ipv6: Fix OOPS, ip -f inet6 route get fec0::1, linux-2.6.26, ip6_route_output, rt6_fill_node+0x175

Alexey Dobriyan wrote:
> On Thu, Aug 07, 2008 at 07:00:56PM +0200, John Gumb wrote:
>> Scenario: no ipv6 default route set.
> 
>> # ip -f inet6 route get fec0::1
>>
>> BUG: unable to handle kernel NULL pointer dereference at 00000000
>> IP: [<c0369b85>] rt6_fill_node+0x175/0x3b0
>> EIP is at rt6_fill_node+0x175/0x3b0
> 
> 0xffffffff80424dd3 is in rt6_fill_node (net/ipv6/route.c:2191).
> 2186                    } else
> 2187    #endif
> 2188                            NLA_PUT_U32(skb, RTA_IIF, iif);
> 2189            } else if (dst) {
> 2190                    struct in6_addr saddr_buf;
> 2191      ====>         if (ipv6_dev_get_saddr(ip6_dst_idev(&rt->u.dst)->dev,
>					       ^^^^^^^^^^^^^^^^^^^^^^^^
>											NULL
> 
> 2192                                           dst, 0, &saddr_buf) == 0)
> 2193                            NLA_PUT(skb, RTA_PREFSRC, 16, &saddr_buf);
> 2194            }

The commit that changed this can't be reverted easily, but the patch
below works for me.

Fix NULL de-reference in rt6_fill_node() when there's no IPv6 input
device present in the dst entry.

Signed-off-by: Brian Haley <brian.haley@hp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv6/route.c

@@ -2187,8 +2187,9 @@ static int rt6_fill_node(struct sk_buff *skb, struct rt6_info *rt,
 #endif
 			NLA_PUT_U32(skb, RTA_IIF, iif);
 	} else if (dst) {
+		struct inet6_dev *idev = ip6_dst_idev(&rt->u.dst);
 		struct in6_addr saddr_buf;
-		if (ipv6_dev_get_saddr(ip6_dst_idev(&rt->u.dst)->dev,
+		if (ipv6_dev_get_saddr(idev ? idev->dev : NULL,
 				       dst, 0, &saddr_buf) == 0)
 			NLA_PUT(skb, RTA_PREFSRC, 16, &saddr_buf);
 	}