Timezone offset parsers accept out-of-range minute fields

[AshleyYakeley]

Codex found this during an algorithm-defect audit of the time codebase.

Audited revision: 8706e568aafcd4562fde792374b94b735ae53a0a.

Summary

Both %z parsing and the ISO 8601 timeOffsetFormat accept numeric timezone offsets without validating their hour/minute components. A minute field of 60 is normalized into an extra hour instead of being rejected.

Reproduction

parseTimeM False defaultTimeLocale "%z" "+2360" :: Maybe TimeZone
-- Just +2400

formatParseM (timeOffsetFormat ExtendedFormat) "+23:60"
-- Just +2400

formatParseM (timeOffsetFormat ExtendedFormat) "+24:01"
-- Just +2401

Expected

Malformed offsets should fail. In particular, the minute component must be in 00..59; the ISO parser should also enforce the permitted overall ISO 8601 offset range.

Actual

The parsers calculate hours * 60 + minutes, accepting invalid input as a different offset.

Affected code

• lib/Data/Time/Format/Parse/Instances.hs: readTzOffset.
• lib/Data/Time/Format/ISO8601.hs: timeOffsetFormat (digits2 plus unrestricted isoMap).