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Subject[PATCH 3.16 082/133] l2tp: pass tunnel pointer to ->session_create()
3.16.51-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Guillaume Nault <g.nault@alphalink.fr>

commit f026bc29a8e093edfbb2a77700454b285c97e8ad upstream.

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>
[bwh: Backported to 3.16: adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
net/l2tp/l2tp_core.h | 4 +++-
net/l2tp/l2tp_eth.c | 11 +++--------
net/l2tp/l2tp_netlink.c | 8 ++++----
net/l2tp/l2tp_ppp.c | 19 +++++++------------
4 files changed, 17 insertions(+), 25 deletions(-)

--- a/net/l2tp/l2tp_core.h
+++ b/net/l2tp/l2tp_core.h
@@ -210,7 +210,9 @@ struct l2tp_tunnel {
};

struct l2tp_nl_cmd_ops {
- int (*session_create)(struct net *net, u32 tunnel_id, u32 session_id, u32 peer_session_id, struct l2tp_session_cfg *cfg);
+ int (*session_create)(struct net *net, struct l2tp_tunnel *tunnel,
+ u32 session_id, u32 peer_session_id,
+ struct l2tp_session_cfg *cfg);
int (*session_delete)(struct l2tp_session *session);
};

--- a/net/l2tp/l2tp_eth.c
+++ b/net/l2tp/l2tp_eth.c
@@ -206,23 +206,18 @@ static void l2tp_eth_show(struct seq_fil
}
#endif

-static int l2tp_eth_create(struct net *net, u32 tunnel_id, u32 session_id, u32 peer_session_id, struct l2tp_session_cfg *cfg)
+static int l2tp_eth_create(struct net *net, struct l2tp_tunnel *tunnel,
+ u32 session_id, u32 peer_session_id,
+ struct l2tp_session_cfg *cfg)
{
struct net_device *dev;
char name[IFNAMSIZ];
- struct l2tp_tunnel *tunnel;
struct l2tp_session *session;
struct l2tp_eth *priv;
struct l2tp_eth_sess *spriv;
int rc;
struct l2tp_eth_net *pn;

- tunnel = l2tp_tunnel_find(net, tunnel_id);
- if (!tunnel) {
- rc = -ENODEV;
- goto out;
- }
-
if (cfg->ifname) {
dev = dev_get_by_name(net, cfg->ifname);
if (dev) {
--- a/net/l2tp/l2tp_netlink.c
+++ b/net/l2tp/l2tp_netlink.c
@@ -540,10 +540,10 @@ static int l2tp_nl_cmd_session_create(st
break;
}

- ret = -EPROTONOSUPPORT;
- if (l2tp_nl_cmd_ops[cfg.pw_type]->session_create)
- ret = (*l2tp_nl_cmd_ops[cfg.pw_type]->session_create)(net, tunnel_id,
- session_id, peer_session_id, &cfg);
+ ret = l2tp_nl_cmd_ops[cfg.pw_type]->session_create(net, tunnel,
+ session_id,
+ peer_session_id,
+ &cfg);

out_tunnel:
l2tp_tunnel_dec_refcount(tunnel);
--- a/net/l2tp/l2tp_ppp.c
+++ b/net/l2tp/l2tp_ppp.c
@@ -807,25 +807,20 @@ end:

#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)
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