[RFC PATCH 13/15] l2tp: add idr consistency check in session_register
From: James Chapman <jchapman@katalix.com>
Date: 2024-07-23 13:51:54
Subsystem:
networking [general], the rest · Maintainers:
"David S. Miller", Eric Dumazet, Jakub Kicinski, Paolo Abeni, Linus Torvalds
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. --- net/l2tp/l2tp_core.c | 11 +++++++++-- 1 file changed, 9 insertions(+), 2 deletions(-)
diff --git a/net/l2tp/l2tp_core.c b/net/l2tp/l2tp_core.c
index cd9b157e8b4d..fd03c17dd20c 100644
--- a/net/l2tp/l2tp_core.c
+++ b/net/l2tp/l2tp_core.c@@ -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);
--
2.34.1