dev-desktops: clean unused checkout safely

ansible/roles/dev-desktop/tasks/cleanup.yml

@@ -5,7 +5,8 @@
     dest: /etc/cron.cleanup_disk_space
     owner: root
     group: root
-    mode: 0744
+    # The script needs to be executable by any user
+    mode: 0755
 
 - name: Set up the cleanup cron job
   template:

ansible/roles/dev-desktop/templates/clean-unused-checkouts.sh

@@ -21,8 +21,16 @@ dry_run=false
 # Default to search for checkouts older than 60 days
 time="60"
 
+# Internal mode used after dropping privileges to a home directory owner.
+cleanup_home_path=""
+
 while [[ $# -gt 0 ]]; do
   case $1 in
+    --cleanup-home)
+      cleanup_home_path="${2}"
+      shift # past argument
+      shift # past value
+      ;;
     --dry-run)
       dry_run=true
       shift # past argument
@@ -39,36 +47,83 @@ while [[ $# -gt 0 ]]; do
   esac
 done
 
-# Find all build or target directories created by users
-#
-# This command combines (`-o`) two different conditions to find all build and
-# target directories that users have created. Within each home directory, we
-# recursively look for directories that either have a file named `x.py` and a
-# directory named `build`, or a file named `Cargo.toml` and a directory named
-# `target`.
-all_cache_directories=$(find /home -type d \( -name build -execdir test -f "x.py" \; -o -name target -execdir test -f "Cargo.toml" \; \) -print | sort | uniq)
-
-# For each checkout, we want to determine if the user has been working on it
-# within the `$time` number of days.
-unused_cache_directories=$(for directory in $all_cache_directories; do
-  project=$(dirname "${directory}")
-
-  # Find all directories with files that have been modified less than $time days ago
-  modified=$(find "${project}" -type f -mtime -"${time}" -printf '%h\n' | xargs -r dirname | sort | uniq)
-
-  # If no files have been modified in the last 90 days, then the project is
-  # considered old.
-  if [[ -z "${modified}" ]]; then
-    echo "${directory}"
+cleanup_home() {
+  local home="${1}"
+  local all_cache_directories
+  local unused_cache_directories
+
+  # This command combines (`-o`) two different conditions to find all build and
+  # target directories that users have created. Within each home directory, we
+  # recursively look for directories that either have a file named `x.py` and a
+  # directory named `build`, or a file named `Cargo.toml` and a directory named
+  # `target`.
+  all_cache_directories=$(find "${home}" -type d \( -name build -execdir test -f "x.py" \; -o -name target -execdir test -f "Cargo.toml" \; \) -print | sort | uniq)
+
+  # For each checkout, we want to determine if the user has been working on it
+  # within the `$time` number of days.
+  unused_cache_directories=$(for directory in $all_cache_directories; do
+    project=$(dirname "${directory}")
+
+    # Find all directories with files that have been modified less than $time days ago
+    modified=$(find "${project}" -type f -mtime -"${time}" -printf '%h\n' | xargs -r dirname | sort | uniq)
+
+    # If no files have been modified in the last `$time` days, then the project is
+    # considered old.
+    if [[ -z "${modified}" ]]; then
+      echo "${directory}"
+    fi
+  done)
+
+  # Delete the build directories in the unused checkouts
+  for directory in $unused_cache_directories; do
+    if [[ "${dry_run}" == true ]]; then
+      du -sh "${directory}"
+    else
+      echo "Deleting ${directory}"
+      rm -rf "${directory}"
+    fi
+  done
+}
+
+if [[ -n "${cleanup_home_path}" ]]; then
+  # Ensure this mode isn't called with root privileges.
+  if [[ "$(id -u)" -eq 0 ]]; then
+    echo "Error: --cleanup-home must not be run as root." >&2
+    exit 1
+  fi
+
+  # Ensure the caller only cleans their own home.
+  if [[ "$(realpath "${cleanup_home_path}")" != "$(realpath "${HOME}")" ]]; then
+    echo "Error: --cleanup-home may only target your own home directory." >&2
+    exit 1
   fi
-done)
 
-# Delete the build directories in the unused checkouts
-for directory in $unused_cache_directories; do
+  cleanup_home "${cleanup_home_path}"
+  exit 0
+fi
+
+# The cron job starts as root so it can enumerate /home.
+# Iterate over home directories with null delimiters so unusual names are safe.
+find /home -mindepth 1 -maxdepth 1 -type d -print0 | while IFS= read -r -d '' home; do
+  # Get the owner of the home directory.
+  uid=$(stat -c '%u' "${home}") || continue
+
+  # Skip home directories owned by root.
+  [[ "${uid}" -eq 0 ]] && continue
+
+  # Prepare args to re-enter this script in single-home cleanup mode, preserving the age cutoff.
+  args=(--cleanup-home "${home}" -t "${time}")
+
+  # Keep dry-run behavior consistent when the root-level cron wrapper delegates.
   if [[ "${dry_run}" == true ]]; then
-    du -sh "${directory}"
-  else
-    echo "Deleting ${directory}"
-    rm -rf "${directory}"
+    args+=(--dry-run)
+  fi
+
+  # Execute this script with the `--cleanup-home` flag to clean up a single user's home directory
+  # using their privileges.
+  # Dropping privileges prevents deleting paths outside the user's home in case of malicious symlinks.
+  # `-H` sets the HOME variable to target user's home dir.
+  if ! sudo -H -u "#${uid}" -- "$0" "${args[@]}"; then
+    echo "Warning: cleanup failed for ${home}; continuing with remaining homes." >&2
   fi
 done