Re: Regression in 5.1.20: Reading long directory fails

From: Chuck Lever
Date: Wed Sep 11 2019 - 13:56:37 EST

> On Sep 11, 2019, at 1:50 PM, Benjamin Coddington <bcodding@xxxxxxxxxx> wrote:
> On 11 Sep 2019, at 13:40, Benjamin Coddington wrote:
>> On 11 Sep 2019, at 13:29, Chuck Lever wrote:
>>>> On Sep 11, 2019, at 1:26 PM, Benjamin Coddington <bcodding@xxxxxxxxxx> wrote:
>>>> On 11 Sep 2019, at 12:39, Chuck Lever wrote:
>>>>>> On Sep 11, 2019, at 12:25 PM, Benjamin Coddington <bcodding@xxxxxxxxxx> wrote:
>>>>>> Instead, I think we want to make sure the mic falls squarely into the tail
>>>>>> every time.
>>>>> I'm not clear how you could do that. The length of the page data is not
>>>>> known to the client before it parses the reply. Are you suggesting that
>>>>> gss_unwrap should do it somehow?
>>>> Is it too niave to always put the mic at the end of the tail?
>>> The size of the page content is variable.
>>> The only way the MIC will fall into the tail is if the page content is
>>> exactly the largest expected size. When the page content is smaller than
>>> that, the receive logic will place part or all of the MIC in ->pages.
>> Ok, right. But what I meant is that xdr_buf_read_netobj() should be renamed
>> and repurposed to be "move the mic from wherever it is to the end of
>> xdr_buf's tail".
>> But now I see what you mean, and I also see that it is already trying to do
>> that.. and we don't want to overlap the copy..
>> So, really, we need the tail to be larger than twice the mic.. less 1. That
>> means the fix is probably just increasing rslack for krb5i.
> .. or we can keep the tighter tail space, and if we detect the mic straddles
> the page and tail, we can move the mic into the tail with 2 copies, first
> move the bit in the tail back, then move the bit in the pages.
> Which is preferred, less allocation, or in the rare case this occurs, doing
> copy twice?

It sounds like the bug is that the current code does not deal correctly
when the MIC crosses the boundary between ->pages and ->tail? I'd like
to see that addressed rather than changing rslack.

Chuck Lever