From 63a763d03a6c962c15159081812e67dc9715d9cc Mon Sep 17 00:00:00 2001 From: Guillaume Nault Date: Fri, 31 Mar 2017 13:02:25 +0200 Subject: l2tp: fix race in l2tp_recv_common() commit 61b9a047729bb230978178bca6729689d0c50ca2 upstream. Taking a reference on sessions in l2tp_recv_common() is racy; this has to be done by the callers. To this end, a new function is required (l2tp_session_get()) to atomically lookup a session and take a reference on it. Callers then have to manually drop this reference. Fixes: fd558d186df2 ("l2tp: Split pppol2tp patch into separate l2tp and ppp parts") Signed-off-by: Guillaume Nault Signed-off-by: David S. Miller [bwh: Backported to 3.2: - Drop changes to l2tp_ip6.c - Add 'pos' parameter to hlist_for_each_entry{,_rcu}() calls - Adjust context] Signed-off-by: Ben Hutchings --- net/l2tp/l2tp_core.c | 74 +++++++++++++++++++++++++++++++++++++++++++--------- net/l2tp/l2tp_core.h | 3 +++ net/l2tp/l2tp_ip.c | 17 ++++++++---- 3 files changed, 76 insertions(+), 18 deletions(-) diff --git a/net/l2tp/l2tp_core.c b/net/l2tp/l2tp_core.c index 7501b22b9c59..a2bb62801902 100644 --- a/net/l2tp/l2tp_core.c +++ b/net/l2tp/l2tp_core.c @@ -225,6 +225,56 @@ struct l2tp_session *l2tp_session_find(struct net *net, struct l2tp_tunnel *tunn } EXPORT_SYMBOL_GPL(l2tp_session_find); +/* Like l2tp_session_find() but takes a reference on the returned session. + * Optionally calls session->ref() too if do_ref is true. + */ +struct l2tp_session *l2tp_session_get(struct net *net, + struct l2tp_tunnel *tunnel, + u32 session_id, bool do_ref) +{ + struct hlist_head *session_list; + struct l2tp_session *session; + struct hlist_node *walk; + + if (!tunnel) { + struct l2tp_net *pn = l2tp_pernet(net); + + session_list = l2tp_session_id_hash_2(pn, session_id); + + rcu_read_lock_bh(); + hlist_for_each_entry_rcu(session, walk, session_list, global_hlist) { + if (session->session_id == session_id) { + l2tp_session_inc_refcount(session); + if (do_ref && session->ref) + session->ref(session); + rcu_read_unlock_bh(); + + return session; + } + } + rcu_read_unlock_bh(); + + return NULL; + } + + session_list = l2tp_session_id_hash(tunnel, session_id); + read_lock_bh(&tunnel->hlist_lock); + hlist_for_each_entry(session, walk, session_list, hlist) { + if (session->session_id == session_id) { + l2tp_session_inc_refcount(session); + if (do_ref && session->ref) + session->ref(session); + read_unlock_bh(&tunnel->hlist_lock); + + return session; + } + } + read_unlock_bh(&tunnel->hlist_lock); + + return NULL; +} +EXPORT_SYMBOL_GPL(l2tp_session_get); + struct l2tp_session *l2tp_session_find_nth(struct l2tp_tunnel *tunnel, int nth) { int hash; @@ -524,6 +574,9 @@ static inline int l2tp_verify_udp_checksum(struct sock *sk, * a data (not control) frame before coming here. Fields up to the * session-id have already been parsed and ptr points to the data * after the session-id. + * + * session->ref() must have been called prior to l2tp_recv_common(). + * session->deref() will be called automatically after skb is processed. */ void l2tp_recv_common(struct l2tp_session *session, struct sk_buff *skb, unsigned char *ptr, unsigned char *optr, u16 hdrflags, @@ -533,14 +586,6 @@ void l2tp_recv_common(struct l2tp_session *session, struct sk_buff *skb, int offset; u32 ns, nr; - /* The ref count is increased since