diff --git a/README.md b/README.md index c4dacf7..de91b11 100644 --- a/README.md +++ b/README.md @@ -29,7 +29,7 @@ descriptions and "use when" triggers. /plugin install skills@mathias ``` -The plugin ships skills, the `secret-guard` + `pre-task-ritual` hooks, and the +The plugin ships skills, the `secret-guard`, `mcp-destructive-guard` and `pre-task-ritual` hooks, and the brain/gitea/infra MCP servers as one versioned unit. Skills are namespaced (`skills:tdd`). Updates land when `.claude-plugin/plugin.json`'s `version` moves — CI bumps it on every release. diff --git a/hooks/hooks.json b/hooks/hooks.json index 8db511f..5eed7bf 100644 --- a/hooks/hooks.json +++ b/hooks/hooks.json @@ -33,6 +33,16 @@ "timeout": 5 } ] + }, + { + "matcher": "mcp__.*", + "hooks": [ + { + "type": "command", + "command": "bash \"${CLAUDE_PLUGIN_ROOT}/hooks/mcp-destructive-guard.sh\"", + "timeout": 5 + } + ] } ] } diff --git a/hooks/mcp-destructive-guard.sh b/hooks/mcp-destructive-guard.sh new file mode 100755 index 0000000..3df075d --- /dev/null +++ b/hooks/mcp-destructive-guard.sh @@ -0,0 +1,86 @@ +#!/usr/bin/env bash +# PreToolUse hook (mcp__.* matcher) — makes a human approve irreversible MCP +# verbs instead of letting the model run them unattended. +# +# Why (infra#508, infra ADR-0027): gitea-mcp authenticates by PAT pass-through, +# so an agent holds the full scope of the caller's PAT. repo_delete's own guard +# (confirm == repo) is filled in by the model on both sides: it stops typos, +# not an injected or mistaken agent. The infra-mcp README claimed client-side +# deny lists covered this; on 2026-10-01 none existed in any settings file. +# +# Policy: match gitea-mcp's verb spellings on ANY server name. The same tool is +# reachable as mcp__plugin_skills_gitea__*, mcp__claude_ai_gitea__* or under +# whatever name a host registers it with, so keying on the server name would +# let a rename bypass the gate. It does NOT recognise other servers' spellings +# of the same operation (e.g. a third-party `delete_repo`). +# +# file_write_branch is gated when it would land on main/master (on infra that +# is a Flux deploy within ~60s — the same effect as pr_merge) or empty a file +# (the same effect as file_delete). Writes to other branches pass. +# +# Emits "ask" or nothing; never "allow" (a hook allow would override the +# user's own deny/ask rules). Always exits 0: Claude Code ignores a hook's +# JSON on a non-zero exit. Anything it cannot parse — including a host +# without jq — fails closed to "ask". The ask JSON is a literal, so the +# fail-closed path needs no tool that might be missing. +# +# Scope limit, recorded in infra ADR-0027: this gates MCP calls only. A +# session with the PAT in its environment can still reach the Gitea REST API +# through a shell. + +set -u + +DESTRUCTIVE='repo_delete|file_delete|branch_delete|pr_merge|tbd_ship|repo_update|repo_mirror_push|workflow_run_trigger|tag_create|release_create' + +ask() { + # $1 must contain only [A-Za-z0-9 _.:()'/-] — it is spliced into JSON verbatim. + printf '{"hookSpecificOutput":{"hookEventName":"PreToolUse","permissionDecision":"ask","permissionDecisionReason":"%s"}}\n' "$1" + exit 0 +} + +INPUT="$(cat)" + +command -v jq >/dev/null 2>&1 \ + || ask "mcp-destructive-guard: jq is not installed, so this MCP call cannot be checked. Approve only if you expected it." + +if ! TOOL_NAME="$(printf '%s' "$INPUT" | jq -er '.tool_name | strings | select(length > 0)' 2>/dev/null)"; then + ask "mcp-destructive-guard: could not read a tool name from this call, so it cannot be shown safe. Approve only if you expected it." +fi + +case "$TOOL_NAME" in + mcp__*__*) ;; + *) exit 0 ;; +esac + +verb="${TOOL_NAME##*__}" +safe_verb="$(printf '%s' "$verb" | tr -cd 'A-Za-z0-9_-')" + +if printf '%s' "$verb" | grep -Eqix "($DESTRUCTIVE)"; then + ask "Irreversible MCP verb '$safe_verb' (infra ADR-0027): needs your approval. The model filled in every argument, including any confirm field." +fi + +if printf '%s' "$verb" | grep -Eqix 'file_write_branch'; then + # Cleared only when there is exactly ONE key that case-folds to "branch" and + # one to "content": gitea-mcp decodes with Go encoding/json, which matches + # keys case-insensitively and lets the last one win, so {"branch":"feat/x", + # "Branch":"main"} landed on main while a lowercase-only read saw feat/x. + # The branch is cleared by SHAPE (allowlist), not by a blocklist of names: + # "refs/heads/main" created a second ref that wedged API writes to main. + verdict="$(printf '%s' "$INPUT" | jq -r ' + .tool_input as $i + | if ($i | type) != "object" then "ask" else + ([$i | to_entries[] | select(.key | ascii_downcase == "branch")]) as $b + | ([$i | to_entries[] | select(.key | ascii_downcase == "content")]) as $c + | if ($b | length) != 1 or ($c | length) != 1 then "ask" + elif ($b[0].key != "branch") or ($c[0].key != "content") then "ask" + elif ($b[0].value | type) != "string" or ($c[0].value | type) != "string" then "ask" + elif ($b[0].value | test("^[A-Za-z0-9][A-Za-z0-9._/-]*$") | not) then "ask" + elif ($b[0].value | test("\\.\\.|^refs/|/$")) then "ask" + elif ($b[0].value | ascii_downcase | . == "main" or . == "master") then "ask" + elif ($c[0].value | test("^\\s*$")) then "ask" + else "pass" end + end' 2>/dev/null || echo ask)" + [ "$verdict" = "pass" ] \ + || ask "file_write_branch to main/master, an unusual branch name, or emptying a file (infra ADR-0027): needs your approval." +fi +exit 0 diff --git a/tests/mcp_destructive_guard_test.sh b/tests/mcp_destructive_guard_test.sh new file mode 100755 index 0000000..dfb3d2c --- /dev/null +++ b/tests/mcp_destructive_guard_test.sh @@ -0,0 +1,118 @@ +#!/bin/sh +# Tests for hooks/mcp-destructive-guard.sh — the PreToolUse gate that makes a +# human approve irreversible MCP verbs (infra#508, infra ADR-0027). +# +# Contract: reads PreToolUse hook JSON on stdin, ALWAYS exits 0, and answers +# in hookSpecificOutput.permissionDecision. "ask" = a human must approve; +# empty stdout ("NONE") = no opinion, normal permission rules apply. The guard +# never emits "allow": an allow from a hook would bypass the user's own rules. +# +# Cases marked (gatekeeper) are escapes found by the skills#52 review: each +# passed the first version of this suite. + +set -u + +ROOT=$(CDPATH= cd -- "$(dirname -- "$0")/.." && pwd) +GUARD="$ROOT/hooks/mcp-destructive-guard.sh" + +pass=0 +fail=0 + +# run_guard [PATH] — invoked exactly as hooks.json does: `bash `. +# Prints " rc=", decision NONE for an empty answer. +run_guard() { + if [ $# -ge 2 ]; then + _out=$(printf '%s' "$1" | PATH="$2" "$BASH_BIN" "$GUARD"); _rc=$? + else + _out=$(printf '%s' "$1" | bash "$GUARD"); _rc=$? + fi + if [ -z "$_out" ]; then _d=NONE + else _d=$(printf '%s' "$_out" | jq -r '.hookSpecificOutput.permissionDecision // "NONE"' 2>/dev/null || echo BROKEN) + fi + printf '%s rc=%s' "$_d" "$_rc" +} +BASH_BIN=$(command -v bash) + +check() { + _want=$1 _json=$2 _label=$3 + _got=$(run_guard "$_json") + if [ "$_got" = "$_want rc=0" ]; then + pass=$((pass + 1)); printf ' ok %s\n' "$_label" + else + fail=$((fail + 1)); printf ' FAIL %s\n want=%s rc=0 got=%s\n in=%s\n' "$_label" "$_want" "$_got" "$_json" + fi +} +tool() { printf '{"tool_name":"%s","tool_input":{"owner":"mathias","repo":"x"}}' "$1"; } + +echo "mcp-destructive-guard tests" + +for v in repo_delete file_delete branch_delete pr_merge tbd_ship repo_update repo_mirror_push \ + workflow_run_trigger tag_create release_create; do + check ask "$(tool "mcp__plugin_skills_gitea__$v")" "plugin gitea $v asks" +done + +# The verb is matched on any server name: connector, bare, or renamed. +check ask "$(tool mcp__claude_ai_gitea__repo_delete)" "connector namespace asks" +check ask "$(tool mcp__gitea__repo_delete)" "bare server name asks" +check ask "$(tool mcp__git__repo_delete)" "renamed server still asks" +check ask "$(tool mcp__plugin_skills_gitea__REPO_DELETE)" "uppercase verb asks" +# The verb is the LAST segment (gatekeeper: parsing the second segment stayed green). +check ask "$(tool mcp__a__b__repo_delete)" "verb