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l2tp: hold tunnel while looking up sessions in l2tp_netlink 

l2tp_tunnel_find() doesn't take a reference on the returned tunnel.
Therefore, it's unsafe to use it because the returned tunnel can go
away on us anytime.

Fix this by defining l2tp_tunnel_get(), which works like
l2tp_tunnel_find(), but takes a reference on the returned tunnel.
Caller then has to drop this reference using l2tp_tunnel_dec_refcount().

As l2tp_tunnel_dec_refcount() needs to be moved to l2tp_core.h, let's
simplify the patch and not move the L2TP_REFCNT_DEBUG part. This code
has been broken (not even compiling) in May 2012 by
commit a4ca44fa57 ("net: l2tp: Standardize logging styles")
and fixed more than two years later by
commit 29abe2fda5 ("l2tp: fix missing line continuation"). So it
doesn't appear to be used by anyone.

Same thing for l2tp_tunnel_free(); instead of moving it to l2tp_core.h,
let's just simplify things and call kfree_rcu() directly in
l2tp_tunnel_dec_refcount(). Extra assertions and debugging code
provided by l2tp_tunnel_free() didn't help catching any of the
reference counting and socket handling issues found while working on
this series.

Fixes: 309795f4be ("l2tp: Add netlink control API for L2TP")
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 2017-08-25 16:51:40 +02:00 committed by David S. Miller
parent 9ee369a405
commit 54652eb12c
3 changed files with 38 additions and 47 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

66
net/l2tp/l2tp_core.c
View File

@ -113,7 +113,6 @@ struct l2tp_net {
spinlock_t l2tp_session_hlist_lock;
};
static void l2tp_tunnel_free(struct l2tp_tunnel *tunnel);
static inline struct l2tp_tunnel *l2tp_tunnel(struct sock *sk)
{
@ -127,39 +126,6 @@ static inline struct l2tp_net *l2tp_pernet(const struct net *net)
return net_generic(net, l2tp_net_id);
}
/* Tunnel reference counts. Incremented per session that is added to
* the tunnel.
*/
static inline void l2tp_tunnel_inc_refcount_1(struct l2tp_tunnel *tunnel)
{
refcount_inc(&tunnel->ref_count);
}
static inline void l2tp_tunnel_dec_refcount_1(struct l2tp_tunnel *tunnel)
{
if (refcount_dec_and_test(&tunnel->ref_count))
l2tp_tunnel_free(tunnel);
}
#ifdef L2TP_REFCNT_DEBUG
#define l2tp_tunnel_inc_refcount(_t) \
do { \
pr_debug("l2tp_tunnel_inc_refcount: %s:%d %s: cnt=%d\n", \
__func__, __LINE__, (_t)->name, \
refcount_read(&_t->ref_count)); \
l2tp_tunnel_inc_refcount_1(_t); \
} while (0)
#define l2tp_tunnel_dec_refcount(_t) \
do { \
pr_debug("l2tp_tunnel_dec_refcount: %s:%d %s: cnt=%d\n", \
__func__, __LINE__, (_t)->name, \
refcount_read(&_t->ref_count)); \
l2tp_tunnel_dec_refcount_1(_t); \
} while (0)
#else
#define l2tp_tunnel_inc_refcount(t) l2tp_tunnel_inc_refcount_1(t)
#define l2tp_tunnel_dec_refcount(t) l2tp_tunnel_dec_refcount_1(t)
#endif
/* Session hash global list for L2TPv3.
* The session_id SHOULD be random according to RFC3931, but several
* L2TP implementations use incrementing session_ids. So we do a real
@ -229,6 +195,27 @@ l2tp_session_id_hash(struct l2tp_tunnel *tunnel, u32 session_id)
return &tunnel->session_hlist[hash_32(session_id, L2TP_HASH_BITS)];
}
/* Lookup a tunnel. A new reference is held on the returned tunnel. */
struct l2tp_tunnel *l2tp_tunnel_get(const struct net *net, u32 tunnel_id)
{
const struct l2tp_net *pn = l2tp_pernet(net);
struct l2tp_tunnel *tunnel;
rcu_read_lock_bh();
list_for_each_entry_rcu(tunnel, &pn->l2tp_tunnel_list, list) {
if (tunnel->tunnel_id == tunnel_id) {
l2tp_tunnel_inc_refcount(tunnel);
rcu_read_unlock_bh();
return tunnel;
}
}
rcu_read_unlock_bh();
return NULL;
}
EXPORT_SYMBOL_GPL(l2tp_tunnel_get);
/* Lookup a session. A new reference is held on the returned session.
* Optionally calls session->ref() too if do_ref is true.
*/
@ -1348,17 +1335,6 @@ static void l2tp_udp_encap_destroy(struct sock *sk)
}
}
/* Really kill the tunnel.
* Come here only when all sessions have been cleared from the tunnel.
*/
static void l2tp_tunnel_free(struct l2tp_tunnel *tunnel)
{
BUG_ON(refcount_read(&tunnel->ref_count) != 0);
BUG_ON(tunnel->sock != NULL);
l2tp_info(tunnel, L2TP_MSG_CONTROL, "%s: free...\n", tunnel->name);
kfree_rcu(tunnel, rcu);
}
/* Workqueue tunnel deletion function */
static void l2tp_tunnel_del_work(struct work_struct *work)
{

13
net/l2tp/l2tp_core.h
View File

@ -231,6 +231,8 @@ out:
return tunnel;
}
struct l2tp_tunnel *l2tp_tunnel_get(const struct net *net, u32 tunnel_id);
struct l2tp_session *l2tp_session_get(const struct net *net,
struct l2tp_tunnel *tunnel,
u32 session_id, bool do_ref);
@ -269,6 +271,17 @@ int l2tp_nl_register_ops(enum l2tp_pwtype pw_type,
void l2tp_nl_unregister_ops(enum l2tp_pwtype pw_type);
int l2tp_ioctl(struct sock *sk, int cmd, unsigned long arg);
static inline void l2tp_tunnel_inc_refcount(struct l2tp_tunnel *tunnel)
{
refcount_inc(&tunnel->ref_count);
}
static inline void l2tp_tunnel_dec_refcount(struct l2tp_tunnel *tunnel)
{
if (refcount_dec_and_test(&tunnel->ref_count))
kfree_rcu(tunnel, rcu);
}
/* Session reference counts. Incremented when code obtains a reference
* to a session.
*/

6
net/l2tp/l2tp_netlink.c
View File

@ -65,10 +65,12 @@ static struct l2tp_session *l2tp_nl_session_get(struct genl_info *info,
(info->attrs[L2TP_ATTR_CONN_ID])) {
tunnel_id = nla_get_u32(info->attrs[L2TP_ATTR_CONN_ID]);
session_id = nla_get_u32(info->attrs[L2TP_ATTR_SESSION_ID]);
tunnel = l2tp_tunnel_find(net, tunnel_id);
if (tunnel)
tunnel = l2tp_tunnel_get(net, tunnel_id);
if (tunnel) {
session = l2tp_session_get(net, tunnel, session_id,
do_ref);
l2tp_tunnel_dec_refcount(tunnel);
}
}
return session;