[PATCH AUTOSEL 5.1 114/141] rds: Accept peer connection reject messages due to incompatible version

Sasha Levin
2019-07-19T04:28:13Z

From: Gerd Rausch <gerd.rausch@oracle.com>

[ Upstream commit 8c6166cfc9cd48e93d9176561e50b63cef4330d5 ]

Prior to
commit d021fabf525ff ("rds: rdma: add consumer reject")

function "rds_rdma_cm_event_handler_cmn" would always honor a rejected
connection attempt by issuing a "rds_conn_drop".

The commit mentioned above added a "break", eliminating
the "fallthrough" case and made the "rds_conn_drop" rather conditional:

Now it only happens if a "consumer defined" reject (i.e. "rdma_reject")
carries an integer-value of "1" inside "private_data":

if (!conn)
break;
err = (int *)rdma_consumer_reject_data(cm_id, event, &len);
if (!err || (err && ((*err) == RDS_RDMA_REJ_INCOMPAT))) {
pr_warn("RDS/RDMA: conn <%pI6c, %pI6c> rejected, dropping connection\n",
&conn->c_laddr, &conn->c_faddr);
conn->c_proposed_version = RDS_PROTOCOL_COMPAT_VERSION;
rds_conn_drop(conn);
}
rdsdebug("Connection rejected: %s\n",
rdma_reject_msg(cm_id, event->status));
break;
/* FALLTHROUGH */
A number of issues are worth mentioning here:
#1) Previous versions of the RDS code simply rejected a connection
by calling "rdma_reject(cm_id, NULL, 0);"
So the value of the payload in "private_data" will not be "1",
but "0".

#2) Now the code has become dependent on host byte order and sizing.
If one peer is big-endian, the other is little-endian,
or there's a difference in sizeof(int) (e.g. ILP64 vs LP64),
the *err check does not work as intended.

#3) There is no check for "len" to see if the data behind *err is even valid.
Luckily, it appears that the "rdma_reject(cm_id, NULL, 0)" will always
carry 148 bytes of zeroized payload.
But that should probably not be relied upon here.

#4) With the added "break;",
we might as well drop the misleading "/* FALLTHROUGH */" comment.

This commit does _not_ address issue #2, as the sender would have to
agree on a byte order as well.

Here is the sequence of messages in this observed error-scenario:
Host-A is pre-QoS changes (excluding the commit mentioned above)
Host-B is post-QoS changes (including the commit mentioned above)

#1 Host-B
issues a connection request via function "rds_conn_path_transition"
connection state transitions to "RDS_CONN_CONNECTING"

#2 Host-A
rejects the incompatible connection request (from #1)
It does so by calling "rdma_reject(cm_id, NULL, 0);"

#3 Host-B
receives an "RDMA_CM_EVENT_REJECTED" event (from #2)
But since the code is changed in the way described above,
it won't drop the connection here, simply because "*err == 0".

#4 Host-A
issues a connection request

#5 Host-B
receives an "RDMA_CM_EVENT_CONNECT_REQUEST" event
and ends up calling "rds_ib_cm_handle_connect".
But since the state is already in "RDS_CONN_CONNECTING"
(as of #1) it will end up issuing a "rdma_reject" without
dropping the connection:
if (rds_conn_state(conn) == RDS_CONN_CONNECTING) {
/* Wait and see - our connect may still be succeeding */
rds_ib_stats_inc(s_ib_connect_raced);
}
goto out;

#6 Host-A
receives an "RDMA_CM_EVENT_REJECTED" event (from #5),
drops the connection and tries again (goto #4) until it gives up.

Tested-by: Zhu Yanjun <yanjun.zhu@oracle.com>
Signed-off-by: Gerd Rausch <gerd.rausch@oracle.com>
Signed-off-by: Santosh Shilimkar <santosh.shilimkar@oracle.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
net/rds/rdma_transport.c | 5 +++--
1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/net/rds/rdma_transport.c b/net/rds/rdma_transport.c
index 46bce8389066..9db455d02255 100644
--- a/net/rds/rdma_transport.c
+++ b/net/rds/rdma_transport.c
@@ -112,7 +112,9 @@ static int rds_rdma_cm_event_handler_cmn(struct rdma_cm_id *cm_id,
if (!conn)
break;
err = (int *)rdma_consumer_reject_data(cm_id, event, &len);
- if (!err || (err && ((*err) == RDS_RDMA_REJ_INCOMPAT))) {
+ if (!err ||
+ (err && len >= sizeof(*err) &&
+ ((*err) <= RDS_RDMA_REJ_INCOMPAT))) {
pr_warn("RDS/RDMA: conn <%pI6c, %pI6c> rejected, dropping connection\n",
&conn->c_laddr, &conn->c_faddr);
conn->c_proposed_version = RDS_PROTOCOL_COMPAT_VERSION;
@@ -122,7 +124,6 @@ static int rds_rdma_cm_event_handler_cmn(struct rdma_cm_id *cm_id,
rdsdebug("Connection rejected: %s\n",
rdma_reject_msg(cm_id, event->status));
break;
- /* FALLTHROUGH */
case RDMA_CM_EVENT_ADDR_ERROR:
case RDMA_CM_EVENT_ROUTE_ERROR:
case RDMA_CM_EVENT_CONNECT_ERROR:
--
2.20.1