netdev - Re: [PATCH] Packet mmap : allow the user to choose the offset of the tx payload.

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: <CAD6jFURTMDL6WFGOJhMdnS3zuejYm0uaBPb1TYuNNdUS-7w89w@mail.gmail.com>
Date:	Fri, 5 Oct 2012 21:37:58 +0200
From:	Daniel Borkmann <danborkmann@...earbox.net>
To:	pchavent <Paul.Chavent@...ra.fr>
Cc:	davem@...emloft.net, edumazet@...gle.com, xemul@...allels.com,
	herbert@...dor.hengli.com.au, netdev@...r.kernel.org,
	johann.baudy@...-log.net, uaca@...mni.uv.es
Subject: Re: [PATCH] Packet mmap : allow the user to choose the offset of the
 tx payload.

On Fri, Oct 5, 2012 at 9:21 PM, pchavent <Paul.Chavent@...ra.fr> wrote:
> On Fri, 5 Oct 2012 16:17:12 +0200, Daniel Borkmann wrote:
>> On Fri, Oct 5, 2012 at 3:10 PM, Paul Chavent <Paul.Chavent@...ra.fr>
>> wrote:
>>>
>>> The tx offset of packet mmap tx ring used to be :
>>> (TPACKET2_HDRLEN - sizeof(struct sockaddr_ll))
>>>
>>> The problem is that depending on the usage of SOCK_DGRAM or
>>> SOCK_RAW, the payload could be aligned or not.
>>>
>>> This patch allow to let the user give an offset for it's tx
>>> payload if he desires.
>>>
>>> Signed-off-by: Paul Chavent <paul.chavent@...ra.fr>
>>
>> Can you provide an example when it doesn't hit TPACKET_ALIGNMENT?
>
> When we use tx ring, the user have to write at (TPACKET_HDRLEN -
> sizeof(struct sockaddr_ll))
>
> This adress is aligned on TPACKET_ALIGNMENT since
> TPACKET_HDRLEN = (TPACKET_ALIGN(sizeof(struct tpacket_hdr)) + sizeof(struct
> sockaddr_ll))
>
> When we use the tx ring with SOCK_RAW option, the mac header is aligned on
> TPACKET_ALIGNMENT, but not the payload (14 bytes away).

Okay, I'm confused about your intentions, maybe I'm missing something.
The man-page of packet(7) clearly says:

The socket_type is either SOCK_RAW for raw packets *including* the
link level header or SOCK_DGRAM for cooked packets with  the link
level header *removed*.

So this is perfectly intended behavior of PF_PACKET.

Cheers,

Daniel
--
To unsubscribe from this list: send the line "unsubscribe netdev" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html