sunrpc: implement rfc2203 rpcsec_gss seqnum cache

This implements a sequence number cache of the last three (right now
hardcoded) sent sequence numbers for a given XID, as suggested by the
RFC.

From RFC2203 5.3.3.1:

"Note that the sequence number algorithm requires that the client
increment the sequence number even if it is retrying a request with
the same RPC transaction identifier.  It is not infrequent for
clients to get into a situation where they send two or more attempts
and a slow server sends the reply for the first attempt. With
RPCSEC_GSS, each request and reply will have a unique sequence
number. If the client wishes to improve turn around time on the RPC
call, it can cache the RPCSEC_GSS sequence number of each request it
sends. Then when it receives a response with a matching RPC
transaction identifier, it can compute the checksum of each sequence
number in the cache to try to match the checksum in the reply's
verifier."

Signed-off-by: Nikhil Jha <njha@janestreet.com>
Acked-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Anna Schumaker <anna.schumaker@oracle.com>

3 files changed, 19 insertions, 4 deletions

diff --git a/include/linux/sunrpc/xprt.h b/include/linux/sunrpc/xprt.h
index 81b952649d35..f46d1fb8f71a 100644
--- a/include/linux/sunrpc/xprt.h
+++ b/include/linux/sunrpc/xprt.h
@@ -30,6 +30,8 @@
 #define RPC_MAXCWND(xprt)	((xprt)->max_reqs << RPC_CWNDSHIFT)
 #define RPCXPRT_CONGESTED(xprt) ((xprt)->cong >= (xprt)->cwnd)
 
+#define RPC_GSS_SEQNO_ARRAY_SIZE 3U
+
 enum rpc_display_format_t {
 	RPC_DISPLAY_ADDR = 0,
 	RPC_DISPLAY_PORT,
@@ -66,7 +68,8 @@ struct rpc_rqst {
 	struct rpc_cred *	rq_cred;	/* Bound cred */
 	__be32			rq_xid;		/* request XID */
 	int			rq_cong;	/* has incremented xprt->cong */
-	u32			rq_seqno;	/* gss seq no. used on req. */
+	u32			rq_seqnos[RPC_GSS_SEQNO_ARRAY_SIZE];	/* past gss req seq nos. */
+	unsigned int		rq_seqno_count;	/* number of entries in rq_seqnos */
 	int			rq_enc_pages_num;
 	struct page		**rq_enc_pages;	/* scratch pages for use by
 						   gss privacy code */
@@ -119,6 +122,18 @@ struct rpc_rqst {
 #define rq_svec			rq_snd_buf.head
 #define rq_slen			rq_snd_buf.len
 
+static inline int xprt_rqst_add_seqno(struct rpc_rqst *req, u32 seqno)
+{
+	if (likely(req->rq_seqno_count < RPC_GSS_SEQNO_ARRAY_SIZE))
+		req->rq_seqno_count++;
+
+	/* Shift array to make room for the newest element at the beginning */
+	memmove(&req->rq_seqnos[1], &req->rq_seqnos[0],
+		(RPC_GSS_SEQNO_ARRAY_SIZE - 1) * sizeof(req->rq_seqnos[0]));
+	req->rq_seqnos[0] = seqno;
+	return 0;
+}
+
 /* RPC transport layer security policies */
 enum xprtsec_policies {
 	RPC_XPRTSEC_NONE = 0,
diff --git a/include/trace/events/rpcgss.h b/include/trace/events/rpcgss.h
index b0b6300a0cab..8aeae06cf434 100644
--- a/include/trace/events/rpcgss.h
+++ b/include/trace/events/rpcgss.h
@@ -409,7 +409,7 @@ TRACE_EVENT(rpcgss_seqno,
 		__entry->task_id = task->tk_pid;
 		__entry->client_id = task->tk_client->cl_clid;
 		__entry->xid = be32_to_cpu(rqst->rq_xid);
-		__entry->seqno = rqst->rq_seqno;
+		__entry->seqno = *rqst->rq_seqnos;
 	),
 
 	TP_printk(SUNRPC_TRACE_TASK_SPECIFIER " xid=0x%08x seqno=%u",
@@ -440,7 +440,7 @@ TRACE_EVENT(rpcgss_need_reencode,
 		__entry->client_id = task->tk_client->cl_clid;
 		__entry->xid = be32_to_cpu(task->tk_rqstp->rq_xid);
 		__entry->seq_xmit = seq_xmit;
-		__entry->seqno = task->tk_rqstp->rq_seqno;
+		__entry->seqno = *task->tk_rqstp->rq_seqnos;
 		__entry->ret = ret;
 	),
 
diff --git a/include/trace/events/sunrpc.h b/include/trace/events/sunrpc.h
index 5d331383047b..751af7b024f9 100644
--- a/include/trace/events/sunrpc.h
+++ b/include/trace/events/sunrpc.h
@@ -1100,7 +1100,7 @@ TRACE_EVENT(xprt_transmit,
 		__entry->client_id = rqst->rq_task->tk_client ?
 			rqst->rq_task->tk_client->cl_clid : -1;
 		__entry->xid = be32_to_cpu(rqst->rq_xid);
-		__entry->seqno = rqst->rq_seqno;
+		__entry->seqno = *rqst->rq_seqnos;
 		__entry->status = status;
 	),