netdev - Re: [PATCH net-next] udp: disable gso with no_check

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Date:   Tue, 01 May 2018 14:21:01 -0400 (EDT)
From:   David Miller <davem@...emloft.net>
To:     willemdebruijn.kernel@...il.com
Cc:     netdev@...r.kernel.org, willemb@...gle.com
Subject: Re: [PATCH net-next] udp: disable gso with no_check_tx

From: Willem de Bruijn <willemdebruijn.kernel@...il.com>
Date: Mon, 30 Apr 2018 15:58:36 -0400

> From: Willem de Bruijn <willemb@...gle.com>
> 
> Syzbot managed to send a udp gso packet without checksum offload into
> the gso stack by disabling tx checksum (UDP_NO_CHECK6_TX).

Impressive...

> This triggered the skb_warn_bad_offload.
> 
>   RIP: 0010:skb_warn_bad_offload+0x2bc/0x600 net/core/dev.c:2658
>    skb_gso_segment include/linux/netdevice.h:4038 [inline]
>    validate_xmit_skb+0x54d/0xd90 net/core/dev.c:3120
>    __dev_queue_xmit+0xbf8/0x34c0 net/core/dev.c:3577
>    dev_queue_xmit+0x17/0x20 net/core/dev.c:3618
> 
> UDP_NO_CHECK6_TX sets skb->ip_summed to CHECKSUM_NONE just after the
> udp gso integrity checks in udp_(v6_)send_skb. Extend those checks to
> catch and fail in this case.
> 
> After the integrity checks jump directly to the CHECKSUM_PARTIAL case
> to avoid reading the no_check_tx flags again (a TOCTTOU race).
> 
> Fixes: bec1f6f69736 ("udp: generate gso with UDP_SEGMENT")
> Signed-off-by: Willem de Bruijn <willemb@...gle.com>

Applied, thanks Willem.