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l2tp: fix duplicate session creation

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l2tp_session_create() relies on its caller for checking for duplicate
sessions. This is racy since a session can be concurrently inserted
after the caller's verification.

Fix this by letting l2tp_session_create() verify sessions uniqueness
upon insertion. Callers need to be adapted to check for
l2tp_session_create()'s return code instead of calling
l2tp_session_find().

pppol2tp_connect() is a bit special because it has to work on existing
sessions (if they're not connected) or to create a new session if none
is found. When acting on a preexisting session, a reference must be
held or it could go away on us. So we have to use l2tp_session_get()
instead of l2tp_session_find() and drop the reference before exiting.

Fixes: d9e31d17ce ("l2tp: Add L2TP ethernet pseudowire support")
Fixes: fd558d186d ("l2tp: Split pppol2tp patch into separate l2tp and ppp parts")
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
2017-03-31 13:02:27 +02:00
committed by David S. Miller
parent 57377d6354
commit dbdbc73b44
3 changed files with 85 additions and 57 deletions
Download Patch File Download Diff File Expand all files Collapse all files

70
net/l2tp/l2tp_core.c
View File

@@ -374,6 +374,48 @@ struct l2tp_session *l2tp_session_find_by_ifname(struct net *net, char *ifname)
}
EXPORT_SYMBOL_GPL(l2tp_session_find_by_ifname);
static int l2tp_session_add_to_tunnel(struct l2tp_tunnel *tunnel,
struct l2tp_session *session)
{
struct l2tp_session *session_walk;
struct hlist_head *g_head;
struct hlist_head *head;
struct l2tp_net *pn;
head = l2tp_session_id_hash(tunnel, session->session_id);
write_lock_bh(&tunnel->hlist_lock);
hlist_for_each_entry(session_walk, head, hlist)
if (session_walk->session_id == session->session_id)
goto exist;
if (tunnel->version == L2TP_HDR_VER_3) {
pn = l2tp_pernet(tunnel->l2tp_net);
g_head = l2tp_session_id_hash_2(l2tp_pernet(tunnel->l2tp_net),
session->session_id);
spin_lock_bh(&pn->l2tp_session_hlist_lock);
hlist_for_each_entry(session_walk, g_head, global_hlist)
if (session_walk->session_id == session->session_id)
goto exist_glob;
hlist_add_head_rcu(&session->global_hlist, g_head);
spin_unlock_bh(&pn->l2tp_session_hlist_lock);
}
hlist_add_head(&session->hlist, head);
write_unlock_bh(&tunnel->hlist_lock);
return 0;
exist_glob:
spin_unlock_bh(&pn->l2tp_session_hlist_lock);
exist:
write_unlock_bh(&tunnel->hlist_lock);
return -EEXIST;
}
/* Lookup a tunnel by id
*/
struct l2tp_tunnel *l2tp_tunnel_find(struct net *net, u32 tunnel_id)
@@ -1785,6 +1827,7 @@ EXPORT_SYMBOL_GPL(l2tp_session_set_header_len);
struct l2tp_session *l2tp_session_create(int priv_size, struct l2tp_tunnel *tunnel, u32 session_id, u32 peer_session_id, struct l2tp_session_cfg *cfg)
{
struct l2tp_session *session;
int err;
session = kzalloc(sizeof(struct l2tp_session) + priv_size, GFP_KERNEL);
if (session != NULL) {
@@ -1840,6 +1883,13 @@ struct l2tp_session *l2tp_session_create(int priv_size, struct l2tp_tunnel *tunn
l2tp_session_set_header_len(session, tunnel->version);
err = l2tp_session_add_to_tunnel(tunnel, session);
if (err) {
kfree(session);
return ERR_PTR(err);
}
/* Bump the reference count. The session context is deleted
* only when this drops to zero.
*/
@@ -1849,28 +1899,14 @@ struct l2tp_session *l2tp_session_create(int priv_size, struct l2tp_tunnel *tunn
/* Ensure tunnel socket isn't deleted */
sock_hold(tunnel->sock);
/* Add session to the tunnel's hash list */
write_lock_bh(&tunnel->hlist_lock);
hlist_add_head(&session->hlist,
l2tp_session_id_hash(tunnel, session_id));
write_unlock_bh(&tunnel->hlist_lock);
/* And to the global session list if L2TPv3 */
if (tunnel->version != L2TP_HDR_VER_2) {
struct l2tp_net *pn = l2tp_pernet(tunnel->l2tp_net);
spin_lock_bh(&pn->l2tp_session_hlist_lock);
hlist_add_head_rcu(&session->global_hlist,
l2tp_session_id_hash_2(pn, session_id));
spin_unlock_bh(&pn->l2tp_session_hlist_lock);
}
/* Ignore management session in session count value */
if (session->session_id != 0)
atomic_inc(&l2tp_session_count);
return session;
}
return session;
return ERR_PTR(-ENOMEM);
}
EXPORT_SYMBOL_GPL(l2tp_session_create);