fix(entrypoint): fail closed on planted symlinks before nginx starts

drop_symlink unlinks as root (never follows the target) and refuses to start if
the path is still a symlink. Immediately before nginx (which opens its logs
under /home/$user/logs as root) starts, logs/, logs/nginx and logs/nodejs must be
real directories and nothing under logs/ may be other than a regular file or
directory, else the entrypoint exits 1.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

scripts/entrypoint.sh

@@ -31,26 +31,33 @@ as_user() {
     runuser -u "$user" -- "$@"
   fi
 }
-# Unlink AS THE CUSTOMER, so a parent dir swapped for a symlink between the
-# check and the rm can only reach what the customer could already.
+# Fail closed: refusing to start only hurts the customer who planted the path,
+# which is preferred to root following it.
+die() {
+  echo "entrypoint: FATAL: $* - refusing to start" >&2
+  exit 1
+}
+# Unlink as root: rm on the final component never touches the link target and
+# the customer cannot deny it. Still a symlink afterwards -> refuse to start.
 drop_symlink() {
   if [ -L "$1" ]; then
     echo "entrypoint: SECURITY: $1 was a symlink to '$(readlink "$1")' - removing" >&2
-    as_user rm -f -- "$1" || echo "entrypoint: WARNING: could not remove symlink $1" >&2
+    rm -f -- "$1"
+    [ -L "$1" ] && die "could not remove symlink $1"
   fi
+  return 0
 }
 if [ -L /home/$user ] || [ ! -d /home/$user ]; then
-  echo "entrypoint: FATAL: /home/$user is not a real directory - refusing to start" >&2
-  exit 1
+  die "/home/$user is not a real directory"
 fi
 chown -h $user:$user /home/$user
 # app/ may legitimately be a symlink (releases/current deploys): it is left
 # alone, and every root-side operation on it below runs as the customer.
 drop_symlink /home/$user/logs
-if [ -d /home/$user/logs ] && [ ! -L /home/$user/logs ]; then
-  # nginx opens its logs here as root. As the customer, find without -L never
-  # follows symlinks; -delete unlinks them.
-  as_user find /home/$user/logs -xdev -type l \
+if [ -d /home/$user/logs ]; then
+  # nginx opens its logs here as root. find without -L never follows symlinks;
+  # -delete unlinks the link itself. Re-checked fail-closed before nginx starts.
+  find /home/$user/logs -xdev -type l \
     -printf 'entrypoint: SECURITY: %p was a symlink to %l - removed\n' -delete >&2 || true
 fi
 
@@ -81,6 +88,15 @@ chown -R $user:$user /home/$user
 chmod 755 /home/$user
 as_user find /home/$user -type d ! -perm -o=x -exec chmod o+x {} + 2>/dev/null || true
 
+# nginx opens its logs under /home/$user/logs as root: last fail-closed check
+# immediately before it starts. logs/, logs/nginx, logs/nodejs must be real
+# dirs and nothing under logs/ may be other than a regular file or directory.
+for d in /home/$user/logs /home/$user/logs/nginx /home/$user/logs/nodejs; do
+  [ -d "$d" ] && [ ! -L "$d" ] || die "$d is not a real directory"
+done
+bad=$(find /home/$user/logs -xdev ! -type f ! -type d -print -quit 2>&1)
+[ -z "$bad" ] || die "unsafe entry under /home/$user/logs: $bad"
+
 # Start nginx
 nginx