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 <[e-mail]>
Acked-by: Chuck Lever <[e-mail]>
Signed-off-by: Anna Schumaker <[e-mail]>

include/linux/sunrpc/xprt.h

···
 #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,
···
 	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 */
···
 };
 #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 {

include/trace/events/rpcgss.h

···
 		__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",
···
 		__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;
 	),
 

include/trace/events/sunrpc.h

···
 		__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;
 	),
 

net/sunrpc/auth_gss/auth_gss.c

···
 	struct kvec	iov;
 	struct xdr_buf	verf_buf;
 	int status;
+	u32 seqno;
 
 	/* Credential */
 
···
 	cred_len = p++;
 
 	spin_lock(&ctx->gc_seq_lock);
-	req->rq_seqno = (ctx->gc_seq < MAXSEQ) ? ctx->gc_seq++ : MAXSEQ;
+	seqno = (ctx->gc_seq < MAXSEQ) ? ctx->gc_seq++ : MAXSEQ;
+	xprt_rqst_add_seqno(req, seqno);
 	spin_unlock(&ctx->gc_seq_lock);
-	if (req->rq_seqno == MAXSEQ)
+	if (*req->rq_seqnos == MAXSEQ)
 		goto expired;
 	trace_rpcgss_seqno(task);
 
 	*p++ = cpu_to_be32(RPC_GSS_VERSION);
 	*p++ = cpu_to_be32(ctx->gc_proc);
-	*p++ = cpu_to_be32(req->rq_seqno);
+	*p++ = cpu_to_be32(*req->rq_seqnos);
 	*p++ = cpu_to_be32(gss_cred->gc_service);
 	p = xdr_encode_netobj(p, &ctx->gc_wire_ctx);
 	*cred_len = cpu_to_be32((p - (cred_len + 1)) << 2);
···
 	return 0;
 }
 
+static u32
+gss_validate_seqno_mic(struct gss_cl_ctx *ctx, u32 seqno, __be32 *seq, __be32 *p, u32 len)
+{
+	struct kvec iov;
+	struct xdr_buf verf_buf;
+	struct xdr_netobj mic;
+
+	*seq = cpu_to_be32(seqno);
+	iov.iov_base = seq;
+	iov.iov_len = 4;
+	xdr_buf_from_iov(&iov, &verf_buf);
+	mic.data = (u8 *)p;
+	mic.len = len;
+	return gss_verify_mic(ctx->gc_gss_ctx, &verf_buf, &mic);
+}
+
 static int
 gss_validate(struct rpc_task *task, struct xdr_stream *xdr)
 {
 	struct rpc_cred *cred = task->tk_rqstp->rq_cred;
 	struct gss_cl_ctx *ctx = gss_cred_get_ctx(cred);
 	__be32		*p, *seq = NULL;
-	struct kvec	iov;
-	struct xdr_buf	verf_buf;
-	struct xdr_netobj mic;
 	u32		len, maj_stat;
 	int		status;
+	int		i = 1; /* don't recheck the first item */
 
 	p = xdr_inline_decode(xdr, 2 * sizeof(*p));
 	if (!p)
···
 	seq = kmalloc(4, GFP_KERNEL);
 	if (!seq)
 		goto validate_failed;
-	*seq = cpu_to_be32(task->tk_rqstp->rq_seqno);
-	iov.iov_base = seq;
-	iov.iov_len = 4;
-	xdr_buf_from_iov(&iov, &verf_buf);
-	mic.data = (u8 *)p;
-	mic.len = len;
-	maj_stat = gss_verify_mic(ctx->gc_gss_ctx, &verf_buf, &mic);
+	maj_stat = gss_validate_seqno_mic(ctx, task->tk_rqstp->rq_seqnos[0], seq, p, len);
+	/* RFC 2203 5.3.3.1 - compute the checksum of each sequence number in the cache */
+	while (unlikely(maj_stat == GSS_S_BAD_SIG && i < task->tk_rqstp->rq_seqno_count))
+		maj_stat = gss_validate_seqno_mic(ctx, task->tk_rqstp->rq_seqnos[i], seq, p, len);
 	if (maj_stat == GSS_S_CONTEXT_EXPIRED)
 		clear_bit(RPCAUTH_CRED_UPTODATE, &cred->cr_flags);
 	if (maj_stat)
···
 	if (!p)
 		goto wrap_failed;
 	integ_len = p++;
-	*p = cpu_to_be32(rqstp->rq_seqno);
+	*p = cpu_to_be32(*rqstp->rq_seqnos);
 
