Commit 0aa45570 authored by James Chapman's avatar James Chapman Committed by David S. Miller
Browse files

l2tp: add idr consistency check in session_register 



l2tp_session_register uses an idr_alloc then idr_replace pattern to
insert sessions into the session IDR. To catch invalid locking, add a
WARN_ON_ONCE if the IDR entry is modified by another thread between
alloc and replace steps.

Also add comments to make expectations clear.

Signed-off-by: default avatarJames Chapman <jchapman@katalix.com>
Signed-off-by: default avatarTom Parkin <tparkin@katalix.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 89b768ec

net/l2tp/l2tp_core.c

+9 −2
Original line number Diff line number Diff line
@@ -474,6 +474,7 @@ int l2tp_session_register(struct l2tp_session *session, 
{

	struct l2tp_net *pn = l2tp_pernet(tunnel->l2tp_net);

	struct l2tp_session *other_session = NULL;

	void *old = NULL;

	u32 session_key;

	int err;
@@ -517,13 +518,19 @@ int l2tp_session_register(struct l2tp_session *session, 
	WRITE_ONCE(session->tunnel, tunnel);

	list_add_rcu(&session->list, &tunnel->session_list);



	/* this makes session available to lockless getters */

	if (tunnel->version == L2TP_HDR_VER_3) {

		if (!other_session)

			idr_replace(&pn->l2tp_v3_session_idr, session, session_key);

			old = idr_replace(&pn->l2tp_v3_session_idr, session, session_key);

	} else {

		idr_replace(&pn->l2tp_v2_session_idr, session, session_key);

		old = idr_replace(&pn->l2tp_v2_session_idr, session, session_key);

	}



	/* old should be NULL, unless something removed or modified

	 * the IDR entry after our idr_alloc_32 above (which shouldn't

	 * happen).

	 */

	WARN_ON_ONCE(old);

out:

	spin_unlock_bh(&pn->l2tp_session_idr_lock);

	spin_unlock_bh(&tunnel->list_lock);