fix(examples): guard shape_buf overflow in npy_writer#167
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writeNpy's shape_buf[256] is filled by snprintf calls whose remaining-size argument `sizeof(shape_buf) - shape_len` unsigned-underflowed when shape_len exceeded 256 (e.g., ndim around 120+, or smaller with multi- digit dims). The underflowed huge size_t bypassed snprintf's bounds check and allowed OOB writes — caught by UBSan at npy_writer.c:22 as "index 257 out of bounds for type 'char[256]'". Fix: extract appendBounded helper that vsnprintf's into a fixed buffer with explicit bounds checking (returns -1 on truncation, error, or already-past-end offset). All four shape_buf append sites route through it; a single rc=6 is returned if any indicates truncation. Regression test builds an ASan+UBSan harness with ndim=200, asserts no sanitizer trip and rc != 0. Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
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Summary
Fix the latent buffer-bounds bug in
examples/_shared/npy_writer.cflagged in #165.writeNpyfilledshape_buf[256]via a snprintf loop whose remaining-size argumentsizeof(shape_buf) - shape_lenunsigned-underflowed whenshape_lenexceeded 256. The underflowed hugesize_tbypassed snprintf's bounds check and allowed OOB writes — caught by UBSan atnpy_writer.c:22asindex 257 out of bounds for type 'char[256]'. Triggered by high-rank shapes (ndim ~120+, or smaller with multi-digit dims).What changed
appendBoundedhelper innpy_writer.cthat wrapsvsnprintfwith explicit bounds checking (offset >= buf_size→ -1; truncation → -1).snprintfsites forshape_bufwithappendBoundedcalls; singlerc=6returned at end if any indicates truncation.#include <stdarg.h>forva_list.Test plan
test_npy_writer_rejects_high_rank_shape_that_overflows_buf(TDD: written before the fix). Compiles an ASan+UBSan harness with ndim=200, asserts no sanitizer trip and rc != 0.UndefinedBehaviorSanitizer: runtime error: index 257 out of bounds for type 'char[256]'atnpy_writer.c:22.unit_test(gcc) 42/42,unit_test_asan42/42,pytest22 passed (was 21, +1 new test).Closes #165
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