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Enhance Linux sandbox security features with Landlock, seccomp, and eBPF monitoring

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JY Tan
2025-12-25 17:33:55 -08:00
parent a8158a39b3
commit 08ed28f88f
20 changed files with 2820 additions and 64 deletions
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ARCHITECTURE.md
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@@ -27,7 +27,7 @@ flowchart TB
```text
fence/
├── cmd/fence/ # CLI entry point
│ └── main.go
│ └── main.go # Includes --landlock-apply wrapper mode
├── internal/ # Private implementation
│ ├── config/ # Configuration loading/validation
│ ├── platform/ # OS detection
@@ -36,9 +36,15 @@ fence/
│ ├── manager.go # Orchestrates sandbox lifecycle
│ ├── macos.go # macOS sandbox-exec profiles
│ ├── linux.go # Linux bubblewrap + socat bridges
│ ├── linux_seccomp.go # Seccomp BPF syscall filtering
│ ├── linux_landlock.go # Landlock filesystem control
│ ├── linux_ebpf.go # eBPF violation monitoring
│ ├── linux_features.go # Kernel feature detection
│ ├── linux_*_stub.go # Non-Linux build stubs
│ ├── monitor.go # macOS log stream violation monitoring
│ ├── dangerous.go # Protected file/directory lists
│ └── utils.go # Path normalization, shell quoting
│ ├── shell.go # Shell quoting utilities
│ └── utils.go # Path normalization
└── pkg/fence/ # Public Go API
└── fence.go
```
@@ -238,14 +244,29 @@ flowchart TD
| Feature | macOS | Linux |
|---------|-------|-------|
| Sandbox mechanism | sandbox-exec (Seatbelt) | bubblewrap (namespaces) |
| Sandbox mechanism | sandbox-exec (Seatbelt) | bubblewrap + Landlock + seccomp |
| Network isolation | Syscall filtering | Network namespace |
| Proxy routing | Environment variables | socat bridges + env vars |
| Filesystem control | Profile rules | Bind mounts |
| Filesystem control | Profile rules | Bind mounts + Landlock (5.13+) |
| Syscall filtering | Implicit (Seatbelt) | seccomp BPF |
| Inbound connections | Profile rules (`network-bind`) | Reverse socat bridges |
| Violation monitoring | log stream + proxy | proxy only |
| Violation monitoring | log stream + proxy | eBPF + proxy |
| Requirements | Built-in | bwrap, socat |
### Linux Security Layers
On Linux, fence uses multiple security layers with graceful fallback:
1. bubblewrap (core isolation via Linux namespaces)
2. seccomp (syscall filtering)
3. Landlock (filesystem access control)
4. eBPF monitoring (violation visibility)
> [!NOTE]
> Seccomp blocks syscalls silently (no logging). With `-m` and root/CAP_BPF, the eBPF monitor catches these failures by tracing syscall exits that return EPERM/EACCES.
See [Linux Security Features](./docs/linux-security-features.md) for details.
## Violation Monitoring
The `-m` (monitor) flag enables real-time visibility into blocked operations.
@@ -257,6 +278,7 @@ The `-m` (monitor) flag enables real-time visibility into blocked operations.
| `[fence:http]` | Both | HTTP/HTTPS proxy (blocked requests only in monitor mode) |
| `[fence:socks]` | Both | SOCKS5 proxy (blocked requests only in monitor mode) |
| `[fence:logstream]` | macOS only | Kernel-level sandbox violations from `log stream` |
| `[fence:ebpf]` | Linux only | Filesystem/syscall failures (requires CAP_BPF or root) |
| `[fence:filter]` | Both | Domain filter rule matches (debug mode only) |
### macOS Log Stream
@@ -281,17 +303,6 @@ Filtered out (too noisy):
- `mDNSResponder` - system DNS resolution
- `/private/var/run/syslog` - system logging
### Linux Limitations
Linux uses network namespace isolation (`--unshare-net`), which prevents connections at the namespace level rather than logging them. There's no kernel-level violation stream equivalent to macOS.
With `-m` on Linux, you only see proxy-level denials:
```text
[fence:http] 14:30:01 ✗ CONNECT 403 evil.com https://evil.com:443 (0s)
[fence:socks] 14:30:02 ✗ CONNECT evil.com:22 BLOCKED
```
### Debug vs Monitor Mode
| Flag | Proxy logs | Filter rules | Log stream | Sandbox command |