…ntracts 3281824 fuzz: prevent invalid `FRESH` entries and surface `BatchWrite` errors (Lőrinc) 780f460 fuzz: avoid invalid `AddCoin` overwrites (Lőrinc) d7e0d51 fuzz: make `AddCoins` query view for overwrites (Lőrinc) b8fa6f0 util: introduce `TrySub` to prevent unsigned underflow (Lőrinc) Pull request description: ### Problem This is an alternative approach to bitcoin#34647, fixes bitcoin#34645. ### Fix First, add `CheckedSub` and use it for decrements of `m_dirty_count` and `cachedCoinsUsage`, so unsigned underflows turn into immediate failures instead of silently wrapping and only failing later. <details><summary>Assertion `j <= i' failed.</summary> ```bash util/overflow.h:44 T CheckedSub(const T, const U) [T = unsigned long, U = bool]: Assertion `j <= i' failed. ==72817== ERROR: libFuzzer: deadly signal #0 0x556e9225eab5 in __sanitizer_print_stack_trace (/mnt/my_storage/bitcoin/build_fuzz/bin/fuzz+0x191dab5) (BuildId: d77c4d5f9dfd38ea06fab463f49341735205e109) #1 0x556e921acafc in fuzzer::PrintStackTrace() (/mnt/my_storage/bitcoin/build_fuzz/bin/fuzz+0x186bafc) (BuildId: d77c4d5f9dfd38ea06fab463f49341735205e109) #2 0x556e92191bb7 in fuzzer::Fuzzer::CrashCallback() (/mnt/my_storage/bitcoin/build_fuzz/bin/fuzz+0x1850bb7) (BuildId: d77c4d5f9dfd38ea06fab463f49341735205e109) #3 0x7164cfc458cf (/lib/x86_64-linux-gnu/libc.so.6+0x458cf) (BuildId: ae7440bbdce614e0e79280c3b2e45b1df44e639c) #4 0x7164cfca49bb in __pthread_kill_implementation nptl/pthread_kill.c:43:17 #5 0x7164cfca49bb in __pthread_kill_internal nptl/pthread_kill.c:89:10 #6 0x7164cfca49bb in pthread_kill nptl/pthread_kill.c:100:10 #7 0x7164cfc4579d in raise signal/../sysdeps/posix/raise.c:26:13 #8 0x7164cfc288cc in abort stdlib/abort.c:73:3 #9 0x556e92f9d591 in assertion_fail(std::source_location const&, std::basic_string_view<char, std::char_traits<char>>) /mnt/my_storage/bitcoin/src/util/check.cpp:41:5 #10 0x556e9250daf0 in bool&& inline_assertion_check<false, bool>(bool&&, std::source_location const&, std::basic_string_view<char, std::char_traits<char>>) /mnt/my_storage/bitcoin/src/util/check.h:90:13 #11 0x556e9250daf0 in unsigned long CheckedSub<unsigned long, bool>(unsigned long, bool) /mnt/my_storage/bitcoin/src/util/overflow.h:44:5 #12 0x556e9250daf0 in CoinsViewCacheCursor::NextAndMaybeErase(std::pair<COutPoint const, CCoinsCacheEntry>&) /mnt/my_storage/bitcoin/src/coins.h:282:25 #13 0x556e92507eb2 in (anonymous namespace)::MutationGuardCoinsViewCache::BatchWrite(CoinsViewCacheCursor&, uint256 const&) /mnt/my_storage/bitcoin/src/test/fuzz/coins_view.cpp:90:75 #14 0x556e92c17a2b in CCoinsViewCache::Flush(bool) /mnt/my_storage/bitcoin/src/coins.cpp:282:11 #15 0x556e924fb732 in TestCoinsView(FuzzedDataProvider&, CCoinsViewCache&, CCoinsView&, bool)::$_1::operator()() const /mnt/my_storage/bitcoin/src/test/fuzz/coins_view.cpp:135:34 #16 0x556e924fb732 in unsigned long