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From: Willem de Bruijn <willemdebruijn.kernel@gmail.com>
To: Alexander Duyck <alexander.duyck@gmail.com>
Cc: Willem de Bruijn <willemdebruijn.kernel@gmail.com>,
	Netdev <netdev@vger.kernel.org>,
	David Miller <davem@davemloft.net>,
	Jakub Kicinski <kuba@kernel.org>,
	Ido Schimmel <idosch@idosch.org>,
	chouhan.shreyansh630@gmail.com
Subject: Re: [PATCH net] ip_gre: validate csum_start only if CHECKSUM_PARTIAL
Date: Sun, 5 Sep 2021 23:02:23 -0400	[thread overview]
Message-ID: <CA+FuTSe+vJgTVLc9SojGuN-f9YQ+xWLPKE_S4f=f+w+_P2hgUg@mail.gmail.com> (raw)
In-Reply-To: <CAKgT0UeH3aTnMKqzmtqfWrtmkW6cB=Mk6OSJi0FvmDEbmNAd+Q@mail.gmail.com>

On Sun, Sep 5, 2021 at 11:53 AM Alexander Duyck
<alexander.duyck@gmail.com> wrote:
>
> On Sun, Sep 5, 2021 at 8:24 AM Willem de Bruijn
> <willemdebruijn.kernel@gmail.com> wrote:
> >
> > On Sat, Sep 4, 2021 at 7:47 PM Alexander Duyck
> > <alexander.duyck@gmail.com> wrote:
>
> <snip>
>
> > > You can do it since you have essentially already written half the code.. :)
> >
> > Sent, but only the ipv4 patch.
> >
> > I actually do not see an equivalent skb_pull path in ip6_gre.c. Will
> > take a closer look later, but don't have time for that now.
> >
> > https://patchwork.kernel.org/project/netdevbpf/patch/20210905152109.1805619-1-willemdebruijn.kernel@gmail.com/
>
> So does that mean that commit 9cf448c200ba ("ip6_gre: add validation
> for csum_start") is adding overhead that doesn't really address
> anything, and is introducing false positives? If so, should we just
> revert it?

I agree.

I didn't immediately understand how there can be an ip6gre_header
analogous to ipgre_header (for headers_ops.create), but no skb_pull
in ip6gre_tunnel_xmit equivalent to the one in ipgre_xmit.

One difference between the two of them is the return value, which
returns an offset: ip6gre_header returns t->hlen. ipgre_header returns
t->hlen + sizeof(*iph). This extra offset was introduced in commit
77a482bdb2e6 ("ip_gre: fix ipgre_header to return correct offset") as
a fix to previous commit c544193214 ("GRE: Refactor GRE tunneling
code."). Before the latter commit the IPv4 header was included in
t->hlen, similar to IPv6. After that commit it is no longer. The latter
patch is also the one that introduces the skb_pull in ipgre_xmit.

I can't say that I fully understand how this works for IPv6.

But I think that is sufficient to understand that this skb_pull issue
does not affect the ip6_gre path and we best just revert that commit.

  reply	other threads:[~2021-09-06  3:03 UTC|newest]

Thread overview: 21+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-09-02 19:34 [PATCH net] ip6_gre: " Willem de Bruijn
2021-09-02 19:34 ` [PATCH net] ip_gre: " Willem de Bruijn
2021-09-02 20:25   ` Alexander Duyck
2021-09-02 20:29     ` Willem de Bruijn
2021-09-02 21:17       ` Alexander Duyck
2021-09-02 21:44         ` Willem de Bruijn
2021-09-03  2:01           ` Alexander Duyck
2021-09-03  2:40             ` Willem de Bruijn
2021-09-03 16:46               ` Alexander Duyck
2021-09-03 19:38                 ` Willem de Bruijn
2021-09-03 23:13                   ` Alexander Duyck
2021-09-04 14:45                     ` Willem de Bruijn
2021-09-04 15:35                       ` Alexander Duyck
2021-09-04 21:40                         ` Willem de Bruijn
2021-09-04 21:53                           ` Alexander Duyck
2021-09-04 22:05                             ` Willem de Bruijn
2021-09-04 23:47                               ` Alexander Duyck
2021-09-05 15:24                                 ` Willem de Bruijn
2021-09-05 15:53                                   ` Alexander Duyck
2021-09-06  3:02                                     ` Willem de Bruijn [this message]
2021-09-02 20:27 ` [PATCH net] ip6_gre: " Alexander Duyck

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