Fix out-of-bounds read in copy_poly_in_matrix for monomials - #379
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When a Groebner basis element whose leading monomial is hit by the multiplication by x_n is a monomial (length 1), copy_poly_in_matrix compared the exponent at lmb + (len - 2) * nv, i.e. lmb - nv, with the exponent following the leading term, which belongs to the next polynomial or lies past the end of bexp. This was reported by AddressSanitizer as a heap-buffer-overflow in the unit test fglm_build_matrixn_nonradical-radicalshape-31. A monomial has no tail, so its row in the multiplication matrix is zero; since dense_mat is zero-initialized, return early in that case. The same guard is added to copy_poly_in_matrixcol, which contains the same code. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
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When a Gröbner basis element whose leading monomial is hit by the multiplication by
x_nis a monomial (length 1),copy_poly_in_matrixcompared the exponent atlmb + (len - 2) * nv, i.e.lmb - nv, with the exponent following the leading term, which belongs to the next polynomial or lies past the end ofbexp.AddressSanitizer reports this as a heap-buffer-overflow in the unit test
fglm_build_matrixn_nonradical-radicalshape-31:A monomial has no tail, so its row in the multiplication matrix is zero; since
dense_matis zero-initialized by all callers, the function now returns early in that case. The same guard is added tocopy_poly_in_matrixcol, which contains identical code.Testing
make checkwith AddressSanitizer (LLVM clang,-g -O1 -fsanitize=address -fno-omit-frame-pointer,ASAN_OPTIONS=detect_leaks=0): 68/68 pass (previouslyfglm_build_matrixn_nonradical-radicalshape-31failed).make checkwith a normal-O2build: 68/68 pass.This change was made with the assistance of generative AI (Claude Code).
Co-authored-by: Claude Opus 5.5 noreply@anthropic.com
🤖 Generated with Claude Code