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From:   Leonardo Bras <leonardo@linux.ibm.com>
To:     netfilter-devel@vger.kernel.org, coreteam@netfilter.org,
        netdev@vger.kernel.org, linux-kernel@vger.kernel.org
Cc:     Leonardo Bras <leonardo@linux.ibm.com>,
        Pablo Neira Ayuso <pablo@netfilter.org>,
        Jozsef Kadlecsik <kadlec@netfilter.org>,
        Florian Westphal <fw@strlen.de>,
        "David S. Miller" <davem@davemloft.net>,
        Alexey Kuznetsov <kuznet@ms2.inr.ac.ru>,
        Hideaki YOSHIFUJI <yoshfuji@linux-ipv6.org>
Subject: [PATCH v2 1/1] netfilter: nf_tables: fib: Drop IPV6 packages if IPv6 is disabled on boot
Date:   Wed, 21 Aug 2019 11:15:06 -0300
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Message-Id: <20190821141505.2394-1-leonardo@linux.ibm.com>
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

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>
---
Changes from v1:
- Move drop logic from nft_fib_inet_eval() to nft_fib6_eval{,_type}
so it can affect other usages of these functions. 

 net/ipv6/netfilter/nft_fib_ipv6.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/net/ipv6/netfilter/nft_fib_ipv6.c b/net/ipv6/netfilter/nft_fib_ipv6.c
index 7ece86afd079..75acc417e2ff 100644
--- a/net/ipv6/netfilter/nft_fib_ipv6.c
+++ b/net/ipv6/netfilter/nft_fib_ipv6.c
@@ -125,6 +125,11 @@ void nft_fib6_eval_type(const struct nft_expr *expr, struct nft_regs *regs,
 	u32 *dest = &regs->data[priv->dreg];
 	struct ipv6hdr *iph, _iph;
 
+	if (!ipv6_mod_enabled()) {
+		regs->verdict.code = NF_DROP;
+		return;
+	}
+
 	iph = skb_header_pointer(pkt->skb, noff, sizeof(_iph), &_iph);
 	if (!iph) {
 		regs->verdict.code = NFT_BREAK;
@@ -150,6 +155,11 @@ void nft_fib6_eval(const struct nft_expr *expr, struct nft_regs *regs,
 	struct rt6_info *rt;
 	int lookup_flags;
 
+	if (!ipv6_mod_enabled()) {
+		regs->verdict.code = NF_DROP;
+		return;
+	}
+
 	if (priv->flags & NFTA_FIB_F_IIF)
 		oif = nft_in(pkt);
 	else if (priv->flags & NFTA_FIB_F_OIF)
-- 
2.20.1