RE: [PATCH] iscsi: Do Not set param when sock is NULL

[Gulam Mohamed]

Hi Michael,

             As per your suggestions in below mail, I have completed the suggested changes and tested them. Can you please review and let me know your comments? Here is the patch:

Description
===========
1. This Kernel panic could be due to a timing issue when there is a race between the sync thread and the initiator was processing of a login response from the target. The session re-open can be invoked from two places
  a. Sessions sync thread when the iscsid restart
  b. From iscsid through iscsi error handler 2. The session reopen sequence is as follows in user-space (iscsi-initiator-utils)
   a. Disconnect the connection
   b. Then send the stop connection request to the kernel which releases the connection (releases the socket)
   c. Queues the reopen for 2 seconds delay
   d. Once the delay expires, create the TCP connection again by calling the connect() call
   e. Poll for the connection
   f. When poll is successful i.e when the TCP connection is established, it performs
      i. Creation of session and connection data structures
      ii. Bind the connection to the session. This is the place where we assign the sock to tcp_sw_conn->sock
      iii. Sets the parameters like target name, persistent address etc .
      iv. Creates the login pdu
       v. Sends the login pdu to kernel
      vi. Returns to the main loop to process further events. The kernel then sends the login request over to the target node
   g. Once login response with success is received, it enters into full feature phase and sets the negotiable parameters like max_recv_data_length, max_transmit_length, data_digest etc .
3. While setting the negotiable parameters by calling "iscsi_session_set_neg_params()", kernel panicked as sock was NULL

What happened here is
---------------------
1. Before initiator received the login response mentioned in above point 2.f.v, another reopen request was sent from the error handler/sync session for the same session, as the initiator utils was in main loop to process further events (as mentioned in point 2.f.vi above).
2. While processing this reopen, it stopped the connection which released the socket and queued this connection and at this point of time the login response was received for the earlier on

Fix
---

1. Create a flag "set_param_fail" in iscsi_cls_conn structure 2. On ep_disconnect and stop_conn set this flag to indicate set_param calls for connection level settings should fail 3. This way, scsi_transport_iscsi can set and check this bit for all drivers 2. On bind_conn clear the bit

Signed-off-by: Gulam Mohamed <gulam.mohamed@xxxxxxxxxx>
---
 drivers/scsi/scsi_transport_iscsi.c | 6 ++++++  include/scsi/scsi_transport_iscsi.h | 3 +++
 2 files changed, 9 insertions(+)

diff --git a/drivers/scsi/scsi_transport_iscsi.c b/drivers/scsi/scsi_transport_iscsi.c
index 2e68c0a87698..15c5a7223a40 100644
--- a/drivers/scsi/scsi_transport_iscsi.c
+++ b/drivers/scsi/scsi_transport_iscsi.c
@@ -2473,6 +2473,8 @@ static void iscsi_if_stop_conn(struct iscsi_cls_conn *conn, int flag)
 	 * it works.
 	 */
 	mutex_lock(&conn_mutex);
+	if (!test_bit(ISCSI_SET_PARAM_FAIL_BIT, &conn->set_param_fail))
+		set_bit(ISCSI_SET_PARAM_FAIL_BIT, &conn->set_param_fail);
 	conn->transport->stop_conn(conn, flag);
 	mutex_unlock(&conn_mutex);
 
@@ -2895,6 +2897,8 @@ iscsi_set_param(struct iscsi_transport *transport, struct iscsi_uevent *ev)
 			session->recovery_tmo = value;
 		break;
 	default:
+		if (test_bit(ISCSI_SET_PARAM_FAIL_BIT, &conn->set_param_fail))
+			return -ENOTCONN;
 		err = transport->set_param(conn, ev->u.set_param.param,
 					   data, ev->u.set_param.len);
 	}
@@ -2956,6 +2960,7 @@ static int iscsi_if_ep_disconnect(struct iscsi_transport *transport,
 		mutex_lock(&conn->ep_mutex);
 		conn->ep = NULL;
 		mutex_unlock(&conn->ep_mutex);
+		set_bit(ISCSI_SET_PARAM_FAIL_BIT, &conn->set_param_fail);
 	}
 
 	transport->ep_disconnect(ep);
@@ -3716,6 +3721,7 @@ iscsi_if_recv_msg(struct sk_buff *skb, struct nlmsghdr *nlh, uint32_t *group)
 		ev->r.retcode =	transport->bind_conn(session, conn,
 						ev->u.b_conn.transport_eph,
 						ev->u.b_conn.is_leading);
+		clear_bit(ISCSI_SET_PARAM_FAIL_BIT, &conn->set_param_fail);
 		mutex_unlock(&conn_mutex);
 
 		if (ev->r.retcode || !transport->ep_connect) diff --git a/include/scsi/scsi_transport_iscsi.h b/include/scsi/scsi_transport_iscsi.h
index 8a26a2ffa952..71b1952b913b 100644
--- a/include/scsi/scsi_transport_iscsi.h
+++ b/include/scsi/scsi_transport_iscsi.h
@@ -29,6 +29,8 @@ struct bsg_job;
 struct iscsi_bus_flash_session;
 struct iscsi_bus_flash_conn;
 
+#define ISCSI_SET_PARAM_FAIL_BIT	1
+
 /**
  * struct iscsi_transport - iSCSI Transport template
  *
@@ -206,6 +208,7 @@ struct iscsi_cls_conn {
 
 	struct device dev;		/* sysfs transport/container device */
 	enum iscsi_connection_state state;
+	unsigned long set_param_fail; /* set_param for connection should fail 
+*/
 };
 
 #define iscsi_dev_to_conn(_dev) \
--
2.27.0

Regards,
Gulam Mohamed.

