[PATCH 1/1] netfilter: nf_tables: fib: Drop IPV6 packages if IPv6 is disabled on boot

[Leonardo Bras <leonardo@linux.ibm.com>]

If IPv6 is disabled on boot (ipv6.disable=1), but nft_fib_inet ends up
dealing with a IPv6 package, it causes a kernel panic in
fib6_node_lookup_1(), crashing in bad_page_fault.

The panic is caused by trying to deference a very low address (0x38
in ppc64le), due to ipv6.fib6_main_tbl = NULL.
BUG: Kernel NULL pointer dereference at 0x00000038

Fix this behavior by dropping IPv6 packages if !ipv6_mod_enabled().

Signed-off-by: Leonardo Bras <leonardo@linux.ibm.com>
---
 net/netfilter/nft_fib_inet.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/net/netfilter/nft_fib_inet.c b/net/netfilter/nft_fib_inet.c
index 465432e0531b..0017afab3c51 100644
--- a/net/netfilter/nft_fib_inet.c
+++ b/net/netfilter/nft_fib_inet.c
@@ -2,6 +2,7 @@
 
 #include <linux/kernel.h>
 #include <linux/init.h>
+#include <linux/ipv6.h>
 #include <linux/module.h>
 #include <linux/netlink.h>
 #include <linux/netfilter.h>
@@ -28,6 +29,8 @@ static void nft_fib_inet_eval(const struct nft_expr *expr,
 		}
 		break;
 	case NFPROTO_IPV6:
+		if (!ipv6_mod_enabled())
+			break;
 		switch (priv->result) {
 		case NFT_FIB_RESULT_OIF:
 		case NFT_FIB_RESULT_OIFNAME:
-- 
2.20.1