7e66936d03
Adds IPAddressDeny= to the sandbox unit covering loopback (127/8 + ::1), link-local (169.254/16 + fe80::/10), multicast (224/4 + ff00::/8), all RFC1918 v4 (10/8, 172.16/12, 192.168/16), CGNAT (100.64/10), and ULA v6 (fc00::/7). The kernel attaches systemd's sd_fw_egress BPF program to the unit's cgroup; egress packets matching any of the deny prefixes are silently dropped at the cgroup boundary. Important: do NOT pair this with `IPAddressAllow=any`. Documentation claims "more specific rule wins" but on this systemd 257 + kernel 6.12 combo, having both set causes the allow to win unconditionally — the deny gets ignored. Empty IPAddressAllow + populated IPAddressDeny is the correct shape: kernel default "allow all" applies to non-listed addresses, and the listed prefixes are blocked. Because the host's resolv.conf typically points at a private-IP DNS server (10.0.0.1 in the test deploy), blocking RFC1918 also kills DNS. Adds a static /etc/left4me/sandbox-resolv.conf with public resolvers (Cloudflare 1.1.1.1, Google 8.8.8.8) and bind-mounts that into the sandbox at /etc/resolv.conf, replacing the host's resolver inside the sandbox only. Smoke-tested on ckn@10.0.4.128: - public 1.1.1.1:443: CONNECTED - public HTTPS via DNS (steamcommunity.com): 200 - localhost web app 127.0.0.1:8000: blocked (TimeoutError) - localhost sshd 127.0.0.1:22: blocked - private LAN ssh 10.0.4.128:22: blocked - private DNS 10.0.0.1:53: blocked AF_UNIX stays in RestrictAddressFamilies — dropping it would risk breaking NSS / syslog for marginal gain, and the IP-level filter addresses the primary threat (reaching the host's HTTP/SSH services). Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
6 lines
330 B
Text
6 lines
330 B
Text
# Sandbox-only resolver config — bind-mounted into script-overlay sandboxes
|
|
# at /etc/resolv.conf. The host's resolver (often a private/LAN DNS server)
|
|
# is unreachable from inside the sandbox because IPAddressDeny= blocks
|
|
# egress to RFC1918 / loopback. Public resolvers keep DNS working.
|
|
nameserver 1.1.1.1
|
|
nameserver 8.8.8.8
|