Re: [PATCH] net/rds: Accept peer connection reject messages due to incompatible version

[Santosh Shilimkar <santosh.shilimkar@oracle.com>]

On 3/5/2019 11:04 PM, Gerd Rausch wrote:
> 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.
> 
> Orabug: 29444532
> 
> Signed-off-by: Gerd Rausch <gerd.rausch@oracle.com>
> ---
>   net/rds/rdma_transport.c | 3 +--
>   1 file changed, 1 insertion(+), 2 deletions(-)
> 
> diff --git a/net/rds/rdma_transport.c b/net/rds/rdma_transport.c
> index 46bce8389066..f628e7fda66d 100644
> --- a/net/rds/rdma_transport.c
> +++ b/net/rds/rdma_transport.c
> @@ -112,7 +112,7 @@ 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 +122,6 @@ 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:
> 
Very similar test diff [1] I sent Yanjun to test yesterday... Thanks for 
checking. Will submit a cleaned up fix Gerd. Thansk for checking

 From 82c638f11137e29220051c704b63e3d7ed7d44d0 Mon Sep 17 00:00:00 2001
From: Santosh Shilimkar <santosh.shilimkar@oracle.com>
Date: Tue, 5 Mar 2019 18:19:52 -0800
Subject: [PATCH] TEST debug patch

Signed-off-by: Santosh Shilimkar <santosh.shilimkar@oracle.com>
---
  net/rds/rdma_transport.c |   16 ++++++++++++++++
  1 files changed, 16 insertions(+), 0 deletions(-)

diff --git a/net/rds/rdma_transport.c b/net/rds/rdma_transport.c
index 46bce83..c7b1fff 100644
--- a/net/rds/rdma_transport.c
+++ b/net/rds/rdma_transport.c
@@ -109,8 +109,10 @@ static int rds_rdma_cm_event_handler_cmn(struct 
rdma_cm_id *cm_id,
  		break;

  	case RDMA_CM_EVENT_REJECTED:
+		err = (int *)event->param.conn.private_data;
  		if (!conn)
  			break;
+#if 0
  		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",
@@ -119,6 +121,20 @@ static int rds_rdma_cm_event_handler_cmn(struct 
rdma_cm_id *cm_id,
  			conn->c_tos = 0;
  			rds_conn_drop(conn);
  		}
+#endif
+		if (event->status == RDS_REJ_CONSUMER_DEFINED &&
+				(*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;
+			conn->c_tos = 0;
+			rds_conn_drop(conn);
+		} else {
+			pr_debug("RDS/RDMA: conn <%pI6c, %pI6c> rejected, dropping 
connection\n",
+				&conn->c_laddr, &conn->c_faddr);
+			rds_conn_drop(conn);
+		}
  		rdsdebug("Connection rejected: %s\n",
  			 rdma_reject_msg(cm_id, event->status));
  		break;
-- 
1.7.1