fix(tools): allow /dev/null redirection and add read/write sandbox split (#967)

* fix(tools): allow /dev/null redirection and add read/write sandbox split

- Remove deny pattern that incorrectly blocked redirects to /dev/null
- Expand block device write pattern to cover nvme, mmcblk, vd, xvd,
  hd, loop, dm-, md, sr and nbd in addition to sd
- Add safe path whitelist for kernel pseudo-devices so workspace path
  check does not reject /dev/null, /dev/zero, /dev/random, /dev/urandom,
  /dev/stdin, /dev/stdout and /dev/stderr
- Add allow_read_outside_workspace config option (default true) so file
  read and list tools are unrestricted while write tools stay sandboxed

Closes https://github.com/sipeed/picoclaw/issues/964
Closes https://github.com/sipeed/picoclaw/issues/965

Signed-off-by: Huang Rui <vowstar@gmail.com>

* feat(tools): add configurable allow patterns and path whitelists

- Add custom_allow_patterns to exec config so users can exempt specific
  commands from deny pattern checks
- Add allow_read_paths and allow_write_paths regex lists to tools config
  for whitelisting specific paths outside the workspace
- Introduce whitelistFs that wraps sandboxFs and falls through to hostFs
  for paths matching whitelist patterns
- Use variadic constructor signatures to keep backward compatibility

Suggested-by: lxowalle
Signed-off-by: Huang Rui <vowstar@gmail.com>

---------

Signed-off-by: Huang Rui <vowstar@gmail.com>

pkg/agent/instance.go

@@ -1,9 +1,11 @@
 package agent
 
 import (
+	"fmt"
 	"log"
 	"os"
 	"path/filepath"
+	"regexp"
 	"strings"
 
 	"github.com/sipeed/picoclaw/pkg/config"
@@ -48,18 +50,24 @@ func NewAgentInstance(
 	fallbacks := resolveAgentFallbacks(agentCfg, defaults)
 
 	restrict := defaults.RestrictToWorkspace
+	readRestrict := restrict && !defaults.AllowReadOutsideWorkspace
+
+	// Compile path whitelist patterns from config.
+	allowReadPaths := compilePatterns(cfg.Tools.AllowReadPaths)
+	allowWritePaths := compilePatterns(cfg.Tools.AllowWritePaths)
+
 	toolsRegistry := tools.NewToolRegistry()
-	toolsRegistry.Register(tools.NewReadFileTool(workspace, restrict))
+	toolsRegistry.Register(tools.NewReadFileTool(workspace, readRestrict, allowReadPaths))
-	toolsRegistry.Register(tools.NewWriteFileTool(workspace, restrict))
+	toolsRegistry.Register(tools.NewWriteFileTool(workspace, restrict, allowWritePaths))
-	toolsRegistry.Register(tools.NewListDirTool(workspace, restrict))
+	toolsRegistry.Register(tools.NewListDirTool(workspace, readRestrict, allowReadPaths))
 	execTool, err := tools.NewExecToolWithConfig(workspace, restrict, cfg)
 	if err != nil {
 		log.Fatalf("Critical error: unable to initialize exec tool: %v", err)
 	}
 	toolsRegistry.Register(execTool)
 
-	toolsRegistry.Register(tools.NewEditFileTool(workspace, restrict))
+	toolsRegistry.Register(tools.NewEditFileTool(workspace, restrict, allowWritePaths))
-	toolsRegistry.Register(tools.NewAppendFileTool(workspace, restrict))
+	toolsRegistry.Register(tools.NewAppendFileTool(workspace, restrict, allowWritePaths))
 
 	sessionsDir := filepath.Join(workspace, "sessions")
 	sessionsManager := session.NewSessionManager(sessionsDir)
@@ -189,6 +197,19 @@ func resolveAgentFallbacks(agentCfg *config.AgentConfig, defaults *config.AgentD
 	return defaults.ModelFallbacks
 }
 
