qeth: Fix crash on initial MTU size change

When the initial MTU size is changed prior to any activity on the device
(e.g. by attaching a z/VM vNIC already configured in Linux to a guestLAN),
we call dev_kfree_skb_irq(NULL) which results in a kernel panic.
Adding a proper check for NULL pointers to address this issue.

Signed-off-by: Stefan Raspl <raspl@linux.vnet.ibm.com>
Signed-off-by: Frank Blaschka <blaschka@linux.vnet.ibm.com>
Reviewed-by: Ursula Braun <braunu@de.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 4 insertions, 2 deletions

diff --git a/drivers/s390/net/qeth_core_main.c b/drivers/s390/net/qeth_core_main.c
index d7d036bf8715..e4ca70475190 100644
--- a/drivers/s390/net/qeth_core_main.c
+++ b/drivers/s390/net/qeth_core_main.c
@@ -1282,8 +1282,10 @@ static void qeth_free_qdio_buffers(struct qeth_card *card)
 
         qeth_free_cq(card);
         cancel_delayed_work_sync(&card->buffer_reclaim_work);
-        for (j = 0; j < QDIO_MAX_BUFFERS_PER_Q; ++j)
-                dev_kfree_skb_any(card->qdio.in_q->bufs[j].rx_skb);
+        for (j = 0; j < QDIO_MAX_BUFFERS_PER_Q; ++j) {
+                if (card->qdio.in_q->bufs[j].rx_skb)
+                        dev_kfree_skb_any(card->qdio.in_q->bufs[j].rx_skb);
+        }
         kfree(card->qdio.in_q);
         card->qdio.in_q = NULL;
         /* inbound buffer pool */