fix: isolate /run with tmpfs and recreate /var/run symlinks in sandbox#54
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fix: isolate /run with tmpfs and recreate /var/run symlinks in sandbox#54
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Previously, buildDenyByDefaultMounts bind-mounted the entire host /run read-only, then overlaid /run/user with a tmpfs for D-Bus isolation. This left host sockets (Docker, Podman, containerd, libvirt, etc.) accessible inside the sandbox. Unix socket connections bypass filesystem read-only restrictions, so any exposed socket with matching permissions allowed full sandbox escape (e.g., docker run with host filesystem mounts). Replace the blanket --ro-bind /run /run with --tmpfs /run (allowlist approach), selectively mounting only: - /run/systemd/resolve/* when /etc/resolv.conf is a symlink into /run - /run/user/<uid>/bus for the filtered D-Bus proxy socket This matches the existing SSH key protection pattern (--ro-bind /dev/null over sensitive files) but is more robust: unknown sockets are excluded by default rather than requiring explicit deny rules.
On modern Linux distros, /var/run is a symlink to /run and /var/lock is a symlink to /run/lock. Many programs (virsh, systemctl, etc.) hardcode /var/run paths. The sandbox already recreates symlinks for /bin, /sbin, /lib, /lib64 but was missing /var, causing programs to fail with "No such file or directory" even when /run paths were correctly configured. Fixes #53
tito
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Summary
This PR includes two fixes for
/runhandling in the Linux sandbox:Isolate
/runwith tmpfs to prevent sandbox escape (d1afb06) - Replace blanket--ro-bind /runwith--tmpfs /runand selectively mount only what's needed. Previously, host sockets (Docker, Podman, containerd, libvirt) were accessible inside the sandbox, allowing full escape via Unix socket connections which bypass read-only mount restrictions.Recreate
/var/runand/var/locksymlinks (d7b3404) - On modern Linux distros,/var/run -> /runand/var/lock -> /run/lock. Many programs (virsh, systemctl, etc.) hardcode/var/runpaths and fail without these symlinks. Follows the same pattern already used for/bin -> usr/bin,/lib -> usr/lib, etc.Fixes #55
Fixes #53
Test plan
./greywall -- docker psfails to connect (socket no longer exposed)./greywall -- ls /var/run/resolves correctly inside sandbox./greywall -- virsh -c qemu:///system listconnects successfully (with libvirt allowRead/allowWrite config)make testpasses/var/runis a real directory (not a symlink) that no symlink is created