netdev - Re: [PATCH net-next] net: mhi-net: Add de-aggeration support

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <CAF=yD-+UFHO8nKsB3Z7n-xhoFtXwge2GEZj-2+-7=EETLjYXFA@mail.gmail.com>
Date:   Mon, 1 Feb 2021 09:23:32 -0500
From:   Willem de Bruijn <willemdebruijn.kernel@...il.com>
To:     Loic Poulain <loic.poulain@...aro.org>
Cc:     Jakub Kicinski <kuba@...nel.org>,
        David Miller <davem@...emloft.net>,
        Network Development <netdev@...r.kernel.org>
Subject: Re: [PATCH net-next] net: mhi-net: Add de-aggeration support

On Mon, Feb 1, 2021 at 3:08 AM Loic Poulain <loic.poulain@...aro.org> wrote:
>
> Hi Jakub, Willem,
>
> On Sat, 30 Jan 2021 at 02:01, Jakub Kicinski <kuba@...nel.org> wrote:
> >
> > On Mon, 25 Jan 2021 16:45:57 +0100 Loic Poulain wrote:
> > > When device side MTU is larger than host side MRU, the packets
> > > (typically rmnet packets) are split over multiple MHI transfers.
> > > In that case, fragments must be re-aggregated to recover the packet
> > > before forwarding to upper layer.
> > >
> > > A fragmented packet result in -EOVERFLOW MHI transaction status for
> > > each of its fragments, except the final one. Such transfer was
> > > previoulsy considered as error and fragments were simply dropped.
> > >
> > > This patch implements the aggregation mechanism allowing to recover
> > > the initial packet. It also prints a warning (once) since this behavior
> > > usually comes from a misconfiguration of the device (modem).
> > >
> > > Signed-off-by: Loic Poulain <loic.poulain@...aro.org>
> >
> > > +static struct sk_buff *mhi_net_skb_append(struct mhi_device *mhi_dev,
> > > +                                       struct sk_buff *skb1,
> > > +                                       struct sk_buff *skb2)
> > > +{
> > > +     struct sk_buff *new_skb;
> > > +
> > > +     /* This is the first fragment */
> > > +     if (!skb1)
> > > +             return skb2;
> > > +
> > > +     /* Expand packet */
> > > +     new_skb = skb_copy_expand(skb1, 0, skb2->len, GFP_ATOMIC);
> > > +     dev_kfree_skb_any(skb1);
> > > +     if (!new_skb)
> > > +             return skb2;
> >
> > I don't get it, if you failed to grow the skb you'll return the next
> > fragment to the caller? So the frame just lost all of its data up to
> > where skb2 started? The entire fragment "train" should probably be
> > dropped at this point.
>
> Right, there is no point in keeping the partial packet in that case.
>
> >
> > I think you can just hang the skbs off skb_shinfo(p)->frag_list.
> >
> > Willem - is it legal to feed frag_listed skbs into netif_rx()?
>
> In QMAP case, the packets will be forwarded to rmnet link, which works
> with linear skb (no NETIF_F_SG), does the linearization will be
> properly performed by the net core, in the same way as for xmit path?

What is this path to rmnet, if not the usual xmit path / validate_xmit_skb?