fix: resolve /etc/resolv.conf symlink on separate mounts#35
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On systems using systemd-resolved, /etc/resolv.conf is a symlink to /run/systemd/resolve/stub-resolv.conf. After bwrap's non-recursive --ro-bind / /, the /run tmpfs is empty so the symlink target is unreachable, causing "Can't create file at /etc/resolv.conf". The previous fix only handled cross-device symlinks (sameDevice check), which missed cases where /run is a separate mount but happens to share a device ID with /. Changes: - Add isSeparateMount() that compares a path's device ID with its parent's, reliably detecting separate mounts like /run as tmpfs - Add resolveSymlinkForBind() helper that generates bwrap --tmpfs/--dir args to make symlink targets reachable inside the sandbox - Bind DNS override resolv.conf to the resolved target path directly, avoiding bwrap's symlink following for the destination - Add unit tests for the new helpers and an integration test verifying /etc/resolv.conf is readable inside the sandbox
Replaced by isSeparateMount in the resolv.conf symlink fix.
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Summary
Fixes #25 (resolv.conf part)
/etc/resolv.confis a symlink to/run/systemd/resolve/stub-resolv.conf. After bwrap's non-recursive--ro-bind / /, the/runtmpfs is empty so the symlink target is unreachable, causingbwrap: Can't create file at /etc/resolv.conf.sameDevicecheck), which missed cases where/runis a separate mount but device IDs happen to match.isSeparateMount()that compares a path's device ID with its parent's, reliably detecting separate mounts.resolveSymlinkForBind()helper that generates bwrap--tmpfs/--dirargs to make symlink targets reachable.Test plan
isSeparateMount(),resolveSymlinkForBind()(non-symlink, nonexistent, cross-mount, resolv.conf)cat /etc/resolv.confsucceeds inside sandboxgreywall -- curl https://greyhaven.co