[PATCH v2 11/20] scsi: ibmvfc: fix UAF and hang in ibmvfc_cancel_all_mq() on send failure

[Tyrel Datwyler <tyreld@linux.ibm.com>]

ibmvfc_cancel_all_mq() discards the return value of ibmvfc_send_event().
When ibmvfc_send_event() fails due to H_CLOSED it internally frees the
event before returning SCSI_MLQUEUE_HOST_BUSY. The caller then performs
list_add_tail() on the freed event — a use-after-free — and subsequently
blocks indefinitely on wait_for_completion(&evt->comp) for a completion
that will never arrive.

Fix by capturing the return value. On failure, drop the locks, log the
error (consistent with ibmvfc_cancel_all_sq()), drain and free any
cancel events already queued from earlier loop iterations, then return 0.
Returning 0 on send failure is correct: when the adapter closes the CRQ
the firmware delivers a transport event through ibmvfc_handle_crq() which
completes all outstanding commands, so the error recovery caller will
naturally see them return.

Fixes: 9c2aa65000f6 ("ibmvfc: don't call locked done variant for MADs on send failure")
Signed-off-by: Tyrel Datwyler <tyreld@linux.ibm.com>
---
 drivers/scsi/ibmvscsi/ibmvfc-core.c | 14 +++++++++++++-
 1 file changed, 13 insertions(+), 1 deletion(-)

diff --git a/drivers/scsi/ibmvscsi/ibmvfc-core.c b/drivers/scsi/ibmvscsi/ibmvfc-core.c
index 623fff503040..080312ff0a93 100644
--- a/drivers/scsi/ibmvscsi/ibmvfc-core.c
+++ b/drivers/scsi/ibmvscsi/ibmvfc-core.c
@@ -2696,6 +2696,7 @@ static int ibmvfc_cancel_all_mq(struct scsi_device *sdev, int type)
 	unsigned long flags;
 	int num_hwq, i;
 	int fail = 0;
+	int rc;
 	LIST_HEAD(cancelq);
 	u16 status;
 
@@ -2722,7 +2723,18 @@ static int ibmvfc_cancel_all_mq(struct scsi_device *sdev, int type)
 				return -ENOMEM;
 			}
 			evt->sync_iu = &queues[i].cancel_rsp;
-			ibmvfc_send_event(evt, vhost, default_timeout);
+			rc = ibmvfc_send_event(evt, vhost, default_timeout);
+			if (rc) {
+				spin_unlock(queues[i].q_lock);
+				spin_unlock_irqrestore(&vhost->host->host_lock, flags);
+				sdev_printk(KERN_ERR, sdev, "Failed to send cancel event. rc=%d\n", rc);
+				list_for_each_entry_safe(evt, temp, &cancelq, cancel) {
+					wait_for_completion(&evt->comp);
+					list_del(&evt->cancel);
+					ibmvfc_free_event(evt);
+				}
+				return 0;
+			}
 			list_add_tail(&evt->cancel, &cancelq);
 		}
 
-- 
2.55.0