Merge pull request #12323 from atoslins/fix-windows-vm-setgid

Clear setgid when hardening Windows VM directories

test/shell.d/windows-vm-compose-test.sh

@@ -112,6 +112,8 @@ pass "pkexec target is only the canonical packaged regular file, never a PATH sy
 reset_case
 external_shared="$TMPDIR/external-shared"
 mkdir -m 0755 -p "$HOME/.windows" "$external_shared" "$HOME/.config/windows"
+# dockur leaves an initially empty share setgid, which a numeric chmod keeps.
+chmod 2777 "$external_shared"
 ln -s "$external_shared" "$HOME/Windows"
 touch "$HOME/.windows/existing-disk" "$external_shared/existing-shared-file"
 LEGACY_COMPOSE_FILE="$HOME/.config/windows/docker-compose.yml"

test/shell.d/windows-vm-mount-boundary-test.sh

@@ -143,6 +143,33 @@ chown root:root "$USERS_DIR"
 mounts_ready || fail "restored production boundaries were rejected"
 pass "root rejects wrong-owned and group-writable production mount boundaries without mutation"
 
+# dockur marks an empty /shared setgid (chmod 2777) on first boot, and a numeric
+# chmod keeps setuid/setgid on directories. Hardening has to clear the special
+# bits behind live anchors and again when the binds are recreated after reboot.
+chmod 2777 /home/shared-target
+chmod 6755 /home/storage-target
+with_vm_lock prepare_caller_mounts || fail "root rejected setgid sources behind live anchors"
+mounts_ready || fail "final guard rejected re-hardened setgid sources"
+umount "$EXPECTED_SHARED"
+umount "$EXPECTED_STORAGE"
+chmod 2777 /home/shared-target
+chmod 6755 /home/storage-target
+with_vm_lock prepare_caller_mounts || fail "root could not rebind setgid sources"
+[[ $(command stat -Lc '%u:%a' "$EXPECTED_STORAGE") == 1000:700 &&
+  $(command stat -Lc '%u:%a' "$EXPECTED_SHARED") == 1000:700 ]] || fail "setgid sources were not hardened to 0700"
+mounts_ready || fail "final guard rejected rebound setgid sources"
+pass "hardening clears the setuid/setgid bits a numeric chmod keeps on directories"
+
+# When hardening still leaves a source non-private, the rejection names the
+# directory and its mode instead of failing silently.
+chmod() { command chmod "$@" && command chmod g+s /home/shared-target; }
+hardening_error=$(with_vm_lock prepare_caller_mounts 2>&1) && fail "root accepted a source that stayed setgid after hardening"
+unset -f chmod
+[[ $hardening_error == *"/home/alice/Windows is mode 2700"* ]] || fail "setgid rejection did not name the directory and mode: $hardening_error"
+chmod g-s /home/shared-target
+mounts_ready || fail "verified anchors were disturbed by the rejected hardening"
+pass "a source that cannot be made private is rejected with its path and mode"
+
 expected_space=$(command df -P -- /home/storage-target | awk 'NR==2 {print int($4/1024/1024)}')
 actual_space=$(available_storage_gb)
 [[ $actual_space == "$expected_space" ]] || fail "disk-space helper did not measure the storage target filesystem"