[PATCH RFC] scsi: qla2xxx: zero default_item last in qla24xx_free_purex_item

[Bryan Gurney <bgurney@redhat.com>]

In order to avoid a null pointer dereference, the vha->default_item
should be set to 0 last if the item pointer passed to the function
matches.

BUG: kernel NULL pointer dereference, address: 0000000000000936
...
RIP: 0010:qla24xx_free_purex_item+0x5e/0x90 [qla2xxx]
...
Call Trace:
 <TASK>
 qla24xx_process_purex_list+0xda/0x110 [qla2xxx]
 qla2x00_do_dpc+0x8ac/0xab0 [qla2xxx]
 ? __pfx_qla2x00_do_dpc+0x10/0x10 [qla2xxx]
 kthread+0xf9/0x240
 ? __pfx_kthread+0x10/0x10
 ret_from_fork+0xf1/0x110
 ? __pfx_kthread+0x10/0x10

Also use a local variable to avoid multiple de-referencing of the item.

Fixes: 6f4b10226b6b ("scsi: qla2xxx: Fix memcpy() field-spanning write issue")
Signed-off-by: Bryan Gurney <bgurney@redhat.com>
---
 drivers/scsi/qla2xxx/qla_os.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/drivers/scsi/qla2xxx/qla_os.c b/drivers/scsi/qla2xxx/qla_os.c
index 98a5c105fdfd..7e28c7e9aa60 100644
--- a/drivers/scsi/qla2xxx/qla_os.c
+++ b/drivers/scsi/qla2xxx/qla_os.c
@@ -6459,9 +6459,11 @@ void qla24xx_process_purex_rdp(struct scsi_qla_host *vha,
 void
 qla24xx_free_purex_item(struct purex_item *item)
 {
-	if (item == &item->vha->default_item) {
-		memset(&item->vha->default_item, 0, sizeof(struct purex_item));
-		memset(&item->vha->__default_item_iocb, 0, QLA_DEFAULT_PAYLOAD_SIZE);
+	scsi_qla_host_t *base_vha = item->vha;
+
+	if (item == &base_vha->default_item) {
+		memset(&base_vha->__default_item_iocb, 0, QLA_DEFAULT_PAYLOAD_SIZE);
+		memset(&base_vha->default_item, 0, sizeof(struct purex_item));
 	} else
 		kfree(item);
 }
-- 
2.51.0