Re: [PATCH v2 0/2] fix gss seqno handling to be more rfc-compliant

[Chuck Lever]

On 6/11/25 3:05 PM, Nikhil Jha wrote:
> On Wed, Jun 11, 2025 at 02:54:09PM -0400, Chuck Lever wrote:
>> On 6/11/25 2:50 PM, Nikhil Jha wrote:
>>> On Thu, Mar 20, 2025 at 09:16:15AM -0400, Chuck Lever wrote:
>>>> On 3/19/25 1:02 PM, Nikhil Jha via B4 Relay wrote:
>>>>> When the client retransmits an operation (for example, because the
>>>>> server is slow to respond), a new GSS sequence number is associated with
>>>>> the XID. In the current kernel code the original sequence number is
>>>>> discarded. Subsequently, if a response to the original request is
>>>>> received there will be a GSS sequence number mismatch. A mismatch will
>>>>> trigger another retransmit, possibly repeating the cycle, and after some
>>>>> number of failed retries EACCES is returned.
>>>>>
>>>>> RFC2203, section 5.3.3.1 suggests a possible solution... “cache the
>>>>> RPCSEC_GSS sequence number of each request it sends” and "compute the
>>>>> checksum of each sequence number in the cache to try to match the
>>>>> checksum in the reply's verifier." This is what FreeBSD’s implementation
>>>>> does (rpc_gss_validate in sys/rpc/rpcsec_gss/rpcsec_gss.c).
>>>>>
>>>>> However, even with this cache, retransmits directly caused by a seqno
>>>>> mismatch can still cause a bad message interleaving that results in this
>>>>> bug. The RFC already suggests ignoring incorrect seqnos on the server
>>>>> side, and this seems symmetric, so this patchset also applies that
>>>>> behavior to the client.
>>>>>
>>>>> These two patches are *not* dependent on each other. I tested them by
>>>>> delaying packets with a Python script hooked up to NFQUEUE. If it would
>>>>> be helpful I can send this script along as well.
>>>>>
>>>>> Signed-off-by: Nikhil Jha <njha@xxxxxxxxxxxxxx>
>>>>> ---
>>>>> Changes since v1:
>>>>>  * Maintain the invariant that the first seqno is always first in
>>>>>    rq_seqnos, so that it doesn't need to be stored twice.
>>>>>  * Minor formatting, and resending with proper mailing-list headers so the
>>>>>    patches are easier to work with.
>>>>>
>>>>> ---
>>>>> Nikhil Jha (2):
>>>>>       sunrpc: implement rfc2203 rpcsec_gss seqnum cache
>>>>>       sunrpc: don't immediately retransmit on seqno miss
>>>>>
>>>>>  include/linux/sunrpc/xprt.h    | 17 +++++++++++-
>>>>>  include/trace/events/rpcgss.h  |  4 +--
>>>>>  include/trace/events/sunrpc.h  |  2 +-
>>>>>  net/sunrpc/auth_gss/auth_gss.c | 59 ++++++++++++++++++++++++++----------------
>>>>>  net/sunrpc/clnt.c              |  9 +++++--
>>>>>  net/sunrpc/xprt.c              |  3 ++-
>>>>>  6 files changed, 64 insertions(+), 30 deletions(-)
>>>>> ---
>>>>> base-commit: 7eb172143d5508b4da468ed59ee857c6e5e01da6
>>>>> change-id: 20250314-rfc2203-seqnum-cache-52389d14f567
>>>>>
>>>>> Best regards,
>>>>
>>>> This seems like a sensible thing to do to me.
>>>>
>>>> Acked-by: Chuck Lever <chuck.lever@xxxxxxxxxx>
>>>>
>>>> -- 
>>>> Chuck Lever
>>>
>>> Hi,
>>>
>>> We've been running this patch for a while now and noticed a (very silly
>>> in hindsight) bug.
>>>
>>> maj_stat = gss_validate_seqno_mic(ctx, task->tk_rqstp->rq_seqnos[i], seq, p, len);
>>>
>>> needs to be
>>>
>>> maj_stat = gss_validate_seqno_mic(ctx, task->tk_rqstp->rq_seqnos[i++], seq, p, len);
>>>
>>> Or the kernel gets stuck in a loop when you have more than two retries.
>>> I can resend this patch but I noticed it's already made its way into
>>> quite a few trees. Should this be a separate patch instead?
>>
>> The course of action depends on what trees you found the patch in.
>>
>>
>> -- 
>> Chuck Lever
> 
> It shows up here, so I think it's in v6.16-rc1 already.
> 
> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?h=v6.16-rc1&id=08d6ee6d8a10aef958c2af16bb121070290ed589

In that case, post your fix delta To: Anna, Cc: linux-nfs@ and she will
apply it for a subsequent upstream pull request for v6.16-rc.


-- 
Chuck Lever