fix(auth): authorize tagging replicas without rejecting replication lag

Share the remote tag read and authorization path between GET and mutations. Authorize every present replica, fail closed on unreadable targets, and skip missing replicas unless all targets are absent. Gate remote reads on possible caller access and preserve retryable local read failures for DELETE tagging.

Signed-off-by: Feng Ruohang <rh@vonng.com>

cmd/auth-handler-unread-tags.go

@@ -50,6 +50,24 @@ func authorizeRequestWithUnreadTags(ctx context.Context, r *http.Request, action
 	if s3Err == ErrNone || toAPIError(ctx, readErr).HTTPStatusCode < http.StatusInternalServerError {
 		return s3Err
 	}
+	return authorizeRequestWithTagCandidates(ctx, r, action, s3Err)
+}
+
+// authorizeRequestWithPotentialTags performs the authorization needed before
+// a remote replica can be read. An empty tag set is enough to reject a caller
+// with no possible access, but a caller whose Allow depends on existing tags
+// must be admitted so the remote copy can supply the authoritative tags.
+// The returned decision is only a gate; the actual tags must be authorized
+// again after they are read.
+func authorizeRequestWithPotentialTags(ctx context.Context, r *http.Request, action policy.Action) APIErrorCode {
+	s3Err := authorizeRequest(ctx, r, action)
+	if s3Err == ErrNone {
+		return ErrNone
+	}
+	return authorizeRequestWithTagCandidates(ctx, r, action, s3Err)
+}
+
+func authorizeRequestWithTagCandidates(ctx context.Context, r *http.Request, action policy.Action, s3Err APIErrorCode) APIErrorCode {
 	for _, existingTags := range policyExistingObjectTags(ctx, r, action) {
 		if authorizeRequestWithExistingTags(ctx, r, action, existingTags) == ErrNone {
 			return ErrNone

cmd/auth-handler-unread-tags_test.go

@@ -87,7 +87,7 @@ func TestExistingObjectTagAuthReadQuorumLost(t *testing.T) {
 	}
 
 	statement := func(effect, resource, conditions string) string {
-		st := fmt.Sprintf(`{"Effect": %q, "Action": ["s3:GetObject", "s3:PutObjectTagging"], "Resource": ["arn:aws:s3:::%s/%s"]`,
+		st := fmt.Sprintf(`{"Effect": %q, "Action": ["s3:GetObject", "s3:GetObjectTagging", "s3:PutObjectTagging", "s3:DeleteObjectTagging"], "Resource": ["arn:aws:s3:::%s/%s"]`,
 			effect, bucket, resource)
 		if conditions != "" {
 			st += `, "Condition": ` + conditions
@@ -263,6 +263,8 @@ func TestExistingObjectTagAuthReadQuorumLost(t *testing.T) {
 	taggingURL := makeTestTargetURL("", bucket, object, url.Values{"tagging": []string{""}})
 	taggingBody := []byte(`<Tagging><TagSet><Tag><Key>k</Key><Value>v</Value></Tag></TagSet></Tagging>`)
 	putTagging := request{"PutObjectTagging", http.MethodPut, taggingURL, nil, taggingBody}
+	getTagging := request{"GetObjectTagging", http.MethodGet, taggingURL, nil, nil}
+	deleteTagging := request{"DeleteObjectTagging", http.MethodDelete, taggingURL, nil, nil}
 	check := func(stage string, creds auth.Credentials, name string, req request, want int) {
 		t.Helper()
 		var rec *httptest.ResponseRecorder
@@ -302,6 +304,7 @@ func TestExistingObjectTagAuthReadQuorumLost(t *testing.T) {
 	var anonymous auth.Credentials
 	for _, u := range users {
 		check("healthy", u.creds, u.name, get, u.healthy)
+		check("healthy", u.creds, u.name, getTagging, u.healthy)
 	}
 	check("healthy", anonymous, "anonymous", get, http.StatusOK)
 	// The tags were read and allow the request: the range error is the answer.
@@ -312,12 +315,13 @@ func TestExistingObjectTagAuthReadQuorumLost(t *testing.T) {
 	missingURL := getGetObjectURL("", bucket, missing)
 	check("missing key", users[0].creds, users[0].name, request{"GET", http.MethodGet, missingURL, nil, nil}, http.StatusForbidden)
 	check("missing key", users[0].creds, users[0].name, request{"HEAD", http.MethodHead, missingURL, nil, nil}, http.StatusForbidden)
+	check("missing key", users[0].creds, users[0].name, request{"GetObjectTagging", http.MethodGet, missingURL + "?tagging", nil, nil}, http.StatusForbidden)
 
