Initial commit

hooks/post-tool-use/03-block-pre-commit-bash.py

@@ -0,0 +1,113 @@
+#!/usr/bin/env python3
+"""
+PostToolUse hook to block Bash commands that modify .git/hooks/pre-commit
+
+Catches sneaky modifications through sed, redirection, chmod, mv, cp, etc.
+"""
+
+import json
+import sys
+import re
+
+# Patterns that indicate pre-commit hook modification
+PRECOMMIT_MODIFICATION_PATTERNS = [
+    # File paths
+    r'\.git/hooks/pre-commit',
+    r'\.git\\hooks\\pre-commit',
+
+    # Redirection to pre-commit
+    r'>.*pre-commit',
+    r'>>.*pre-commit',
+
+    # sed/awk/perl modifying pre-commit
+    r'(sed|awk|perl).*-i.*pre-commit',
+    r'(sed|awk|perl).*pre-commit.*>',
+
+    # Moving/copying to pre-commit
+    r'(mv|cp).*\s+.*\.git/hooks/pre-commit',
+    r'(mv|cp).*\s+.*pre-commit',
+
+    # chmod on pre-commit (might be preparing to modify)
+    r'chmod.*\.git/hooks/pre-commit',
+
+    # echo/cat piped to pre-commit
+    r'(echo|cat).*>.*\.git/hooks/pre-commit',
+    r'(echo|cat).*>>.*\.git/hooks/pre-commit',
+
+    # tee to pre-commit
+    r'tee.*\.git/hooks/pre-commit',
+
+    # Creating pre-commit hook
+    r'cat\s*>\s*\.git/hooks/pre-commit',
+    r'cat\s*<<.*\.git/hooks/pre-commit',
+]
+
+def check_precommit_modification(command):
+    """Check if command modifies pre-commit hook."""
+    if not command:
+        return None
+
+    for pattern in PRECOMMIT_MODIFICATION_PATTERNS:
+        match = re.search(pattern, command, re.IGNORECASE)
+        if match:
+            return match.group(0)
+
+    return None
+
+def main():
+    # Read tool use event from stdin
+    try:
+        input_data = json.load(sys.stdin)
+    except json.JSONDecodeError:
+        # If we can't parse JSON, allow the operation
+        sys.exit(0)
+
+    tool_name = input_data.get("tool_name", "")
+    tool_input = input_data.get("tool_input", {})
+
+    # Only check Bash tool calls
+    if tool_name != "Bash":
+        sys.exit(0)
+
+    command = tool_input.get("command", "")
+
+    # Check for pre-commit modification
+    modification_pattern = check_precommit_modification(command)
+
+    if modification_pattern:
+        # Block the command and provide helpful feedback
+        output = {
+            "hookSpecificOutput": {
+                "hookEventName": "PostToolUse",
+                "permissionDecision": "deny",
+                "permissionDecisionReason": (
+                    f"🚫 PRE-COMMIT HOOK MODIFICATION BLOCKED\n\n"
+                    f"Detected modification attempt via: {modification_pattern}\n"
+                    f"Command: {command[:200]}{'...' if len(command) > 200 else ''}\n\n"
+                    "Git hooks should not be modified directly by Claude.\n\n"
+                    "Why this is blocked:\n"
+                    "- Pre-commit hooks enforce critical quality standards\n"
+                    "- Direct modifications bypass code review\n"
+                    "- Changes can break CI/CD pipelines\n"
+                    "- Hook modifications should be version controlled\n\n"
+                    "If you need to modify hooks:\n"
+                    "1. Edit the source hook template in version control\n"
+                    "2. Use proper tooling (husky, pre-commit framework, etc.)\n"
+                    "3. Document changes and get them reviewed\n"
+                    "4. Never bypass hooks with --no-verify\n\n"
+                    "If the hook is causing issues:\n"
+                    "- Fix the underlying problem the hook detected\n"
+                    "- Ask the user for permission to modify hooks\n"
+                    "- Use the test-runner agent to handle verbose hook output\n\n"
+                    "Common mistake: Trying to disable hooks instead of fixing issues."
+                )
+            }
+        }
+        print(json.dumps(output))
+        sys.exit(0)
+
+    # Allow command if no pre-commit modification detected
+    sys.exit(0)
+
+if __name__ == "__main__":
+    main()