When vmxnet3_rq_create() fails to allocate rq->data_ring.base due to page
allocation failure, subsequent call to vmxnet3_rq_rx_complete() can result in
NULL pointer dereference.

To fix this bug, check not only that rxDataRingUsed is true but also that
adapter->rxdataring_enabled is true before calling memcpy() in
vmxnet3_rq_rx_complete().

[1728352.477993] ethtool: page allocation failure: order:9, mode:0x6000c0(GFP_KERNEL), nodemask=(null),cpuset=/,mems_allowed=0
...
[1728352.478009] Call Trace:
[1728352.478028]  dump_stack+0x41/0x60
[1728352.478035]  warn_alloc.cold.120+0x7b/0x11b
[1728352.478038]  ? _cond_resched+0x15/0x30
[1728352.478042]  ? __alloc_pages_direct_compact+0x15f/0x170
[1728352.478043]  __alloc_pages_slowpath+0xcd3/0xd10
[1728352.478047]  __alloc_pages_nodemask+0x2e2/0x320
[1728352.478049]  __dma_direct_alloc_pages.constprop.25+0x8a/0x120
[1728352.478053]  dma_direct_alloc+0x5a/0x2a0
[1728352.478056]  vmxnet3_rq_create.part.57+0x17c/0x1f0 [vmxnet3]
...
[1728352.478188] vmxnet3 0000:0b:00.0 ens192: rx data ring will be disabled
...
[1728352.515347] BUG: unable to handle kernel NULL pointer dereference at 0000000000000034
...
[1728352.515440] RIP: 0010:memcpy_orig+0x54/0x130
...
[1728352.515655] Call Trace:
[1728352.515665]  <IRQ>
[1728352.515672]  vmxnet3_rq_rx_complete+0x419/0xef0 [vmxnet3]
[1728352.515690]  vmxnet3_poll_rx_only+0x31/0xa0 [vmxnet3]
...
Signed-off-by: Seiji Nishikawa <snishika@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>