 	defer objectReadFault(z, bucket, object, 10)()
 	if _, err := z.GetObjectInfo(ctx, bucket, object, ObjectOptions{}); !isErrReadQuorum(err) {
 		t.Fatalf("GetObjectInfo with 10 of 16 drives failing: %v, want InsufficientReadQuorum", err)
 	}
-	for _, req := range []request{get, head, putTagging} {
+	for _, req := range []request{get, head, getTagging, putTagging, deleteTagging} {
 		for _, u := range users {
 			check("read quorum lost", u.creds, u.name, req, u.quorumLost)
 		}

cmd/bucket-replication.go

@@ -2773,67 +2773,107 @@ func scheduleReplication(ctx context.Context, oi ObjectInfo, o ObjectLayer, dsc
 	}
 }
 
-// proxyTaggingToRepTarget proxies tagging requests to remote targets for
-// active-active replicated setups
-func proxyTaggingToRepTarget(ctx context.Context, bucket, object string, tags *tags.Tags, opts ObjectOptions, proxyTargets *madmin.BucketTargets, authorize func(string, error) APIErrorCode) (proxy proxyResult, authErr APIErrorCode) {
-	if opts.ProxyRequest || (opts.ProxyHeaderSet && !opts.ProxyRequest) {
-		return proxy, ErrNone
-	}
-	// Keep the exact clients whose addressed versions we read. A second
-	// discovery could include a newly available, unauthorized destination.
-	var targets []*TargetClient
+// taggingProxyTarget keeps the exact client and tags that were authorized.
+// A second discovery must not introduce an unauthorized destination.
+type taggingProxyTarget struct {
+	client *TargetClient
+	tags   *tags.Tags
+}
+
+// readTaggingProxyTargets authorizes all present replicas before returning any
+// tags or allowing any mutation. Missing replicas may simply lag replication;
+// unreadable replicas must still fail closed.
+func readTaggingProxyTargets(ctx context.Context, bucket, object string, opts ObjectOptions, proxyTargets *madmin.BucketTargets, authorize func(string, error) APIErrorCode) ([]taggingProxyTarget, proxyResult, APIErrorCode) {
+	var targets []taggingProxyTarget
 	for _, target := range proxyTargets.Targets {
 		tgt := globalBucketTargetSys.GetRemoteTargetClient(bucket, target.Arn)
 		if tgt == nil || globalBucketTargetSys.isOffline(tgt.EndpointURL()) || tgt.disableProxy {
 			continue
 		}
-		targets = append(targets, tgt)
+		targets = append(targets, taggingProxyTarget{client: tgt})
 	}
 	if len(targets) == 0 {
 		err := RemoteTargetConnectionErr{Bucket: bucket, Err: errors.New("no available remote replication target")}
-		return proxyResult{Err: err}, authorize("", err)
+		return nil, proxyResult{Err: err}, authorize("", err)
 	}
 
