netdev - Re: [PATCH v2 4/7] skbuff: introduce skb_gso_validate

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Date:	Tue, 31 May 2016 13:47:16 -0700
From:	Alexander Duyck <alexander.duyck@...il.com>
To:	Marcelo Ricardo Leitner <marcelo.leitner@...il.com>
Cc:	Netdev <netdev@...r.kernel.org>, linux-sctp@...r.kernel.org,
	Xin Long <lucien.xin@...il.com>,
	Neil Horman <nhorman@...driver.com>,
	David Laight <David.Laight@...lab.com>,
	Vlad Yasevich <vyasevich@...il.com>,
	Daniel Borkmann <daniel@...earbox.net>,
	Florian Westphal <fw@...len.de>,
	Eric Dumazet <eric.dumazet@...il.com>
Subject: Re: [PATCH v2 4/7] skbuff: introduce skb_gso_validate_mtu

On Tue, May 31, 2016 at 12:54 PM, Marcelo Ricardo Leitner
<marcelo.leitner@...il.com> wrote:
> On Tue, May 31, 2016 at 12:07:54PM -0700, Alexander Duyck wrote:
>> On Tue, May 31, 2016 at 11:55 AM, Marcelo Ricardo Leitner
>> <marcelo.leitner@...il.com> wrote:
>> > skb_gso_network_seglen is not enough for checking fragment sizes if
>> > skb is using GSO_BY_FRAGS as we have to check frag per frag.
>> >
>> > This patch introduces skb_gso_validate_mtu, based on the former, which
>> > will wrap the use case inside it as all calls to skb_gso_network_seglen
>> > were to validate if it fits on a given TMU, and improve the check.
>> >
>> > Signed-off-by: Marcelo Ricardo Leitner <marcelo.leitner@...il.com>
>> > Tested-by: Xin Long <lucien.xin@...il.com>
>> > ---
>> >  include/linux/skbuff.h |  1 +
>> >  net/core/skbuff.c      | 31 +++++++++++++++++++++++++++++++
>> >  net/ipv4/ip_forward.c  |  2 +-
>> >  net/ipv4/ip_output.c   |  2 +-
>> >  net/ipv6/ip6_output.c  |  2 +-
>> >  net/mpls/af_mpls.c     |  2 +-
>> >  6 files changed, 36 insertions(+), 4 deletions(-)
>> >
>> > diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
>> > index 1f713541cb2fc232cb0e8417232cb9942409c9fc..2109c2dc9767d454b2cd08696af039b6bcd1ace7 100644
>> > --- a/include/linux/skbuff.h
>> > +++ b/include/linux/skbuff.h
>> > @@ -2992,6 +2992,7 @@ void skb_split(struct sk_buff *skb, struct sk_buff *skb1, const u32 len);
>> >  int skb_shift(struct sk_buff *tgt, struct sk_buff *skb, int shiftlen);
>> >  void skb_scrub_packet(struct sk_buff *skb, bool xnet);
>> >  unsigned int skb_gso_transport_seglen(const struct sk_buff *skb);
>> > +bool skb_gso_validate_mtu(const struct sk_buff *skb, unsigned int mtu);
>> >  struct sk_buff *skb_segment(struct sk_buff *skb, netdev_features_t features);
>> >  struct sk_buff *skb_vlan_untag(struct sk_buff *skb);
>> >  int skb_ensure_writable(struct sk_buff *skb, int write_len);
>> > diff --git a/net/core/skbuff.c b/net/core/skbuff.c
>> > index 97c32c75e704af1f31b064e8f1e0475ff1505d67..5ca562b56ec39d39e1225d96547e242732518ffe 100644
>> > --- a/net/core/skbuff.c
>> > +++ b/net/core/skbuff.c
>> > @@ -4392,6 +4392,37 @@ unsigned int skb_gso_transport_seglen(const struct sk_buff *skb)
>> >  }
>> >  EXPORT_SYMBOL_GPL(skb_gso_transport_seglen);
>> >
>> > +/**
>> > + * skb_gso_validate_mtu - Return in case such skb fits a given MTU
>> > + *
>> > + * @skb: GSO skb
>> > + *
>> > + * skb_gso_validate_mtu validates if a given skb will fit a wanted MTU
>> > + * once split.
>> > + */
>> > +bool skb_gso_validate_mtu(const struct sk_buff *skb, unsigned int mtu)
>> > +{
>> > +       const struct skb_shared_info *shinfo = skb_shinfo(skb);
>> > +       const struct sk_buff *iter;
>> > +       unsigned int hlen;
>> > +
>> > +       hlen = skb_gso_network_seglen(skb);
>> > +
>> > +       if (shinfo->gso_size != GSO_BY_FRAGS)
>> > +               return hlen <= mtu;
>> > +
>> > +       /* Undo this so we can re-use header sizes */
>> > +       hlen -= GSO_BY_FRAGS;
>>
>> Isn't this just "hlen = 0"?  If so you could probably just remove this
>> line and the references to hlen below and instead just loop through
>> verifying skb_headlen() instead of adding a value that should be 0.

I see what you are saying.  It also doesn't help I misread this as
hlen != GSO_BY_FRAGS, not shinfo->gso_size.

> By when this func is called the frags lack any headers, this is how I
> a ccount them.  So I expect it to be different than 0 in most of the
> cases as it will contain the value of network header size, and it should
> have contained the size of sctp header too. Now reviewing it, I should
> have added a new check on skb_gso_transport_seglen() for sctp gso I
> think. As in:
>
> diff --git a/net/core/skbuff.c b/net/core/skbuff.c
> index 5ca562b56ec3..fcc286b8b90c 100644
> --- a/net/core/skbuff.c
> +++ b/net/core/skbuff.c
> @@ -4383,6 +4383,8 @@ unsigned int skb_gso_transport_seglen(const struct sk_buff *skb)
>                         thlen += inner_tcp_hdrlen(skb);
>         } else if (likely(shinfo->gso_type & (SKB_GSO_TCPV4 | SKB_GSO_TCPV6))) {
>                 thlen = tcp_hdrlen(skb);
> +       } else if (unlikely(shinfo->gso_type & SKB_GSO_SCTP)) {
> +               thlen = sizeof(struct sctphdr);
>         }
>         /* UFO sets gso_size to the size of the fragmentation
>          * payload, i.e. the size of the L4 (UDP) header is already
>
> This chunk would be on 6th patch. (v3 will be needed due to this)
>
> I can ignore that and recalculate it but this way (with -GSO_BY_FRAGS)
> seemed cleaner as it reuses all that.

Okay that works.

- Alex