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l2tp: pass tunnel pointer to ->session_create()

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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: 309795f4be ("l2tp: Add netlink control API for L2TP")
Fixes: d9e31d17ce ("l2tp: Add L2TP ethernet pseudowire support")
Signed-off-by: Guillaume Nault <g.nault@alphalink.fr>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Guillaume Nault 2017-09-01 17:58:51 +02:00 committed by David S. Miller
parent f3c66d4e14
commit f026bc29a8
4 changed files with 17 additions and 25 deletions
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4
net/l2tp/l2tp_core.h
View file

@ -201,7 +201,9 @@ 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);
};

11
net/l2tp/l2tp_eth.c
View file

@ -262,24 +262,19 @@ static void l2tp_eth_adjust_mtu(struct l2tp_tunnel *tunnel,
dev->needed_headroom += session->hdr_len;
}
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)
{
unsigned char name_assign_type;
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) {
strlcpy(name, cfg->ifname, IFNAMSIZ);
name_assign_type = NET_NAME_USER;

8
net/l2tp/l2tp_netlink.c
View file

@ -643,10 +643,10 @@ static int l2tp_nl_cmd_session_create(struct sk_buff *skb, struct genl_info *inf
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);
if (ret >= 0) {
session = l2tp_session_get(net, tunnel, session_id, false);

19
net/l2tp/l2tp_ppp.c
View file

@ -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)