 	var wg sync.WaitGroup
 	errs := make([]error, len(targets))
-	existingTags := make([]string, len(targets))
-	for i, tgt := range targets {
+	for i := range targets {
 		wg.Go(func() {
-			remoteTags, err := tgt.GetObjectTagging(ctx, tgt.Bucket, object, minio.GetObjectTaggingOptions{
+			tgt := &targets[i]
+			tgt.tags, errs[i] = tgt.client.GetObjectTagging(ctx, tgt.client.Bucket, object, minio.GetObjectTaggingOptions{
 				VersionID: opts.VersionID,
 				Internal:  minio.AdvancedObjectTaggingOptions{ReplicationProxyRequest: "true"},
 			})
-			errs[i] = err
-			if remoteTags != nil {
-				existingTags[i] = remoteTags.String()
-			}
 		})
 	}
 	wg.Wait()
-	// Authorize every contacted target before any mutation. A tag-based deny
-	// on one copy must not be hidden by a more permissive copy on another.
-	var readErr error
-	for i, err := range errs {
-		if code := authorize(existingTags[i], err); code != ErrNone {
-			return proxy, code
+
+	var firstNotFound, readErr error
+	for _, err := range errs {
+		switch {
+		case err == nil:
+		case isRemoteTaggingNotFound(err):
+			if firstNotFound == nil {
+				firstNotFound = err
+			}
+		default:
+			if code := authorize("", err); code != ErrNone {
+				return nil, proxyResult{}, code
+			}
+			if readErr == nil {
+				readErr = err
+			}
 		}
-		if err != nil && !isRemoteTaggingNotFound(err) && readErr == nil {
-			readErr = err
+	}
+	present := make([]taggingProxyTarget, 0, len(targets))
+	for i, tgt := range targets {
+		if errs[i] != nil {
+			continue
 		}
+		if tgt.tags == nil {
+			tgt.tags, _ = tags.MapToObjectTags(nil)
+		}
+		if code := authorize(tgt.tags.String(), nil); code != ErrNone {
+			return nil, proxyResult{}, code
+		}
+		present = append(present, tgt)
 	}
 	if readErr != nil {
-		return proxyResult{Err: readErr}, ErrNone
+		return nil, proxyResult{Err: readErr}, ErrNone
+	}
+	if len(present) == 0 {
+		// With no object anywhere, authorize the empty tag set once before
+		// disclosing its absence. No write RPC can help a missing replica.
+		return nil, proxyResult{Err: firstNotFound}, authorize("", firstNotFound)
+	}
+	return present, proxyResult{}, ErrNone
+}
+
+// proxyTaggingToRepTarget proxies tagging requests to remote targets for
+// active-active replicated setups.
+func proxyTaggingToRepTarget(ctx context.Context, bucket, object string, tags *tags.Tags, opts ObjectOptions, proxyTargets *madmin.BucketTargets, authorize func(string, error) APIErrorCode) (proxy proxyResult, authErr APIErrorCode) {
+	if opts.ProxyRequest || (opts.ProxyHeaderSet && !opts.ProxyRequest) {
+		return proxy, ErrNone
+	}
+	targets, proxy, authErr := readTaggingProxyTargets(ctx, bucket, object, opts, proxyTargets, authorize)
+	if authErr != ErrNone || proxy.Err != nil {
+		return proxy, authErr
 	}
 
-	for i, tgt := range targets {
+	var wg sync.WaitGroup
+	writeErrs := make([]error, len(targets))
+	for i, target := range targets {
 		wg.Go(func() {
+			tgt := target.client
 			if tags != nil {
-				errs[i] = tgt.PutObjectTagging(ctx, tgt.Bucket, object, tags, minio.PutObjectTaggingOptions{
+				writeErrs[i] = tgt.PutObjectTagging(ctx, tgt.Bucket, object, tags, minio.PutObjectTaggingOptions{
 					VersionID: opts.VersionID,
 					Internal:  minio.AdvancedObjectTaggingOptions{ReplicationProxyRequest: "true"},
 				})
 			} else {
-				errs[i] = tgt.RemoveObjectTagging(ctx, tgt.Bucket, object, minio.RemoveObjectTaggingOptions{
+				writeErrs[i] = tgt.RemoveObjectTagging(ctx, tgt.Bucket, object, minio.RemoveObjectTaggingOptions{
 					VersionID: opts.VersionID,
 					Internal:  minio.AdvancedObjectTaggingOptions{ReplicationProxyRequest: "true"},
 				})
@@ -2841,9 +2881,8 @@ func proxyTaggingToRepTarget(ctx context.Context, bucket, object string, tags *t
 		})
 	}
 	wg.Wait()
-	// Preserve partial success, counting only targets actually contacted.
 	var lastErr error
-	for _, err := range errs {
+	for _, err := range writeErrs {
 		if err == nil {
 			return proxy, ErrNone
 		}
@@ -2853,72 +2892,16 @@ func proxyTaggingToRepTarget(ctx context.Context, bucket, object string, tags *t
 }
 