+func compilePatterns(patterns []string) []*regexp.Regexp {
+	compiled := make([]*regexp.Regexp, 0, len(patterns))
+	for _, p := range patterns {
+		re, err := regexp.Compile(p)
+		if err != nil {
+			fmt.Printf("Warning: invalid path pattern %q: %v\n", p, err)
+			continue
+		}
+		compiled = append(compiled, re)
+	}
+	return compiled
+}
+
 func expandHome(path string) string {
 	if path == "" {
 		return path

pkg/config/config.go

@@ -168,17 +168,18 @@ type SessionConfig struct {
 }
 
 type AgentDefaults struct {
-	Workspace           string   `json:"workspace"                       env:"PICOCLAW_AGENTS_DEFAULTS_WORKSPACE"`
+	Workspace                 string   `json:"workspace"                       env:"PICOCLAW_AGENTS_DEFAULTS_WORKSPACE"`
-	RestrictToWorkspace bool     `json:"restrict_to_workspace"           env:"PICOCLAW_AGENTS_DEFAULTS_RESTRICT_TO_WORKSPACE"`
+	RestrictToWorkspace       bool     `json:"restrict_to_workspace"           env:"PICOCLAW_AGENTS_DEFAULTS_RESTRICT_TO_WORKSPACE"`
-	Provider            string   `json:"provider"                        env:"PICOCLAW_AGENTS_DEFAULTS_PROVIDER"`
+	AllowReadOutsideWorkspace bool     `json:"allow_read_outside_workspace"    env:"PICOCLAW_AGENTS_DEFAULTS_ALLOW_READ_OUTSIDE_WORKSPACE"`
-	ModelName           string   `json:"model_name,omitempty"            env:"PICOCLAW_AGENTS_DEFAULTS_MODEL_NAME"`
+	Provider                  string   `json:"provider"                        env:"PICOCLAW_AGENTS_DEFAULTS_PROVIDER"`
-	Model               string   `json:"model"                           env:"PICOCLAW_AGENTS_DEFAULTS_MODEL"` // Deprecated: use model_name instead
+	ModelName                 string   `json:"model_name,omitempty"            env:"PICOCLAW_AGENTS_DEFAULTS_MODEL_NAME"`
-	ModelFallbacks      []string `json:"model_fallbacks,omitempty"`
+	Model                     string   `json:"model"                           env:"PICOCLAW_AGENTS_DEFAULTS_MODEL"` // Deprecated: use model_name instead
-	ImageModel          string   `json:"image_model,omitempty"           env:"PICOCLAW_AGENTS_DEFAULTS_IMAGE_MODEL"`
+	ModelFallbacks            []string `json:"model_fallbacks,omitempty"`
-	ImageModelFallbacks []string `json:"image_model_fallbacks,omitempty"`
+	ImageModel                string   `json:"image_model,omitempty"           env:"PICOCLAW_AGENTS_DEFAULTS_IMAGE_MODEL"`
-	MaxTokens           int      `json:"max_tokens"                      env:"PICOCLAW_AGENTS_DEFAULTS_MAX_TOKENS"`
+	ImageModelFallbacks       []string `json:"image_model_fallbacks,omitempty"`
-	Temperature         *float64 `json:"temperature,omitempty"           env:"PICOCLAW_AGENTS_DEFAULTS_TEMPERATURE"`
+	MaxTokens                 int      `json:"max_tokens"                      env:"PICOCLAW_AGENTS_DEFAULTS_MAX_TOKENS"`
-	MaxToolIterations   int      `json:"max_tool_iterations"             env:"PICOCLAW_AGENTS_DEFAULTS_MAX_TOOL_ITERATIONS"`
+	Temperature               *float64 `json:"temperature,omitempty"           env:"PICOCLAW_AGENTS_DEFAULTS_TEMPERATURE"`
+	MaxToolIterations         int      `json:"max_tool_iterations"             env:"PICOCLAW_AGENTS_DEFAULTS_MAX_TOOL_ITERATIONS"`
 }
 
