fix(windows-vm): strip setgid bit on shared folder to preserve 0700 mount safety - #11891
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… privacy Fixes omacom#11879 When dockurr/windows runs, its Samba service sets the setgid bit on the shared folder (~/Windows), leaving it with mode 2700 instead of 0700. On Linux/BTRFS, a numeric 'chmod 0700' does not clear an existing setgid bit. Consequently, subsequent launches fail the [[ $shared_mode != 700 ]] safety check in prepare_caller_mounts() and fail to start the VM. 1. In prepare_caller_mounts(), use 'chmod 00700' and explicitly strip setgid and setuid ('chmod ug-s') on pinned storage and shared descriptors. 2. In mounted_leaf_matches(), strip setgid/setuid on the caller-owned mount leaf before checking mode 700 to accommodate containers that mutate permissions. 3. In prepare_user_mount_sources(), also use 'chmod 00700' and 'chmod ug-s'. 4. Add regression test in windows-vm-mount-boundary-test.sh ensuring a setgid shared directory has setgid stripped and preserves 0700 mount privacy.
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Problem
When running
dockurr/windowsviaomarchy-windows-vm, Samba or the container's initialization sets the setgid bit on the bound shared folder (~/Windows), resulting in directory permissions2700instead of0700.On Linux / BTRFS, numeric
chmod 0700does not clear an existing setgid bit on a directory. Becauseprepare_caller_mounts()strictly enforces that both storage and shared directories must be mode700([[ $storage_mode != 700 || $shared_mode != 700 ]]), every subsequent launch of the Windows VM fails.Fixes #11879 (part 1)
Solution
prepare_caller_mounts(), usechmod 00700and explicitly runchmod ug-son the pinned file descriptors to strip any setgid/setuid bits left by container services before checking mode700.mounted_leaf_matches(), also clearchmod ug-sbefore comparing the directory mode against700.prepare_user_mount_sources(), usechmod 00700andchmod ug-s.test/shell.d/windows-vm-mount-boundary-test.shverifying that an existing2700(setgid) shared directory has setgid stripped and maintains verified0700privacy across mount checks.Verification
test/shell.d/windows-vm-mount-boundary-test.sh(all 10 checks pass).windows-key-test.sh,windows-vm-compose-test.sh,windows-vm-mount-boundary-test.sh,windows-vm-test.sh) with 100% pass rate.