 // proxyGetTaggingToRepTarget proxies get tagging requests to remote targets for
-// active-active replicated setups
-func proxyGetTaggingToRepTarget(ctx context.Context, bucket, object string, opts ObjectOptions, proxyTargets *madmin.BucketTargets) (tgs *tags.Tags, proxy proxyResult) {
-	// this option is set when active-active replication is in place between site A -> B,
-	// and request hits site B that does not have the object yet.
-	if opts.ProxyRequest || (opts.ProxyHeaderSet && !opts.ProxyRequest) { // true only when site B sets MinIOSourceProxyRequest header
-		return nil, proxy
+// active-active replicated setups.
+func proxyGetTaggingToRepTarget(ctx context.Context, bucket, object string, opts ObjectOptions, proxyTargets *madmin.BucketTargets, authorize func(string, error) APIErrorCode) (tgs *tags.Tags, proxy proxyResult, authErr APIErrorCode) {
+	if opts.ProxyRequest || (opts.ProxyHeaderSet && !opts.ProxyRequest) {
+		return nil, proxy, ErrNone
 	}
-	var wg sync.WaitGroup
-	errs := make([]error, len(proxyTargets.Targets))
-	tagSlc := make([]map[string]string, len(proxyTargets.Targets))
-	contacted := 0
-	for idx, t := range proxyTargets.Targets {
-		tgt := globalBucketTargetSys.GetRemoteTargetClient(bucket, t.Arn)
-		if tgt == nil || globalBucketTargetSys.isOffline(tgt.EndpointURL()) {
-			continue
-		}
-		// if proxying explicitly disabled on remote target
-		if tgt.disableProxy {
-			continue
-		}
-		contacted++
-		idx := idx
-		wg.Add(1)
-		go func(idx int, tgt *TargetClient) {
-			defer wg.Done()
-			gopts := minio.GetObjectTaggingOptions{
-				VersionID: opts.VersionID,
-				Internal: minio.AdvancedObjectTaggingOptions{
-					ReplicationProxyRequest: "true",
-				},
-			}
-			remoteTags, err := tgt.GetObjectTagging(ctx, tgt.Bucket, object, gopts)
-			if err != nil {
-				errs[idx] = err
-			} else if remoteTags != nil {
-				tagSlc[idx] = remoteTags.ToMap()
-			}
-		}(idx, tgt)
+	targets, proxy, authErr := readTaggingProxyTargets(ctx, bucket, object, opts, proxyTargets, authorize)
+	if authErr != ErrNone || proxy.Err != nil {
+		return nil, proxy, authErr
 	}
-	wg.Wait()
-	if contacted == 0 {
-		return nil, proxyResult{Err: RemoteTargetConnectionErr{
-			Bucket: bucket,
-			Err:    errors.New("no available remote replication target"),
-		}}
-	}
-	var firstNotFound error
-	for idx, err := range errs {
-		errCode := minio.ToErrorResponse(err).Code
-		if err != nil {
-			if errCode != "NoSuchKey" && errCode != "NoSuchVersion" {
-				return nil, proxyResult{Err: err}
-			}
-			if firstNotFound == nil {
-				firstNotFound = err
-			}
-			continue
-		}
-		if tagSlc[idx] != nil && tgs == nil {
-			tgs, _ = tags.MapToObjectTags(tagSlc[idx])
-		}
-	}
-	if tgs == nil {
-		proxy.Err = firstNotFound
-	}
-	return tgs, proxy
+	return targets[0].tags, proxy, ErrNone
 }
 
 func scheduleReplicationDelete(ctx context.Context, dv DeletedObjectReplicationInfo, o ObjectLayer) {