 // GetModelName returns the effective model name for the agent defaults.
@@ -532,8 +533,9 @@ type CronToolsConfig struct {
 }
 
 type ExecConfig struct {
-	EnableDenyPatterns bool     `json:"enable_deny_patterns" env:"PICOCLAW_TOOLS_EXEC_ENABLE_DENY_PATTERNS"`
+	EnableDenyPatterns  bool     `json:"enable_deny_patterns"  env:"PICOCLAW_TOOLS_EXEC_ENABLE_DENY_PATTERNS"`
-	CustomDenyPatterns []string `json:"custom_deny_patterns" env:"PICOCLAW_TOOLS_EXEC_CUSTOM_DENY_PATTERNS"`
+	CustomDenyPatterns  []string `json:"custom_deny_patterns"  env:"PICOCLAW_TOOLS_EXEC_CUSTOM_DENY_PATTERNS"`
+	CustomAllowPatterns []string `json:"custom_allow_patterns" env:"PICOCLAW_TOOLS_EXEC_CUSTOM_ALLOW_PATTERNS"`
 }
 
 type MediaCleanupConfig struct {
@@ -543,11 +545,13 @@ type MediaCleanupConfig struct {
 }
 
 type ToolsConfig struct {
-	Web          WebToolsConfig     `json:"web"`
+	AllowReadPaths  []string           `json:"allow_read_paths"  env:"PICOCLAW_TOOLS_ALLOW_READ_PATHS"`
-	Cron         CronToolsConfig    `json:"cron"`
+	AllowWritePaths []string           `json:"allow_write_paths" env:"PICOCLAW_TOOLS_ALLOW_WRITE_PATHS"`
-	Exec         ExecConfig         `json:"exec"`
+	Web             WebToolsConfig     `json:"web"`
-	Skills       SkillsToolsConfig  `json:"skills"`
+	Cron            CronToolsConfig    `json:"cron"`
-	MediaCleanup MediaCleanupConfig `json:"media_cleanup"`
+	Exec            ExecConfig         `json:"exec"`
+	Skills          SkillsToolsConfig  `json:"skills"`
+	MediaCleanup    MediaCleanupConfig `json:"media_cleanup"`
 }
 
 type SkillsToolsConfig struct {

pkg/tools/edit.go

@@ -5,6 +5,7 @@ import (
 	"errors"
 	"fmt"
 	"io/fs"
+	"regexp"
 	"strings"
 )
 
@@ -15,14 +16,12 @@ type EditFileTool struct {
 }
 
 // NewEditFileTool creates a new EditFileTool with optional directory restriction.
-func NewEditFileTool(workspace string, restrict bool) *EditFileTool {
+func NewEditFileTool(workspace string, restrict bool, allowPaths ...[]*regexp.Regexp) *EditFileTool {
-	var fs fileSystem
+	var patterns []*regexp.Regexp
-	if restrict {
+	if len(allowPaths) > 0 {
-		fs = &sandboxFs{workspace: workspace}
+		patterns = allowPaths[0]
-	} else {
-		fs = &hostFs{}
 	}
-	return &EditFileTool{fs: fs}
+	return &EditFileTool{fs: buildFs(workspace, restrict, patterns)}
 }
 
 func (t *EditFileTool) Name() string {
@@ -80,14 +79,12 @@ type AppendFileTool struct {
 	fs fileSystem
 }
 
-func NewAppendFileTool(workspace string, restrict bool) *AppendFileTool {
+func NewAppendFileTool(workspace string, restrict bool, allowPaths ...[]*regexp.Regexp) *AppendFileTool {
-	var fs fileSystem
+	var patterns []*regexp.Regexp
-	if restrict {
+	if len(allowPaths) > 0 {
-		fs = &sandboxFs{workspace: workspace}
+		patterns = allowPaths[0]
-	} else {
-		fs = &hostFs{}
 	}
-	return &AppendFileTool{fs: fs}
+	return &AppendFileTool{fs: buildFs(workspace, restrict, patterns)}
 }
 
 func (t *AppendFileTool) Name() string {

pkg/tools/filesystem.go

@@ -6,6 +6,7 @@ import (
 	"io/fs"
 	"os"
 	"path/filepath"
+	"regexp"
 	"strings"
 	"time"
 
