[cifs-protocol] Create Context SMB2_CREATE_QUERY_ON_DISK_ID payload

Jeremy Allison jra at samba.org
Thu Nov 14 19:53:32 UTC 2019

On Thu, Nov 14, 2019 at 07:05:20PM +0100, Aurélien Aptel via cifs-protocol wrote:
> Hi,
> There is a create context SMB2_CREATE_QUERY_ON_DISK_ID that MS-SMB2
> describes as, for the request:
>     ("QFid")
>     The client is requesting that the server return a 32-
>     byte opaque BLOB that uniquely identifies the file
>     being opened on disk. No data is passed to the
>     server by the client.
> for the response:
>     ("QFid")
>     The server returned DiskID of the open file in a volume.
>     SMB2_CREATE_CONTEXT Response takes the same
>     form as defined in section
> So on one side it reads "32-byte opaque blob" but on the other
> "DiskID". I could not find a reference to what is a DiskId.
> After some testing Windows Server seems to return the persistent file id
> + something, which Samba does as well, with the following note:
>     /* From conversations with Microsoft engineers at
>        the MS plugfest. The first 8 bytes are the "volume index"
>        == inode, the second 8 bytes are the "volume id",
>        == dev. This will be updated in the SMB2 doc. */
> Samba returns
> - file id (8 bytes)
> - device id (4 bytes)
> - padded to 32 bytes with garbage


FYI the padding is with zeros, not garbage.

This is important so as to not leak server memory.

Just wanted to be clear.


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