Serialization should not behave differently on different architectures. See also the related commit 3789215f73466606eb111714f596a2a5e9bb1933.
However, on fees.dat file corruption, 32-bit builds may run into an unsigned integer overflow and report the wrong corruption reason, or may even silently continue after the corruption.
This is a bit hard to reproduce, because 32-bit platforms are rare and most of them don’t support running the unsigned integer overflow sanitizer. So the possible options to reproduce are:
- Run on armhf and manually annotate the code to detect the overflow
- Run on i386 with the integer sanitizer (possibly via
podman run -it --rm --platform linux/i386 'debian:trixie') - Run the integer sanitizer on any 64-bit platform and manually replace type in the affected line by
uint32_t
Afterwards, the steps to reproduce are:
0export DEBIAN_FRONTEND=noninteractive && apt update && apt install curl wget htop git vim ccache -y && git clone https://github.com/bitcoin/bitcoin.git --depth=1 ./b-c && cd b-c && apt install build-essential cmake pkg-config python3-zmq libzmq3-dev libevent-dev libboost-dev libsqlite3-dev systemtap-sdt-dev libcapnp-dev capnproto libqrencode-dev qt6-tools-dev qt6-l10n-tools qt6-base-dev clang llvm libc++-dev libc++abi-dev -y
1
2cmake -B ./bld-cmake -DCMAKE_BUILD_TYPE=Debug -DCMAKE_C_COMPILER='clang' -DCMAKE_CXX_COMPILER='clang++' -DSANITIZERS=undefined,integer,float-divide-by-zero --preset=dev-mode
3
4cmake --build ./bld-cmake --parallel $(nproc)
5
6curl -fLO 'https://github.com/bitcoin-core/qa-assets/raw/b5ad78e070e4cf36beb415d7b490d948d70ba73f/fuzz_corpora/policy_estimator_io/607473137013139e3676e30ec4b29639e673fa9b'
7
8UBSAN_OPTIONS="suppressions=$(pwd)/test/sanitizer_suppressions/ubsan:print_stacktrace=1:halt_on_error=1:report_error_type=1" FUZZ=policy_estimator_io ./bld-cmake/bin/fuzz ./607473137013139e3676e30ec4b29639e673fa9b
The output will be something like:
0/b-c/src/policy/fees/block_policy_estimator.cpp:448:25: runtime error: unsigned integer overflow: 346685954 * 219 cannot be represented in type 'unsigned int'
1 [#0](/bitcoin-bitcoin/0/) 0x5b0b1bbe in TxConfirmStats::Read(AutoFile&, unsigned int) /b-c/bld-cmake/src/./policy/fees/block_policy_estimator.cpp:448:25
2 [#1](/bitcoin-bitcoin/1/) 0x5b0b7d3f in CBlockPolicyEstimator::Read(AutoFile&) /b-c/bld-cmake/src/./policy/fees/block_policy_estimator.cpp:1037:29
3 [#2](/bitcoin-bitcoin/2/) 0x592a9783 in policy_estimator_io_fuzz_target(std::span<unsigned char const, 4294967295u>) /b-c/bld-cmake/src/test/fuzz/./test/fuzz/policy_estimator_io.cpp:32:32
4 [#3](/bitcoin-bitcoin/3/) 0x5896ba8e in void std::__invoke_impl<void, void (*&)(std::span<unsigned char const, 4294967295u>), std::span<unsigned char const, 4294967295u>>(std::__invoke_other, void (*&)(std::span<unsigned char const, 4294967295u>), std::span<unsigned char const, 4294967295u>&&) /usr/lib/gcc/i686-linux-gnu/14/../../../../include/c++/14/bits/invoke.h:61:14
5 [#4](/bitcoin-bitcoin/4/) 0x5896b8eb in std::enable_if<is_invocable_r_v<void, void (*&)(std::span<unsigned char const, 4294967295u>), std::span<unsigned char const, 4294967295u>>, void>::type std::__invoke_r<void, void (*&)(std::span<unsigned char const, 4294967295u>), std::span<unsigned char const, 4294967295u>>(void (*&)(std::span<unsigned char const, 4294967295u>), std::span<unsigned char const, 4294967295u>&&) /usr/lib/gcc/i686-linux-gnu/14/../../../../include/c++/14/bits/invoke.h:111:2
6 [#5](/bitcoin-bitcoin/5/) 0x5896b44b in std::_Function_handler<void (std::span<unsigned char const, 4294967295u>), void (*)(std::span<unsigned char const, 4294967295u>)>::_M_invoke(std::_Any_data const&, std::span<unsigned char const, 4294967295u>&&) /usr/lib/gcc/i686-linux-gnu/14/../../../../include/c++/14/bits/std_function.h:290:9
7 [#6](/bitcoin-bitcoin/6/) 0x59845c95 in std::function<void (std::span<unsigned char const, 4294967295u>)>::operator()(std::span<unsigned char const, 4294967295u>) const /usr/lib/gcc/i686-linux-gnu/14/../../../../include/c++/14/bits/std_function.h:591:9
8 [#7](/bitcoin-bitcoin/7/) 0x5983a0da in test_one_input(std::span<unsigned char const, 4294967295u>) /b-c/bld-cmake/src/test/fuzz/util/./test/fuzz/fuzz.cpp:88:5
9 [#8](/bitcoin-bitcoin/8/) 0x5983cb80 in main /b-c/bld-cmake/src/test/fuzz/util/./test/fuzz/fuzz.cpp:271:13
10 [#9](/bitcoin-bitcoin/9/) 0xf75aecc2 (/lib/i386-linux-gnu/libc.so.6+0x24cc2) (BuildId: 2dc5f2945fad35c1b07d1a5a32520b3c41afaa75)
11 [#10](/bitcoin-bitcoin/10/) 0xf75aed87 in __libc_start_main (/lib/i386-linux-gnu/libc.so.6+0x24d87) (BuildId: 2dc5f2945fad35c1b07d1a5a32520b3c41afaa75)
12 [#11](/bitcoin-bitcoin/11/) 0x58932db6 in _start (/b-c/bld-cmake/bin/fuzz+0x235ddb6) (BuildId: 7d8d83a77923f14e99c0de64acbc5f5bfc2cce9b)
13
14SUMMARY: UndefinedBehaviorSanitizer: unsigned-integer-overflow /b-c/src/policy/fees/block_policy_estimator.cpp:448:25
Note: This is marked a “refactor”, because the code change does not affect 64-bit builds, and on the still remaining rare 32-bit builds today it is extremely unlikely to happen in production.
