From: James Chapman Date: Mon, 29 Jul 2024 15:38:12 +0000 (+0100) Subject: l2tp: add idr consistency check in session_register X-Git-Tag: v6.12-rc1~232^2~355^2~2 X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=0aa45570c3241e3bdba1a8b5b30d200c819b5b15;p=thirdparty%2Fkernel%2Flinux.git 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: James Chapman Signed-off-by: Tom Parkin Signed-off-by: David S. Miller --- diff --git a/net/l2tp/l2tp_core.c b/net/l2tp/l2tp_core.c index cd9b157e8b4de..fd03c17dd20c2 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);