linux-kernel - Re: [PATCH net] sctp: call gso_reset_checksum when computing checksum in sctp_gso

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Date:   Tue, 12 Feb 2019 14:15:35 -0200
From:   Marcelo Ricardo Leitner <marcelo.leitner@...il.com>
To:     Xin Long <lucien.xin@...il.com>
Cc:     linux-kernel@...r.kernel.org, network dev <netdev@...r.kernel.org>,
        linux-sctp@...r.kernel.org, davem@...emloft.net,
        Neil Horman <nhorman@...driver.com>
Subject: Re: [PATCH net] sctp: call gso_reset_checksum when computing
 checksum in sctp_gso_segment

On Tue, Feb 12, 2019 at 06:47:30PM +0800, Xin Long wrote:
> Jianlin reported a panic when running sctp gso over gre over vlan device:
> 
>   [   84.772930] RIP: 0010:do_csum+0x6d/0x170
>   [   84.790605] Call Trace:
>   [   84.791054]  csum_partial+0xd/0x20
>   [   84.791657]  gre_gso_segment+0x2c3/0x390
>   [   84.792364]  inet_gso_segment+0x161/0x3e0
>   [   84.793071]  skb_mac_gso_segment+0xb8/0x120
>   [   84.793846]  __skb_gso_segment+0x7e/0x180
>   [   84.794581]  validate_xmit_skb+0x141/0x2e0
>   [   84.795297]  __dev_queue_xmit+0x258/0x8f0
>   [   84.795949]  ? eth_header+0x26/0xc0
>   [   84.796581]  ip_finish_output2+0x196/0x430
>   [   84.797295]  ? skb_gso_validate_network_len+0x11/0x80
>   [   84.798183]  ? ip_finish_output+0x169/0x270
>   [   84.798875]  ip_output+0x6c/0xe0
>   [   84.799413]  ? ip_append_data.part.50+0xc0/0xc0
>   [   84.800145]  iptunnel_xmit+0x144/0x1c0
>   [   84.800814]  ip_tunnel_xmit+0x62d/0x930 [ip_tunnel]
>   [   84.801699]  gre_tap_xmit+0xac/0xf0 [ip_gre]
>   [   84.802395]  dev_hard_start_xmit+0xa5/0x210
>   [   84.803086]  sch_direct_xmit+0x14f/0x340
>   [   84.803733]  __dev_queue_xmit+0x799/0x8f0
>   [   84.804472]  ip_finish_output2+0x2e0/0x430
>   [   84.805255]  ? skb_gso_validate_network_len+0x11/0x80
>   [   84.806154]  ip_output+0x6c/0xe0
>   [   84.806721]  ? ip_append_data.part.50+0xc0/0xc0
>   [   84.807516]  sctp_packet_transmit+0x716/0xa10 [sctp]
>   [   84.808337]  sctp_outq_flush+0xd7/0x880 [sctp]
> 
> It was caused by SKB_GSO_CB(skb)->csum_start not set in sctp_gso_segment.
> sctp_gso_segment() calls skb_segment() with 'feature | NETIF_F_HW_CSUM',
> which causes SKB_GSO_CB(skb)->csum_start not to be set in skb_segment().
> 
> For TCP/UDP, when feature supports HW_CSUM, CHECKSUM_PARTIAL will be set
> and gso_reset_checksum will be called to set SKB_GSO_CB(skb)->csum_start.
> 
> So SCTP should do the same as TCP/UDP, to call gso_reset_checksum() when
> computing checksum in sctp_gso_segment.
> 
> Reported-by: Jianlin Shi <jishi@...hat.com>
> Signed-off-by: Xin Long <lucien.xin@...il.com>

Acked-by: Marcelo Ricardo Leitner <marcelo.leitner@...il.com>

> ---
>  net/sctp/offload.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/net/sctp/offload.c b/net/sctp/offload.c
> index 123e9f2..edfcf16 100644
> --- a/net/sctp/offload.c
> +++ b/net/sctp/offload.c
> @@ -36,6 +36,7 @@ static __le32 sctp_gso_make_checksum(struct sk_buff *skb)
>  {
>  	skb->ip_summed = CHECKSUM_NONE;
>  	skb->csum_not_inet = 0;
> +	gso_reset_checksum(skb, ~0);
>  	return sctp_compute_cksum(skb, skb_transport_offset(skb));
>  }
>  
> -- 
> 2.1.0
>