cmd/object-handlers.go

@@ -3726,9 +3726,22 @@ func (api objectAPIHandlers) GetObjectTaggingHandler(w http.ResponseWriter, r *h
 		if isErrObjectNotFound(err) || isErrVersionNotFound(err) {
 			proxytgts := getProxyTargets(ctx, bucket, object, opts)
 			if !proxytgts.Empty() {
+				if s3Error := authorizeRequestWithPotentialTags(ctx, r, policy.GetObjectTaggingAction); s3Error != ErrNone {
+					writeErrorResponse(ctx, w, errorCodes.ToAPIErr(s3Error), r.URL)
+					return
+				}
 				globalReplicationStats.Load().incProxy(bucket, getObjectTaggingAPI, false)
 				// proxy to replication target if site replication is in place.
-				tags, gerr := proxyGetTaggingToRepTarget(ctx, bucket, object, opts, proxytgts)
+				tags, gerr, s3Error := proxyGetTaggingToRepTarget(ctx, bucket, object, opts, proxytgts, func(existingTags string, readErr error) APIErrorCode {
+					if readErr != nil && !isRemoteTaggingNotFound(readErr) {
+						return authorizeRequestWithUnreadTags(ctx, r, policy.GetObjectTaggingAction, readErr)
+					}
+					return authorizeRequestWithExistingTags(ctx, r, policy.GetObjectTaggingAction, existingTags)
+				})
+				if s3Error != ErrNone {
+					writeErrorResponse(ctx, w, errorCodes.ToAPIErr(s3Error), r.URL)
+					return
+				}
 				if gerr.Err != nil || tags == nil {
 					globalReplicationStats.Load().incProxy(bucket, getObjectTaggingAPI, true)
 					writeErrorResponse(ctx, w, toAPIError(ctx, gerr.Err), r.URL)
@@ -3737,10 +3750,18 @@ func (api objectAPIHandlers) GetObjectTaggingHandler(w http.ResponseWriter, r *h
 				ot = tags
 				w.Header()[xhttp.MinIOTaggingProxied] = []string{"true"} // indicate that the request was proxied.
 			} else {
+				if s3Error := authorizeRequestWithExistingTags(ctx, r, policy.GetObjectTaggingAction, ""); s3Error != ErrNone {
+					writeErrorResponse(ctx, w, errorCodes.ToAPIErr(s3Error), r.URL)
+					return
+				}
 				writeErrorResponse(ctx, w, toAPIError(ctx, err), r.URL)
 				return
 			}
 		} else {
+			if s3Error := authorizeRequestWithUnreadTags(ctx, r, policy.GetObjectTaggingAction, err); s3Error != ErrNone {
+				writeErrorResponse(ctx, w, errorCodes.ToAPIErr(s3Error), r.URL)
+				return
+			}
 			writeErrorResponse(ctx, w, toAPIError(ctx, err), r.URL)
 			return
 		}
@@ -3841,6 +3862,10 @@ func (api objectAPIHandlers) PutObjectTaggingHandler(w http.ResponseWriter, r *h
 		if isErrObjectNotFound(err) || isErrVersionNotFound(err) {
 			proxytgts := getProxyTargets(ctx, bucket, object, opts)
 			if !proxytgts.Empty() {
+				if s3Error := authorizeRequestWithPotentialTags(ctx, r, policy.PutObjectTaggingAction); s3Error != ErrNone {
+					writeErrorResponse(ctx, w, errorCodes.ToAPIErr(s3Error), r.URL)
+					return
+				}
 				perr, s3Error := proxyTaggingToRepTarget(ctx, bucket, object, tags, opts, proxytgts, func(existingTags string, readErr error) APIErrorCode {
 					if readErr != nil && !isRemoteTaggingNotFound(readErr) {
 						return authorizeRequestWithUnreadTags(ctx, r, policy.PutObjectTaggingAction, readErr)
@@ -3969,6 +3994,10 @@ func (api objectAPIHandlers) DeleteObjectTaggingHandler(w http.ResponseWriter, r
 		if isErrObjectNotFound(err) || isErrVersionNotFound(err) {
 			proxytgts := getProxyTargets(ctx, bucket, object, opts)
 			if !proxytgts.Empty() {
+				if s3Error := authorizeRequestWithPotentialTags(ctx, r, policy.DeleteObjectTaggingAction); s3Error != ErrNone {
+					writeErrorResponse(ctx, w, errorCodes.ToAPIErr(s3Error), r.URL)
+					return
+				}
 				perr, s3Error := proxyTaggingToRepTarget(ctx, bucket, object, nil, opts, proxytgts, func(existingTags string, readErr error) APIErrorCode {
 					if readErr != nil && !isRemoteTaggingNotFound(readErr) {
 						return authorizeRequestWithUnreadTags(ctx, r, policy.DeleteObjectTaggingAction, readErr)
@@ -4001,7 +4030,13 @@ func (api objectAPIHandlers) DeleteObjectTaggingHandler(w http.ResponseWriter, r
 				return
 			}
 		}
-		if s3Error := authorizeRequestWithExistingTags(ctx, r, policy.DeleteObjectTaggingAction, ""); s3Error != ErrNone {
+		var s3Error APIErrorCode
+		if isErrObjectNotFound(err) || isErrVersionNotFound(err) {
+			s3Error = authorizeRequestWithExistingTags(ctx, r, policy.DeleteObjectTaggingAction, "")
+		} else {
+			s3Error = authorizeRequestWithUnreadTags(ctx, r, policy.DeleteObjectTaggingAction, err)
+		}
+		if s3Error != ErrNone {
 			writeErrorResponse(ctx, w, errorCodes.ToAPIErr(s3Error), r.URL)
 			return
 		}

