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PARTICIPANT_DECLARATION_RE ended in an anchored `(?P<rest>.*)$`. On the
single lines the pattern is fed the anchor changed no result, since greedy
`.*` already runs to the end, but it gave the pattern a tail that can fail:
a newline in the name made `.*$` fail, and the engine then retried the tail
at every position it could backtrack `[^\s#]+` to -- quadratic in the name's
length (~0.4s at 8000 characters, against 0.08ms without the anchor).
Dropping the anchor makes the tail succeed on first try, so the name
repetition is never backtracked into. Behaviour is unchanged: the two
patterns return identical groupdicts across 108 declaration forms (quoted
and bare names, aliases, order/color/stereotype modifiers, indentation,
unterminated quotes and non-declarations).
No caller could reach the quadratic path, since participant_declarations
and rename.py both split the puml into lines first, so this hardens the
pattern rather than fixing a live defect. A timing test pins the linear
bound so the anchor is not reinstated.
Reported by CodeQL as py/polynomial-redos. Note for future triage that the
alert's suggested input ('participant !' with many '!!') is not in fact
slow -- it matches in linear time; the newline is what triggers the
backtracking.
rnva
marked this pull request as draft
October 8, 2026 18:41
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PARTICIPANT_DECLARATION_RE ended in an anchored
(?P<rest>.*)$. On the single lines the pattern is fed the anchor changed no result, since greedy.*already runs to the end, but it gave the pattern a tail that can fail: a newline in the name made.*$fail, and the engine then retried the tail at every position it could backtrack[^\s#]+to -- quadratic in the name's length (~0.4s at 8000 characters, against 0.08ms without the anchor).Dropping the anchor makes the tail succeed on first try, so the name repetition is never backtracked into. Behaviour is unchanged: the two patterns return identical groupdicts across 108 declaration forms (quoted and bare names, aliases, order/color/stereotype modifiers, indentation, unterminated quotes and non-declarations).
No caller could reach the quadratic path, since participant_declarations and rename.py both split the puml into lines first, so this hardens the pattern rather than fixing a live defect. A timing test pins the linear bound so the anchor is not reinstated.
Reported by CodeQL as py/polynomial-redos. Note for future triage that the alert's suggested input ('participant !' with many '!!') is not in fact slow -- it matches in linear time; the newline is what triggers the backtracking.