CallOneOf<TestCoinsView(FuzzedDataProvider&, CCoinsViewCache&, CCoinsView&, bool)::$_0, TestCoinsView(FuzzedDataProvider&, CCoinsViewCache&, CCoinsView&, bool)::$_1, TestCoinsView(FuzzedDataProvider&, CCoinsViewCache&, CCoinsView&, bool)::$_2, TestCoinsView(FuzzedDataProvider&, CCoinsViewCache&, CCoinsView&, bool)::$_3, TestCoinsView(FuzzedDataProvider&, CCoinsViewCache&, CCoinsView&, bool)::$_4, TestCoinsView(FuzzedDataProvider&, CCoinsViewCache&, CCoinsView&, bool)::$_5, TestCoinsView(FuzzedDataProvider&, CCoinsViewCache&, CCoinsView&, bool)::$_6, TestCoinsView(FuzzedDataProvider&, CCoinsViewCache&, CCoinsView&, bool)::$_7, TestCoinsView(FuzzedDataProvider&, CCoinsViewCache&, CCoinsView&, bool)::$_8, TestCoinsView(FuzzedDataProvider&, CCoinsViewCache&, CCoinsView&, bool)::$_9, TestCoinsView(FuzzedDataProvider&, CCoinsViewCache&, CCoinsView&, bool)::$_10, TestCoinsView(FuzzedDataProvider&, CCoinsViewCache&, CCoinsView&, bool)::$_11>(FuzzedDataProvider&, TestCoinsView(FuzzedDataProvider&, CCoinsViewCache&, CCoinsView&, bool)::$_0, TestCoinsView(FuzzedDataProvider&, CCoinsViewCache&, CCoinsView&, bool)::$_1, TestCoinsView(FuzzedDataProvider&, CCoinsViewCache&, CCoinsView&, bool)::$_2, TestCoinsView(FuzzedDataProvider&, CCoinsViewCache&, CCoinsView&, bool)::$_3, TestCoinsView(FuzzedDataProvider&, CCoinsViewCache&, CCoinsView&, bool)::$_4, TestCoinsView(FuzzedDataProvider&, CCoinsViewCache&, CCoinsView&, bool)::$_5, TestCoinsView(FuzzedDataProvider&, CCoinsViewCache&, CCoinsView&, bool)::$_6, TestCoinsView(FuzzedDataProvider&, CCoinsViewCache&, CCoinsView&, bool)::$_7, TestCoinsView(FuzzedDataProvider&, CCoinsViewCache&, CCoinsView&, bool)::$_8, TestCoinsView(FuzzedDataProvider&, CCoinsViewCache&, CCoinsView&, bool)::$_9, TestCoinsView(FuzzedDataProvider&, CCoinsViewCache&, CCoinsView&, bool)::$_10, TestCoinsView(FuzzedDataProvider&, CCoinsViewCache&, CCoinsView&, bool)::$_11) /mnt/my_storage/bitcoin/src/test/fuzz/util.h:42:27 #17 0x556e924fb732 in TestCoinsView(FuzzedDataProvider&, CCoinsViewCache&, CCoinsView&, bool) /mnt/my_storage/bitcoin/src/test/fuzz/coins_view.cpp:114:9 #18 0x556e92503b0c in coins_view_overlay_fuzz_target(std::span<unsigned char const, 18446744073709551615ul>) /mnt/my_storage/bitcoin/src/test/fuzz/coins_view.cpp:404:5 #19 0x556e92bcb7a5 in std::function<void (std::span<unsigned char const, 18446744073709551615ul>)>::operator()(std::span<unsigned char const, 18446744073709551615ul>) const /usr/lib/gcc/x86_64-linux-gnu/15/../../../../include/c++/15/bits/std_function.h:593:9 #20 0x556e92bcb7a5 in test_one_input(std::span<unsigned char const, 18446744073709551615ul>) /mnt/my_storage/bitcoin/src/test/fuzz/fuzz.cpp:88:5 #21 0x556e92bcb7a5 in LLVMFuzzerTestOneInput /mnt/my_storage/bitcoin/src/test/fuzz/fuzz.cpp:216:5 #22 0x556e9219318f in fuzzer::Fuzzer::ExecuteCallback(unsigned char const*, unsigned long) (/mnt/my_storage/bitcoin/build_fuzz/bin/fuzz+0x185218f) (BuildId: d77c4d5f9dfd38ea06fab463f49341735205e109) #23 0x556e92192799 in fuzzer::Fuzzer::RunOne(unsigned char const*, unsigned long, bool, fuzzer::InputInfo*, bool, bool*) (/mnt/my_storage/bitcoin/build_fuzz/bin/fuzz+0x1851799) (BuildId: d77c4d5f9dfd38ea06fab463f49341735205e109) #24 0x556e92194139 in fuzzer::Fuzzer::MutateAndTestOne() (/mnt/my_storage/bitcoin/build_fuzz/bin/fuzz+0x1853139) (BuildId: