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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,
        Lorenzo Bianconi <lorenzo.bianconi@redhat.com>,
        "David S. Miller" <davem@davemloft.net>
Subject: [PATCH 4.4 102/124] ipv4: remove BUG_ON() from fib_compute_spec_dst
Date:   Sat,  4 Aug 2018 11:01:31 +0200
Message-Id: <20180804082706.290364095@linuxfoundation.org>
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4.4-stable review patch.  If anyone has any objections, please let me know.

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

From: Lorenzo Bianconi <lorenzo.bianconi@redhat.com>

[ Upstream commit 9fc12023d6f51551d6ca9ed7e02ecc19d79caf17 ]

Remove BUG_ON() from fib_compute_spec_dst routine and check
in_dev pointer during flowi4 data structure initialization.
fib_compute_spec_dst routine can be run concurrently with device removal
where ip_ptr net_device pointer is set to NULL. This can happen
if userspace enables pkt info on UDP rx socket and the device
is removed while traffic is flowing

Fixes: 35ebf65e851c ("ipv4: Create and use fib_compute_spec_dst() helper")
Signed-off-by: Lorenzo Bianconi <lorenzo.bianconi@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 net/ipv4/fib_frontend.c |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

--- a/net/ipv4/fib_frontend.c
+++ b/net/ipv4/fib_frontend.c
@@ -289,19 +289,19 @@ __be32 fib_compute_spec_dst(struct sk_bu
 		return ip_hdr(skb)->daddr;
 
 	in_dev = __in_dev_get_rcu(dev);
-	BUG_ON(!in_dev);
 
 	net = dev_net(dev);
 
 	scope = RT_SCOPE_UNIVERSE;
 	if (!ipv4_is_zeronet(ip_hdr(skb)->saddr)) {
+		bool vmark = in_dev && IN_DEV_SRC_VMARK(in_dev);
 		struct flowi4 fl4 = {
 			.flowi4_iif = LOOPBACK_IFINDEX,
 			.flowi4_oif = l3mdev_master_ifindex_rcu(dev),
 			.daddr = ip_hdr(skb)->saddr,
 			.flowi4_tos = RT_TOS(ip_hdr(skb)->tos),
 			.flowi4_scope = scope,
-			.flowi4_mark = IN_DEV_SRC_VMARK(in_dev) ? skb->mark : 0,
+			.flowi4_mark = vmark ? skb->mark : 0,
 		};
 		if (!fib_lookup(net, &fl4, &res, 0))
 			return FIB_RES_PREFSRC(net, res);