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

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <81cd5e1e-218d-4e24-b127-c8d1757e4d99@oracle.com>
Date: Wed, 11 Jun 2025 14:54:09 -0400
From: Chuck Lever <chuck.lever@...cle.com>
To: Nikhil Jha <njha@...estreet.com>
Cc: Trond Myklebust <trondmy@...nel.org>, Anna Schumaker <anna@...nel.org>,
        Jeff Layton <jlayton@...nel.org>, Neil Brown <neilb@...e.de>,
        Olga Kornievskaia <okorniev@...hat.com>, Dai Ngo <Dai.Ngo@...cle.com>,
        Tom Talpey <tom@...pey.com>, "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>, Simon Horman <horms@...nel.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Masami Hiramatsu
 <mhiramat@...nel.org>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        linux-nfs@...r.kernel.org, linux-kernel@...r.kernel.org,
        netdev@...r.kernel.org, linux-trace-kernel@...r.kernel.org
Subject: Re: [PATCH v2 0/2] fix gss seqno handling to be more rfc-compliant

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@...estreet.com>
>>> ---
>>> 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@...cle.com>
>>
>> -- 
>> 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