[cifs-protocol] 112101850229631] Scope of a File.LeaseKey on the client

[Tarun Chopra]

Hi Metze

Kindly let us know if you have any other queries on this issue. If not, shall we go ahead and close the case. Please confirm.

Thanks
Tarun Chopra.

-----Original Message-----
From: Tarun Chopra 
Sent: Thursday, October 25, 2012 12:24 PM
To: 'Stefan (metze) Metzmacher'
Cc: MSSolve Case Email; 'cifs-protocol at cifs.org'; 'pfif at tridgell.net'
Subject: [RE: 112101850229631] Scope of a File.LeaseKey on the client

Hi Metze

Per analysis, yes, your understanding is correct on LeaseKey and pathname. In windows, Lease is closely tied to the path used while opening the file and so the client will use the same Lease when different users try to open a file using same path. Windows clients “assume” that the same path always refer to the same file.  So yes, (with or without leases), the scenario below will be broken on a Windows client. The same scenario would be broken even without leases in play, for example traditional op-locks or even without op-locks. 

Furthermore, the relationship between a “pathname” and a “lease” is purely a client implementation detail and is NOT mandated by the protocol. It is true that windows client maintains a 1:1 relationship between a pathname and a lease key.

Please let us know if this resolves your query or you require any additional clarification.

Thanks
Tarun Chopra


-----Original Message-----
From: Tarun Chopra 
Sent: Thursday, October 18, 2012 7:05 AM
To: Stefan (metze) Metzmacher
Cc: MSSolve Case Email; cifs-protocol at cifs.org; pfif at tridgell.net
Subject: [RE:112101850229631] Scope of a File.LeaseKey on the client

Hi Metze

Thanks for contacting Microsoft Support. We have created a case, 112101850229631, to track your inquiry and a support engineer will contact you to assist further.

Thanks
Tarun Chopra.

-----Original Message-----
From: Stefan (metze) Metzmacher [mailto:metze at samba.org] 
Sent: Thursday, October 18, 2012 12:56 AM
To: Interoperability Documentation Help; cifs-protocol at cifs.org; pfif at tridgell.net
Subject: Scope of a File.LeaseKey on the client

Hi DocHelp,

is it correct that the LeaseKey on a file is shared between different user contexts?

From 3.2.4.3 Application Requests Opening a File:

  [...]

  If the client implements the SMB 2.1 or SMB 3.0 dialect and Connection.SupportsFileLeasing is
  TRUE, the client MUST search the GlobalFileTable for an entry matching one of the following:

  - The application-supplied PathName if TreeConnect.IsDfsShare is TRUE.
  - The concatenation of Connection.ServerName, TreeConnect.ShareName, and the
    application-supplied PathName, joined with pathname separators
(example: server\share\path),
    if TreeConnect.IsDfsShare is FALSE.

  If an entry is not found, a new File entry MUST be created and added to the GlobalFileTable and a
  File.LeaseKey, as specified in section 3.2.1.5, MUST be assigned to the entry. File.OpenTable
  MUST be initialized to an empty table and File.LeaseState MUST be initialized to
  SMB2_LEASE_NONE.

  [...]

  If the client accesses a file through multiple paths, such as using different server names or share
  names or parent directory names, it will create multiple File elements, and therefore multiple
  File.LeaseKeys for the same remote file. This loses the performance benefits of sharing cache state
  across all Opens of the same file, and may cause additional lease breaks to be generated, as
  actions by a client through one path will affect caching by that client through other paths. However,
  the impact is a matter of performance; cache correctness is preserved.

  [...]

It seems that the LeaseKey is purely tight to the full path to the file from the client perspective.

I guess on a terminal server where multiple users access the same path on the server, the LeaseKey is shared between them, is that correct?

If this is true, then this implies that each user sees the same content in a file, which might not be true.

E.g. in Samba we allow shares to expose different FSA level directories based on user account.
The typical example is the "homes" share which exposes the unix home directory of the specific user.

I fear that we have to disable such powerful features if we want to take advantage of leases, otherwise the client would treat \\sambaserver\homes\commonfile.doc of
user1 and
\\sambaserver\homes\commonfile.doc of user2 as the same file.

I assume user1 and user2 should share the client_guid and lease_key, which means data corruption and/or security problems are very likely, if the server grants leases in this case.

metze