netdev - [PATCH net] skbuff: Fix skb checksum flag on skb pull

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Date:	Mon, 31 Aug 2015 15:55:46 -0700
From:	Pravin B Shelar <pshelar@...ira.com>
To:	netdev@...r.kernel.org
Cc:	Pravin B Shelar <pshelar@...ira.com>
Subject: [PATCH net] skbuff: Fix skb checksum flag on skb pull

VXLAN device can receive skb with checksum partial. But the checksum
offset could be in outer header which is pulled on receive. Such skb
can cause the panic when checksum is calculated on skb. Following patch
fixes the bug by setting checksum unnecessary while pulling outer header.

---8<---
[ 13.800141] RIP: 0010:[<ffffffff81518034>] [<ffffffff81518034>] skb_checksum_help+0x144/0x150
[ 13.800141] RSP: 0000:ffff88011fd83940 EFLAGS: 00010292
[ 13.800141] RAX: 0000000000000042 RBX: ffff880114dd56c0 RCX: ffff8801188d9580
...
...
[ 13.852308] Call Trace:
[ 13.852308] <IRQ>
[ 13.852308] [<ffffffffa0164c28>] queue_userspace_packet+0x408/0x470 [openvswitch]
[ 13.852308] [<ffffffffa016614d>] ovs_dp_upcall+0x5d/0x60 [openvswitch]
[ 13.852308] [<ffffffffa0166236>] ovs_dp_process_packet_with_key+0xe6/0x100 [openvswitch]
[ 13.852308] [<ffffffffa016629b>] ovs_dp_process_received_packet+0x4b/0x80 [openvswitch]
[ 13.852308] [<ffffffffa016c51a>] ovs_vport_receive+0x2a/0x30 [openvswitch]
[ 13.852308] [<ffffffffa0171383>] vxlan_rcv+0x53/0x60 [openvswitch]
[ 13.852308] [<ffffffffa01734cb>] vxlan_udp_encap_recv+0x8b/0xf0 [openvswitch]
[ 13.852308] [<ffffffff8157addc>] udp_queue_rcv_skb+0x2dc/0x3b0
[ 13.852308] [<ffffffff8157b56f>] __udp4_lib_rcv+0x1cf/0x6c0
[ 13.852308] [<ffffffff8157ba7a>] udp_rcv+0x1a/0x20
[ 13.852308] [<ffffffff8154fdbd>] ip_local_deliver_finish+0xdd/0x280
[ 13.852308] [<ffffffff81550128>] ip_local_deliver+0x88/0x90
[ 13.852308] [<ffffffff8154fa7d>] ip_rcv_finish+0x10d/0x370
[ 13.852308] [<ffffffff81550365>] ip_rcv+0x235/0x300
[ 13.852308] [<ffffffff8151ba1d>] __netif_receive_skb+0x55d/0x620
[ 13.852308] [<ffffffff8151c360>] netif_receive_skb+0x80/0x90
[ 13.852308] [<ffffffff81459935>] virtnet_poll+0x555/0x6f0
[ 13.852308] [<ffffffff8151cd04>] net_rx_action+0x134/0x290
[ 13.852308] [<ffffffff810683d8>] __do_softirq+0xa8/0x210
[ 13.852308] [<ffffffff8162fe6c>] call_softirq+0x1c/0x30
[ 13.852308] [<ffffffff810161a5>] do_softirq+0x65/0xa0
[ 13.852308] [<ffffffff810687be>] irq_exit+0x8e/0xb0
[ 13.852308] [<ffffffff81630733>] do_IRQ+0x63/0xe0
[ 13.852308] [<ffffffff81625f2e>] common_interrupt+0x6e/0x6e
[ 13.852308] <EOI>
[ 13.852308] [<ffffffff8162dc02>] ? system_call_fastpath+0x16/0x1b

Reported-by: Anupam Chanda <achanda@...are.com>
Signed-off-by: Pravin B Shelar <pshelar@...ira.com>
---
 include/linux/skbuff.h |    3 +++
 1 files changed, 3 insertions(+), 0 deletions(-)

diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index 9b88536..6238e9f 100644
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -2601,6 +2601,9 @@ static inline void skb_postpull_rcsum(struct sk_buff *skb,
 {
 	if (skb->ip_summed == CHECKSUM_COMPLETE)
 		skb->csum = csum_sub(skb->csum, csum_partial(start, len, 0));
+	else if (skb->ip_summed == CHECKSUM_PARTIAL &&
+		 skb_checksum_start_offset(skb) <= len)
+		skb->ip_summed = CHECKSUM_UNNECESSARY;
 }
 
 unsigned char *skb_pull_rcsum(struct sk_buff *skb, unsigned int len);
-- 
1.7.1

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