compose-lint: `fix --apply` can delete a line the user did not select, including a security setting

Impact

compose-lint fix --apply converts the line numbers its fixers work with into positions in the file. The YAML parser treats a lone carriage return, U+0085, U+2028 and U+2029 as line breaks, but the conversion counted only \n. One of those characters inside a quoted value, which most editors and diff views don't show, shifted every later edit down by one line.

A Compose file from a pull request can use this to make a fix delete the line after the one it meant to change. For example, fixing CL-0014 (logging: driver: none) instead removes driver: none and the following networks: [internal], moving the service off an internal-only network onto the default bridge. The result is still valid Compose, every check fix runs after editing passes, and the command reports applied 1 fix(es) and exits 0. A later compose-lint check passes too, because no rule requires networks:. The dry-run diff (without --apply) does show the removed lines, but --apply prints only the note for the fix that was selected.

A related crash on the same files could empty the SARIF output for every file in the run. GitHub Code Scanning rejects an empty SARIF upload, which fails the step, so that part does not report a false clean result there.

Found during an internal pre-1.0 security review.

Docker image. composelint/compose-lint tags 0.9.0 through 0.17.0, and the matching minor tags, are affected when used to run fix --apply. Fixed from 0.18.0.

The GitHub Action does not run fix and is not affected.

Patches

Fixed in 0.18.0. Line splitting and position conversion now share one definition of a line break, so they can't disagree. A Compose file containing an ambiguous line break (a lone \r, U+0085, U+2028 or U+2029) is refused with exit code 2, because no line numbering is correct for both the parser and the editor. CRLF and LF files are unaffected.

Workarounds

• Upgrade to 0.18.0 or later.
• On older versions, review the dry-run diff before --apply, and don't run fix --apply over files from untrusted pull requests.

Reproduction

services:
  web:
    image: nginx@sha256:<digest>
    labels:
      note: "line one<U+2028>line two"
    logging:
      driver: none
    networks: [internal]
networks:
  internal:
    internal: true

compose-lint fix --apply compose.yml on 0.17.0 reports applied 1 fix(es), exits 0, and removes both driver: none and networks: [internal].