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l2tp: add idr consistency check in session_register

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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 <jchapman@katalix.com>
Signed-off-by: Tom Parkin <tparkin@katalix.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
James Chapman 2024-07-29 16:38:12 +01:00 committed by David S. Miller
parent 89b768ec2d
commit 0aa45570c3
1 changed files with 9 additions and 2 deletions
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11
net/l2tp/l2tp_core.c
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@ -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);