ANDROID: xt_qtaguid: Remove tag_entry from process list on untag

A sock_tag_entry can only be part of one process's
pqd_entry->sock_tag_list. Retagging the socket only updates
sock_tag_entry->tag, and does not add the tag entry to the current
process's pqd_entry list, nor update sock_tag_entry->pid.
So the sock_tag_entry is only ever present in the
pqd_entry list of the process that initially tagged the socket.

A sock_tag_entry can also get created and not be added to any process's
pqd_entry list. This happens if the process that initially tags the
socket has not opened /dev/xt_qtaguid.

ctrl_cmd_untag() supports untagging from a context other than the
process that initially tagged the socket. Currently, the sock_tag_entry is
only removed from its containing pqd_entry->sock_tag_list if the
process that does the untagging has opened /dev/xt_qtaguid. However, the
tag entry should always be deleted from its pqd entry list (if present).

Bug: 176919394
Signed-off-by: Kalesh Singh <kaleshsingh@google.com>
Change-Id: I5b6f0c36c0ebefd98cc6873a4057104c7d885ccc

net/netfilter/xt_qtaguid.c

@@ -2412,15 +2412,20 @@ int qtaguid_untag(struct socket *el_socket, bool kernel)
 	 * At first, we want to catch user-space code that is not
 	 * opening the /dev/xt_qtaguid.
 	 */
-	if (IS_ERR_OR_NULL(pqd_entry) || !sock_tag_entry->list.next) {
+	if (IS_ERR_OR_NULL(pqd_entry))
 		pr_warn_once("qtaguid: %s(): "
 			     "User space forgot to open /dev/xt_qtaguid? "
 			     "pid=%u tgid=%u sk_pid=%u, uid=%u\n", __func__,
 			     current->pid, current->tgid, sock_tag_entry->pid,
 			     from_kuid(&init_user_ns, current_fsuid()));
-	} else {
+	/*
+	 * This check is needed because tagging from a process that
+	 * didn’t open /dev/xt_qtaguid still adds the sock_tag_entry
+	 * to sock_tag_tree.
+	 */
+	if (sock_tag_entry->list.next)
 		list_del(&sock_tag_entry->list);
-	}
+
 	spin_unlock_bh(&uid_tag_data_tree_lock);
 	/*
 	 * We don't free tag_ref from the utd_entry here,