@@ -87,14 +88,12 @@ type ReadFileTool struct {
 	fs fileSystem
 }
 
-func NewReadFileTool(workspace string, restrict bool) *ReadFileTool {
+func NewReadFileTool(workspace string, restrict bool, allowPaths ...[]*regexp.Regexp) *ReadFileTool {
-	var fs fileSystem
+	var patterns []*regexp.Regexp
-	if restrict {
+	if len(allowPaths) > 0 {
-		fs = &sandboxFs{workspace: workspace}
+		patterns = allowPaths[0]
-	} else {
-		fs = &hostFs{}
 	}
-	return &ReadFileTool{fs: fs}
+	return &ReadFileTool{fs: buildFs(workspace, restrict, patterns)}
 }
 
 func (t *ReadFileTool) Name() string {
@@ -135,14 +134,12 @@ type WriteFileTool struct {
 	fs fileSystem
 }
 
-func NewWriteFileTool(workspace string, restrict bool) *WriteFileTool {
+func NewWriteFileTool(workspace string, restrict bool, allowPaths ...[]*regexp.Regexp) *WriteFileTool {
-	var fs fileSystem
+	var patterns []*regexp.Regexp
-	if restrict {
+	if len(allowPaths) > 0 {
-		fs = &sandboxFs{workspace: workspace}
+		patterns = allowPaths[0]
-	} else {
-		fs = &hostFs{}
 	}
-	return &WriteFileTool{fs: fs}
+	return &WriteFileTool{fs: buildFs(workspace, restrict, patterns)}
 }
 
 func (t *WriteFileTool) Name() string {
@@ -192,14 +189,12 @@ type ListDirTool struct {
 	fs fileSystem
 }
 
-func NewListDirTool(workspace string, restrict bool) *ListDirTool {
+func NewListDirTool(workspace string, restrict bool, allowPaths ...[]*regexp.Regexp) *ListDirTool {
-	var fs fileSystem
+	var patterns []*regexp.Regexp
-	if restrict {
+	if len(allowPaths) > 0 {
-		fs = &sandboxFs{workspace: workspace}
+		patterns = allowPaths[0]
-	} else {
-		fs = &hostFs{}
 	}
-	return &ListDirTool{fs: fs}
+	return &ListDirTool{fs: buildFs(workspace, restrict, patterns)}
 }
 
 func (t *ListDirTool) Name() string {
@@ -394,6 +389,57 @@ func (r *sandboxFs) ReadDir(path string) ([]os.DirEntry, error) {
 	return entries, err
 }
 
+// whitelistFs wraps a sandboxFs and allows access to specific paths outside
+// the workspace when they match any of the provided patterns.
+type whitelistFs struct {
+	sandbox  *sandboxFs
+	host     hostFs
+	patterns []*regexp.Regexp
+}
+
+func (w *whitelistFs) matches(path string) bool {
+	for _, p := range w.patterns {
+		if p.MatchString(path) {
+			return true
+		}
+	}
+	return false
+}
+
+func (w *whitelistFs) ReadFile(path string) ([]byte, error) {
+	if w.matches(path) {
+		return w.host.ReadFile(path)
+	}
+	return w.sandbox.ReadFile(path)
+}
+
+func (w *whitelistFs) WriteFile(path string, data []byte) error {
+	if w.matches(path) {
+		return w.host.WriteFile(path, data)
+	}
+	return w.sandbox.WriteFile(path, data)
+}
+
+func (w *whitelistFs) ReadDir(path string) ([]os.DirEntry, error) {
+	if w.matches(path) {
+		return w.host.ReadDir(path)
+	}
+	return w.sandbox.ReadDir(path)
+}
+
+// buildFs returns the appropriate fileSystem implementation based on restriction
+// settings and optional path whitelist patterns.
+func buildFs(workspace string, restrict bool, patterns []*regexp.Regexp) fileSystem {
+	if !restrict {
+		return &hostFs{}
+	}
+	sandbox := &sandboxFs{workspace: workspace}
+	if len(patterns) > 0 {
+		return &whitelistFs{sandbox: sandbox, patterns: patterns}
+	}
+	return sandbox
+}
+
 // Helper to get a safe relative path for os.Root usage
 func getSafeRelPath(workspace, path string) (string, error) {
 	if workspace == "" {

pkg/tools/filesystem_test.go

@@ -5,6 +5,7 @@ import (
 	"io"
 	"os"
 	"path/filepath"
+	"regexp"
 	"strings"
 	"testing"
 
