[PATCH 3.2 52/60] skbuff: Fix skb checksum flag on skb pull

[Ben Hutchings]

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

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

From: Pravin B Shelar <pshelar@xxxxxxxxxx>

[ Upstream commit 6ae459bdaaeebc632b16e54dcbabb490c6931d61 ]

VXLAN device can receive skb with checksum partial. But the checksum
offset could be in outer header which is pulled on receive. This results
in negative checksum offset for the skb. Such skb can cause the assert
failure in skb_checksum_help(). Following patch fixes the bug by setting
checksum-none while pulling outer header.

Following is the kernel panic msg from old kernel hitting the bug.

------------[ cut here ]------------
kernel BUG at net/core/dev.c:1906!
RIP: 0010:[<ffffffff81518034>] skb_checksum_help+0x144/0x150
Call Trace:
<IRQ>
[<ffffffffa0164c28>] queue_userspace_packet+0x408/0x470 [openvswitch]
[<ffffffffa016614d>] ovs_dp_upcall+0x5d/0x60 [openvswitch]
[<ffffffffa0166236>] ovs_dp_process_packet_with_key+0xe6/0x100 [openvswitch]
[<ffffffffa016629b>] ovs_dp_process_received_packet+0x4b/0x80 [openvswitch]
[<ffffffffa016c51a>] ovs_vport_receive+0x2a/0x30 [openvswitch]
[<ffffffffa0171383>] vxlan_rcv+0x53/0x60 [openvswitch]
[<ffffffffa01734cb>] vxlan_udp_encap_recv+0x8b/0xf0 [openvswitch]
[<ffffffff8157addc>] udp_queue_rcv_skb+0x2dc/0x3b0
[<ffffffff8157b56f>] __udp4_lib_rcv+0x1cf/0x6c0
[<ffffffff8157ba7a>] udp_rcv+0x1a/0x20
[<ffffffff8154fdbd>] ip_local_deliver_finish+0xdd/0x280
[<ffffffff81550128>] ip_local_deliver+0x88/0x90
[<ffffffff8154fa7d>] ip_rcv_finish+0x10d/0x370
[<ffffffff81550365>] ip_rcv+0x235/0x300
[<ffffffff8151ba1d>] __netif_receive_skb+0x55d/0x620
[<ffffffff8151c360>] netif_receive_skb+0x80/0x90
[<ffffffff81459935>] virtnet_poll+0x555/0x6f0
[<ffffffff8151cd04>] net_rx_action+0x134/0x290
[<ffffffff810683d8>] __do_softirq+0xa8/0x210
[<ffffffff8162fe6c>] call_softirq+0x1c/0x30
[<ffffffff810161a5>] do_softirq+0x65/0xa0
[<ffffffff810687be>] irq_exit+0x8e/0xb0
[<ffffffff81630733>] do_IRQ+0x63/0xe0
[<ffffffff81625f2e>] common_interrupt+0x6e/0x6e

Reported-by: Anupam Chanda <achanda@xxxxxxxxxx>
Signed-off-by: Pravin B Shelar <pshelar@xxxxxxxxxx>
Acked-by: Tom Herbert <tom@xxxxxxxxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
 include/linux/skbuff.h |    3 +++
 1 file changed, 3 insertions(+)

--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -2045,6 +2045,9 @@ static inline void skb_postpull_rcsum(st
 {
 	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_NONE;
 }
 
 unsigned char *skb_pull_rcsum(struct sk_buff *skb, unsigned int len);

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