l2tp: pass tunnel pointer to ->session_create()
Using l2tp_tunnel_find() in pppol2tp_session_create() and
l2tp_eth_create() is racy, because no reference is held on the
returned session. These functions are only used to implement the
->session_create callback which is run by l2tp_nl_cmd_session_create().
Therefore searching for the parent tunnel isn't necessary because
l2tp_nl_cmd_session_create() already has a pointer to it and holds a
reference.
This patch modifies ->session_create()'s prototype to directly pass the
the parent tunnel as parameter, thus avoiding searching for it in
pppol2tp_session_create() and l2tp_eth_create().
Since we have to touch the ->session_create() call in
l2tp_nl_cmd_session_create(), let's also remove the useless conditional:
we know that ->session_create isn't NULL at this point because it's
already been checked earlier in this same function.
Finally, one might be tempted to think that the removed
l2tp_tunnel_find() calls were harmless because they would return the
same tunnel as the one held by l2tp_nl_cmd_session_create() anyway.
But that tunnel might be removed and a new one created with same tunnel
Id before the l2tp_tunnel_find() call. In this case l2tp_tunnel_find()
would return the new tunnel which wouldn't be protected by the
reference held by l2tp_nl_cmd_session_create().
Fixes: 309795f4bec2 ("l2tp: Add netlink control API for L2TP")
Fixes: d9e31d17ceba ("l2tp: Add L2TP ethernet pseudowire support")
Signed-off-by: Guillaume Nault <g.nault@alphalink.fr>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/l2tp/l2tp_ppp.c b/net/l2tp/l2tp_ppp.c
index f0edb72..50e3ee9 100644
--- a/net/l2tp/l2tp_ppp.c
+++ b/net/l2tp/l2tp_ppp.c
@@ -788,25 +788,20 @@ static int pppol2tp_connect(struct socket *sock, struct sockaddr *uservaddr,
#ifdef CONFIG_L2TP_V3
-/* Called when creating sessions via the netlink interface.
- */
-static int pppol2tp_session_create(struct net *net, u32 tunnel_id, u32 session_id, u32 peer_session_id, struct l2tp_session_cfg *cfg)
+/* Called when creating sessions via the netlink interface. */
+static int pppol2tp_session_create(struct net *net, struct l2tp_tunnel *tunnel,
+ u32 session_id, u32 peer_session_id,
+ struct l2tp_session_cfg *cfg)
{
int error;
- struct l2tp_tunnel *tunnel;
struct l2tp_session *session;
struct pppol2tp_session *ps;
- tunnel = l2tp_tunnel_find(net, tunnel_id);
-
- /* Error if we can't find the tunnel */
- error = -ENOENT;
- if (tunnel == NULL)
- goto out;
-
/* Error if tunnel socket is not prepped */
- if (tunnel->sock == NULL)
+ if (!tunnel->sock) {
+ error = -ENOENT;
goto out;
+ }
/* Default MTU values. */
if (cfg->mtu == 0)