[PATCH 4.9 35/63] sit: check if IPv6 enabled before calling ip6_err_gen_icmpv6_unreach()

[Greg Kroah-Hartman]

4.9-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Hangbin Liu <liuhangbin@xxxxxxxxx>

[ Upstream commit 173656accaf583698bac3f9e269884ba60d51ef4 ]

If we disabled IPv6 from the kernel command line (ipv6.disable=1), we should
not call ip6_err_gen_icmpv6_unreach(). This:

  ip link add sit1 type sit local 192.0.2.1 remote 192.0.2.2 ttl 1
  ip link set sit1 up
  ip addr add 198.51.100.1/24 dev sit1
  ping 198.51.100.2

if IPv6 is disabled at boot time, will crash the kernel.

v2: there's no need to use in6_dev_get(), use __in6_dev_get() instead,
    as we only need to check that idev exists and we are under
    rcu_read_lock() (from netif_receive_skb_internal()).

Reported-by: Jianlin Shi <jishi@xxxxxxxxxx>
Fixes: ca15a078bd90 ("sit: generate icmpv6 error when receiving icmpv4 error")
Cc: Oussama Ghorbel <ghorbel@xxxxxxxxxxxxxxxx>
Signed-off-by: Hangbin Liu <liuhangbin@xxxxxxxxx>
Reviewed-by: Stefano Brivio <sbrivio@xxxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 net/ipv6/sit.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

--- a/net/ipv6/sit.c
+++ b/net/ipv6/sit.c
@@ -540,7 +540,8 @@ static int ipip6_err(struct sk_buff *skb
 	}
 
 	err = 0;
-	if (!ip6_err_gen_icmpv6_unreach(skb, iph->ihl * 4, type, data_len))
+	if (__in6_dev_get(skb->dev) &&
+	    !ip6_err_gen_icmpv6_unreach(skb, iph->ihl * 4, type, data_len))
 		goto out;
 
 	if (t->parms.iph.daddr == 0)