 	if (rpcauth_wrap_req_encode(task, xdr))
 		goto wrap_failed;
···
 	if (!p)
 		goto wrap_failed;
 	opaque_len = p++;
-	*p = cpu_to_be32(rqstp->rq_seqno);
+	*p = cpu_to_be32(*rqstp->rq_seqnos);
 
 	if (rpcauth_wrap_req_encode(task, xdr))
 		goto wrap_failed;
···
 	offset = rcv_buf->len - xdr_stream_remaining(xdr);
 	if (xdr_stream_decode_u32(xdr, &seqno))
 		goto unwrap_failed;
-	if (seqno != rqstp->rq_seqno)
+	if (seqno != *rqstp->rq_seqnos)
 		goto bad_seqno;
 	if (xdr_buf_subsegment(rcv_buf, &gss_data, offset, len))
 		goto unwrap_failed;
···
 	trace_rpcgss_unwrap_failed(task);
 	goto out;
 bad_seqno:
-	trace_rpcgss_bad_seqno(task, rqstp->rq_seqno, seqno);
+	trace_rpcgss_bad_seqno(task, *rqstp->rq_seqnos, seqno);
 	goto out;
 bad_mic:
 	trace_rpcgss_verify_mic(task, maj_stat);
···
 	if (maj_stat != GSS_S_COMPLETE)
 		goto bad_unwrap;
 	/* gss_unwrap decrypted the sequence number */
-	if (be32_to_cpup(p++) != rqstp->rq_seqno)
+	if (be32_to_cpup(p++) != *rqstp->rq_seqnos)
 		goto bad_seqno;
 
 	/* gss_unwrap redacts the opaque blob from the head iovec.
···
 	trace_rpcgss_unwrap_failed(task);
 	return -EIO;
 bad_seqno:
-	trace_rpcgss_bad_seqno(task, rqstp->rq_seqno, be32_to_cpup(--p));
+	trace_rpcgss_bad_seqno(task, *rqstp->rq_seqnos, be32_to_cpup(--p));
 	return -EIO;
 bad_unwrap:
 	trace_rpcgss_unwrap(task, maj_stat);
···
 	if (!ctx)
 		goto out;
 
-	if (gss_seq_is_newer(req->rq_seqno, READ_ONCE(ctx->gc_seq)))
+	if (gss_seq_is_newer(*req->rq_seqnos, READ_ONCE(ctx->gc_seq)))
 		goto out_ctx;
 
 	seq_xmit = READ_ONCE(ctx->gc_seq_xmit);
-	while (gss_seq_is_newer(req->rq_seqno, seq_xmit)) {
+	while (gss_seq_is_newer(*req->rq_seqnos, seq_xmit)) {
 		u32 tmp = seq_xmit;
 
-		seq_xmit = cmpxchg(&ctx->gc_seq_xmit, tmp, req->rq_seqno);
+		seq_xmit = cmpxchg(&ctx->gc_seq_xmit, tmp, *req->rq_seqnos);
 		if (seq_xmit == tmp) {
 			ret = false;
 			goto out_ctx;
···
 
 	win = ctx->gc_win;
 	if (win > 0)
-		ret = !gss_seq_is_newer(req->rq_seqno, seq_xmit - win);
+		ret = !gss_seq_is_newer(*req->rq_seqnos, seq_xmit - win);
 
 out_ctx:
 	gss_put_ctx(ctx);

net/sunrpc/xprt.c

···
 				INIT_LIST_HEAD(&req->rq_xmit2);
 				goto out;
 			}
-		} else if (!req->rq_seqno) {
+		} else if (req->rq_seqno_count == 0) {
 			list_for_each_entry(pos, &xprt->xmit_queue, rq_xmit) {
 				if (pos->rq_task->tk_owner != task->tk_owner)
 					continue;
···
 	req->rq_snd_buf.bvec = NULL;
 	req->rq_rcv_buf.bvec = NULL;
 	req->rq_release_snd_buf = NULL;
+	req->rq_seqno_count = 0;
 	xprt_init_majortimeo(task, req, task->tk_client->cl_timeout);
 
 	trace_xprt_reserve(req);