scsi: lpfc: Fix null pointer dereference in lpfc_prep_els_iocb()

It is possible to call lpfc_issue_els_plogi() passing a did for which no
matching ndlp is found. A call is then made to lpfc_prep_els_iocb() with a
null pointer to a lpfc_nodelist structure resulting in a null pointer
dereference.

Fix by returning an error status if no valid ndlp is found. Fix up comments
regarding ndlp reference counting.

Link: https://lore.kernel.org/r/20210301171821.3427-10-jsmart2021@gmail.com
Fixes: 4430f7fd ("scsi: lpfc: Rework locations of ndlp reference taking")
Co-developed-by: NDick Kennedy <dick.kennedy@broadcom.com>
Signed-off-by: NDick Kennedy <dick.kennedy@broadcom.com>
Signed-off-by: NJames Smart <jsmart2021@gmail.com>
Signed-off-by: NMartin K. Petersen <martin.petersen@oracle.com>

drivers/scsi/lpfc/lpfc_els.c

 /*******************************************************************
  * This file is part of the Emulex Linux Device Driver for         *
  * Fibre Channel Host Bus Adapters.                                *
- * Copyright (C) 2017-2020 Broadcom. All Rights Reserved. The term *
+ * Copyright (C) 2017-2021 Broadcom. All Rights Reserved. The term *
  * “Broadcom” refers to Broadcom Inc. and/or its subsidiaries.     *
  * Copyright (C) 2004-2016 Emulex.  All rights reserved.           *
  * EMULEX and SLI are trademarks of Emulex.                        *
@@ -2052,13 +2052,12 @@ lpfc_cmpl_els_plogi(struct lpfc_hba *phba, struct lpfc_iocbq *cmdiocb,
  * This routine issues a Port Login (PLOGI) command to a remote N_Port
  * (with the @did) for a @vport. Before issuing a PLOGI to a remote N_Port,
  * the ndlp with the remote N_Port DID must exist on the @vport's ndlp list.
- * This routine constructs the proper feilds of the PLOGI IOCB and invokes
+ * This routine constructs the proper fields of the PLOGI IOCB and invokes
  * the lpfc_sli_issue_iocb() routine to send out PLOGI ELS command.
  *
- * Note that, in lpfc_prep_els_iocb() routine, the reference count of ndlp
- * will be incremented by 1 for holding the ndlp and the reference to ndlp
- * will be stored into the context1 field of the IOCB for the completion
- * callback function to the PLOGI ELS command.
+ * Note that the ndlp reference count will be incremented by 1 for holding
+ * the ndlp and the reference to ndlp will be stored into the context1 field
+ * of the IOCB for the completion callback function to the PLOGI ELS command.
  *
  * Return code
  *   0 - Successfully issued a plogi for @vport
@@ -2076,29 +2075,28 @@ lpfc_issue_els_plogi(struct lpfc_vport *vport, uint32_t did, uint8_t retry)
 	int ret;
 
 	ndlp = lpfc_findnode_did(vport, did);
+	if (!ndlp)
+		return 1;
 
-	if (ndlp) {
-		/* Defer the processing of the issue PLOGI until after the
-		 * outstanding UNREG_RPI mbox command completes, unless we
-		 * are going offline. This logic does not apply for Fabric DIDs
-		 */
-		if ((ndlp->nlp_flag & NLP_UNREG_INP) &&
-		    ((ndlp->nlp_DID & Fabric_DID_MASK) != Fabric_DID_MASK) &&
-		    !(vport->fc_flag & FC_OFFLINE_MODE)) {
-			lpfc_printf_vlog(vport, KERN_INFO, LOG_DISCOVERY,
-					 "4110 Issue PLOGI x%x deferred "
-					 "on NPort x%x rpi x%x Data: x%px\n",
-					 ndlp->nlp_defer_did, ndlp->nlp_DID,
-					 ndlp->nlp_rpi, ndlp);
-
-			/* We can only defer 1st PLOGI */
-			if (ndlp->nlp_defer_did == NLP_EVT_NOTHING_PENDING)
-				ndlp->nlp_defer_did = did;
-			return 0;
-		}
+	/* Defer the processing of the issue PLOGI until after the
+	 * outstanding UNREG_RPI mbox command completes, unless we
+	 * are going offline. This logic does not apply for Fabric DIDs
+	 */
+	if ((ndlp->nlp_flag & NLP_UNREG_INP) &&
+	    ((ndlp->nlp_DID & Fabric_DID_MASK) != Fabric_DID_MASK) &&
+	    !(vport->fc_flag & FC_OFFLINE_MODE)) {
+		lpfc_printf_vlog(vport, KERN_INFO, LOG_DISCOVERY,
+				 "4110 Issue PLOGI x%x deferred "
+				 "on NPort x%x rpi x%x Data: x%px\n",
+				 ndlp->nlp_defer_did, ndlp->nlp_DID,
+				 ndlp->nlp_rpi, ndlp);
+
+		/* We can only defer 1st PLOGI */
+		if (ndlp->nlp_defer_did == NLP_EVT_NOTHING_PENDING)
+			ndlp->nlp_defer_did = did;
+		return 0;
 	}
 
-	/* If ndlp is not NULL, we will bump the reference count on it */
 	cmdsize = (sizeof(uint32_t) + sizeof(struct serv_parm));
 	elsiocb = lpfc_prep_els_iocb(vport, 1, cmdsize, retry, ndlp, did,
 				     ELS_CMD_PLOGI);