From d9ea4cff011b36454857cc779e92bfc1b339bde8 Mon Sep 17 00:00:00 2001
From: Harlan Zhou <zhouhua258@outlook.com>
Date: Mon, 14 Sep 2026 09:11:53 +0000
Subject: [PATCH] fix: stop blocking harmless /dev/null redirections in
 CommandValidator
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The pattern '>/dev/' blocked any redirect to any /dev/ file, including
/dev/null, /dev/stdout, /dev/stderr and /dev/full — breaking the standard
'2>/dev/null' stderr-discard idiom.

Replace with a whitelist of real storage device prefixes (sd, hd, vd,
xvd, nvme, mmcblk, loop, mapper, sr, fd) so only overwrites of actual
block devices are rejected. Future harmless /dev/* character devices are
allowed by default.
---
 src/remoteshell_mcp/command_validator.py    | 9 +++++++--
 tests/test_command_validator_integration.py | 7 +++++++
 2 files changed, 14 insertions(+), 2 deletions(-)

diff --git a/src/remoteshell_mcp/command_validator.py b/src/remoteshell_mcp/command_validator.py
index 58ac4d0..5784ac8 100644
--- a/src/remoteshell_mcp/command_validator.py
+++ b/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'),
diff --git a/tests/test_command_validator_integration.py b/tests/test_command_validator_integration.py
index 5ba5378..b5a04b8 100644
--- a/tests/test_command_validator_integration.py
+++ b/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: