[PATCH xen/stable-2.6.32.x] fix ethtool_get_drvinfo NULL pointer dereference

[Paolo Bonzini <pbonzini@redhat.com>]

Fixes the following crash on "ethtool -i":

BUG: unable to handle kernel NULL pointer dereference at 0000000000000148
IP: [<ffffffff813bcfe2>] ethtool_get_drvinfo+0x106/0x1a5
PGD d8040067 PUD d8041067 PMD 0
Oops: 0000 [#1] SMP
last sysfs file: /sys/devices/pci0000:00/0000:00:1c.0/0000:09:00.0/irq 
...
Call Trace:
[<ffffffff813bd298>] dev_ethtool+0x93/0x1153
[<ffffffff810dd957>] ? __alloc_pages_nodemask+0x122/0x62d
[<ffffffff810dd957>] ? __alloc_pages_nodemask+0x122/0x62d
[<ffffffff811ee21e>] ? avc_has_perm+0x5c/0x6e
[<ffffffff811158ad>] ? try_get_mem_cgroup_from_mm+0x39/0x49 
...
RIP  [<ffffffff813bcfe2>] ethtool_get_drvinfo+0x106/0x1a5 

The backport of 01414802 was incomplete.  This is the patch we are
using in RHEL6.

Reported-by: M A Young <m.a.young@durham.ac.uk>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Cc: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
---
 ethtool.c |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/net/core/ethtool.c b/net/core/ethtool.c
index ff35ce3..8ca3a26 100644
--- a/net/core/ethtool.c
+++ b/net/core/ethtool.c
@@ -211,9 +211,9 @@ static int ethtool_get_drvinfo(struct net_device *dev, void __user *useraddr)
 	} else {
 		/* code path for obsolete hooks */
 
-		if (ops->self_test_count)
+		if (ops && ops->self_test_count)
 			info.testinfo_len = ops->self_test_count(dev);
-		if (ops->get_stats_count)
+		if (ops && ops->get_stats_count)
 			info.n_stats = ops->get_stats_count(dev);
 	}
 	if (ops && ops->get_regs_len)