RDMA/irdma: avoid invalid read in irdma_net_event

irdma_net_event() should not dereference anything from "neigh" (alias
"ptr") until it has checked that the event is NETEVENT_NEIGH_UPDATE.
Other events come with different structures pointed to by "ptr" and they
may be smaller than struct neighbour.

Move the read of neigh->dev under the NETEVENT_NEIGH_UPDATE case.

The bug is mostly harmless, but it triggers KASAN on debug kernels:

 BUG: KASAN: stack-out-of-bounds in irdma_net_event+0x32e/0x3b0 [irdma]
 Read of size 8 at addr ffffc900075e07f0 by task kworker/27:2/542554

 CPU: 27 PID: 542554 Comm: kworker/27:2 Kdump: loaded Not tainted 5.14.0-630.el9.x86_64+debug #1
 Hardware name: [...]
 Workqueue: events rt6_probe_deferred
 Call Trace:
  <IRQ>
  dump_stack_lvl+0x60/0xb0
  print_address_description.constprop.0+0x2c/0x3f0
  print_report+0xb4/0x270
  kasan_report+0x92/0xc0
  irdma_net_event+0x32e/0x3b0 [irdma]
  notifier_call_chain+0x9e/0x180
  atomic_notifier_call_chain+0x5c/0x110
  rt6_do_redirect+0xb91/0x1080
  tcp_v6_err+0xe9b/0x13e0
  icmpv6_notify+0x2b2/0x630
  ndisc_redirect_rcv+0x328/0x530
  icmpv6_rcv+0xc16/0x1360
  ip6_protocol_deliver_rcu+0xb84/0x12e0
  ip6_input_finish+0x117/0x240
  ip6_input+0xc4/0x370
  ipv6_rcv+0x420/0x7d0
  __netif_receive_skb_one_core+0x118/0x1b0
  process_backlog+0xd1/0x5d0
  __napi_poll.constprop.0+0xa3/0x440
  net_rx_action+0x78a/0xba0
  handle_softirqs+0x2d4/0x9c0
  do_softirq+0xad/0xe0
  </IRQ>

Fixes: 915cc7a ("RDMA/irdma: Add miscellaneous utility definitions")
Link: https://patch.msgid.link/r/[email protected]
Signed-off-by: Michal Schmidt <[email protected]>
Signed-off-by: Jason Gunthorpe <[email protected]>

Author: michich

drivers/infiniband/hw/irdma/utils.c

@@ -251,7 +251,7 @@ int irdma_net_event(struct notifier_block *notifier, unsigned long event,
 		    void *ptr)
 {
 	struct neighbour *neigh = ptr;
-	struct net_device *real_dev, *netdev = (struct net_device *)neigh->dev;
+	struct net_device *real_dev, *netdev;
 	struct irdma_device *iwdev;
 	struct ib_device *ibdev;
 	__be32 *p;
@@ -260,6 +260,7 @@ int irdma_net_event(struct notifier_block *notifier, unsigned long event,
 
 	switch (event) {
 	case NETEVENT_NEIGH_UPDATE:
+		netdev = neigh->dev;
 		real_dev = rdma_vlan_dev_real_dev(netdev);
 		if (!real_dev)
 			real_dev = netdev;