Re: [RFC v3 36/45] NFSv4: Fix GETATTR bitmap verification

[Trond Myklebust]

On Thu, May 28, 2015 at 4:33 PM, J. Bruce Fields <bfields@xxxxxxxxxxxx> wrote:
> On Fri, Apr 24, 2015 at 01:04:33PM +0200, Andreas Gruenbacher wrote:
>> The NFSv4 client sends the server GETATTR requests with different sets of
>> requested attributes depending on the situation.  The requested set of
>> attributes is encoded in a bitmap; the server replies with the set of
>> attributes it could return.  These bitmaps can be several words wide.  The
>> bitmap returned by the server is a subset of the bitmap sent by the client.
>>
>> While decoding the reply, the client tries to verify the reply bitmap: it
>> checks if any previous, unexpected attributes are left in the same word of the
>> bitmap for each attribute it tries to decode, then it clears the current
>> attribute's bit in the bitmap for the next decode function.
>>
>> The client fails to detect when unexpected attributes are sent after the last
>> expected attribute in each word in the bitmap.
>
> Is it important that the client catch that?

Right. What is the actual problem or bug that this patch is trying to
fix? Why do we care if a buggy server sends us extra info that we
didn't ask for?

Trond
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