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Subject[PATCH 4.4 49/65] l2tp: hold tunnel while looking up sessions in l2tp_netlink
Date
From: Guillaume Nault <g.nault@alphalink.fr>

commit 54652eb12c1b72e9602d09cb2821d5760939190f upstream.

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 a4ca44fa578c ("net: l2tp: Standardize logging styles")
and fixed more than two years later by
commit 29abe2fda54f ("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.

Backporting Notes

l2tp_core.c: This patch deletes some code / moves some code to
l2tp_core.h and follows the patch (not including in this series) that
switched from atomic to refcount_t. Moved code changed back to atomic.

Fixes: 309795f4bec2 ("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>
Signed-off-by: Giuliano Procida <gprocida@google.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
net/l2tp/l2tp_core.c | 66 +++++++++++++++---------------------------------
net/l2tp/l2tp_core.h | 13 +++++++++
net/l2tp/l2tp_netlink.c | 6 ++--
3 files changed, 38 insertions(+), 47 deletions(-)

--- a/net/l2tp/l2tp_core.c
+++ b/net/l2tp/l2tp_core.c
@@ -112,7 +112,6 @@ 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)
{
@@ -126,39 +125,6 @@ static inline struct l2tp_net *l2tp_pern
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)
-{
- atomic_inc(&tunnel->ref_count);
-}
-
-static inline void l2tp_tunnel_dec_refcount_1(struct l2tp_tunnel *tunnel)
-{
- if (atomic_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, \
- atomic_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, \
- atomic_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
@@ -228,6 +194,27 @@ l2tp_session_id_hash(struct l2tp_tunnel
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.
*/
@@ -1351,17 +1338,6 @@ static void l2tp_udp_encap_destroy(struc
}
}

-/* 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(atomic_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)
{
--- a/net/l2tp/l2tp_core.h
+++ b/net/l2tp/l2tp_core.h
@@ -234,6 +234,8 @@ 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);
@@ -272,6 +274,17 @@ int l2tp_nl_register_ops(enum l2tp_pwtyp
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)
+{
+ atomic_inc(&tunnel->ref_count);
+}
+
+static inline void l2tp_tunnel_dec_refcount(struct l2tp_tunnel *tunnel)
+{
+ if (atomic_dec_and_test(&tunnel->ref_count))
+ kfree_rcu(tunnel, rcu);
+}
+
/* Session reference counts. Incremented when code obtains a reference
* to a session.
*/
--- a/net/l2tp/l2tp_netlink.c
+++ b/net/l2tp/l2tp_netlink.c
@@ -72,10 +72,12 @@ static struct l2tp_session *l2tp_nl_sess
(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;

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