fix(config): bound option-line parsing - #2259
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Byron merged 1 commit intoSep 30, 2026
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`GitConfigParser.OPTCRE` matched an option line with `(?P<option>[^:=#;]*)` immediately followed by `\s*(?P<vi>[:=])`. The option name class and that `\s*` both match spaces, so a line that never reaches a `:` or `=` separator (a key followed by a long run of whitespace) makes the regex engine retry every space position, taking `O(n^2)` time in the length of the run. Config files are parsed straight from repository content. `.gitmodules` in particular is read whenever submodules of an inspected or cloned repository are enumerated, so the line is fully attacker-controlled. A crafted key line costs about `0.25s` of CPU at 8,000 spaces and roughly `160s` at 200,000, stalling any caller that reads the config. The trailing `\s*` is redundant: `[^:=#;]*` already consumes any spaces up to the indicator, and the captured name is right-stripped after parsing. Dropping it leaves a single quantifier over the whitespace run, so matching is linear. The collapsed pattern accepts exactly the same lines and yields the same groups as the previous one, checked over 200,000 fuzzed inputs with zero differences. Add `test_option_line_with_long_whitespace_run_is_not_quadratic`, a CPU-time regression that fails on the previous pattern and passes here, and that confirms a valid key before the malformed line still parses.
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Copilot review overview
🟢 Approval recommended
The regex change is behavior-preserving and directly covered by a focused performance regression test.
Review effort: Balanced
Findings: None
What changed in this PR
Bounds config option parsing by removing overlapping regex quantifiers that permit quadratic backtracking.
Changes:
- Simplifies
OPTCREwhile preserving parsing behavior. - Adds a CPU-time regression test for long whitespace runs.
| File | Description |
|---|---|
git/config.py |
Removes redundant whitespace matching from the option regex. |
test/test_config.py |
Tests linear-time parsing and preserved preceding values. |
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Byron
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Thanks a lot!
Armchair review, and trust in Copilot, make me think merging this is a good idea.
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Timing
OPTCRE.matchon"branch" + " " * n(a config key with a trailing whitespace run and no=/:):[^:=#;]*in the option group and the\s*before the value indicator both match spaces, so a line that never reaches a:/=backtracks over every space position..gitmodulesis parsed from repository content whenever submodules of an inspected or cloned repo are enumerated, so the line is attacker-controlled. Dropping the redundant\s*(the option class already consumes those spaces, and the name is right-stripped afterward) leaves a single quantifier over the run, so matching is linear. I compared the collapsed pattern against the old one over 200k fuzzed inputs with zero match/group differences. Added a CPU-time regression that fails on the old pattern.I am an AI agent contributing through this account; this change was prepared with AI assistance.