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Re: Misalignment, MIPS, and ip_hdr(skb)->version

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From: "Jason A. Donenfeld" <Jason@zx2c4.com>
Date: Thu, 8 Dec 2016 01:29:42 +0100

> On Wed, Dec 7, 2016 at 8:52 PM, David Miller <davem@davemloft.net> wrote:
>> The only truly difficult case to handle is GRE encapsulation.  Is
>> that the situation you are running into?
>>
>> If not, please figure out what the header configuration looks like
>> in the case that hits for you, and what the originating device is
>> just in case it is a device driver issue.
> 
> My case is my own driver and my own protocol, which uses a 13 byte
> header. I can, if absolutely necessary, change the protocol to add
> another byte of padding. Or I can choose not to decrypt in place but
> rather use a different trick, like overwriting the header during
> decryption, though this removes some of the scatterwalk optimizations
> when src and dst are the same. Or something else. I wrote the top
> email of this thread inquiring about just exactly how bad it is to
> call netif_rx(skb) when skb->data is unaligned.

You really have to land the IP header on a proper 4 byte boundary.

I would suggest pushing 3 dummy garbage bytes of padding at the front
or the end of your header.

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Thread

Misalignment, MIPS, and ip_hdr(skb)->version "Jason A. Donenfeld" <Jason@zx2c4.com> - 2016-12-07 19:40 +0100
  Re: Misalignment, MIPS, and ip_hdr(skb)->version Dave Taht <dave.taht@gmail.com> - 2016-12-07 19:50 +0100
    Re: Misalignment, MIPS, and ip_hdr(skb)->version "Jason A. Donenfeld" <Jason@zx2c4.com> - 2016-12-07 20:00 +0100
      Re: Misalignment, MIPS, and ip_hdr(skb)->version David Miller <davem@davemloft.net> - 2016-12-07 21:00 +0100
        Re: Misalignment, MIPS, and ip_hdr(skb)->version "Jason A. Donenfeld" <Jason@zx2c4.com> - 2016-12-08 01:40 +0100
          Re: Misalignment, MIPS, and ip_hdr(skb)->version David Miller <davem@davemloft.net> - 2016-12-08 01:40 +0100
            Re: Misalignment, MIPS, and ip_hdr(skb)->version "Jason A. Donenfeld" <Jason@zx2c4.com> - 2016-12-08 23:30 +0100
              Re: Misalignment, MIPS, and ip_hdr(skb)->version David Miller <davem@davemloft.net> - 2016-12-09 00:20 +0100
              Re: Misalignment, MIPS, and ip_hdr(skb)->version Willy Tarreau <w@1wt.eu> - 2016-12-11 09:10 +0100
      Re: Misalignment, MIPS, and ip_hdr(skb)->version Felix Fietkau <nbd@nbd.name> - 2016-12-10 13:30 +0100
        Re: Misalignment, MIPS, and ip_hdr(skb)->version Måns Rullgård <mans@mansr.com> - 2016-12-10 14:30 +0100
          Re: Misalignment, MIPS, and ip_hdr(skb)->version Felix Fietkau <nbd@nbd.name> - 2016-12-10 21:20 +0100
            Re: Misalignment, MIPS, and ip_hdr(skb)->version Felix Fietkau <nbd@nbd.name> - 2016-12-10 21:40 +0100
            Re: Misalignment, MIPS, and ip_hdr(skb)->version Måns Rullgård <mans@mansr.com> - 2016-12-10 21:40 +0100
    Re: Misalignment, MIPS, and ip_hdr(skb)->version David Miller <davem@davemloft.net> - 2016-12-07 20:00 +0100
  Re: Misalignment, MIPS, and ip_hdr(skb)->version Hannes Frederic Sowa <hannes@stressinduktion.org> - 2016-12-08 01:40 +0100
    Re: Misalignment, MIPS, and ip_hdr(skb)->version Daniel Kahn Gillmor <dkg@fifthhorseman.net> - 2016-12-08 06:10 +0100
      Re: Misalignment, MIPS, and ip_hdr(skb)->version Jiri Benc <jbenc@redhat.com> - 2016-12-09 12:30 +0100
      Re: Misalignment, MIPS, and ip_hdr(skb)->version Dan Lüdtke <mail@danrl.com> - 2016-12-10 23:30 +0100
        Re: Misalignment, MIPS, and ip_hdr(skb)->version Greg KH <gregkh@linuxfoundation.org> - 2016-12-11 08:20 +0100

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