taken from last segment" +check NONE "$(tool mcp__repo_delete__issue_get)" "server named like a verb does not trigger" + +# file_write_branch: content landing on main, or emptying a file, is the same +# effect as the gated pr_merge / file_delete (gatekeeper). +fwb() { printf '{"tool_name":"mcp__plugin_skills_gitea__file_write_branch","tool_input":{"branch":"%s","content":"%s"}}' "$1" "$2"; } +check ask "$(fwb main x)" "file_write_branch to main asks" +check ask "$(fwb master x)" "file_write_branch to master asks" +check ask "$(fwb feat/y '')" "file_write_branch emptying a file asks" +check ask '{"tool_name":"mcp__plugin_skills_gitea__file_write_branch","tool_input":{"content":"x"}}' "file_write_branch without branch asks" +check NONE "$(fwb feat/y x)" "file_write_branch to a feature branch passes" + +# Go's encoding/json matches keys case-insensitively, last one wins: gitea-mcp +# wrote to main from {"branch":"feat/y8","Branch":"main"} while the hook read +# only `branch` (gatekeeper round 2, verified against a real Gitea). So the +# guard clears a write only when exactly one key case-folds to branch/content. +FWB=mcp__plugin_skills_gitea__file_write_branch +check ask "{\"tool_name\":\"$FWB\",\"tool_input\":{\"branch\":\"feat/y8\",\"Branch\":\"main\",\"content\":\"x\"}}" "case-variant Branch key asks" +check ask "{\"tool_name\":\"$FWB\",\"tool_input\":{\"branch\":\"feat/y\",\"content\":\"x\",\"Content\":\"\"}}" "case-variant Content key asks" +check ask "{\"tool_name\":\"$FWB\",\"tool_input\":{\"BRANCH\":\"feat/y\",\"content\":\"x\"}}" "only an uppercase BRANCH key asks" +check ask "$(fwb Main x)" "file_write_branch to Main asks" +check ask "{\"tool_name\":\"$FWB\",\"tool_input\":{\"branch\":\"feat/y\"}}" "missing content key asks" +check ask "$(fwb feat/y ' ')" "whitespace-only content asks" +check ask "{\"tool_name\":\"$FWB\",\"tool_input\":\"branch=feat/y\"}" "non-object tool_input asks" +# Branch names are cleared by shape, not by blocklist: refs/heads/main created a +# second ref that wedged every API write to main (gatekeeper side finding). +check ask "$(fwb refs/heads/main x)" "refs/ prefixed branch asks" +check ask "$(fwb ' main' x)" "branch with whitespace asks" +check ask "$(fwb '../main' x)" "branch with .. asks" +check NONE "$(fwb release/v1.2_x x)" "ordinary branch name passes" + +# Reversible / read verbs pass through. +for v in issue_close issue_create file_read repo_list pr_create; do + check NONE "$(tool "mcp__plugin_skills_gitea__$v")" "$v passes through" +done +check NONE "$(tool mcp__plugin_skills_gitea__repo_delete_dry_run_list)" "suffix near-miss passes" +check NONE "$(tool Bash)" "non-MCP tool passes" +check NONE "$(tool repo_delete)" "non-MCP tool named like a verb passes" + +# Malformed input fails CLOSED (gatekeeper: non-string tool_name got NONE). +check ask 'not json' "non-JSON asks" +check ask '{}' "missing tool_name asks" +check ask '{"tool_name":null}' "null tool_name asks" +check ask '{"tool_name":""}' "empty tool_name asks" +check ask '{"tool_name":5}' "number tool_name asks" +check ask '{"tool_name":["mcp__x__repo_delete"]}' "array tool_name asks" +check ask '{"tool_name":{"a":1}}' "object tool_name asks" + +# Without jq on PATH the guard must still answer ask, not stay silent +# (gatekeeper: the fail-closed path itself needed jq). +nojq=$(mktemp -d); trap 'rm -rf "$nojq"' EXIT +for b in bash cat grep tr sed; do ln -s "$(command -v $b)" "$nojq/$b"; done +_got=$(run_guard "$(tool mcp__plugin_skills_gitea__repo_delete)" "$nojq") +if [ "$_got" = "ask rc=0" ]; then pass=$((pass+1)); echo " ok no jq on PATH still asks"; else fail=$((fail+1)); echo " FAIL no jq on PATH: got=$_got"; fi +_got=$(run_guard "$(tool mcp__plugin_skills_gitea__issue_get)" "$nojq") +if [ "$_got" = "ask rc=0" ]; then pass=$((pass+1)); echo " ok no jq on PATH asks even for a read verb (cannot parse = cannot clear)"; else fail=$((fail+1)); echo " FAIL no jq read verb: got=$_got"; fi + +printf '\n%d passed, %d failed\n' "$pass" "$fail" +[ "$fail" -eq 0 ]