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
