[cifs-protocol] SMBv1 LockAndX return status on lock conflict

[Tom Jebo]

Hi Steven,

Thanks for your question regarding SMBv1 LockAndX.  One of the Open Specification Documentation team will be in touch with you soon.

Best regards,
Tom Jebo
Open Specification Documentation Support

From: Steven Danneman [mailto:steven.danneman at isilon.com]
Sent: Wednesday, November 25, 2009 6:54 PM
To: Interoperability Documentation Help; cifs-protocol at samba.org; pfif at tridgell.net
Subject: SMBv1 LockAndX return status on lock conflict

Hello,

When requesting a byte-range lock over SMBv1 on a range of a file which is already locked and thus will contend, the error code returned is inconsistent.  The first attempt to acquire a held lock will return STATUS_LOCK_NOT_GRANTED.  Subsequent requests will return STATUS_FILE_LOCK_CONFLICT.

This seems as though it may be an error in the implementation of the SMBv1 protocol as the explanation of the two errors in MS-ERREF implies that STATUS_LOCK_NOT_GRANTED should always be returned in this circumstance:

STATUS_LOCK_NOT_GRANTED              A requested file lock cannot be granted due to other existing locks.
STATUS_FILE_LOCK_CONFLICT               A requested read/write cannot be granted due to a conflicting file lock.

And in this same scenario the SMBv2 protocol always returns STATUS_LOCK_NOT_GRANTED.

I aware this is a well known issue, as the Samba torture test demonstrating this behavior have existed for a number of years, but I haven't found any Microsoft documentation describing the semantics of this behavior.  I've looked in MS-CIFS, MS-SMB, MS-SMB2, and MS-FSA.

Furthermore, which error code is returned becomes even more complicated when additional lock requests are interspersed.  For example the attached pcap against a W2K8R2 server shows:

1) Two file handles opened to the same file 0x400b, 0x400c
2) Packet 27,28: Handle 0x400b successfully acquiring an exclusive lock on range 100 - 110
3) Packet 29-32: Handles 0x400b and 0x400c requesting the same held range and receiving STATUS_LOCK_NOT_GRANTED
4) Packet 33-44: Again requesting the same held range and receiving STATUS_FILE_LOCK_CONFLICT
5) Packet 45-54: Requesting a lock on an overlapping range, 105-115, and receiving the same pattern of errors
6) Packet 55-64: Requesting a lock on the previous range, 100-110, and now having the response be "reset" back to STATUS_LOCK_NOT_GRANTED

I'd like to have some documentation of the algorithm for determining which error to return based on the state of existing locks, or history of previously requested locks.

Thanks,

Steven Danneman | Software Development Engineer
Isilon Systems    P +1-206-315-7500     F  +1-206-315-7501
www.isilon.com<http://www.isilon.com>

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