Commit 0d0d9a38 authored Feb 04, 2020 by Ridge Kennedy Committed by David S. Miller Feb 04, 2020

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: dbdbc73b ("l2tp: fix duplicate session creation")
Signed-off-by: Ridge Kennedy <ridge.kennedy@alliedtelesis.co.nz>
Acked-by: James Chapman <jchapman@katalix.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

parent b4b771fd

net/l2tp/l2tp_core.c

+6 −1

Original line number	Diff line number	Diff line
		@@ -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;
		}

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