@@ -486,3 +487,36 @@ func TestRootRW_Write(t *testing.T) {
 	assert.NoError(t, err)
 	assert.Equal(t, newData, content)
 }
+
+// TestWhitelistFs_AllowsMatchingPaths verifies that whitelistFs allows access to
+// paths matching the whitelist patterns while blocking non-matching paths.
+func TestWhitelistFs_AllowsMatchingPaths(t *testing.T) {
+	workspace := t.TempDir()
+	outsideDir := t.TempDir()
+	outsideFile := filepath.Join(outsideDir, "allowed.txt")
+	os.WriteFile(outsideFile, []byte("outside content"), 0o644)
+
+	// Pattern allows access to the outsideDir.
+	patterns := []*regexp.Regexp{regexp.MustCompile(`^` + regexp.QuoteMeta(outsideDir))}
+
+	tool := NewReadFileTool(workspace, true, patterns)
+
+	// Read from whitelisted path should succeed.
+	result := tool.Execute(context.Background(), map[string]any{"path": outsideFile})
+	if result.IsError {
+		t.Errorf("expected whitelisted path to be readable, got: %s", result.ForLLM)
+	}
+	if !strings.Contains(result.ForLLM, "outside content") {
+		t.Errorf("expected file content, got: %s", result.ForLLM)
+	}
+
+	// Read from non-whitelisted path outside workspace should fail.
+	otherDir := t.TempDir()
+	otherFile := filepath.Join(otherDir, "blocked.txt")
+	os.WriteFile(otherFile, []byte("blocked"), 0o644)
+
+	result = tool.Execute(context.Background(), map[string]any{"path": otherFile})
+	if !result.IsError {
+		t.Errorf("expected non-whitelisted path to be blocked, got: %s", result.ForLLM)
+	}
+}

pkg/tools/shell.go

@@ -21,6 +21,7 @@ type ExecTool struct {
 	timeout             time.Duration
 	denyPatterns        []*regexp.Regexp
 	allowPatterns       []*regexp.Regexp
+	customAllowPatterns []*regexp.Regexp
 	restrictToWorkspace bool
 }
 
@@ -34,7 +35,10 @@ var (
 			`\b(format|mkfs|diskpart)\b\s`,
 		),
 		regexp.MustCompile(`\bdd\s+if=`),
-		regexp.MustCompile(`>\s*/dev/sd[a-z]\b`), // Block writes to disk devices (but allow /dev/null)
+		// Block writes to block devices (all common naming schemes).
+		regexp.MustCompile(
+			`>\s*/dev/(sd[a-z]|hd[a-z]|vd[a-z]|xvd[a-z]|nvme\d|mmcblk\d|loop\d|dm-\d|md\d|sr\d|nbd\d)`,
+		),
 		regexp.MustCompile(`\b(shutdown|reboot|poweroff)\b`),
 		regexp.MustCompile(`:\(\)\s*\{.*\};\s*:`),
 		regexp.MustCompile(`\$\([^)]+\)`),
@@ -45,7 +49,6 @@ var (
 		regexp.MustCompile(`;\s*rm\s+-[rf]`),
 		regexp.MustCompile(`&&\s*rm\s+-[rf]`),
 		regexp.MustCompile(`\|\|\s*rm\s+-[rf]`),
-		regexp.MustCompile(`>\s*/dev/null\s*>&?\s*\d?`),
 		regexp.MustCompile(`<<\s*EOF`),
 		regexp.MustCompile(`\$\(\s*cat\s+`),
 		regexp.MustCompile(`\$\(\s*curl\s+`),
@@ -75,6 +78,19 @@ var (
 
