netdev - Re: [PATCH v2 net-next] net: fix GSO for SG-enabled devices.

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Date:   Wed, 20 Jan 2021 10:17:44 +0800
From:   Xin Long <lucien.xin@...il.com>
To:     Paolo Abeni <pabeni@...hat.com>
Cc:     network dev <netdev@...r.kernel.org>,
        "David S . Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Alexander Duyck <alexanderduyck@...com>
Subject: Re: [PATCH v2 net-next] net: fix GSO for SG-enabled devices.

On Wed, Jan 20, 2021 at 12:57 AM Paolo Abeni <pabeni@...hat.com> wrote:
>
> The commit dbd50f238dec ("net: move the hsize check to the else
> block in skb_segment") introduced a data corruption for devices
> supporting scatter-gather.
>
> The problem boils down to signed/unsigned comparison given
> unexpected results: if signed 'hsize' is negative, it will be
> considered greater than a positive 'len', which is unsigned.
>
> This commit addresses resorting to the old checks order, so that
> 'hsize' never has a negative value when compared with 'len'.
>
> v1 -> v2:
>  - reorder hsize checks instead of explicit cast (Alex)
>
> Bisected-by: Matthieu Baerts <matthieu.baerts@...sares.net>
> Fixes: dbd50f238dec ("net: move the hsize check to the else block in skb_segment")
> Signed-off-by: Paolo Abeni <pabeni@...hat.com>
Reviewed-by: Xin Long <lucien.xin@...il.com>
> ---
>  net/core/skbuff.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/net/core/skbuff.c b/net/core/skbuff.c
> index e835193cabcc3..cf2c4dcf42579 100644
> --- a/net/core/skbuff.c
> +++ b/net/core/skbuff.c
> @@ -3938,10 +3938,10 @@ struct sk_buff *skb_segment(struct sk_buff *head_skb,
>                         skb_release_head_state(nskb);
>                         __skb_push(nskb, doffset);
>                 } else {
> +                       if (hsize < 0)
> +                               hsize = 0;
>                         if (hsize > len || !sg)
>                                 hsize = len;
> -                       else if (hsize < 0)
> -                               hsize = 0;
>
>                         nskb = __alloc_skb(hsize + doffset + headroom,
>                                            GFP_ATOMIC, skb_alloc_rx_flag(head_skb),
> --
> 2.26.2
>
Reviewed-by: Xin Long <lucien.xin@...il.com>