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fix(core): bound arithmetic and sequence sizes in safe_expr - #947
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elijahbenizzy wants to merge 2 commits into
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elijahbenizzy wants to merge 2 commits into
elijahbenizzy wants to merge 2 commits into
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Condition.safe_expr() allowed a handful of operators whose result size is not bounded by the size of the expression: int ** int, sequence * n, sequence + sequence, and printf-style % on strings. Bound them: - at most 500 AST nodes per expression (checked before the recursive validator runs) - int ** int: |exponent| <= 64 and base <= 64 bits; non-numeric operands rejected; float ** left to Python (bounded by float range) - sequence * n: n <= 10_000 and result <= 1_000_000 elements; same result cap for sequence + sequence - % is no longer applied to strings - general backstop: no arithmetic step or int literal wider than 4096 bits Literal-only subexpressions (e.g. 10 ** 10 ** 10) are checked at safe_expr() call time; state-dependent values raise ValueError from run(). Docstring updated and tests added for each bound.
The node-count bound runs on the parsed tree, but on Python 3.11 the parser
itself gives up on a 3000-term chain with RecursionError before that check
is reached. Two complementary bounds, both applied before/around ast.parse:
- the expression string may be at most 10_000 characters
(_SAFE_EXPR_MAX_SOURCE_CHARS)
- RecursionError / MemoryError raised by ast.parse are re-raised as
ValueError('safe_expr: expression is too deeply nested'); SyntaxError
is unchanged
Tests: the deep-chain node-count case now uses 600 terms (parses on every
supported Python), the 3000-term chain is asserted to raise ValueError
regardless of which bound trips first, and a 20_000-character expression
is rejected on length. Docstring updated.
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Condition.safe_expr()is documented for expressions from less-trusted sources, but its interpreter placed no bound on arithmetic.10**10**10or"a" * 10000000000passed validation and then ran until the process was killed.This change adds explicit bounds, documented in the docstring: expression size (500 nodes), exponent and base width for
**, repeat count and result length for sequence*/+, and a 4096-bit backstop on every integer result. Literal-only subtrees are checked atsafe_expr()construction so the obvious cases fail early; everything else fails atrun()with a plainValueError.%with a string left operand is rejected for the same reason.No existing test changed; 12 added.