 	// absolutePathPattern matches absolute file paths in commands (Unix and Windows).
 	absolutePathPattern = regexp.MustCompile(`[A-Za-z]:\\[^\\\"']+|/[^\s\"']+`)
+
+	// safePaths are kernel pseudo-devices that are always safe to reference in
+	// commands, regardless of workspace restriction. They contain no user data
+	// and cannot cause destructive writes.
+	safePaths = map[string]bool{
+		"/dev/null":    true,
+		"/dev/zero":    true,
+		"/dev/random":  true,
+		"/dev/urandom": true,
+		"/dev/stdin":   true,
+		"/dev/stdout":  true,
+		"/dev/stderr":  true,
+	}
 )
 
 func NewExecTool(workingDir string, restrict bool) (*ExecTool, error) {
@@ -83,6 +99,7 @@ func NewExecTool(workingDir string, restrict bool) (*ExecTool, error) {
 
 func NewExecToolWithConfig(workingDir string, restrict bool, config *config.Config) (*ExecTool, error) {
 	denyPatterns := make([]*regexp.Regexp, 0)
+	customAllowPatterns := make([]*regexp.Regexp, 0)
 
 	if config != nil {
 		execConfig := config.Tools.Exec
@@ -103,6 +120,13 @@ func NewExecToolWithConfig(workingDir string, restrict bool, config *config.Conf
 			// If deny patterns are disabled, we won't add any patterns, allowing all commands.
 			fmt.Println("Warning: deny patterns are disabled. All commands will be allowed.")
 		}
+		for _, pattern := range execConfig.CustomAllowPatterns {
+			re, err := regexp.Compile(pattern)
+			if err != nil {
+				return nil, fmt.Errorf("invalid custom allow pattern %q: %w", pattern, err)
+			}
+			customAllowPatterns = append(customAllowPatterns, re)
+		}
 	} else {
 		denyPatterns = append(denyPatterns, defaultDenyPatterns...)
 	}
@@ -112,6 +136,7 @@ func NewExecToolWithConfig(workingDir string, restrict bool, config *config.Conf
 		timeout:             60 * time.Second,
 		denyPatterns:        denyPatterns,
 		allowPatterns:       nil,
+		customAllowPatterns: customAllowPatterns,
 		restrictToWorkspace: restrict,
 	}, nil
 }
@@ -266,9 +291,20 @@ func (t *ExecTool) guardCommand(command, cwd string) string {
 	cmd := strings.TrimSpace(command)
 	lower := strings.ToLower(cmd)
 
-	for _, pattern := range t.denyPatterns {
+	// Custom allow patterns exempt a command from deny checks.
+	explicitlyAllowed := false
+	for _, pattern := range t.customAllowPatterns {
 		if pattern.MatchString(lower) {
-			return "Command blocked by safety guard (dangerous pattern detected)"
+			explicitlyAllowed = true
+			break
+		}
+	}
+
+	if !explicitlyAllowed {
+		for _, pattern := range t.denyPatterns {
+			if pattern.MatchString(lower) {
+				return "Command blocked by safety guard (dangerous pattern detected)"
+			}
 		}
 	}
 
@@ -303,6 +339,10 @@ func (t *ExecTool) guardCommand(command, cwd string) string {
 				continue
 			}
 
+			if safePaths[p] {
+				continue
+			}
+
 			rel, err := filepath.Rel(cwdPath, p)
 			if err != nil {
 				continue

pkg/tools/shell_test.go

@@ -7,6 +7,8 @@ import (
 	"strings"
 	"testing"
 	"time"
+
+	"github.com/sipeed/picoclaw/pkg/config"
 )
 
 // TestShellTool_Success verifies successful command execution
@@ -309,3 +311,115 @@ func TestShellTool_RestrictToWorkspace(t *testing.T) {
 		)
 	}
 }
+
+// TestShellTool_DevNullAllowed verifies that /dev/null redirections are not blocked (issue #964).
+func TestShellTool_DevNullAllowed(t *testing.T) {
+	tmpDir := t.TempDir()
+	tool, err := NewExecTool(tmpDir, true)
+	if err != nil {
+		t.Fatalf("unable to configure exec tool: %s", err)
+	}
+
+	commands := []string{
+		"echo hello 2>/dev/null",
+		"echo hello >/dev/null",
+		"echo hello > /dev/null",
+		"echo hello 2> /dev/null",
+		"echo hello >/dev/null 2>&1",
+		"find " + tmpDir + " -name '*.go' 2>/dev/null",
+	}
+
+	for _, cmd := range commands {
+		result := tool.Execute(context.Background(), map[string]any{"command": cmd})
+		if result.IsError && strings.Contains(result.ForLLM, "blocked") {
+			t.Errorf("command should not be blocked: %s\n  error: %s", cmd, result.ForLLM)
+		}
+	}
+}
+
+// TestShellTool_BlockDevices verifies that writes to block devices are blocked (issue #965).
+func TestShellTool_BlockDevices(t *testing.T) {
+	tool, err := NewExecTool("", false)
+	if err != nil {
+		t.Fatalf("unable to configure exec tool: %s", err)
+	}
+
+	blocked := []string{
+		"echo x > /dev/sda",
+		"echo x > /dev/hda",
+		"echo x > /dev/vda",
+		"echo x > /dev/xvda",
+		"echo x > /dev/nvme0n1",
+		"echo x > /dev/mmcblk0",
+		"echo x > /dev/loop0",
+		"echo x > /dev/dm-0",
+		"echo x > /dev/md0",
+		"echo x > /dev/sr0",
+		"echo x > /dev/nbd0",
+	}
+
+	for _, cmd := range blocked {
+		result := tool.Execute(context.Background(), map[string]any{"command": cmd})
+		if !result.IsError {
+			t.Errorf("expected block device write to be blocked: %s", cmd)
+		}
+	}
+}
+
+// TestShellTool_SafePathsInWorkspaceRestriction verifies that safe kernel pseudo-devices
+// are allowed even when workspace restriction is active.
+func TestShellTool_SafePathsInWorkspaceRestriction(t *testing.T) {
+	tmpDir := t.TempDir()
+	tool, err := NewExecTool(tmpDir, true)
+	if err != nil {
+		t.Fatalf("unable to configure exec tool: %s", err)
+	}
+
+	// These reference paths outside workspace but should be allowed via safePaths.
+	commands := []string{
+		"cat /dev/urandom | head -c 16 | od",
+		"echo test > /dev/null",
+		"dd if=/dev/zero bs=1 count=1",
+	}
+
+	for _, cmd := range commands {
+		result := tool.Execute(context.Background(), map[string]any{"command": cmd})
+		if result.IsError && strings.Contains(result.ForLLM, "path outside working dir") {
+			t.Errorf("safe path should not be blocked by workspace check: %s\n  error: %s", cmd, result.ForLLM)
+		}
+	}
+}
+
+// TestShellTool_CustomAllowPatterns verifies that custom allow patterns exempt
+// commands from deny pattern checks.
+func TestShellTool_CustomAllowPatterns(t *testing.T) {
+	cfg := &config.Config{
+		Tools: config.ToolsConfig{
+			Exec: config.ExecConfig{
+				EnableDenyPatterns:  true,
+				CustomAllowPatterns: []string{`\bgit\s+push\s+origin\b`},
+			},
+		},
+	}
+
+	tool, err := NewExecToolWithConfig("", false, cfg)
+	if err != nil {
+		t.Fatalf("unable to configure exec tool: %s", err)
+	}
+
+	// "git push origin main" should be allowed by custom allow pattern.
+	result := tool.Execute(context.Background(), map[string]any{
+		"command": "git push origin main",
+	})
+	if result.IsError && strings.Contains(result.ForLLM, "blocked") {
+		t.Errorf("custom allow pattern should exempt 'git push origin main', got: %s", result.ForLLM)
+	}
+
+	// "git push upstream main" should still be blocked (does not match allow pattern).
+	result = tool.Execute(context.Background(), map[string]any{
+		"command": "git push upstream main",
+	})
+	if !result.IsError {
+		t.Errorf("'git push upstream main' should still be blocked by deny pattern")
+	}
+}