From: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
To: Willem de Bruijn <willemb@google.com>
Cc: Network Development <netdev@vger.kernel.org>,
Eric Dumazet <edumazet@google.com>,
David Miller <davem@davemloft.net>,
johann.baudy@gnu-log.net, paulus@samba.org
Subject: Re: [PATCH] packet: Allow packets with only a header (but no payload)
Date: Fri, 31 Jul 2015 00:15:46 +0200 [thread overview]
Message-ID: <CAFBinCBYv44ttGNyny11gEwNMJDwYzO=YYJC5scwOE-PN2nn4A@mail.gmail.com> (raw)
In-Reply-To: <CA+FuTSfw+-6Xb_0xchM5E6vCMSsyiSvSYF3MbuE25pEt07RRbw@mail.gmail.com>
On Wed, Jul 29, 2015 at 8:05 AM, Willem de Bruijn <willemb@google.com> wrote:
> Martin, to return to your initial statement that PPPoE PADI packets can
> have a zero payload: the PPPoE RFC states that PADI packets "MUST
> contain exactly one TAG of TAG_TYPE Service-Name, indicating the
> service the Host is requesting, and any number of other TAG types."
> (RFC 2516, 5.1). Is the observed behavior (no payload) perhaps
> incorrect?
As far as I can see you are right, but the real world seems to be different.
My ISP for example lists the PPPoE connection settings, but they are
nowhere mentioning the "service name".
I have also re-read pppd's source code again and that seems to confirm
what you are reading in the RFC: Leaving the service name away makes
seems to violate the RFC, but pppd still accepts those configurations.
> Even if it is, if this is breaking established userspace expectations,
> we should look into it. Ethernet specifies a minimum payload size of
> 46 on the wire, but perhaps that is handled with padding, so that
> 0 length should be valid within the stack. Also, there may be other
> valid uses of 0 length payload on top of link layers that are not Ethernet.
Good catch. I would also like to note that the documentation for
"hard_header_len" describes it as "Hardware header length". When the
purpose of this field we should check whether the documentation should
be updated to "Minimum hardware header length" -> that would mean the
condition has to be a "len < hard_header_len" instead of a "len <=
hard_header_len" (as it is now).
PS: I have also added the pppd maintainer (Paul Mackerras) to this
thread because I think he should know about this issue (and he can
probably provide more details if required).
As a quick summary for him: linux >= 3.19 rejects PADI packets when
no service name is configured.
Regards,
Martin
next prev parent reply other threads:[~2015-07-30 22:16 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-07-21 16:14 [PATCH] packet: Allow packets with only a header (but no payload) Martin Blumenstingl
2015-07-21 16:28 ` Willem de Bruijn
2015-07-21 16:38 ` Martin Blumenstingl
2015-07-21 16:51 ` Willem de Bruijn
2015-07-27 22:35 ` Martin Blumenstingl
2015-07-29 6:05 ` Willem de Bruijn
2015-07-30 22:15 ` Martin Blumenstingl [this message]
2015-11-07 13:11 ` Felix Fietkau
2015-11-09 17:53 ` Willem de Bruijn
2015-11-09 19:02 ` Felix Fietkau
2015-11-21 0:50 ` Martin Blumenstingl
2015-11-21 21:32 ` Sergei Shtylyov
2015-11-22 16:46 ` [PATCH v3] " Martin Blumenstingl
2015-11-30 3:18 ` David Miller
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