[PATCH 4.9 103/148] rds: tcp: Sequence teardown of listen and acceptor sockets to avoid races

Greg Kroah-Hartman
2017-12-12T13:13:37Z

From: Sowmini Varadhan <sowmini.varadhan@oracle.com>

[ Upstream commit b21dd4506b71bdb9c5a20e759255cd2513ea7ebe ]

Commit a93d01f5777e ("RDS: TCP: avoid bad page reference in
rds_tcp_listen_data_ready") added the function
rds_tcp_listen_sock_def_readable() to handle the case when a
partially set-up acceptor socket drops into rds_tcp_listen_data_ready().
However, if the listen socket (rtn->rds_tcp_listen_sock) is itself going
through a tear-down via rds_tcp_listen_stop(), the (*ready)() will be
null and we would hit a panic of the form
BUG: unable to handle kernel NULL pointer dereference at (null)
IP: (null)
:
? rds_tcp_listen_data_ready+0x59/0xb0 [rds_tcp]
tcp_data_queue+0x39d/0x5b0
tcp_rcv_established+0x2e5/0x660
tcp_v4_do_rcv+0x122/0x220
tcp_v4_rcv+0x8b7/0x980
:
In the above case, it is not fatal to encounter a NULL value for
ready- we should just drop the packet and let the flush of the
acceptor thread finish gracefully.

In general, the tear-down sequence for listen() and accept() socket
that is ensured by this commit is:
rtn->rds_tcp_listen_sock = NULL; /* prevent any new accepts */
In rds_tcp_listen_stop():
serialize with, and prevent, further callbacks using lock_sock()
flush rds_wq
flush acceptor workq
sock_release(listen socket)

Signed-off-by: Sowmini Varadhan <sowmini.varadhan@oracle.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <alexander.levin@verizon.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
net/rds/tcp.c | 15 ++++++++++-----
net/rds/tcp.h | 2 +-
net/rds/tcp_listen.c | 9 +++++++--
3 files changed, 18 insertions(+), 8 deletions(-)

--- a/net/rds/tcp.c
+++ b/net/rds/tcp.c
@@ -478,9 +478,10 @@ static void __net_exit rds_tcp_exit_net(
* we do need to clean up the listen socket here.
*/
if (rtn->rds_tcp_listen_sock) {
- rds_tcp_listen_stop(rtn->rds_tcp_listen_sock);
+ struct socket *lsock = rtn->rds_tcp_listen_sock;
+
rtn->rds_tcp_listen_sock = NULL;
- flush_work(&rtn->rds_tcp_accept_w);
+ rds_tcp_listen_stop(lsock, &rtn->rds_tcp_accept_w);
}
}

@@ -517,10 +518,10 @@ static void rds_tcp_kill_sock(struct net
struct rds_tcp_connection *tc, *_tc;
LIST_HEAD(tmp_list);
struct rds_tcp_net *rtn = net_generic(net, rds_tcp_netid);
+ struct socket *lsock = rtn->rds_tcp_listen_sock;

- rds_tcp_listen_stop(rtn->rds_tcp_listen_sock);
rtn->rds_tcp_listen_sock = NULL;
- flush_work(&rtn->rds_tcp_accept_w);
+ rds_tcp_listen_stop(lsock, &rtn->rds_tcp_accept_w);
spin_lock_irq(&rds_tcp_conn_lock);
list_for_each_entry_safe(tc, _tc, &rds_tcp_conn_list, t_tcp_node) {
struct net *c_net = read_pnet(&tc->t_cpath->cp_conn->c_net);
@@ -540,8 +541,12 @@ static void rds_tcp_kill_sock(struct net
void *rds_tcp_listen_sock_def_readable(struct net *net)
{
struct rds_tcp_net *rtn = net_generic(net, rds_tcp_netid);
+ struct socket *lsock = rtn->rds_tcp_listen_sock;
+
+ if (!lsock)
+ return NULL;

- return rtn->rds_tcp_listen_sock->sk->sk_user_data;
+ return lsock->sk->sk_user_data;
}

static int rds_tcp_dev_event(struct notifier_block *this,
--- a/net/rds/tcp.h
+++ b/net/rds/tcp.h
@@ -66,7 +66,7 @@ void rds_tcp_state_change(struct sock *s

/* tcp_listen.c */
struct socket *rds_tcp_listen_init(struct net *);
-void rds_tcp_listen_stop(struct socket *);
+void rds_tcp_listen_stop(struct socket *sock, struct work_struct *acceptor);
void rds_tcp_listen_data_ready(struct sock *sk);
int rds_tcp_accept_one(struct socket *sock);
int rds_tcp_keepalive(struct socket *sock);
--- a/net/rds/tcp_listen.c
+++ b/net/rds/tcp_listen.c
@@ -227,6 +227,9 @@ void rds_tcp_listen_data_ready(struct so
* before it has been accepted and the accepter has set up their
* data_ready.. we only want to queue listen work for our listening
* socket
+ *
+ * (*ready)() may be null if we are racing with netns delete, and
+ * the listen socket is being torn down.
*/
if (sk->sk_state == TCP_LISTEN)
rds_tcp_accept_work(sk);
@@ -235,7 +238,8 @@ void rds_tcp_listen_data_ready(struct so

out:
read_unlock_bh(&sk->sk_callback_lock);
- ready(sk);
+ if (ready)
+ ready(sk);
}

struct socket *rds_tcp_listen_init(struct net *net)
@@ -275,7 +279,7 @@ out:
return NULL;
}

-void rds_tcp_listen_stop(struct socket *sock)
+void rds_tcp_listen_stop(struct socket *sock, struct work_struct *acceptor)
{
struct sock *sk;

@@ -296,5 +300,6 @@ void rds_tcp_listen_stop(struct socket *

/* wait for accepts to stop and close the socket */
flush_workqueue(rds_wq);
+ flush_work(acceptor);
sock_release(sock);
}