[PATCH 3.16 299/366] ipv4: remove BUG_ON() from fib_compute_spec_dst

[Ben Hutchings]

3.16.61-rc1 review patch.  If anyone has any objections, please let me know.

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

From: Lorenzo Bianconi <lorenzo.bianconi@xxxxxxxxxx>

commit 9fc12023d6f51551d6ca9ed7e02ecc19d79caf17 upstream.

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@xxxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
[bwh: Backported to 3.16: adjust context]
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
--- a/net/ipv4/fib_frontend.c
+++ b/net/ipv4/fib_frontend.c
@@ -209,19 +209,20 @@ __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);
+
 		fl4.flowi4_oif = 0;
 		fl4.flowi4_iif = LOOPBACK_IFINDEX;
 		fl4.daddr = ip_hdr(skb)->saddr;
 		fl4.saddr = 0;
 		fl4.flowi4_tos = RT_TOS(ip_hdr(skb)->tos);
 		fl4.flowi4_scope = scope;
-		fl4.flowi4_mark = IN_DEV_SRC_VMARK(in_dev) ? skb->mark : 0;
+		fl4.flowi4_mark = vmark ? skb->mark : 0;
 		if (!fib_lookup(net, &fl4, &res))
 			return FIB_RES_PREFSRC(net, res);
 	} else {