From 0d0d9a388a858e271bb70e71e99e7fe2a6fd6f64 Mon Sep 17 00:00:00 2001 From: Ridge Kennedy Date: Tue, 4 Feb 2020 12:24:00 +1300 Subject: [PATCH] l2tp: Allow duplicate session creation with UDP In the past it was possible to create multiple L2TPv3 sessions with the same session id as long as the sessions belonged to different tunnels. The resulting sessions had issues when used with IP encapsulated tunnels, but worked fine with UDP encapsulated ones. Some applications began to rely on this behaviour to avoid having to negotiate unique session ids. Some time ago a change was made to require session ids to be unique across all tunnels, breaking the applications making use of this "feature". This change relaxes the duplicate session id check to allow duplicates if both of the colliding sessions belong to UDP encapsulated tunnels. Fixes: dbdbc73b4478 ("l2tp: fix duplicate session creation") Signed-off-by: Ridge Kennedy Acked-by: James Chapman Signed-off-by: David S. Miller --- net/l2tp/l2tp_core.c | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-) diff --git a/net/l2tp/l2tp_core.c b/net/l2tp/l2tp_core.c index c99223cb3338..fcb53ed1c4fb 100644 --- a/net/l2tp/l2tp_core.c +++ b/net/l2tp/l2tp_core.c @@ -320,8 +320,13 @@ int l2tp_session_register(struct l2tp_session *session, spin_lock_bh(&pn->l2tp_session_hlist_lock); + /* IP encap expects session IDs to be globally unique, while + * UDP encap doesn't. + */ hlist_for_each_entry(session_walk, g_head, global_hlist) - if (session_walk->session_id == session->session_id) { + if (session_walk->session_id == session->session_id && + (session_walk->tunnel->encap == L2TP_ENCAPTYPE_IP || + tunnel->encap == L2TP_ENCAPTYPE_IP)) { err = -EEXIST; goto err_tlock_pnlock; }