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Snigdha OSDecentralized

Application Isolation Architecture

AppArmor MAC enforce profiles, Bubblewrap user namespaces, and Seccomp-BPF filters.

5 min readUpdated: 2026-11-12

Snigdha OS Decentralized - Confinement & Application Isolation Architecture

Subsystem: Snigdha Isolation (Phase 5)
Author: Snigdha OS Distribution Architecture Core
Applicability: Snigdha OS Decentralized (Live System)
Status: COMPLETE & ENFORCED

1. Architectural Philosophy

Snigdha Isolation implements defense-in-depth confinement for all desktop applications and system background daemons. Rather than relying on a single monolithic sandbox tool, isolation is achieved through the layered orchestration of:

  1. Mandatory Access Control (AppArmor): Enforces mandatory kernel-level file, capability, network, and unix-socket rules regardless of process UID.
  2. Interactive Application Sandboxing (Bubblewrap): Constructs hermetic execution environments utilizing Linux unprivileged user, mount, PID, IPC, and UTS namespaces.
  3. Session D-Bus Filtering (xdg-dbus-proxy): Intercepts and filters desktop IPC calls, blocking access to administrative daemons.
  4. System Call Filtering (Seccomp-BPF): Attaches compiled Berkeley Packet Filters to disallow dangerous kernel interfaces (ptrace, module loading, reboot, keyrings).
  5. System Service Hardening (systemd drop-ins): Hardens all system services individually using declarative unit constraints (ProtectSystem, PrivateTmp, RestrictSUIDSGID, CapabilityBoundingSet).

2. Multi-Layer Security Architecture 

+-----------------------------------------------------------------------------------+
|                           SNIGDHA APPLICATION EXECUTION                           |
+-----------------------------------------------------------------------------------+
                                      │
                                      ▼
                        [ 1. snigdha-sandbox Launcher ]
                   Validates ID, schema, and binary presence
                                      │
        ┌─────────────────────────────┼─────────────────────────────┐
        ▼                             ▼                             ▼
 [ 2. AppArmor MAC ]       [ 3. xdg-dbus-proxy ]        [ 4. Seccomp-BPF ]
 Kernel LSM enforcement      Filters D-Bus methods      Blocks dangerous syscalls
 Path / Capability denies    Rejects privileged calls   (ptrace, reboot, modules)
        │                             │                             │
        └─────────────────────────────┼─────────────────────────────┘
                                      │
                                      ▼
                       [ 5. Bubblewrap Sandbox Engine ]
     ┌────────────────────────────────┴────────────────────────────────┐
     │  * Namespaces: User, Mount, PID, IPC, UTS                       │
     │  * Filesystem: Read-only /usr, private volatile /tmp, masked etc │
     │  * Network Policy: host-enforced (NetGuard Tor) OR offline      │
     │  * Persistence: Masked with empty tmpfs when locked             │
     │  * Devices: Minimal /dev (null, zero, urandom, dri)             │
     └────────────────────────────────┬────────────────────────────────┘
                                      │
                                      ▼
                      [ Target Unprivileged Execution ]
               Confined execution inside disposable sandbox

3. Subsystem Components

3.1 AppArmor Kernel Foundation

  • Kernel Parameter: Loaded at boot via lsm=landlock,lockdown,yama,integrity,apparmor,bpf apparmor=1 security=apparmor.
  • Ordering: Preserves Landlock, Lockdown, Yama, Integrity, and BPF in standard Arch Linux ordering while activating AppArmor.
  • Profiles: Located in /etc/apparmor.d/ on rootfs, including:
    • Daemons: snigdha-netguardd, snigdha-persistenced, snigdha-amnesia-guard, snigdha-amnesia-shutdown, snigdha-media-watchdog, snigdha-firewall, snigdha-tor.
    • Applications: snigdha-kitty, snigdha-thunar, snigdha-rofi, snigdha-feh, snigdha-desktop-utilities.
  • Enforcement: All profiles are in strict ENFORCE mode (flags=(enforce)). Complain mode is never used for production confinement.

