net: wwan: t7xx: Fix napi rx poll issue

When driver handles the napi rx polling requests, the netdev might
have been released by the dellink logic triggered by the disconnect
operation on user plane. However, in the logic of processing skb in
polling, an invalid netdev is still being used, which causes a panic.

BUG: kernel NULL pointer dereference, address: 00000000000000f1
Oops: 0000 [kernel-patches#1] PREEMPT SMP NOPTI
RIP: 0010:dev_gro_receive+0x3a/0x620
[...]
Call Trace:
 <IRQ>
 ? __die_body+0x68/0xb0
 ? page_fault_oops+0x379/0x3e0
 ? exc_page_fault+0x4f/0xa0
 ? asm_exc_page_fault+0x22/0x30
 ? __pfx_t7xx_ccmni_recv_skb+0x10/0x10 [mtk_t7xx (HASH:1400 7)]
 ? dev_gro_receive+0x3a/0x620
 napi_gro_receive+0xad/0x170
 t7xx_ccmni_recv_skb+0x48/0x70 [mtk_t7xx (HASH:1400 7)]
 t7xx_dpmaif_napi_rx_poll+0x590/0x800 [mtk_t7xx (HASH:1400 7)]
 net_rx_action+0x103/0x470
 irq_exit_rcu+0x13a/0x310
 sysvec_apic_timer_interrupt+0x56/0x90
 </IRQ>

Fixes: 5545b7b ("net: wwan: t7xx: Add NAPI support")
Signed-off-by: Jinjian Song <[email protected]>
Signed-off-by: NipaLocal <nipa@local>

Author: Jinjian-Song

drivers/net/wwan/t7xx/t7xx_netdev.c

@@ -302,7 +302,7 @@ static int t7xx_ccmni_wwan_newlink(void *ctxt, struct net_device *dev, u32 if_id
 	ccmni->ctlb = ctlb;
 	ccmni->dev = dev;
 	atomic_set(&ccmni->usage, 0);
-	ctlb->ccmni_inst[if_id] = ccmni;
+	WRITE_ONCE(ctlb->ccmni_inst[if_id], ccmni);
 
 	ret = register_netdevice(dev);
 	if (ret)
@@ -324,6 +324,7 @@ static void t7xx_ccmni_wwan_dellink(void *ctxt, struct net_device *dev, struct l
 	if (WARN_ON(ctlb->ccmni_inst[if_id] != ccmni))
 		return;
 
+	WRITE_ONCE(ctlb->ccmni_inst[if_id], NULL);
 	unregister_netdevice(dev);
 }
 
@@ -419,7 +420,7 @@ static void t7xx_ccmni_recv_skb(struct t7xx_ccmni_ctrl *ccmni_ctlb, struct sk_bu
 
 	skb_cb = T7XX_SKB_CB(skb);
 	netif_id = skb_cb->netif_idx;
-	ccmni = ccmni_ctlb->ccmni_inst[netif_id];
+	ccmni = READ_ONCE(ccmni_ctlb->ccmni_inst[netif_id]);
 	if (!ccmni) {
 		dev_kfree_skb(skb);
 		return;
@@ -441,7 +442,7 @@ static void t7xx_ccmni_recv_skb(struct t7xx_ccmni_ctrl *ccmni_ctlb, struct sk_bu
 
 static void t7xx_ccmni_queue_tx_irq_notify(struct t7xx_ccmni_ctrl *ctlb, int qno)
 {
-	struct t7xx_ccmni *ccmni = ctlb->ccmni_inst[0];
+	struct t7xx_ccmni *ccmni = READ_ONCE(ctlb->ccmni_inst[0]);
 	struct netdev_queue *net_queue;
 
 	if (netif_running(ccmni->dev) && atomic_read(&ccmni->usage) > 0) {
@@ -453,7 +454,7 @@ static void t7xx_ccmni_queue_tx_irq_notify(struct t7xx_ccmni_ctrl *ctlb, int qno
 
 static void t7xx_ccmni_queue_tx_full_notify(struct t7xx_ccmni_ctrl *ctlb, int qno)
 {
-	struct t7xx_ccmni *ccmni = ctlb->ccmni_inst[0];
+	struct t7xx_ccmni *ccmni = READ_ONCE(ctlb->ccmni_inst[0]);
 	struct netdev_queue *net_queue;
 
 	if (atomic_read(&ccmni->usage) > 0) {
@@ -471,7 +472,7 @@ static void t7xx_ccmni_queue_state_notify(struct t7xx_pci_dev *t7xx_dev,
 	if (ctlb->md_sta != MD_STATE_READY)
 		return;
 
-	if (!ctlb->ccmni_inst[0]) {
+	if (!READ_ONCE(ctlb->ccmni_inst[0])) {
 		dev_warn(&t7xx_dev->pdev->dev, "No netdev registered yet\n");
 		return;
 	}