[RESEND][PATCH] scsi: wd719x: fix a missing check on list iterator

[Xiaomeng Tong]

The bug is here:
    if (SCB_out == scb->phys)

The list iterator 'scb' will point to a bogus position containing
HEAD if the list is empty or no element is found. This case must
be checked before any use of the iterator, otherwise it will lead
to a invalid memory access.

To fix this bug, add an check. Use a new variable 'iter' as the
list iterator, while use the old variable 'scb' as a dedicated
pointer to point to the found element.

Cc: stable@xxxxxxxxxxxxxxx
Fixes: 48a3103006631 ("wd719x: Introduce Western Digital WD7193/7197/7296 PCI SCSI card driver")
Signed-off-by: Xiaomeng Tong <xiam0nd.tong@xxxxxxxxx>
---
 drivers/scsi/wd719x.c | 12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

diff --git a/drivers/scsi/wd719x.c b/drivers/scsi/wd719x.c
index 1a7947554581..6087ff4c05da 100644
--- a/drivers/scsi/wd719x.c
+++ b/drivers/scsi/wd719x.c
@@ -684,11 +684,15 @@ static irqreturn_t wd719x_interrupt(int irq, void *dev_id)
 	case WD719X_INT_SPIDERFAILED:
 		/* was the cmd completed a direct or SCB command? */
 		if (regs.bytes.OPC == WD719X_CMD_PROCESS_SCB) {
-			struct wd719x_scb *scb;
-			list_for_each_entry(scb, &wd->active_scbs, list)
-				if (SCB_out == scb->phys)
+			struct wd719x_scb *scb = NULL, *iter;
+
+			list_for_each_entry(iter, &wd->active_scbs, list)
+				if (SCB_out == iter->phys) {
+					scb = iter;
 					break;
-			if (SCB_out == scb->phys)
+				}
+
+			if (scb)
 				wd719x_interrupt_SCB(wd, regs, scb);
 			else
 				dev_err(&wd->pdev->dev, "card returned invalid SCB pointer\n");
-- 
2.17.1