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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, Jianlin Shi <jishi@redhat.com>,
        Oussama Ghorbel <ghorbel@pivasoftware.com>,
        Hangbin Liu <liuhangbin@gmail.com>,
        Stefano Brivio <sbrivio@redhat.com>,
        "David S. Miller" <davem@davemloft.net>
Subject: [PATCH 4.20 139/183] sit: check if IPv6 enabled before calling ip6_err_gen_icmpv6_unreach()
Date:   Mon, 25 Feb 2019 22:11:52 +0100
Message-Id: <20190225195118.311902893@linuxfoundation.org>
In-Reply-To: <20190225195054.748060397@linuxfoundation.org>
References: <20190225195054.748060397@linuxfoundation.org>
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4.20-stable review patch.  If anyone has any objections, please let me know.

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

From: Hangbin Liu <liuhangbin@gmail.com>

[ 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@redhat.com>
Fixes: ca15a078bd90 ("sit: generate icmpv6 error when receiving icmpv4 error")
Cc: Oussama Ghorbel <ghorbel@pivasoftware.com>
Signed-off-by: Hangbin Liu <liuhangbin@gmail.com>
Reviewed-by: Stefano Brivio <sbrivio@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 net/ipv6/sit.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

--- a/net/ipv6/sit.c
+++ b/net/ipv6/sit.c
@@ -546,7 +546,8 @@ 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)