From 45faeff11b48b9390ee946668119472b8941de90 Mon Sep 17 00:00:00 2001 From: Tom Parkin Date: Thu, 3 Sep 2020 09:54:51 +0100 Subject: l2tp: make magic feather checks more useful The l2tp tunnel and session structures contain a "magic feather" field which was originally intended to help trace lifetime bugs in the code. Since the introduction of the shared kernel refcount code in refcount.h, and l2tp's porting to those APIs, we are covered by the refcount code's checks and warnings. Duplicating those checks in the l2tp code isn't useful. However, magic feather checks are still useful to help to detect bugs stemming from misuse/trampling of the sk_user_data pointer in struct sock. The l2tp code makes extensive use of sk_user_data to stash pointers to the tunnel and session structures, and if another subsystem overwrites sk_user_data it's important to detect this. As such, rework l2tp's magic feather checks to focus on validating the tunnel and session data structures when they're extracted from sk_user_data. * Add a new accessor function l2tp_sk_to_tunnel which contains a magic feather check, and is used by l2tp_core and l2tp_ip[6] * Comment l2tp_udp_encap_recv which doesn't use this new accessor function because of the specific nature of the codepath it is called in * Drop l2tp_session_queue_purge's check on the session magic feather: it is called from code which is walking the tunnel session list, and hence doesn't need validation * Drop l2tp_session_free's check on the tunnel magic feather: the intention of this check is covered by refcount.h's reference count sanity checking * Add session magic validation in pppol2tp_ioctl. On failure return -EBADF, which mirrors the approach in pppol2tp_[sg]etsockopt. Signed-off-by: Tom Parkin Signed-off-by: David S. Miller --- net/l2tp/l2tp_core.h | 5 +++++ 1 file changed, 5 insertions(+) (limited to 'net/l2tp/l2tp_core.h') diff --git a/net/l2tp/l2tp_core.h b/net/l2tp/l2tp_core.h index 3ce90c3f3491..cb21d906343e 100644 --- a/net/l2tp/l2tp_core.h +++ b/net/l2tp/l2tp_core.h @@ -273,6 +273,11 @@ void l2tp_nl_unregister_ops(enum l2tp_pwtype pw_type); /* IOCTL helper for IP encap modules. */ int l2tp_ioctl(struct sock *sk, int cmd, unsigned long arg); +/* Extract the tunnel structure from a socket's sk_user_data pointer, + * validating the tunnel magic feather. + */ +struct l2tp_tunnel *l2tp_sk_to_tunnel(struct sock *sk); + static inline int l2tp_get_l2specific_len(struct l2tp_session *session) { switch (session->l2specific_type) { -- cgit v1.2.3-58-ga151