Race Windows VM mount sources concurrently

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

@@ -213,6 +213,65 @@ mv -T -- "$raced_shared" "$HOME/Windows"
 unset -f dc
 pass "a post-validation path swap cannot redirect Docker away from the pinned shared inode"
 
+# Run the same attack as a genuinely concurrent process. A successful bring-up
+# deliberately waits inside the Docker boundary until the attacker has replaced
+# the familiar path with /, then verifies that the real bind anchor still names
+# the caller-owned directory that was pinned before the race.
+reset_case
+prepare_user_mount_sources
+touch "$HOME/Windows/safe-marker"
+write 4G 2 64G concurrent pw UTC
+resolve_caller
+concurrent_shared_id=$(stat -Lc '%d:%i' "$HOME/Windows")
+host_root_id=$(stat -Lc '%d:%i' /)
+race_source="$HOME/Windows.race-source"
+race_stop="$TMPDIR/stop-concurrent-race"
+race_swaps="$TMPDIR/concurrent-race-swaps"
+(
+  set +e
+  while [[ ! -e $race_stop ]]; do
+    if [[ -d $HOME/Windows && ! -L $HOME/Windows ]] && mv -T -- "$HOME/Windows" "$race_source" 2>/dev/null; then
+      ln -s / "$HOME/Windows" 2>/dev/null || true
+      printf x >>"$race_swaps"
+      sleep 0.002
+    fi
+    if [[ -L $HOME/Windows ]]; then
+      rm -f -- "$HOME/Windows"
+      mv -T -- "$race_source" "$HOME/Windows" 2>/dev/null || true
+      sleep 0.005
+    fi
+  done
+) &
+racer_pid=$!
+concurrent_dc_calls=0
+dc() {
+  local attempt
+  [[ $1 == up && ${2:-} == -d ]] || return 1
+  for ((attempt = 0; attempt < 20000; attempt++)); do
+    if [[ -L $HOME/Windows && $(readlink "$HOME/Windows" 2>/dev/null) == / ]]; then
+      break
+    fi
+  done
+  [[ -L $HOME/Windows && $(readlink "$HOME/Windows" 2>/dev/null) == / ]] || return 1
+  ((concurrent_dc_calls++))
+  [[ $(get_mount_source /shared) == "$EXPECTED_SHARED" ]] || return 1
+  [[ $(stat -Lc '%d:%i' "$EXPECTED_SHARED") == "$concurrent_shared_id" ]] || return 1
+  [[ $(stat -Lc '%d:%i' "$EXPECTED_SHARED") != "$host_root_id" ]] || return 1
+  [[ -f $EXPECTED_SHARED/safe-marker ]]
+}
+for ((attempt = 0; attempt < 200; attempt++)); do
+  if __priv_up 2>/dev/null; then break; fi
+done
+touch "$race_stop"
+wait "$racer_pid"
+unset -f dc
+if [[ -L $HOME/Windows ]]; then rm -f -- "$HOME/Windows"; fi
+if [[ ! -e $HOME/Windows && -d $race_source ]]; then mv -T -- "$race_source" "$HOME/Windows"; fi
+[[ -s $race_swaps ]] || fail "concurrent attacker never swapped the shared path"
+((concurrent_dc_calls > 0)) || fail "concurrent race never reached Docker while the familiar path named host root"
+[[ $(stat -Lc '%d:%i' "$EXPECTED_SHARED") == "$concurrent_shared_id" ]] || fail "concurrent race changed the protected shared inode"
+pass "a concurrent home-path swap cannot redirect Docker away from the pinned shared inode"
+
 # Same-inode sources fail before mounting and close both descriptors.
 reset_case
 same="$TMPDIR/same-source"