Re: Write delegation stateid permission checks

[Chuck Lever <chuck.lever@oracle.com>]

On 1/2/25 5:07 PM, Sagi Grimberg wrote:
> 
> 
> 
> On 02/01/2025 15:41, Jeff Layton wrote:
>> On Thu, 2025-01-02 at 11:08 +0200, Shaul Tamari wrote:
>>> Should the server check permissions for read access as well when
>>> OPEN4_SHARE_ACCESS_WRITE is requested and DELEGATION_WRITE is granted
>>> ?
>>>
>> Possibly? When trying to grant a write delegation, the server should
>> probably also do an opportunistic permission check for read as well,
>> and only grant the delegation if that passes. If it fails, you could
>> still allow the open and just not grant the delegation.
> 
> Yes, that is what Chuck suggested at the time.
> 
>>
>> ISTR that Sagi may have tried this approach though and there was a
>> problem with it?
> 
> Not a problem per se, IIRC the thread left off that we need to sort out
> access reference accounting for nfsd_file for both reads and writes for
> a single write deleg...

I've been pondering this recently.

The desired outcome would be to deal with a OPEN(SHARE_ACCESS_WRITE)
by opening the file twice: once, WR_ONLY, for the OPEN state ID, and
once RW, for the write delegation.

Will that work? won't the two opens conflict with each other and
trigger a delegation recall?

Seems like NFSD will need a lot more logic to make this approach
work right.


-- 
Chuck Lever