d77c4d5f9dfd38ea06fab463f49341735205e109) #25 0x556e92194c95 in fuzzer::Fuzzer::Loop(std::vector<fuzzer::SizedFile, std::allocator<fuzzer::SizedFile>>&) (/mnt/my_storage/bitcoin/build_fuzz/bin/fuzz+0x1853c95) (BuildId: d77c4d5f9dfd38ea06fab463f49341735205e109) #26 0x556e92181255 in fuzzer::FuzzerDriver(int*, char***, int (*)(unsigned char const*, unsigned long)) (/mnt/my_storage/bitcoin/build_fuzz/bin/fuzz+0x1840255) (BuildId: d77c4d5f9dfd38ea06fab463f49341735205e109) #27 0x556e921ad696 in main (/mnt/my_storage/bitcoin/build_fuzz/bin/fuzz+0x186c696) (BuildId: d77c4d5f9dfd38ea06fab463f49341735205e109) #28 0x7164cfc2a577 in __libc_start_call_main csu/../sysdeps/nptl/libc_start_call_main.h:58:16 #29 0x7164cfc2a63a in __libc_start_main csu/../csu/libc-start.c:360:3 #30 0x556e921757e4 in _start (/mnt/my_storage/bitcoin/build_fuzz/bin/fuzz+0x18347e4) (BuildId: d77c4d5f9dfd38ea06fab463f49341735205e109) NOTE: libFuzzer has rudimentary signal handlers. Combine libFuzzer with AddressSanitizer or similar for better crash reports. SUMMARY: libFuzzer: deadly signal MS: 2 PersAutoDict-CopyPart- DE: "\005\000"-; base unit: ecb626aff8724f0fdde38a0a6965718f2096d474 artifact_prefix='/tmp/fuzz_artifacts/'; Test unit written to /tmp/fuzz_artifacts/crash-1d19026c1a23f08bfe693fd684a56ce51187c6e5 ./build_fuzz/bin/fuzz /tmp/fuzz_corpus/coins_view_overlay -max_total_time=3600 -rss_limit_mb=2560 -artifact_prefix=/tmp/fuzz_artifacts/ >fuzz-16.log 2>&1 ``` </details> The coins view fuzz targets can call `AddCoin`/`AddCoins` and construct `BatchWrite` cursors in ways that violate `CCoinsViewCache` caller contracts. These invalid states can trigger `BatchWrite` `std::logic_error` and can desync dirty-entry accounting (caught by `Assume(m_dirty_count == 0)` currently). Make the fuzzer avoid generating invalid states instead of catching and resetting: * Derive `AddCoin`’s `possible_overwrite` from `PeekCoin`, so `possible_overwrite=false` is only used when the outpoint is absent - similarly to https://github.com/bitcoin/bitcoin/blob/67c0d1798e6147f48d4bafc2c9e5ff30f2a62340/src/test/fuzz/coinscache_sim.cpp#L312-L317 - Only use `AddCoins(check=false)` when we have confirmed the txid has no unspent outputs; otherwise fall back to `check=true` so `AddCoins` determines overwrites via the view. - When constructing a `CoinsViewCacheCursor`, avoid setting `FRESH` when the parent already has an unspent coin, and ensure `FRESH` implies `DIRTY`. ### Fuzzing The original error could be reproduced in ~10 minutes using `coins_view_overlay`. I ran the `coins_view`, `coins_view_db`, `coins_view_overlay`, and `coinscache_sim` fuzzers for this PR overnight and they didn't fail anymore. ACKs for top commit: achow101: ACK 3281824 sipa: ACK 3281824. Ran the 4 relevant fuzz tests for ~1 CPU day each. Will run more overnight. andrewtoth: ACK 3281824 Tree-SHA512: b8155e8d21740eb7800e373c27a8a1457eb84468c24af879bac5a1ed251ade2aec99c34a350a31f2ebb74e41bb7380bf20214d38d14fe23310a43282d2434fb7

Exit cleanly after loading utxosnapshot #22

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