ath10k: protect src_ring state with ce_lock in tx_sg()

It was possible to read invalid state of CE ring
buffer indexes. This could lead to scatter-gather
transfer failure in mid-way and crash firmware
later by leaving garbage data on the ring.

Reported-By: Avery Pennarun <apenwarr@gmail.com>
Signed-off-by: Michal Kazior <michal.kazior@tieto.com>
Signed-off-by: Kalle Valo <kvalo@qca.qualcomm.com>

drivers/net/wireless/ath/ath10k/pci.c

@@ -762,13 +762,17 @@ static int ath10k_pci_hif_tx_sg(struct ath10k *ar, u8 pipe_id,
 	struct ath10k_pci_pipe *pci_pipe = &ar_pci->pipe_info[pipe_id];
 	struct ath10k_ce_pipe *ce_pipe = pci_pipe->ce_hdl;
 	struct ath10k_ce_ring *src_ring = ce_pipe->src_ring;
-	unsigned int nentries_mask = src_ring->nentries_mask;
-	unsigned int sw_index = src_ring->sw_index;
-	unsigned int write_index = src_ring->write_index;
+	unsigned int nentries_mask;
+	unsigned int sw_index;
+	unsigned int write_index;
 	int err, i;
 
 	spin_lock_bh(&ar_pci->ce_lock);
 
+	nentries_mask = src_ring->nentries_mask;
+	sw_index = src_ring->sw_index;
+	write_index = src_ring->write_index;
+
 	if (unlikely(CE_RING_DELTA(nentries_mask,
 				   write_index, sw_index - 1) < n_items)) {
 		err = -ENOBUFS;