fix: stop blocking harmless /dev/null redirections in CommandValidator

src/remoteshell_mcp/command_validator.py

@@ -48,8 +48,13 @@ class CommandValidator:
         (r'\bchmod\s+.*777\s+.*/', 'Modify root directory permissions'),
         (r'\bchown\s+.*root\s+.*/', 'Modify root directory ownership'),
 
-        # Other dangerous operations
-        (r'>\s*/dev/', 'Redirect to device file'),
+        # Other dangerous operations.
+        # Only block redirection to real storage devices (block devices that a
+        # stray write can destroy). Harmless character devices such as
+        # /dev/null, /dev/stdout, /dev/stderr, /dev/full are intentionally
+        # allowed: `2>/dev/null` is the standard idiom for discarding stderr.
+        (r'>\s*/dev/(?:sd[a-z]|hd[a-z]|vd[a-z]|xvd[a-z]|nvme|mmcblk|loop|mapper|sr\d|fd\d)',
+         'Overwrite block device'),
         (r':\(\)\s*\{\s*:\s*\|\s*:\s*&\s*\}\s*;', 'Fork bomb'),
         (r'\bhalt\b', 'System halt'),
         (r'\bpoweroff\b', 'System poweroff'),

tests/test_command_validator_integration.py

@@ -19,6 +19,9 @@ def test_command_validator_blocks_dangerous_commands(self):
             "rm -rf /root",
             "dd if=/dev/zero of=/dev/sda",
             "mkfs.ext4 /dev/sda",
+            "echo x > /dev/sda",
+            "echo x >/dev/nvme0n1",
+            "echo x > /dev/mapper/vg-root",
             "halt",
             "shutdown -h now",
             ":(){ :|:& };:",
@@ -40,6 +43,10 @@ def test_command_validator_allows_safe_commands(self):
             "mkdir test_dir",
             "cp file1 file2",
             "grep pattern file.txt",
+            "echo hello 2>/dev/null",
+            "cmd > /dev/null 2>&1",
+            "cat /etc/hostname > /dev/full",
+            "echo x 1>/dev/stdout 2>/dev/stderr",
         ]
 
         for command in safe_commands: