Reject shell-unsafe paths in FreeBSD rc.d install

Validate executable and state directory paths before rendering the
rc.d script so crafted values cannot inject shell syntax.

Signed-off-by: Bryan Frimin <bryan@probo.com>

pkg/deviceagent/service/service_freebsd.go

@@ -59,6 +59,10 @@ func Install(cfg Config) error {
 		return errors.New("state directory is required")
 	}
 
+	if err := validateServicePaths(cfg); err != nil {
+		return err
+	}
+
 	rcTmpl, err := template.New("rc").Parse(rcScriptTmpl)
 	if err != nil {
 		return fmt.Errorf("cannot parse rc.d template: %w", err)

pkg/deviceagent/service/validate.go

@@ -0,0 +1,44 @@
+// Copyright (c) 2025-2026 Probo Inc <hello@getprobo.com>.
+//
+// Permission to use, copy, modify, and/or distribute this software for any
+// purpose with or without fee is hereby granted, provided that the above
+// copyright notice and this permission notice appear in all copies.
+//
+// THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES WITH
+// REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY
+// AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT,
+// INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM
+// LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR
+// OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
+// PERFORMANCE OF THIS SOFTWARE.
+
+package service
+
+import "fmt"
+
+func validateServicePaths(cfg Config) error {
+	if err := validateShellSafePath("executable path", cfg.ExePath); err != nil {
+		return err
+	}
+
+	return validateShellSafePath("state directory", cfg.Dir)
+}
+
+func validateShellSafePath(label, path string) error {
+	if path == "" {
+		return nil
+	}
+
+	for _, r := range path {
+		switch r {
+		case '"', '\'', '`', '$', ';', '\n', '\r', '\000':
+			return fmt.Errorf(
+				"%s contains shell-unsafe character %q",
+				label,
+				r,
+			)
+		}
+	}
+
+	return nil
+}