[Pvfs2-developers] File truncated on failed permissions check

[Phil Carns]

The ENOENT part of the problem is fixed in CVS trunk now.

-Phil

> 
> b) is a bug.  That is coming from a follow up operation (setattr or 
> getattr) after the truncate that has its permissions checked by the 
> metadata server.  There is a problem there in which if all permission 
> checks fail on the server side PVFS returns enoent:
> 
> https://trac.mcs.anl.gov/projects/pvfs/ticket/104
> 
> It shouldn't be too hard to cook up a patch for each of these issues. 
> I'll look into it.
> 
> -Phil
> 
> Bart Taylor wrote:
>> Hey guys, we have run into another odd permissions case.
>>
>> The problem happens when updating a user's access to a file while it 
>> is still stored in another client's acache. In our test a client does 
>> an ls, their write permissions are removed from another client, and 
>> while the cache entry is still valid they try to overwrite the file. 
>> The result is a truncated file of zero bytes with an ENOENT return 
>> value. The test fails as expected and does not truncate the file if 
>> acache is turned off.
>>
>> Attached is a bash script that sets up the test for you, but it does 
>> require manually running a couple of commands at the right time on 
>> another client. Our clients are using an acache time out of 30 seconds.
>>
>> To run:
>> Client1 - start the bash script and waith for the first prompt ( 
>> ./perms-update-test.sh myuser mygroup /mnt/pvfs2 )
>> Client2 - execute an ls in the directory passed to the script  ( from 
>> /mnt/pvfs2: ls )
>> Client1 - wait for the second prompt
>> Client2 - overwrite the file (echo "text" > file1.txt)
>> Client1 - check the file size if file1.txt in the output
>>
>> I also attached a server log that shows the truncate succeeding and 
>> immediately calling setattr which fails. The server logging was turned 
>> on only for the file overwrite.
>>
>> Should the server be checking the file's permissions before the 
>> truncate happens?
>>
>> Bart.
>>
>>
>>
>> ------------------------------------------------------------------------
>>
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