
BufInStream inStream;
inStream.SetData(Data, Size);
FakeOutStream outStream;
CSeqInStreamWrap inWrap;
CSeqOutStreamWrap outWrap;
CCompressProgressWrap progressWrap;
inWrap.Init(&inStream);
outWrap.Init(&outStream);
SRes res = XzDecMt_Decode(p, &props, NULL, CODER_FINISH_ANY, &outWrap.vt,
&inWrap.vt, &stat, &isMT, NULL);
XzDecMt_Destroy(p);
return 0;
}