3.2 Bubblewrap (snigdha-sandbox)

  • Namespace Isolation:
    • --unshare-user: Maps user namespace without setuid helpers.
    • --unshare-pid: Masks host processes; sandbox only observes its own child processes.
    • --unshare-ipc: Prevents shared memory and message queue snooping.
    • --unshare-uts: Isolates hostname.
    • --new-session: Prevents terminal ioctl (TIOCSTI) injection.
    • --die-with-parent: Eliminates orphaned processes upon parent exit.
  • Network Policies:
    • host-enforced: Retains host network namespace so all traffic is intercepted by NetGuard nftables rules and routed through Tor.
    • offline: Employs --unshare-net (loopback only) with zero external network connectivity.
  • Filesystem Construction:
    • System: Strictly read-only /usr, symlinked /lib, /lib64, /bin, /sbin.
    • Sensitive Paths: /etc/shadow, /etc/gshadow masked with /dev/null; /etc/tor, /etc/nftables.d masked with empty tmpfs.
    • Private Home: Ephemeral tmpfs over $HOME, exposing only approved config paths under ~/.var/app/{id}.

3.3 Session D-Bus Filtering (xdg-dbus-proxy)

  • Started automatically by snigdha-sandbox when policy specifies dbus.policy != "none".
  • Provides an isolated proxy socket bound to /run/user/{uid}/bus inside the sandbox.
  • Enforces --filter, allowing only declared bus names (e.g., org.freedesktop.Notifications).
  • Denies privileged services: org.snigdha.NetGuard1, org.snigdha.Persistence1, org.freedesktop.systemd1.
  • Automatically terminates when parent file descriptor closes (--fd=FD).

3.4 Seccomp System Call Filtering

  • Declarative policies compiled into raw BPF bytecode using native libseccomp compiler (snigdha-seccomp-compiler).
  • Filters passed directly to bubblewrap via file descriptor (--seccomp <fd>).
  • Disallows: init_module, finit_module, delete_module, reboot, kexec_load, ptrace, process_vm_readv, process_vm_writev, mount, umount2, pivot_root, chroot, syslog, perf_event_open, bpf, keyctl, swapon, swapoff, settimeofday.
  • Offline profiles additionally block socket creation (socket(), connect(), bind()).

3.5 systemd Service Hardening

All 9 system background services are hardened using drop-in configurations (/etc/systemd/system/*.service.d/hardening.conf):

  • ProtectSystem=strict
  • ProtectHome=yes (or read-only where persistence mount is required)
  • PrivateTmp=yes
  • ProtectKernelTunables=yes
  • ProtectKernelModules=yes
  • ProtectControlGroups=yes
  • RestrictSUIDSGID=yes
  • LockPersonality=yes
  • SystemCallArchitectures=native
  • CapabilityBoundingSet restricted to essential capabilities only.

4. Confinement Diagnostics Tool (snigdha-isolation)

Provides an operator and testing interface:

snigdha-isolation status       # Overall confinement health summary
snigdha-isolation list         # List registered application profiles
snigdha-isolation inspect ID   # Inspect specific policy details
snigdha-isolation verify       # Execute deterministic invariant verification
snigdha-isolation apparmor     # Audit AppArmor LSM modules and profiles
snigdha-isolation namespaces   # Audit Linux namespace capabilities
snigdha-isolation seccomp      # Audit Seccomp BPF filters
snigdha-isolation services     # Audit systemd service hardening
snigdha-isolation diagnose     # Complete diagnostic dump (supports --json)

5. Snigdha Security Center Integration (Phase 7)

Snigdha Isolation provides live confinement inspection over D-Bus system bus via interface org.snigdha.Isolation1 (/org/snigdha/Isolation1):

  • LSM & AppArmor Metrics: GetStatus() reports active AppArmor status, count of enforcing vs complaining profiles, active Bubblewrap container count, and seccomp filter support.
  • Profiles & Sandboxes Audit: GetProfiles() and AuditSandboxes() feed real-time profile lists and live sandbox process metrics to the Snigdha Security Center Isolation page (snigdha-security-center).
  • Confinement of Security Center: Security Center itself is confined by AppArmor profile /etc/apparmor.d/snigdha-security-center, ensuring it cannot bypass isolation or access raw hardware blocks.