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fix(sanitize,okf,active_content): three quadratic patterns, two on the input path

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The generalised sweep found what 0.3.2's hand-written rows missed. All three are
the documented class -- a run in front of a required literal that never arrives,
so every start position rescans the tail -- and all three are worse than the
0.3.3 findings, because `sanitize`, `neutralize`, `scan_active_content` and the
okf link graph apply NO input cap. `scan_lexicon`/`scan_output` are the only
entry points that do, so there is no ceiling to extrapolate to.

  sanitize._HTML_COMMENT_RE   `<!--`*100_000        20.1s, exponent 1.96-2.14
  active_content.URL_IN_TEXT_RE  `<a `+`A`*100_000  12.99s / 14.9s, exponent ~2.0
  okf._MD_LINK_RE             `[`*100_000            7.1s, exponent 1.99-2.05

Each fix is the one the pattern's own shape allows, not a copied choice:

  - The comment stripper drops the regex for `str.find`. Excluding `<` would lose
    every comment containing markup; bounding the run would be a carrier bypass
    of the exact construct the stripper exists to remove.
  - `URL_IN_TEXT_RE` bounds its scheme run to an RFC 3986 scheme (`{0,63}`).
    Bounding is safe *here* only because it is a defanger inside a tag already
    flagged `active:raw-html`. A lookbehind was measured too and rejected: it
    drops `-http://evil.com`, a one-character evasion. Bounded: 0.185s at 1M.
  - `_MD_LINK_RE` excludes `[`, matching `active_content.MD_LINK_RE` exactly,
    including the nested-label trade already documented there.

`sanitize` claimed "no catastrophic backtracking" in a comment; that claim was
wrong in the same way `output`'s was before 0.3.2, and is corrected in place.

676 tests (+10), coverage 128/128 + 6/6 gaps, sweep clean across 150 patterns.
The okf destination run gets no row: `[^)\s]+` cannot fail, so a row for it
could never go red.
This commit is contained in:
Kjell Tore Guttormsen 2026-08-01 20:06:36 +02:00
commit 73fa1b99ae
9 changed files with 223 additions and 7 deletions
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7
docs/redos-sweep.py
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@ -249,8 +249,11 @@ def collect_output() -> list[Target]:
TABLES = {
"lexicon": collect_lexicon,
# The normalizers run `.sub()` over EVERY input before any pattern matches;
# 0.3.3 swept the 83 patterns and not these.
"normalize": lambda: collect_module("lexicon", "normalize"),
# 0.3.3 swept the 83 patterns and not these. `_LEXICON_CACHE` is skipped: it
# is empty until `load_lexicon()` runs, so counting it would make this
# table's size depend on whether `lexicon` was swept first.
"normalize": lambda: collect_module("lexicon", "normalize",
skip={"_LEXICON_CACHE"}),
"active_content": lambda: collect_module("active_content", "active_content"),
"entropy": lambda: collect_module("entropy", "entropy") + [
# Inline literals in is_base64_like / is_hex_blob (entropy.py:111,118),