3.16.54-rc1 review patch. If anyone has any objections, please let me know.
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From: Guillaume Nault g.nault@alphalink.fr
commit f98be6c6359e7e4a61aaefb9964c1db31cb9ec0c upstream.
pppol2tp_connect() initialises L2TP sessions after they've been exposed to the rest of the system by l2tp_session_register(). This puts sessions into transient states that are the source of several races, in particular with session's deletion path.
This patch centralises the initialisation code into pppol2tp_session_init(), which is called before the registration phase. The only field that can't be set before session registration is the pppol2tp socket pointer, which has already been converted to RCU. So pppol2tp_connect() should now be race-free.
The session's .session_close() callback is now set before registration. Therefore, it's always called when l2tp_core deletes the session, even if it was created by pppol2tp_session_create() and hasn't been plugged to a pppol2tp socket yet. That'd prevent session free because the extra reference taken by pppol2tp_session_close() wouldn't be dropped by the socket's ->sk_destruct() callback (pppol2tp_session_destruct()). We could set .session_close() only while connecting a session to its pppol2tp socket, or teach pppol2tp_session_close() to avoid grabbing a reference when the session isn't connected, but that'd require adding some form of synchronisation to be race free.
Instead of that, we can just let the pppol2tp socket hold a reference on the session as soon as it starts depending on it (that is, in pppol2tp_connect()). Then we don't need to utilise pppol2tp_session_close() to hold a reference at the last moment to prevent l2tp_core from dropping it.
When releasing the socket, pppol2tp_release() now deletes the session using the standard l2tp_session_delete() function, instead of merely removing it from hash tables. l2tp_session_delete() drops the reference the sessions holds on itself, but also makes sure it doesn't remove a session twice. So it can safely be called, even if l2tp_core already tried, or is concurrently trying, to remove the session. Finally, pppol2tp_session_destruct() drops the reference held by the socket.
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 3.16: adjust context] Signed-off-by: Ben Hutchings ben@decadent.org.uk --- net/l2tp/l2tp_ppp.c | 69 +++++++++++++++++++++++++++++------------------------ 1 file changed, 38 insertions(+), 31 deletions(-)
--- a/net/l2tp/l2tp_ppp.c +++ b/net/l2tp/l2tp_ppp.c @@ -468,9 +468,6 @@ static void pppol2tp_session_close(struc inet_shutdown(sk->sk_socket, SEND_SHUTDOWN); sock_put(sk); } - - /* Don't let the session go away before our socket does */ - l2tp_session_inc_refcount(session); }
/* Really kill the session socket. (Called from sock_put() if @@ -526,8 +523,7 @@ static int pppol2tp_release(struct socke if (session != NULL) { struct pppol2tp_session *ps;
- __l2tp_session_unhash(session); - l2tp_session_queue_purge(session); + l2tp_session_delete(session);
ps = l2tp_session_priv(session); mutex_lock(&ps->sk_lock); @@ -619,6 +615,35 @@ static void pppol2tp_show(struct seq_fil } #endif
+static void pppol2tp_session_init(struct l2tp_session *session) +{ + struct pppol2tp_session *ps; + struct dst_entry *dst; + + session->recv_skb = pppol2tp_recv; + session->session_close = pppol2tp_session_close; +#if IS_ENABLED(CONFIG_L2TP_DEBUGFS) + session->show = pppol2tp_show; +#endif + + ps = l2tp_session_priv(session); + mutex_init(&ps->sk_lock); + ps->tunnel_sock = session->tunnel->sock; + ps->owner = current->pid; + + /* If PMTU discovery was enabled, use the MTU that was discovered */ + dst = sk_dst_get(session->tunnel->sock); + if (dst) { + u32 pmtu = dst_mtu(dst); + + if (pmtu) { + session->mtu = pmtu - PPPOL2TP_HEADER_OVERHEAD; + session->mru = pmtu - PPPOL2TP_HEADER_OVERHEAD; + } + dst_release(dst); + } +} + /* connect() handler. Attach a PPPoX socket to a tunnel UDP socket */ static int pppol2tp_connect(struct socket *sock, struct sockaddr *uservaddr, @@ -630,7 +655,6 @@ static int pppol2tp_connect(struct socke struct l2tp_session *session = NULL; struct l2tp_tunnel *tunnel; struct pppol2tp_session *ps; - struct dst_entry *dst; struct l2tp_session_cfg cfg = { 0, }; int error = 0; u32 tunnel_id, peer_tunnel_id; @@ -775,8 +799,8 @@ static int pppol2tp_connect(struct socke goto end; }
+ pppol2tp_session_init(session); ps = l2tp_session_priv(session); - mutex_init(&ps->sk_lock); l2tp_session_inc_refcount(session);
mutex_lock(&ps->sk_lock); @@ -789,26 +813,6 @@ static int pppol2tp_connect(struct socke drop_refcnt = true; }
- ps->owner = current->pid; - ps->tunnel_sock = tunnel->sock; - - session->recv_skb = pppol2tp_recv; - session->session_close = pppol2tp_session_close; -#if defined(CONFIG_L2TP_DEBUGFS) || defined(CONFIG_L2TP_DEBUGFS_MODULE) - session->show = pppol2tp_show; -#endif - - /* If PMTU discovery was enabled, use the MTU that was discovered */ - dst = sk_dst_get(tunnel->sock); - if (dst != NULL) { - u32 pmtu = dst_mtu(dst); - - if (pmtu != 0) - session->mtu = session->mru = pmtu - - PPPOL2TP_HEADER_OVERHEAD; - dst_release(dst); - } - /* Special case: if source & dest session_id == 0x0000, this * socket is being created to manage the tunnel. Just set up * the internal context for use by ioctl() and sockopt() @@ -842,6 +846,12 @@ out_no_ppp: rcu_assign_pointer(ps->sk, sk); mutex_unlock(&ps->sk_lock);
+ /* Keep the reference we've grabbed on the session: sk doesn't expect + * the session to disappear. pppol2tp_session_destruct() is responsible + * for dropping it. + */ + drop_refcnt = false; + sk->sk_state = PPPOX_CONNECTED; l2tp_info(session, PPPOL2TP_MSG_CONTROL, "%s: created\n", session->name); @@ -865,7 +875,6 @@ static int pppol2tp_session_create(struc { int error; struct l2tp_session *session; - struct pppol2tp_session *ps;
/* Error if tunnel socket is not prepped */ if (!tunnel->sock) { @@ -888,9 +897,7 @@ static int pppol2tp_session_create(struc goto err; }
- ps = l2tp_session_priv(session); - mutex_init(&ps->sk_lock); - ps->tunnel_sock = tunnel->sock; + pppol2tp_session_init(session);
error = l2tp_session_register(session, tunnel); if (error < 0)