Jailed terminal: per-session passwd so customers can't enumerate tenants

The jail's /etc/passwd listed every hosting username (no passwords — shadow isn't
in the jail — but it enumerated tenants). The launcher now binds a per-session
/etc/passwd|group (root + the current user only) inside each session's mount
namespace, and the shared jail passwd no longer carries hosting users.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

deployment/ladill-jailsh

@@ -1,8 +1,7 @@
 #!/bin/bash
-# Ladill jailed shell for the hosting browser terminal. Confines a hosting
+# Ladill jailed shell for the hosting browser terminal. Per session (private mount
-# account to /home/jail with ONLY its own home visible: a private mount namespace
+# ns): /home holds only this user's dir, and /etc/passwd|group expose only root +
-# plus a per-session tmpfs /home that contains just this user's directory (so
+# this user. The customer can never see other tenants, the host fs, or secrets.
-# 'ls /home' shows their own folder and never other tenants).
 # Usage: ladill-jailsh <username> [relpath]
 set -euo pipefail
 JAIL=/home/jail
@@ -15,14 +14,19 @@ GID_=$(id -g "$U" 2>/dev/null || true)
 HOMEDIR=/home/$U
 [ -d "$HOMEDIR" ] || { echo 'no home directory'; exit 1; }
 case "$REL" in *..*) REL=/public_html;; esac
-# re-exec into a private mount namespace so all mounts are per-session
 if [ -z "${LADILL_JAIL_NS:-}" ]; then
   exec env LADILL_JAIL_NS=1 unshare --mount --propagation private -- "$0" "$U" "$REL"
 fi
-# Fresh, listable /home holding ONLY this user's directory (no tenant leak).
+# /home with only this user's directory
 mount -t tmpfs -o mode=0755,nosuid,nodev tmpfs "$JAIL/home"
 mkdir -p "$JAIL/home/$U"
 mount --bind "$HOMEDIR" "$JAIL/home/$U"
+# passwd/group exposing only root + this user (no tenant enumeration)
+mount -t tmpfs -o mode=0755,nosuid,nodev tmpfs "$JAIL/run"
+{ echo 'root:x:0:0:root:/root:/bin/bash'; getent passwd "$U"; } > "$JAIL/run/passwd"
+{ echo 'root:x:0:'; getent group "$U"; } > "$JAIL/run/group"
+mount --bind "$JAIL/run/passwd" "$JAIL/etc/passwd"
+mount --bind "$JAIL/run/group" "$JAIL/etc/group"
 export HOME="/home/$U" USER="$U" LOGNAME="$U" SHELL=/bin/bash PATH=/usr/bin:/bin
 export TERM="${TERM:-xterm-256color}"
 exec /usr/sbin/chroot --userspec="$UID_:$GID_" "$JAIL" /bin/bash -l -c "cd '/home/$U$REL' 2>/dev/null || cd ~; exec /bin/bash -l"

deployment/setup-terminal-jail.sh

@@ -23,13 +23,9 @@ cp -rn /usr/share/terminfo/x "$JAIL/usr/share/terminfo/" 2>/dev/null || true
 install -d -o root -g root -m 711 "$JAIL/home"
 install -d -m 1777 "$JAIL/tmp"
 
-echo "==> Syncing hosting users into the jail passwd/group (for name resolution)"
+# NOTE: do NOT sync hosting users into the shared jail passwd — that would let
-while IFS=: read -r name _ uid gid _ home shell; do
+# any customer enumerate every tenant. ladill-jailsh injects a per-session
-  [ "$uid" -ge 1000 ] 2>/dev/null || continue
+# passwd/group (root + the current user only) inside each session's namespace.
-  [ -d "/home/$name" ] || continue
-  grep -q "^$name:" "$JAIL/etc/passwd" || getent passwd "$name" >> "$JAIL/etc/passwd"
-  grep -q "^$name:" "$JAIL/etc/group" || getent group "$name" >> "$JAIL/etc/group"
-done < <(getent passwd)
 
 echo "==> Installing the jailed-shell launcher + scoped sudoers"
 install -o root -g root -m 755 "$(dirname "$0")/ladill-jailsh" /usr/local/sbin/ladill-jailsh