3.2.96-rc1 review patch. If anyone has any objections, please let me know.
------------------
From: Guillaume Nault g.nault@alphalink.fr
commit f3c66d4e144a0904ea9b95d23ed9f8eb38c11bfb upstream.
l2tp_tunnel_destruct() sets tunnel->sock to NULL, then removes the tunnel from the pernet list and finally closes all its sessions. Therefore, it's possible to add a session to a tunnel that is still reachable, but for which tunnel->sock has already been reset. This can make l2tp_session_create() dereference a NULL pointer when calling sock_hold(tunnel->sock).
This patch adds the .acpt_newsess field to struct l2tp_tunnel, which is used by l2tp_tunnel_closeall() to prevent addition of new sessions to tunnels. Resetting tunnel->sock is done after l2tp_tunnel_closeall() returned, so that l2tp_session_add_to_tunnel() can safely take a reference on it when .acpt_newsess is true.
The .acpt_newsess field is modified in l2tp_tunnel_closeall(), rather than in l2tp_tunnel_destruct(), so that it benefits all tunnel removal mechanisms. E.g. on UDP tunnels, a session could be added to a tunnel after l2tp_udp_encap_destroy() proceeded. This would prevent the tunnel from being removed because of the references held by this new session on the tunnel and its socket. Even though the session could be removed manually later on, this defeats the purpose of commit 9980d001cec8 ("l2tp: add udp encap socket destroy handler").
Fixes: fd558d186df2 ("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 [bwh: Backported to 3.2: - Drop changes in l2tp_tunnel_destruct(), as the assignment to tunnel->sock is already after the call to l2tp_tunnel_closeall() - Adjust context] Signed-off-by: Ben Hutchings ben@decadent.org.uk --- --- a/net/l2tp/l2tp_core.c +++ b/net/l2tp/l2tp_core.c @@ -335,13 +335,21 @@ static int l2tp_session_add_to_tunnel(st struct hlist_head *head; struct l2tp_net *pn; struct hlist_node *walk; + int err;
head = l2tp_session_id_hash(tunnel, session->session_id);
write_lock_bh(&tunnel->hlist_lock); + if (!tunnel->acpt_newsess) { + err = -ENODEV; + goto err_tlock; + } + hlist_for_each_entry(session_walk, walk, head, hlist) - if (session_walk->session_id == session->session_id) - goto exist; + if (session_walk->session_id == session->session_id) { + err = -EEXIST; + goto err_tlock; + }
if (tunnel->version == L2TP_HDR_VER_3) { pn = l2tp_pernet(tunnel->l2tp_net); @@ -349,12 +357,21 @@ static int l2tp_session_add_to_tunnel(st session->session_id);
spin_lock_bh(&pn->l2tp_session_hlist_lock); + hlist_for_each_entry(session_walk, walk, g_head, global_hlist) - if (session_walk->session_id == session->session_id) - goto exist_glob; + if (session_walk->session_id == session->session_id) { + err = -EEXIST; + goto err_tlock_pnlock; + }
+ l2tp_tunnel_inc_refcount(tunnel); + sock_hold(tunnel->sock); hlist_add_head_rcu(&session->global_hlist, g_head); + spin_unlock_bh(&pn->l2tp_session_hlist_lock); + } else { + l2tp_tunnel_inc_refcount(tunnel); + sock_hold(tunnel->sock); }
hlist_add_head(&session->hlist, head); @@ -362,12 +379,12 @@ static int l2tp_session_add_to_tunnel(st
return 0;
-exist_glob: +err_tlock_pnlock: spin_unlock_bh(&pn->l2tp_session_hlist_lock); -exist: +err_tlock: write_unlock_bh(&tunnel->hlist_lock);
- return -EEXIST; + return err; }
/* Lookup a tunnel by id @@ -1282,6 +1299,7 @@ static void l2tp_tunnel_closeall(struct "%s: closing all sessions...\n", tunnel->name);
write_lock_bh(&tunnel->hlist_lock); + tunnel->acpt_newsess = false; for (hash = 0; hash < L2TP_HASH_SIZE; hash++) { again: hlist_for_each_safe(walk, tmp, &tunnel->session_hlist[hash]) { @@ -1504,6 +1522,7 @@ int l2tp_tunnel_create(struct net *net, tunnel->magic = L2TP_TUNNEL_MAGIC; sprintf(&tunnel->name[0], "tunl %u", tunnel_id); rwlock_init(&tunnel->hlist_lock); + tunnel->acpt_newsess = true;
/* The net we belong to */ tunnel->l2tp_net = net; @@ -1719,11 +1738,6 @@ struct l2tp_session *l2tp_session_create return ERR_PTR(err); }
- l2tp_tunnel_inc_refcount(tunnel); - - /* Ensure tunnel socket isn't deleted */ - sock_hold(tunnel->sock); - /* Ignore management session in session count value */ if (session->session_id != 0) atomic_inc(&l2tp_session_count); --- a/net/l2tp/l2tp_core.h +++ b/net/l2tp/l2tp_core.h @@ -159,6 +159,10 @@ struct l2tp_tunnel { int magic; /* Should be L2TP_TUNNEL_MAGIC */ struct rcu_head rcu; rwlock_t hlist_lock; /* protect session_hlist */ + bool acpt_newsess; /* Indicates whether this + * tunnel accepts new sessions. + * Protected by hlist_lock. + */ struct hlist_head session_hlist[L2TP_HASH_SIZE]; /* hashed list of sessions, * hashed by id */