[PATCH 5.5 347/399] rtw88: fix potential NULL skb access in TX ISR

[Greg Kroah-Hartman]

From: Yan-Hsuan Chuang <yhchuang@xxxxxxxxxxx>

[ Upstream commit f4f84ff8377d4cedf18317747bc407b2cf657d0f ]

Sometimes the TX queue may be empty and we could possible
dequeue a NULL pointer, crash the kernel. If the skb is NULL
then there is nothing to do, just leave the ISR.

And the TX queue should not be empty here, so print an error
to see if there is anything wrong for DMA ring.

Fixes: e3037485c68e ("rtw88: new Realtek 802.11ac driver")
Signed-off-by: Yan-Hsuan Chuang <yhchuang@xxxxxxxxxxx>
Signed-off-by: Kalle Valo <kvalo@xxxxxxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 drivers/net/wireless/realtek/rtw88/pci.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/drivers/net/wireless/realtek/rtw88/pci.c b/drivers/net/wireless/realtek/rtw88/pci.c
index a58e8276a41a3..a6746b5a9ff2d 100644
--- a/drivers/net/wireless/realtek/rtw88/pci.c
+++ b/drivers/net/wireless/realtek/rtw88/pci.c
@@ -832,6 +832,11 @@ static void rtw_pci_tx_isr(struct rtw_dev *rtwdev, struct rtw_pci *rtwpci,
 
 	while (count--) {
 		skb = skb_dequeue(&ring->queue);
+		if (!skb) {
+			rtw_err(rtwdev, "failed to dequeue %d skb TX queue %d, BD=0x%08x, rp %d -> %d\n",
+				count, hw_queue, bd_idx, ring->r.rp, cur_rp);
+			break;
+		}
 		tx_data = rtw_pci_get_tx_data(skb);
 		pci_unmap_single(rtwpci->pdev, tx_data->dma, skb->len,
 				 PCI_DMA_TODEVICE);
-- 
2.20.1