NFSD: Fix the NFSv4.1 CREATE_SESSION operation

RFC 8881 Section 18.36.4 discusses the implementation of the NFSv4.1
CREATE_SESSION operation. The section defines four phases of
operation.

Phase 2 processes the CREATE_SESSION sequence ID. As a separate
step, Phase 3 evaluates the CREATE_SESSION arguments.

The problem we are concerned with is when phase 2 is successful but
phase 3 fails. The spec language in this case is "No changes are
made to any client records on the server."

RFC 8881 Section 18.35.4 defines a "client record", and it does
/not/ contain any details related to the special CREATE_SESSION
slot. Therefore NFSD is incorrect to skip incrementing the
CREATE_SESSION sequence id when phase 3 (see Section 18.36.4) of
CREATE_SESSION processing fails. In other words, even though NFSD
happens to store the cs_slot in a client record, in terms of the
protocol the slot is logically separate from the client record.

Three complications:

1. The world has moved on since commit 86c3e16cc7 ("nfsd4: confirm
   only on succesful create_session") broke this. So we can't simply
   revert that commit.

2. NFSD's CREATE_SESSION implementation does not cleanly delineate
   the logic of phases 2 and 3. So this won't be a surgical fix.

3. Because of the way it currently handles the CREATE_SESSION slot
   sequence number, nfsd4_create_session() isn't caching error
   responses in the CREATE_SESSION slot. Instead of replaying the
   response cache in those cases, it's executing the transaction
   again.

Reorganize the CREATE_SESSION slot sequence number accounting. This
requires that error responses are appropriately cached in the
CREATE_SESSION slot (once it is found).

Reported-by: Connor Smith <connor.smith@hitachivantara.com>
Closes: https://bugzilla.kernel.org/show_bug.cgi?id=218382
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>

fs/nfsd/nfs4state.c

@@ -3562,6 +3562,9 @@ nfsd4_exchange_id(struct svc_rqst *rqstp, struct nfsd4_compound_state *cstate,
 	new->cl_spo_must_allow.u.words[0] = exid->spo_must_allow[0];
 	new->cl_spo_must_allow.u.words[1] = exid->spo_must_allow[1];
 
+	/* Contrived initial CREATE_SESSION response */
+	new->cl_cs_slot.sl_status = nfserr_seq_misordered;
+
 	add_to_unconfirmed(new);
 	swap(new, conf);
 out_copy:
@@ -3732,10 +3735,10 @@ nfsd4_create_session(struct svc_rqst *rqstp,
 	struct nfsd4_create_session *cr_ses = &u->create_session;
 	struct sockaddr *sa = svc_addr(rqstp);
 	struct nfs4_client *conf, *unconf;
+	struct nfsd4_clid_slot *cs_slot;
 	struct nfs4_client *old = NULL;
 	struct nfsd4_session *new;
 	struct nfsd4_conn *conn;
-	struct nfsd4_clid_slot *cs_slot = NULL;
 	__be32 status = 0;
 	struct nfsd_net *nn = net_generic(SVC_NET(rqstp), nfsd_net_id);
 
@@ -3761,50 +3764,51 @@ nfsd4_create_session(struct svc_rqst *rqstp,
 	spin_lock(&nn->client_lock);
 	unconf = find_unconfirmed_client(&cr_ses->clientid, true, nn);
 	conf = find_confirmed_client(&cr_ses->clientid, true, nn);
-	WARN_ON_ONCE(conf && unconf);
+	if (!conf && !unconf) {
+		status = nfserr_stale_clientid;
+		goto out_free_conn;
+	}
+
+	if (conf)
+		cs_slot = &conf->cl_cs_slot;
+	else
+		cs_slot = &unconf->cl_cs_slot;
+	status = check_slot_seqid(cr_ses->seqid, cs_slot->sl_seqid, 0);
+	if (status) {
+		if (status == nfserr_replay_cache) {
+			status = nfsd4_replay_create_session(cr_ses, cs_slot);
+			goto out_free_conn;
+		}
+		goto out_cache_error;
+	}
+	cs_slot->sl_seqid++;
+	cr_ses->seqid = cs_slot->sl_seqid;
 
 	if (conf) {
 		status = nfserr_wrong_cred;
 		if (!nfsd4_mach_creds_match(conf, rqstp))
-			goto out_free_conn;
+			goto out_cache_error;
-		cs_slot = &conf->cl_cs_slot;
+	} else {
-		status = check_slot_seqid(cr_ses->seqid, cs_slot->sl_seqid, 0);
-		if (status) {
-			if (status == nfserr_replay_cache)
-				status = nfsd4_replay_create_session(cr_ses, cs_slot);
-			goto out_free_conn;
-		}
-	} else if (unconf) {
 		status = nfserr_clid_inuse;
 		if (!same_creds(&unconf->cl_cred, &rqstp->rq_cred) ||
 		    !rpc_cmp_addr(sa, (struct sockaddr *) &unconf->cl_addr)) {
 			trace_nfsd_clid_cred_mismatch(unconf, rqstp);
-			goto out_free_conn;
+			goto out_cache_error;
 		}
 		status = nfserr_wrong_cred;
 		if (!nfsd4_mach_creds_match(unconf, rqstp))
-			goto out_free_conn;
+			goto out_cache_error;
-		cs_slot = &unconf->cl_cs_slot;
-		status = check_slot_seqid(cr_ses->seqid, cs_slot->sl_seqid, 0);
-		if (status) {
-			/* an unconfirmed replay returns misordered */
-			status = nfserr_seq_misordered;
-			goto out_free_conn;
-		}
 		old = find_confirmed_client_by_name(&unconf->cl_name, nn);
 		if (old) {
 			status = mark_client_expired_locked(old);
 			if (status) {
 				old = NULL;
-				goto out_free_conn;
+				goto out_cache_error;
 			}
 			trace_nfsd_clid_replaced(&old->cl_clientid);
 		}
 		move_to_confirmed(unconf);
 		conf = unconf;
-	} else {
-		status = nfserr_stale_clientid;
-		goto out_free_conn;
 	}
 	status = nfs_ok;
 	/* Persistent sessions are not supported */
@@ -3817,8 +3821,6 @@ nfsd4_create_session(struct svc_rqst *rqstp,
 
 	memcpy(cr_ses->sessionid.data, new->se_sessionid.data,
 	       NFS4_MAX_SESSIONID_LEN);
-	cs_slot->sl_seqid++;
-	cr_ses->seqid = cs_slot->sl_seqid;
 
 	/* cache solo and embedded create sessions under the client_lock */
 	nfsd4_cache_create_session(cr_ses, cs_slot, status);
@@ -3831,6 +3833,9 @@ nfsd4_create_session(struct svc_rqst *rqstp,
 	if (old)
 		expire_client(old);
 	return status;
+
+out_cache_error:
+	nfsd4_cache_create_session(cr_ses, cs_slot, status);
 out_free_conn:
 	spin_unlock(&nn->client_lock);
 	free_conn(conn);