Re: [PATCH] SUNRPC: Check if we need to recalculate slack estimates

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

On 1/2/26 7:34 AM, Salvatore Bonaccorso wrote:
> Hi Chuck, Scott,
> 
> On Wed, Nov 19, 2025 at 10:48:47AM -0500, Chuck Lever wrote:
>> On 11/19/25 8:32 AM, Scott Mayhew wrote:
>>> If the incoming GSS verifier is larger than what we previously recorded
>>> on the gss_auth, that would indicate the GSS cred/context used for that
>>> RPC is using a different enctype than the one used by the machine
>>> cred/context, and we should recalculate the slack variables accordingly.
>>>
>>> Link: https://bugs.debian.org/1120598
>>> Signed-off-by: Scott Mayhew <smayhew@redhat.com>
>>> ---
>>>  net/sunrpc/auth_gss/auth_gss.c | 8 ++++++++
>>>  1 file changed, 8 insertions(+)
>>>
>>> diff --git a/net/sunrpc/auth_gss/auth_gss.c b/net/sunrpc/auth_gss/auth_gss.c
>>> index 5c095cb8cb20..6da9ca08370d 100644
>>> --- a/net/sunrpc/auth_gss/auth_gss.c
>>> +++ b/net/sunrpc/auth_gss/auth_gss.c
>>> @@ -1721,6 +1721,14 @@ gss_validate(struct rpc_task *task, struct xdr_stream *xdr)
>>>  	if (maj_stat)
>>>  		goto bad_mic;
>>>  
>>> +	/*
>>> +	 * Normally we only recalculate the slack variables once after
>>> +	 * creating a new gss_auth, but we should also do it if the incoming
>>> +	 * verifier has a larger size than what was previously recorded.
>>
>> No quibble with the code change, but IMO the comment should work a
>> little harder to explain why the increase is needed. Something like:
>>
>> 	* When the incoming verifier is larger than expected, the
>> 	* GSS context is using a different enctype than the one used
>> 	* initially by the machine credential. Force a slack size update
>> 	* to maintain good payload alignment.
>>
>> I'm summarizing based on your commit message above...
>>
>>
>>> +	 */
>>> +	if (cred->cr_auth->au_verfsize < (XDR_QUADLEN(len) + 2))
>>> +		__set_bit(RPCAUTH_AUTH_UPDATE_SLACK, &cred->cr_auth->au_flags);
>>> +
>>>  	/* We leave it to unwrap to calculate au_rslack. For now we just
>>>  	 * calculate the length of the verifier: */
>>>  	if (test_bit(RPCAUTH_AUTH_UPDATE_SLACK, &cred->cr_auth->au_flags))
> 
> I was looking in Debian for the state of this and noticed this was
> later on never applied/submitted to mainline, is this correct? Did it
> felt through the cracks or is it considered not to be a problem to
> further tackle?

Hello Salvatore -

After further consideration, we concluded the above change is not an
adequate repair for this issue. The winter holidays have prevented
further progress, but I expect Scott will continue looking into a better
fix starting next week.


-- 
Chuck Lever