[PATCH net] net: bcmgenet: fix NULL dereference in set_coalesce before first open

The Rx ring priv and index are only set in bcmgenet_init_rx_ring(),
which runs at open. Setting the Rx coalescing parameters on an interface
that was never opened, e.g. "ethtool -C eth0 rx-usecs 50", dereferences
a NULL ring->priv. The oops happens with RTNL held, so networking
stays stuck until a reboot:

  Unable to handle kernel paging request at virtual address 0000000000002788
  pc : bcmgenet_set_rx_coalesce.isra.0+0x10/0x88
  lr : bcmgenet_set_coalesce+0xe8/0x180
  Call trace:
   bcmgenet_set_rx_coalesce.isra.0+0x10/0x88 (P)
   __ethnl_set_coalesce.isra.0+0x490/0x570
   ethnl_set_coalesce+0x48/0xc0
   ethnl_default_set_doit+0xf4/0x230
   genl_family_rcv_msg_doit+0xe8/0x160
   genl_rcv_msg+0x220/0x2a0
   netlink_rcv_skb+0x68/0x140
   genl_rcv+0x40/0x60
   netlink_unicast+0x338/0x3c0
   netlink_sendmsg+0x19c/0x3f8
   __sock_sendmsg+0x64/0xc0
   __sys_sendto+0x124/0x198
   __arm64_sys_sendto+0x30/0x48

Set priv and index at probe. Writing the registers while the interface
is down is harmless because open resets the MAC and
bcmgenet_init_rx_coalesce() reapplies the stored values.

Fixes: 9f4ca05827a2 ("net: bcmgenet: Add support for adaptive RX coalescing")
Signed-off-by: Nicolai Buchwitz <nb@tipi-net.de>
---
 drivers/net/ethernet/broadcom/genet/bcmgenet.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/drivers/net/ethernet/broadcom/genet/bcmgenet.c b/drivers/net/ethernet/broadcom/genet/bcmgenet.c
index f725d26e6020..e8908916558b 100644
--- a/drivers/net/ethernet/broadcom/genet/bcmgenet.c
+++ b/drivers/net/ethernet/broadcom/genet/bcmgenet.c

@@ -4151,8 +4151,11 @@ static int bcmgenet_probe(struct platform_device *pdev)
 	netif_set_real_num_rx_queues(priv->dev, priv->hw_params->rx_queues + 1);
 
 	/* Set default coalescing parameters */
-	for (i = 0; i <= priv->hw_params->rx_queues; i++)
+	for (i = 0; i <= priv->hw_params->rx_queues; i++) {
+		priv->rx_rings[i].priv = priv;
+		priv->rx_rings[i].index = i;
 		priv->rx_rings[i].rx_max_coalesced_frames = 1;
+	}
 
 	/* Initialize u64 stats seq counter for 32bit machines */
 	for (i = 0; i <= GENET_MAX_MQ_CNT; i++) {

-- 
2.53.0