[cifs-protocol] After reconnect a SMB2 connection turns into a SMB3 connection

Ralph Wuerthner ralphw at de.ibm.com
Tue Feb 2 11:57:00 UTC 2016


When testing SMB2 and SMB3 with Samaba 4.2 and Windows Server acting as
SMB client I noticed the following unexpected behaviour:

A Windows Server 2012R2 is connected to a SMB2.1 share and the share is
mapped as a network drive. Next the SMB server is closing the
connection, causing the SMB client to immediately reopening the
connection. This time the SMB server is responding with SMB3.0 in the
negotiation response.

The expected behaviour would be that the network drive is unavailable
for a short amount of time and further access works without issues.

The actual behaviour is different: after connecting to the previously
opened share a
FSCTL_VALIDATE_NEGOTIATE_INFO request is submitted with an invalid
signature and the SMB server is responding with ACCESS_DENIED. The
client continues with a second tree connect to the same share followed
by an invalidly signed FSCTL_VALIDATE_NEGOTIATE_INFO request and so on.
In the end there are 20-30 tree connects to the same share and when
trying to access the network drive the following error message pops up:

	An error occurred while reconnecting Z: to
	Microsoft Windows Network: The local device name is already in use.

	This connections has not been restored

For recovering from this error state and regain access to the network
drive I identified the two different procedures:
- unmap and remap the network drive
- reboot the SMB client

Please see also the attached network trace.

What is wrong here? Is this a client or server bug? Are there any other
possibilities to recover the SMB client?

With best regards,

	Ralph Wuerthner

IBM Deutschland Research & Development GmbH
Vorsitzende des Aufsichtsrats: Martina Koederitz
Geschäftsführung: Dirk Wittkopp
Sitz der Gesellschaft: Böblingen / Registergericht: Amtsgericht
Stuttgart, HRB 243294
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