dns_secure.hpp

1. Overview

The dns_secure.hpp header declares the reexec_inside_bwrap_with_custom_dns function, which is responsible for re-executing the current process inside a Bubblewrap (bwrap) sandbox while applying a custom DNS configuration. This mechanism is typically used to harden network resolution behavior, enforce trusted resolvers, and reduce exposure to local or untrusted DNS infrastructure.

Functionally, this module provides:

  • Process re-execution within a Bubblewrap sandbox environment
  • Custom DNS resolver injection or enforcement inside the sandbox
  • CLI argument forwarding to preserve the original execution context
  • Network hardening support for security-sensitive workflows

2. Dependencies and Includes

This header does not declare explicit includes. Implementations typically require standard C/C++ headers for process control and execution (e.g., <unistd.h>, <cstdlib>, <vector>), as well as any OS-specific utilities used to configure DNS within a sandbox.

3. Public Interface

3.1 Sandboxed Re-Execution with Custom DNS

void reexec_inside_bwrap_with_custom_dns(int argc, char** argv);

Re-executes the current process within a Bubblewrap sandbox using the provided argument vector. The function is expected to apply a controlled DNS setup inside the sandbox before launching the target program logic.

Parameters:

  • argc – number of command-line arguments
  • argv – argument vector passed to the process

4. Execution Model

This function is typically called early in application startup. If the process is not already sandboxed, it constructs and executes a bwrap command line that:

  • Creates an isolated filesystem and/or namespace environment
  • Injects a custom resolver configuration (e.g., by binding a controlled resolv.conf)
  • Re-launches the program with the same arguments
  • Ensures the original (unsandboxed) instance does not continue execution

5. Intended Use Cases

  • Hardening DNS resolution for secure browsing and network operations
  • Ensuring consistent resolver policy across desktop environments
  • Reducing reliance on potentially hostile local DNS configurations
  • Running sensitive network clients inside a constrained sandbox

6. Security and Operational Considerations

  • Re-exec safety: the function should ensure that execution continues only in the sandboxed process and that the parent process terminates cleanly
  • Argument handling: command-line arguments must be forwarded safely and without reinterpretation to avoid injection vulnerabilities
  • DNS integrity: the resolver configuration introduced inside the sandbox should be immutable or protected against runtime modification
  • Binary availability: implementations should verify that bwrap is installed and return or fall back gracefully when unavailable
  • Least privilege: apply minimal filesystem and network permissions required for correct operation
  • Observability: failures to enter the sandbox or apply DNS policy should be logged with actionable diagnostics
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