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

[Chuck Lever]

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