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Reject unbalanced and overly deep type names - #587
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slabko merged 2 commits intoOct 29, 2026
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TypeParser::Parse() calls top() and pop() on its element stack for every ')' and ',', so a type name with a surplus closing parenthesis such as "UInt8))" or ")," reads from an empty std::stack and crashes. It also has no nesting limit, while CreateColumnFromAst() and the TypeAst destructor recurse once per level, so a type nested 100000 levels deep, closed or not, overflows the stack. Parse() now fails on a ')' or ',' with no open parenthesis and on nesting deeper than 512 levels: current servers reject column types nested deeper than 499 levels, and 512 keeps the recursive paths to about 250 KiB of stack in an optimized build.
TypeParser::kMaxNestingDepth was declared public in types/type_parser.h, which CMake installs, so the limit became part of the shipped API even though the only production reference is in TypeParser::Parse. Move it to a file-local constant in type_parser.cpp, matching the other internal constants there (kTypeCode, kUnescapeMap), so the value stays tunable without a breaking change. The tests referenced the constant to derive their boundaries, which made them tautological: asserting that depth N parses and N+1 does not holds for any limit, so lowering it to a value too small for the types real servers send would not have failed TypeParser.NestingDepthLimit. Pin 512 and 513 by value instead.
slabko
approved these changes
Oct 29, 2026
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Two server-supplied type strings crash
CreateColumnByType.A surplus
)or,makesTypeParser::Parse()intypes/type_parser.cppcallopen_elements_.top()andpop()on an emptystd::stack, which is undefined behaviour on an empty deque. Release builds segfault onUInt8)),),or))).Deep nesting overflows the stack.
CreateColumnFromAstincolumns/factory.cpprecurses once per nesting level, and so does theTypeAstdestructor. A type string of about 700 KB (Array(repeated 100,000 times) overflows the stack whether or not it is closed.Fix:
Parse()returns false on a)or,with no open element, and on nesting deeper thanTypeParser::kMaxNestingDepth(512). That bounds both the factory recursion and AST destruction. Current servers reject column types nested deeper than 499 levels (26.9 accepts at most 497 nestedArray(levels at default settings, 499 with the AST limits raised), so 512 rejects nothing a server can produce. It also keeps the worst-case stack near 250 KiB in an optimized build. A side effect: top-level commas (UInt8, String) andUInt8)(are now rejected; neither is a valid type.Reproducer type strings:
UInt8)),),,))), andArray(× 100000 followed byUInt8(closed or unclosed).Tests in
ut/type_parser_ut.cpp:UnbalancedClosingParenthesiscovers 13 malformed strings.NestingDepthLimitaccepts depth 512 and rejects 513 and 100000, closed and unclosed.NestingDepthLimitBoundsColumnFactorychecks that a 499-level type still builds a column and deeper types return nullptr.BalancedNestedControlscoversMap(String, Array(Nullable(UInt8))),Tuple(a UInt8, b String)and deepArray.The first three crash on master; the controls pass on both.