The previous commit's regex-based stripper removed EVERY heredoc body,
which review flagged as bypassable: a fake '<<EOF' marker inside a
comment or quoted string enters the unterminated path and swallows a
later REAL background operator, and unquoted ('cat <<EOF' — expansion
runs) or shell-consumed ('bash <<'EOF'' — body IS shell) bodies are
executable content that must stay visible to the guard.
Replace it with tools/shell_heredoc.strip_inert_heredoc_bodies(), a
conservative shell-state scanner: a body is masked ONLY when every
delimiter on the opener is quoted (no expansion), every heredoc is
terminated by an exact delimiter line, the opener composes a single
command (no list/pipeline operators, no nested $()/backtick/process-
substitution scope), and the consumer is an allowlisted non-shell
interpreter (python/osascript/cat). Anything ambiguous is returned
unchanged — a false positive on exotic syntax is acceptable; hiding a
real background operator is not. Masked bodies become newlines so line
structure is preserved for MULTILINE regexes.
The helper is a standalone stdlib-only module (precedent:
tools/ansi_strip.py) because the same heredoc-as-data false-positive
class exists in the blocked-command regex checks (#83104) and the
gateway lifecycle guard (#81721/#79835, cron/lifecycle_guard.py) —
which must not import the terminal-tool module graph.
Adapted from Wolfram Ravenwolf's security-hardened rework of #63788
(69c7663c6de6b6cb05bf99203fa39673efe01ccf); test scenarios for the
bypass cases derive from his suite.
Co-authored-by: Wolfram Ravenwolf <github.com@wolfram.ravenwolf.de>
_strip_quotes documented that it stripped heredoc bodies but only handled
single/double/backtick quotes. As a result _foreground_background_guidance
scanned heredoc body text for a backgrounding '&' and wrongly rejected valid
foreground commands whose heredoc body contained a spaced ampersand — e.g.
AppleScript string concat (osascript <<'EOF' ... "a" & b ... EOF), Python
bitwise-and, or literal UI text like 'FaceTime & Privacy'.
Add a _strip_heredocs pass (runs before quote-stripping, since a heredoc
delimiter may itself be quoted) covering <<EOF, <<-EOF, <<'EOF', <<"EOF".
The same-line tail after the opener (redirects/args) is preserved and the
opener token is blanked so a real backgrounding '&' after the heredoc is
still detected.
Adds tests/tools/test_terminal_heredoc_background_guard.py.
kshitij
Taylor Mingos