[PATCH] cxgbit: check skb dequeue result in cxgbit_send_tx_flowc_wr()

[Denis Plotnikov]

Skb dequeuing may end up with returning NULL if a queue is empty,
which, in turn, may end up with further null pointer dereference.

Fix it by checking the return value of skb dequeuing end returning
before the pointer dereference.

Found by Linux Verification Center(linuxtesting.org) with SVACE.

Fixes: 9730ffcb8957 ("cxgbit: add files for cxgbit.ko")
Signed-off-by: Denis Plotnikov <den-plotnikov@xxxxxxxxxxxxxx>
---
 drivers/target/iscsi/cxgbit/cxgbit_cm.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/drivers/target/iscsi/cxgbit/cxgbit_cm.c b/drivers/target/iscsi/cxgbit/cxgbit_cm.c
index d9204c590d9ab..426a5c795fd93 100644
--- a/drivers/target/iscsi/cxgbit/cxgbit_cm.c
+++ b/drivers/target/iscsi/cxgbit/cxgbit_cm.c
@@ -1424,10 +1424,13 @@ u32 cxgbit_send_tx_flowc_wr(struct cxgbit_sock *csk)
 #ifdef CONFIG_CHELSIO_T4_DCB
 	u16 vlan = ((struct l2t_entry *)csk->l2t)->vlan;
 #endif
+	skb = __skb_dequeue(&csk->skbq);
+
+	if (!skb)
+		return 0;
 
 	flowclen16 = cxgbit_tx_flowc_wr_credits(csk, &nparams, &flowclen);
 
-	skb = __skb_dequeue(&csk->skbq);
 	flowc = __skb_put_zero(skb, flowclen);
 
 	flowc->op_to_nparams = cpu_to_be32(FW_WR_OP_V(FW_FLOWC_WR) |
-- 
2.25.1