datapath: Backport "skbuff: Fix skb checksum flag on skb pull"

datapath: Backport "skbuff: Fix skb checksum flag on skb pull"

Upstream commit:

    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@vmware.com>
    Signed-off-by: Pravin B Shelar <pshelar@nicira.com>
    Acked-by: Tom Herbert <tom@herbertland.com>
    Signed-off-by: David S. Miller <davem@davemloft.net>
Upstream: 6ae459bdaae ("skbuff: Fix skb checksum flag on skb pull")
Signed-off-by: Pravin B Shelar <pshelar@nicira.com>
Acked-by: Jesse Gross <jesse@nicira.com>