we now hold a pointer to - * the session. Take care to decrement the refcnt when exiting - * this function from now on... - */ - l2tp_session_inc_refcount(session); - if (session->ref) - (*session->ref)(session); - /* Parse and check optional cookie */ if (session->peer_cookie_len > 0) { if (memcmp(ptr, &session->peer_cookie[0], session->peer_cookie_len)) { @@ -711,8 +756,6 @@ void l2tp_recv_common(struct l2tp_session *session, struct sk_buff *skb, /* Try to dequeue as many skbs from reorder_q as we can. */ l2tp_recv_dequeue(session); - l2tp_session_dec_refcount(session); - return; discard: @@ -721,8 +764,6 @@ discard: if (session->deref) (*session->deref)(session); - - l2tp_session_dec_refcount(session); } EXPORT_SYMBOL(l2tp_recv_common); @@ -818,8 +859,14 @@ static int l2tp_udp_recv_core(struct l2tp_tunnel *tunnel, struct sk_buff *skb, } /* Find the session context */ - session = l2tp_session_find(tunnel->l2tp_net, tunnel, session_id); + session = l2tp_session_get(tunnel->l2tp_net, tunnel, session_id, true); if (!session || !session->recv_skb) { + if (session) { + if (session->deref) + session->deref(session); + l2tp_session_dec_refcount(session); + } + /* Not found? Pass to userspace to deal with */ PRINTK(tunnel->debug, L2TP_MSG_DATA, KERN_INFO, "%s: no session found (%u/%u). Passing up.\n", @@ -828,6 +875,7 @@ static int l2tp_udp_recv_core(struct l2tp_tunnel *tunnel, struct sk_buff *skb, } l2tp_recv_common(session, skb, ptr, optr, hdrflags, length, payload_hook); + l2tp_session_dec_refcount(session); return 0; diff --git a/net/l2tp/l2tp_core.h b/net/l2tp/l2tp_core.h index ad6f73d1e34a..daf4c8e2bc2d 100644 --- a/net/l2tp/l2tp_core.h +++ b/net/l2tp/l2tp_core.h @@ -222,6 +222,9 @@ out: return tunnel; } +struct l2tp_session *l2tp_session_get(struct net *net, + struct l2tp_tunnel *tunnel, + u32 session_id, bool do_ref); extern struct l2tp_session *l2tp_session_find(struct net *net, struct l2tp_tunnel *tunnel, u32 session_id); extern struct l2tp_session *l2tp_session_find_nth(struct l2tp_tunnel *tunnel, int nth); extern struct l2tp_session *l2tp_session_find_by_ifname(struct net *net, char *ifname); diff --git a/net/l2tp/l2tp_ip.c b/net/l2tp/l2tp_ip.c index 67cc3e79ec27..a753c9b2336f 100644 --- a/net/l2tp/l2tp_ip.c +++ b/net/l2tp/l2tp_ip.c @@ -148,19 +148,19 @@ static int l2tp_ip_recv(struct sk_buff *skb) } /* Ok, this is a data packet. Lookup the session. */ - session = l2tp_session_find(&init_net, NULL, session_id); - if (session == NULL) + session = l2tp_session_get(&init_net, NULL, session_id, true); + if (!session) goto discard; tunnel = session->tunnel; - if (tunnel == NULL) - goto discard; + if (!tunnel) + goto discard_sess; /* Trace packet contents, if enabled */ if (tunnel->debug & L2TP_MSG_DATA) { length = min(32u, skb->len); if (!pskb_may_pull(skb, length)) - goto discard; + goto discard_sess; /* Point to L2TP header */ optr = ptr = skb->data; @@ -176,6 +176,7 @@ static int l2tp_ip_recv(struct sk_buff *skb) } l2tp_recv_common(session, skb, ptr, optr, 0, skb->len, tunnel->recv_payload_hook); + l2tp_session_dec_refcount(session); return 0; @@ -211,6 +212,12 @@ pass_up: return sk_receive_skb(sk, skb, 1); +discard_sess: + if (session->deref) + session->deref(session); + l2tp_session_dec_refcount(session); + goto discard; + discard_put: sock_put(sk); -- cgit v1.2.3