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Add ASan redzones between zone allocations - #1194
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The zone carves many objects out of one malloc()ed chunk, so an overflow from one zone-allocated object into its neighbour stays inside a live heap block and AddressSanitizer cannot see it. When building with ASan, follow every allocation with a poisoned redzone, keep chunks of the configured size poisoned until handed out, and re-poison on clear() and undo_allocate(). Oversized chunks are not pre-poisoned, so a huge allocation costs no shadow updates proportional to its size. Builds without ASan are unchanged. Define MSGPACK_ZONE_NO_ASAN_ANNOTATIONS to opt out. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
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msgpack::zonecarves many objects out of onemalloc()ed chunk. An overflow from one zone-allocated object into its neighbour stays inside a live heap block, so AddressSanitizer stays silent. This is detector hardening, not a bug fix, and the technique isn't new: it's the manual allocator poisoning described in Trail of Bits' "Sanitize your C++ containers: ASan annotations step-by-step" (https://blog.trailofbits.com/2024/09/10/sanitize-your-c-containers-asan-annotations-step-by-step/). zstd'sZSTD_CWKSP_ASAN_REDZONE_SIZEis a similar precedent.__SANITIZE_ADDRESS__/__has_feature(address_sanitizer)). Non-ASan builds are unchanged; with-DNDEBUGthe objects are byte-identical (gcc/clang, C++03/11/17).-DMSGPACK_ZONE_NO_ASAN_ANNOTATIONSopts out, e.g. when instrumented and uninstrumented code share a zone. At runtime,ASAN_OPTIONS=allow_user_poisoning=0also disables it.MSGPACK_ZONE_ASAN_REDZONE_SIZE, default 16). Chunks of the configured size stay poisoned until handed out, andclear()/undo_allocate()re-poison. Oversized chunks aren't pre-poisoned, so one huge allocation costs nothing proportional to its size.cpp03_zone.hppand its.erbtemplate get the same change.test/zone.cpp: under ASan,allocate_no_alignchecks for the redzone instead of contiguity.Validation: unpacking
92 91 01 91 02and writing one element past the first inner array silently corrupts the neighbour on stock. With this patch it reportsuse-after-poison, and it is silent again with-DMSGPACK_ZONE_NO_ASAN_ANNOTATIONS. All tests pass under ASan (clang-18 C++11/17/20, gcc-13 C++17), with annotations on and off. The OSS-Fuzz public corpus plus about 46Munpack_pack_fuzzerexecutions show no reports. ASan overhead is about +14% time and +7% peak memory on a corpus unpack/pack/clone benchmark; non-ASan builds are unaffected.Scope: only overflows between separately allocated zone objects. Indexing inside a single allocation is not covered, nor are reads into the unused tail of an oversized chunk.
Companion PR for the C zone on
c_master: #1195.🤖 Generated with Claude Code