From eb192840266fab3e3da644018121eed30153355d Mon Sep 17 00:00:00 2001 From: Sowmini Varadhan Date: Mon, 2 May 2016 11:24:51 -0700 Subject: [PATCH] RDS:TCP: Synchronize rds_tcp_accept_one with rds_send_xmit when resetting t_sock There is a race condition between rds_send_xmit -> rds_tcp_xmit and the code that deals with resolution of duelling syns added by commit 241b271952eb ("RDS-TCP: Reset tcp callbacks if re-using an outgoing socket in rds_tcp_accept_one()"). Specifically, we may end up derefencing a null pointer in rds_send_xmit if we have the interleaving sequence: rds_tcp_accept_one rds_send_xmit conn is RDS_CONN_UP, so invoke rds_tcp_xmit tc = conn->c_transport_data rds_tcp_restore_callbacks /* reset t_sock */ null ptr deref from tc->t_sock The race condition can be avoided without adding the overhead of additional locking in the xmit path: have rds_tcp_accept_one wait for rds_tcp_xmit threads to complete before resetting callbacks. The synchronization can be done in the same manner as rds_conn_shutdown(). First set the rds_conn_state to something other than RDS_CONN_UP (so that new threads cannot get into rds_tcp_xmit()), then wait for RDS_IN_XMIT to be cleared in the conn->c_flags indicating that any threads in rds_tcp_xmit are done. Fixes: 241b271952eb ("RDS-TCP: Reset tcp callbacks if re-using an outgoing socket in rds_tcp_accept_one()") Signed-off-by: Sowmini Varadhan Acked-by: Santosh Shilimkar Signed-off-by: David S. Miller --- net/rds/tcp.c | 2 +- net/rds/tcp_listen.c | 40 ++++++++++++++++++++++++---------------- 2 files changed, 25 insertions(+), 17 deletions(-) diff --git a/net/rds/tcp.c b/net/rds/tcp.c index 61ed2a8764ba..9134544941c2 100644 --- a/net/rds/tcp.c +++ b/net/rds/tcp.c @@ -127,7 +127,7 @@ void rds_tcp_restore_callbacks(struct socket *sock, /* * This is the only path that sets tc->t_sock. Send and receive trust that - * it is set. The RDS_CONN_CONNECTED bit protects those paths from being + * it is set. The RDS_CONN_UP bit protects those paths from being * called while it isn't set. */ void rds_tcp_set_callbacks(struct socket *sock, struct rds_connection *conn) diff --git a/net/rds/tcp_listen.c b/net/rds/tcp_listen.c index 0936a4a32b47..0896187243d6 100644 --- a/net/rds/tcp_listen.c +++ b/net/rds/tcp_listen.c @@ -115,24 +115,32 @@ int rds_tcp_accept_one(struct socket *sock) * rds_tcp_state_change() will do that cleanup */ rs_tcp = (struct rds_tcp_connection *)conn->c_transport_data; - if (rs_tcp->t_sock && - ntohl(inet->inet_saddr) < ntohl(inet->inet_daddr)) { - struct sock *nsk = new_sock->sk; - - nsk->sk_user_data = NULL; - nsk->sk_prot->disconnect(nsk, 0); - tcp_done(nsk); - new_sock = NULL; - ret = 0; - goto out; - } else if (rs_tcp->t_sock) { - rds_tcp_restore_callbacks(rs_tcp->t_sock, rs_tcp); - conn->c_outgoing = 0; - } - rds_conn_transition(conn, RDS_CONN_DOWN, RDS_CONN_CONNECTING); + if (rs_tcp->t_sock) { + /* Need to resolve a duelling SYN between peers. + * We have an outstanding SYN to this peer, which may + * potentially have transitioned to the RDS_CONN_UP state, + * so we must quiesce any send threads before resetting + * c_transport_data. + */ + wait_event(conn->c_waitq, + !test_bit(RDS_IN_XMIT, &conn->c_flags)); + if (ntohl(inet->inet_saddr) < ntohl(inet->inet_daddr)) { + struct sock *nsk = new_sock->sk; + + nsk->sk_user_data = NULL; + nsk->sk_prot->disconnect(nsk, 0); + tcp_done(nsk); + new_sock = NULL; + ret = 0; + goto out; + } else if (rs_tcp->t_sock) { + rds_tcp_restore_callbacks(rs_tcp->t_sock, rs_tcp); + conn->c_outgoing = 0; + } + } rds_tcp_set_callbacks(new_sock, conn); - rds_connect_complete(conn); + rds_connect_complete(conn); /* marks RDS_CONN_UP */ new_sock = NULL; ret = 0; -- GitLab