Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753756AbdGPORx (ORCPT ); Sun, 16 Jul 2017 10:17:53 -0400 Received: from shadbolt.e.decadent.org.uk ([88.96.1.126]:44370 "EHLO shadbolt.e.decadent.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753714AbdGPORt (ORCPT ); Sun, 16 Jul 2017 10:17:49 -0400 Content-Type: text/plain; charset="UTF-8" Content-Disposition: inline Content-Transfer-Encoding: 8bit MIME-Version: 1.0 From: Ben Hutchings To: linux-kernel@vger.kernel.org, stable@vger.kernel.org CC: akpm@linux-foundation.org, "Guillaume Nault" , "David S. Miller" Date: Sun, 16 Jul 2017 14:56:46 +0100 Message-ID: X-Mailer: LinuxStableQueue (scripts by bwh) Subject: [PATCH 3.16 113/178] l2tp: fix duplicate session creation In-Reply-To: X-SA-Exim-Connect-IP: 2a02:8011:400e:2:6f00:88c8:c921:d332 X-SA-Exim-Mail-From: ben@decadent.org.uk X-SA-Exim-Scanned: No (on shadbolt.decadent.org.uk); SAEximRunCond expanded to false Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 8315 Lines: 273 3.16.46-rc1 review patch. If anyone has any objections, please let me know. ------------------ From: Guillaume Nault commit dbdbc73b44782e22b3b4b6e8b51e7a3d245f3086 upstream. 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: d9e31d17ceba ("l2tp: Add L2TP ethernet pseudowire support") Fixes: fd558d186df2 ("l2tp: Split pppol2tp patch into separate l2tp and ppp parts") Signed-off-by: Guillaume Nault Signed-off-by: David S. Miller Signed-off-by: Ben Hutchings --- net/l2tp/l2tp_core.c | 70 +++++++++++++++++++++++++++++++++++++++------------- net/l2tp/l2tp_eth.c | 10 ++------ net/l2tp/l2tp_ppp.c | 60 ++++++++++++++++++++++---------------------- 3 files changed, 84 insertions(+), 56 deletions(-) --- a/net/l2tp/l2tp_core.c +++ b/net/l2tp/l2tp_core.c @@ -373,6 +373,48 @@ struct l2tp_session *l2tp_session_find_b } 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) @@ -1822,6 +1864,7 @@ EXPORT_SYMBOL_GPL(l2tp_session_set_heade 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) { @@ -1877,6 +1920,13 @@ struct l2tp_session *l2tp_session_create 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. */ @@ -1886,28 +1936,14 @@ struct l2tp_session *l2tp_session_create /* 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); --- a/net/l2tp/l2tp_eth.c +++ b/net/l2tp/l2tp_eth.c @@ -222,12 +222,6 @@ static int l2tp_eth_create(struct net *n goto out; } - session = l2tp_session_find(net, tunnel, session_id); - if (session) { - rc = -EEXIST; - goto out; - } - if (cfg->ifname) { dev = dev_get_by_name(net, cfg->ifname); if (dev) { @@ -241,8 +235,8 @@ static int l2tp_eth_create(struct net *n session = l2tp_session_create(sizeof(*spriv), tunnel, session_id, peer_session_id, cfg); - if (!session) { - rc = -ENOMEM; + if (IS_ERR(session)) { + rc = PTR_ERR(session); goto out; } --- a/net/l2tp/l2tp_ppp.c +++ b/net/l2tp/l2tp_ppp.c @@ -602,6 +602,7 @@ static int pppol2tp_connect(struct socke int error = 0; u32 tunnel_id, peer_tunnel_id; u32 session_id, peer_session_id; + bool drop_refcnt = false; int ver = 2; int fd; @@ -703,36 +704,36 @@ static int pppol2tp_connect(struct socke if (tunnel->peer_tunnel_id == 0) tunnel->peer_tunnel_id = peer_tunnel_id; - /* Create session if it doesn't already exist. We handle the - * case where a session was previously created by the netlink - * interface by checking that the session doesn't already have - * a socket and its tunnel socket are what we expect. If any - * of those checks fail, return EEXIST to the caller. - */ - session = l2tp_session_find(sock_net(sk), tunnel, session_id); - if (session == NULL) { - /* Default MTU must allow space for UDP/L2TP/PPP - * headers. + session = l2tp_session_get(sock_net(sk), tunnel, session_id, false); + if (session) { + drop_refcnt = true; + ps = l2tp_session_priv(session); + + /* Using a pre-existing session is fine as long as it hasn't + * been connected yet. */ - cfg.mtu = cfg.mru = 1500 - PPPOL2TP_HEADER_OVERHEAD; + if (ps->sock) { + error = -EEXIST; + goto end; + } - /* Allocate and initialize a new session context. */ - session = l2tp_session_create(sizeof(struct pppol2tp_session), - tunnel, session_id, - peer_session_id, &cfg); - if (session == NULL) { - error = -ENOMEM; + /* consistency checks */ + if (ps->tunnel_sock != tunnel->sock) { + error = -EEXIST; goto end; } } else { - ps = l2tp_session_priv(session); - error = -EEXIST; - if (ps->sock != NULL) - goto end; + /* Default MTU must allow space for UDP/L2TP/PPP headers */ + cfg.mtu = 1500 - PPPOL2TP_HEADER_OVERHEAD; + cfg.mru = cfg.mtu; - /* consistency checks */ - if (ps->tunnel_sock != tunnel->sock) + session = l2tp_session_create(sizeof(struct pppol2tp_session), + tunnel, session_id, + peer_session_id, &cfg); + if (IS_ERR(session)) { + error = PTR_ERR(session); goto end; + } } /* Associate session with its PPPoL2TP socket */ @@ -797,6 +798,8 @@ out_no_ppp: session->name); end: + if (drop_refcnt) + l2tp_session_dec_refcount(session); release_sock(sk); return error; @@ -824,12 +827,6 @@ static int pppol2tp_session_create(struc if (tunnel->sock == NULL) goto out; - /* Check that this session doesn't already exist */ - error = -EEXIST; - session = l2tp_session_find(net, tunnel, session_id); - if (session != NULL) - goto out; - /* Default MTU values. */ if (cfg->mtu == 0) cfg->mtu = 1500 - PPPOL2TP_HEADER_OVERHEAD; @@ -837,12 +834,13 @@ static int pppol2tp_session_create(struc cfg->mru = cfg->mtu; /* Allocate and initialize a new session context. */ - error = -ENOMEM; session = l2tp_session_create(sizeof(struct pppol2tp_session), tunnel, session_id, peer_session_id, cfg); - if (session == NULL) + if (IS_ERR(session)) { + error = PTR_ERR(session); goto out; + } ps = l2tp_session_priv(session); ps->tunnel_sock = tunnel->sock;