inet: frag: Always orphan skbs inside ip_defrag()

Later parts of the stack (including fragmentation) expect that there is
never a socket attached to frag in a frag_list, however this invariant
was not enforced on all defrag paths. This could lead to the
BUG_ON(skb->sk) during ip_do_fragment(), as per the call stack at the
end of this commit message.

While the call could be added to openvswitch to fix this particular
error, the head and tail of the frags list are already orphaned
indirectly inside ip_defrag(), so it seems like the remaining fragments
should all be orphaned in all circumstances.

kernel BUG at net/ipv4/ip_output.c:586!
[...]
Call Trace:
 <IRQ>
 [<ffffffffa0205270>] ? do_output.isra.29+0x1b0/0x1b0 [openvswitch]
 [<ffffffffa02167a7>] ovs_fragment+0xcc/0x214 [openvswitch]
 [<ffffffff81667830>] ? dst_discard_out+0x20/0x20
 [<ffffffff81667810>] ? dst_ifdown+0x80/0x80
 [<ffffffffa0212072>] ? find_bucket.isra.2+0x62/0x70 [openvswitch]
 [<ffffffff810e0ba5>] ? mod_timer_pending+0x65/0x210
 [<ffffffff810b732b>] ? __lock_acquire+0x3db/0x1b90
 [<ffffffffa03205a2>] ? nf_conntrack_in+0x252/0x500 [nf_conntrack]
 [<ffffffff810b63c4>] ? __lock_is_held+0x54/0x70
 [<ffffffffa02051a3>] do_output.isra.29+0xe3/0x1b0 [openvswitch]
 [<ffffffffa0206411>] do_execute_actions+0xe11/0x11f0 [openvswitch]
 [<ffffffff810b63c4>] ? __lock_is_held+0x54/0x70
 [<ffffffffa0206822>] ovs_execute_actions+0x32/0xd0 [openvswitch]
 [<ffffffffa020b505>] ovs_dp_process_packet+0x85/0x140 [openvswitch]
 [<ffffffff810b63c4>] ? __lock_is_held+0x54/0x70
 [<ffffffffa02068a2>] ovs_execute_actions+0xb2/0xd0 [openvswitch]
 [<ffffffffa020b505>] ovs_dp_process_packet+0x85/0x140 [openvswitch]
 [<ffffffffa0215019>] ? ovs_ct_get_labels+0x49/0x80 [openvswitch]
 [<ffffffffa0213a1d>] ovs_vport_receive+0x5d/0xa0 [openvswitch]
 [<ffffffff810b732b>] ? __lock_acquire+0x3db/0x1b90
 [<ffffffff810b732b>] ? __lock_acquire+0x3db/0x1b90
 [<ffffffff810b732b>] ? __lock_acquire+0x3db/0x1b90
 [<ffffffffa0214895>] ? internal_dev_xmit+0x5/0x140 [openvswitch]
 [<ffffffffa02148fc>] internal_dev_xmit+0x6c/0x140 [openvswitch]
 [<ffffffffa0214895>] ? internal_dev_xmit+0x5/0x140 [openvswitch]
 [<ffffffff81660299>] dev_hard_start_xmit+0x2b9/0x5e0
 [<ffffffff8165fc21>] ? netif_skb_features+0xd1/0x1f0
 [<ffffffff81660f20>] __dev_queue_xmit+0x800/0x930
 [<ffffffff81660770>] ? __dev_queue_xmit+0x50/0x930
 [<ffffffff810b53f1>] ? mark_held_locks+0x71/0x90
 [<ffffffff81669876>] ? neigh_resolve_output+0x106/0x220
 [<ffffffff81661060>] dev_queue_xmit+0x10/0x20
 [<ffffffff816698e8>] neigh_resolve_output+0x178/0x220
 [<ffffffff816a8e6f>] ? ip_finish_output2+0x1ff/0x590
 [<ffffffff816a8e6f>] ip_finish_output2+0x1ff/0x590
 [<ffffffff816a8cee>] ? ip_finish_output2+0x7e/0x590
 [<ffffffff816a9a31>] ip_do_fragment+0x831/0x8a0
 [<ffffffff816a8c70>] ? ip_copy_metadata+0x1b0/0x1b0
 [<ffffffff816a9ae3>] ip_fragment.constprop.49+0x43/0x80
 [<ffffffff816a9c9c>] ip_finish_output+0x17c/0x340
 [<ffffffff8169a6f4>] ? nf_hook_slow+0xe4/0x190
 [<ffffffff816ab4c0>] ip_output+0x70/0x110
 [<ffffffff816a9b20>] ? ip_fragment.constprop.49+0x80/0x80
 [<ffffffff816aa9f9>] ip_local_out+0x39/0x70
 [<ffffffff816abf89>] ip_send_skb+0x19/0x40
 [<ffffffff816abfe3>] ip_push_pending_frames+0x33/0x40
 [<ffffffff816df21a>] icmp_push_reply+0xea/0x120
 [<ffffffff816df93d>] icmp_reply.constprop.23+0x1ed/0x230
 [<ffffffff816df9ce>] icmp_echo.part.21+0x4e/0x50
 [<ffffffff810b63c4>] ? __lock_is_held+0x54/0x70
