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l2tp: fix race in l2tp_recv_common()

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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 <g.nault@alphalink.fr>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Will Deacon <will@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Guillaume Nault 2020-04-02 18:32:45 +01:00 committed by Greg Kroah-Hartman
parent d7021e80e2
commit 128db36fae
4 changed files with 88 additions and 23 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

73
net/l2tp/l2tp_core.c
View File

@ -277,6 +277,55 @@ 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;
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, 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, 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_get_nth(struct l2tp_tunnel *tunnel, int nth,
bool do_ref)
{
@ -636,6 +685,9 @@ discard:
* 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,
@ -645,14 +697,6 @@ 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)) {
@ -803,8 +847,6 @@ 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:
@ -813,8 +855,6 @@ discard:
if (session->deref)
(*session->deref)(session);
l2tp_session_dec_refcount(session);
}
EXPORT_SYMBOL(l2tp_recv_common);
@ -921,8 +961,14 @@ 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 */
l2tp_info(tunnel, L2TP_MSG_DATA,
"%s: no session found (%u/%u). Passing up.\n",
@ -935,6 +981,7 @@ static int l2tp_udp_recv_core(struct l2tp_tunnel *tunnel, struct sk_buff *skb,
goto error;
l2tp_recv_common(session, skb, ptr, optr, hdrflags, length, payload_hook);
l2tp_session_dec_refcount(session);
return 0;

3
net/l2tp/l2tp_core.h
View File

@ -243,6 +243,9 @@ out:
return tunnel;
}
struct l2tp_session *l2tp_session_get(struct net *net,
struct l2tp_tunnel *tunnel,
u32 session_id, bool do_ref);
struct l2tp_session *l2tp_session_find(struct net *net,
struct l2tp_tunnel *tunnel,
u32 session_id);

17
net/l2tp/l2tp_ip.c
View File

@ -142,19 +142,19 @@ static int l2tp_ip_recv(struct sk_buff *skb)
}
/* Ok, this is a data packet. Lookup the session. */
session = l2tp_session_find(net, NULL, session_id);
if (session == NULL)
session = l2tp_session_get(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;
@ -167,6 +167,7 @@ static int l2tp_ip_recv(struct sk_buff *skb)
goto discard;
l2tp_recv_common(session, skb, ptr, optr, 0, skb->len, tunnel->recv_payload_hook);
l2tp_session_dec_refcount(session);
return 0;
@ -204,6 +205,12 @@ 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);

18
net/l2tp/l2tp_ip6.c
View File

@ -154,19 +154,19 @@ static int l2tp_ip6_recv(struct sk_buff *skb)
}
/* Ok, this is a data packet. Lookup the session. */
session = l2tp_session_find(net, NULL, session_id);
if (session == NULL)
session = l2tp_session_get(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;
@ -180,6 +180,8 @@ static int l2tp_ip6_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;
pass_up:
@ -217,6 +219,12 @@ 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);