[PATCH 2/2 linux-next] cifs: Make big endian multiplex ID sequences monotonic on the wire

Tim Gardner timg at tpi.com
Wed Oct 16 10:39:27 MDT 2013

On 10/16/2013 09:25 AM, Shirish Pargaonkar wrote:
> On Wed, Oct 16, 2013 at 10:09 AM, Tim Gardner <timg at tpi.com> wrote:
>> The multiplex identifier (MID) in the SMB header is only
>> ever used by the client, in conjunction with PID, to match responses
>> from the server. As such, the endianess of the MID is not important.
>> However, When tracing packet sequences on the wire, protocol analyzers
>> such as wireshark display MID as little endian. It is much more informative
>> for the on-the-wire MID sequences to match debug information emitted by the
>> CIFS driver.  Therefore, one should write and read MID in the SMB header
>> assuming it is always little endian.
>> Observed from wireshark during the protocol negotiation
>> and session setup:
>>         Multiplex ID: 256
>>         Multiplex ID: 256
>>         Multiplex ID: 512
>>         Multiplex ID: 512
>>         Multiplex ID: 768
>>         Multiplex ID: 768
>> After this patch on-the-wire MID values begin at 1 and increase monotonically.
>> Introduce get_next_mid64() for the internal consumers that use the full 64 bit
>> multiplex identifier.
>> Introduce the helpers get_mid() and compare_mid() to make the endian
>> translation clear.
>> Cc: Steve French <sfrench at samba.org>
>> Signed-off-by: Tim Gardner <timg at tpi.com>
>> ---
>> I'm looking at some of this code in excrutiating detail because I'm having trouble
>> with a backport of CIFS from 3.9.7 on an embedded 2.6.31 powerpc. Its failing the RawNTLMSSP
>> authentication and is almost certainly an endian issue. x86 on the same code base works
>> quite well. Am I making a rash assumption that CIFS in 3.9 stable worked on big endian ?
> Do you have this commit  fdf96a907c1fbb93c633e2b7ede3b8df26d6a4c0 ?
> This might help if you do not have it in your code base.

Yep - I found that one pretty early on. It solved a powerpc issue with
session startup to an x86 Linux CIFS server. The current failing session
startup is to an Apple 10.8.5 (Lion) server (serverNOS=@(#)PROGRAM:smbd

Tim Gardner timg at tpi.com www.tpi.com
OR 503-601-0234 x102 MT 406-443-5357

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