netdev - Re: [PATCH net v2] skbuff: Fix skb checksum flag on skb pull

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Date:	Tue, 22 Sep 2015 14:28:18 -0700
From:	Tom Herbert <tom@...bertland.com>
To:	Pravin B Shelar <pshelar@...ira.com>
Cc:	Linux Kernel Network Developers <netdev@...r.kernel.org>
Subject: Re: [PATCH net v2] skbuff: Fix skb checksum flag on skb pull

On Tue, Sep 22, 2015 at 12:57 PM, Pravin B Shelar <pshelar@...ira.com> wrote:
> 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@...are.com>
> Signed-off-by: Pravin B Shelar <pshelar@...ira.com>
> ---
> v1-v2:
> Set skb to CHECKSUM_NONE rather than CHECKSUM_UNNECESSARY.
> ---
>  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 9987af0..2b0a30a 100644
> --- a/include/linux/skbuff.h
> +++ b/include/linux/skbuff.h
> @@ -2707,6 +2707,9 @@ 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_NONE;
>  }
>
Acked-by: Tom Herbert <tom@...bertland.com>

>  unsigned char *skb_pull_rcsum(struct sk_buff *skb, unsigned int len);
> --
> 1.7.1
>
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