-----Original Message-----
From: Michael Christie 
Sent: Tuesday, November 24, 2020 4:37 AM
To: Gulam Mohamed <gulam.mohamed@xxxxxxxxxx>
Cc: Lee Duncan <lduncan@xxxxxxxx>; Chris Leech <cleech@xxxxxxxxxx>; James E.J. Bottomley <jejb@xxxxxxxxxxxxx>; Martin K. Petersen <martin.petersen@xxxxxxxxxx>; open-iscsi@xxxxxxxxxxxxxxxx; linux-scsi@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; Junxiao Bi <junxiao.bi@xxxxxxxxxx>
Subject: Re: [PATCH] iscsi: Do Not set param when sock is NULL



> On Nov 4, 2020, at 11:40 PM, Gulam Mohamed <gulam.mohamed@xxxxxxxxxx> wrote:
> 
> Description
> =========
> 1. This Kernel panic could be due to a timing issue when there is a race between the sync thread and the initiator was processing of a login response from the target. The session re-open can be invoked from two places
>          a.	Sessions sync thread when the iscsid restart
>          b.	From iscsid through iscsi error handler
> 2. The session reopen sequence is as follows in user-space (iscsi-initiator-utils)
>          a.	Disconnect the connection
>          b.	Then send the stop connection request to the kernel which releases the connection (releases the socket)
>          c.	Queues the reopen for 2 seconds delay
>         d.	Once the delay expires, create the TCP connection again by calling the connect() call
>         e.	Poll for the connection
>          f.	When poll is successful i.e when the TCP connection is established, it performs
> 	i. Creation of session and connection data structures
> 	ii. Bind the connection to the session. This is the place where we assign the sock to tcp_sw_conn->sock
> 	iii. Sets the parameters like target name, persistent address etc .
> 	iv. Creates the login pdu
> 	v. Sends the login pdu to kernel
> 	vi. Returns to the main loop to process further events. The kernel then sends the login request over to the target node
> 	g. Once login response with success is received, it enters into full feature phase and sets the negotiable parameters like max_recv_data_length, max_transmit_length, data_digest etc .
> 3. While setting the negotiable parameters by calling 
> "iscsi_session_set_neg_params()", kernel panicked as sock was NULL
> 
> What happened here is
> --------------------------------
> 1.	Before initiator received the login response mentioned in above point 2.f.v, another reopen request was sent from the error handler/sync session for the same session, as the initiator utils was in main loop to process further events (as 
> 	mentioned in point 2.f.vi above). 
> 2.	While processing this reopen, it stopped the connection which released the socket and queued this connection and at this point of time the login response was received for the earlier one


To make sure I got this you are saying before iscsi_sw_tcp_conn_stop calls iscsi_sw_tcp_release_conn that the recv path has called iscsi_recv_pdu right?


> 3.	The kernel passed over this response to user-space which then sent the set_neg_params request to kernel
> 4.	As the connection was stopped, the sock was NULL and hence while the kernel was processing the set param request from user-space, it panicked
> 
> Fix
> ----
> 1.	While setting the set_param in kernel, we need to check if sock is NULL
> 2.	If the sock is NULL, then return EPERM (operation not permitted)
> 3.	Due to this error handler will be invoked in user-space again to recover the session
> 
> Signed-off-by: Gulam Mohamed <gulam.mohamed@xxxxxxxxxx>
> Reviewed-by: Junxiao Bi <junxiao.bi@xxxxxxxxxx>
> ---
> diff --git a/drivers/scsi/iscsi_tcp.c b/drivers/scsi/iscsi_tcp.c index 
> df47557a02a3..fd668a194053 100644
> --- a/drivers/scsi/iscsi_tcp.c
> +++ b/drivers/scsi/iscsi_tcp.c
> @@ -711,6 +711,12 @@ static int iscsi_sw_tcp_conn_set_param(struct iscsi_cls_conn *cls_conn,
>        struct iscsi_tcp_conn *tcp_conn = conn->dd_data;
>        struct iscsi_sw_tcp_conn *tcp_sw_conn = tcp_conn->dd_data;
> 
> +       if (!tcp_sw_conn->sock) {
> +               iscsi_conn_printk(KERN_ERR, conn,
> +                               "Cannot set param as sock is NULL\n");
> +               return -ENOTCONN;
> +       }
> +

I think this might have 2 issues:

1. It only fixes iscsi_tcp. What about other drivers that free/null resources/fields in ep_disconnect that we layer need to access in the set_param callback (the cxgbi drivers)?

2. What about drivers that do not free/null fields (be2iscsi, bnx2i, ql4xxx and qedi) so the set_param calls end up just working. What state will userspace be in where we have logged in, but iscsid also thinks we are in the middle of trying to login?

I think we could do:

1. On ep_disconnect and stop_conn set some iscsi_cls_conn bit that indicates set_param calls for connection level settings should fail. scsi_transport_iscsi could set and check this bit for all drivers.
2. On bind_conn clear the bit.