 [<ffffffff810d5f9e>] ? rcu_read_lock_held+0x5e/0x70
 [<ffffffff816dfa06>] icmp_echo+0x36/0x70
 [<ffffffff816e0d11>] icmp_rcv+0x271/0x450
 [<ffffffff816a4ca7>] ip_local_deliver_finish+0x127/0x3a0
 [<ffffffff816a4bc1>] ? ip_local_deliver_finish+0x41/0x3a0
 [<ffffffff816a5160>] ip_local_deliver+0x60/0xd0
 [<ffffffff816a4b80>] ? ip_rcv_finish+0x560/0x560
 [<ffffffff816a46fd>] ip_rcv_finish+0xdd/0x560
 [<ffffffff816a5453>] ip_rcv+0x283/0x3e0
 [<ffffffff810b6302>] ? match_held_lock+0x192/0x200
 [<ffffffff816a4620>] ? inet_del_offload+0x40/0x40
 [<ffffffff8165d062>] __netif_receive_skb_core+0x392/0xae0
 [<ffffffff8165e68e>] ? process_backlog+0x8e/0x230
 [<ffffffff810b53f1>] ? mark_held_locks+0x71/0x90
 [<ffffffff8165d7c8>] __netif_receive_skb+0x18/0x60
 [<ffffffff8165e678>] process_backlog+0x78/0x230
 [<ffffffff8165e6dd>] ? process_backlog+0xdd/0x230
 [<ffffffff8165e355>] net_rx_action+0x155/0x400
 [<ffffffff8106b48c>] __do_softirq+0xcc/0x420
 [<ffffffff816a8e87>] ? ip_finish_output2+0x217/0x590
 [<ffffffff8178e78c>] do_softirq_own_stack+0x1c/0x30
 <EOI>
 [<ffffffff8106b88e>] do_softirq+0x4e/0x60
 [<ffffffff8106b948>] __local_bh_enable_ip+0xa8/0xb0
 [<ffffffff816a8eb0>] ip_finish_output2+0x240/0x590
 [<ffffffff816a9a31>] ? ip_do_fragment+0x831/0x8a0
 [<ffffffff816a9a31>] ip_do_fragment+0x831/0x8a0
 [<ffffffff816a8c70>] ? ip_copy_metadata+0x1b0/0x1b0
 [<ffffffff816a9ae3>] ip_fragment.constprop.49+0x43/0x80
 [<ffffffff816a9c9c>] ip_finish_output+0x17c/0x340
 [<ffffffff8169a6f4>] ? nf_hook_slow+0xe4/0x190
 [<ffffffff816ab4c0>] ip_output+0x70/0x110
 [<ffffffff816a9b20>] ? ip_fragment.constprop.49+0x80/0x80
 [<ffffffff816aa9f9>] ip_local_out+0x39/0x70
 [<ffffffff816abf89>] ip_send_skb+0x19/0x40
 [<ffffffff816abfe3>] ip_push_pending_frames+0x33/0x40
 [<ffffffff816d55d3>] raw_sendmsg+0x7d3/0xc30
 [<ffffffff810b732b>] ? __lock_acquire+0x3db/0x1b90
 [<ffffffff816e7557>] ? inet_sendmsg+0xc7/0x1d0
 [<ffffffff810b63c4>] ? __lock_is_held+0x54/0x70
 [<ffffffff816e759a>] inet_sendmsg+0x10a/0x1d0
 [<ffffffff816e7495>] ? inet_sendmsg+0x5/0x1d0
 [<ffffffff8163e398>] sock_sendmsg+0x38/0x50
 [<ffffffff8163ec5f>] ___sys_sendmsg+0x25f/0x270
 [<ffffffff811aadad>] ? handle_mm_fault+0x8dd/0x1320
 [<ffffffff8178c147>] ? _raw_spin_unlock+0x27/0x40
 [<ffffffff810529b2>] ? __do_page_fault+0x1e2/0x460
 [<ffffffff81204886>] ? __fget_light+0x66/0x90
 [<ffffffff8163f8e2>] __sys_sendmsg+0x42/0x80
 [<ffffffff8163f932>] SyS_sendmsg+0x12/0x20
 [<ffffffff8178cb17>] entry_SYSCALL_64_fastpath+0x12/0x6f
Code: 00 00 44 89 e0 e9 7c fb ff ff 4c 89 ff e8 e7 e7 ff ff 41 8b 9d 80 00 00 00 2b 5d d4 89 d8 c1 f8 03 0f b7 c0 e9 33 ff ff f
 66 66 66 2e 0f 1f 84 00 00 00 00 00 66 66 66 66 90 55 48
RIP  [<ffffffff816a9a92>] ip_do_fragment+0x892/0x8a0
 RSP <ffff88006d603170>

Fixes: 7f8a436 ("openvswitch: Add conntrack action")
Signed-off-by: Joe Stringer <joe@ovn.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv4/ip_fragment.c

@@ -661,6 +661,7 @@ int ip_defrag(struct net *net, struct sk_buff *skb, u32 user)
 	struct ipq *qp;
 
 	IP_INC_STATS_BH(net, IPSTATS_MIB_REASMREQDS);
+	skb_orphan(skb);
 
 	/* Lookup (or create) queue header */
 	qp = ip_find(net, ip_hdr(skb), user, vif);

net/ipv4/netfilter/nf_defrag_ipv4.c

@@ -27,8 +27,6 @@ static int nf_ct_ipv4_gather_frags(struct net *net, struct sk_buff *skb,
 {
 	int err;
 
-	skb_orphan(skb);
-
 	local_bh_disable();
 	err = ip_defrag(net, skb, user);
 	local_bh_enable();