cmd/tagging-proxy-authz_test.go

@@ -33,11 +33,18 @@ import (
 func TestAPITaggingProxyAuthorization(t *testing.T) {
 	ExecObjectLayerAPITest(ExecObjectLayerAPITestArgs{t: t, objAPITest: func(obj ObjectLayer, backend, bucket string, router http.Handler, root auth.Credentials, t *testing.T) {
 		conditional := newDeleteAuthzPolicyUser(t, backend, bucket, fmt.Sprintf(`[
-			{"Effect":"Allow","Action":["s3:PutObjectTagging","s3:DeleteObjectTagging"],"Resource":["arn:aws:s3:::%s/*"]},
-			{"Effect":"Deny","Action":["s3:PutObjectTagging","s3:DeleteObjectTagging"],"Resource":["arn:aws:s3:::%s/*"],"Condition":{"StringEquals":{"s3:ExistingObjectTag/secret":"true"}}}
+			{"Effect":"Allow","Action":["s3:GetObjectTagging","s3:PutObjectTagging","s3:DeleteObjectTagging"],"Resource":["arn:aws:s3:::%s/*"]},
+			{"Effect":"Deny","Action":["s3:GetObjectTagging","s3:PutObjectTagging","s3:DeleteObjectTagging"],"Resource":["arn:aws:s3:::%s/*"],"Condition":{"StringEquals":{"s3:ExistingObjectTag/secret":"true"}}}
 		]`, bucket, bucket))
+		tagAllow := newDeleteAuthzPolicyUser(t, backend, bucket, fmt.Sprintf(`[
+			{"Effect":"Allow","Action":["s3:GetObjectTagging","s3:PutObjectTagging","s3:DeleteObjectTagging"],"Resource":["arn:aws:s3:::%s/*"],"Condition":{"StringEquals":{"s3:ExistingObjectTag/secret":"false"}}}
+		]`, bucket))
+		denied := newDeleteAuthzPolicyUser(t, backend, bucket, fmt.Sprintf(`[
+			{"Effect":"Deny","Action":["s3:*"],"Resource":["arn:aws:s3:::%s/*"]}
+		]`, bucket))
+		zero := iamAdminUser(t.Context(), t, globalIAMSys, "tagging-no-policy-"+mustGetUUID(), "")
 		versionID := mustGetUUID()
-		for _, method := range []string{http.MethodPut, http.MethodDelete} {
+		for _, method := range []string{http.MethodGet, http.MethodPut, http.MethodDelete} {
 			for _, tc := range []struct {
 				name                                string
 				tags                                []string
@@ -45,17 +52,32 @@ func TestAPITaggingProxyAuthorization(t *testing.T) {
 				readStatus, writeStatus, wantStatus int
 				wantWrites                          int32
 				disabledFirst                       bool
+				firstReadStatus                     int
+				noReads                             bool
 			}{
 				{name: "deny-second-target", tags: []string{"false", "true"}, cred: conditional, wantStatus: http.StatusForbidden},
 				{name: "deny-first-target", tags: []string{"true", "false"}, cred: conditional, wantStatus: http.StatusForbidden},
 				{name: "all-authorized", tags: []string{"false", "false"}, cred: conditional, wantWrites: 2},
-				{name: "anonymous", tags: []string{"false"}, wantStatus: http.StatusForbidden},
-				{name: "invalid-credentials", tags: []string{"false"}, cred: auth.Credentials{AccessKey: root.AccessKey, SecretKey: "wrong-secret-key"}, wantStatus: http.StatusForbidden},
+				{name: "anonymous", tags: []string{"false"}, wantStatus: http.StatusForbidden, noReads: true},
+				{name: "invalid-credentials", tags: []string{"false"}, cred: auth.Credentials{AccessKey: root.AccessKey, SecretKey: "wrong-secret-key"}, wantStatus: http.StatusForbidden, noReads: true},
+				{name: "zero-permissions", tags: []string{"false"}, cred: zero, wantStatus: http.StatusForbidden, noReads: true},
+				{name: "zero-permissions-missing", tags: []string{"false"}, cred: zero, readStatus: http.StatusNotFound, wantStatus: http.StatusForbidden, noReads: true},
+				{name: "unconditional-deny", tags: []string{"false"}, cred: denied, wantStatus: http.StatusForbidden, noReads: true},
 				{name: "unreadable", tags: []string{"false"}, cred: root, readStatus: http.StatusServiceUnavailable, wantStatus: http.StatusServiceUnavailable},
-				{name: "missing-version", tags: []string{"false"}, cred: root, readStatus: http.StatusNotFound, writeStatus: http.StatusNotFound, wantStatus: http.StatusNotFound, wantWrites: 1},
+				{name: "missing-version", tags: []string{"false", "false"}, cred: root, readStatus: http.StatusNotFound, wantStatus: http.StatusNotFound},
+				{name: "tag-allow-missing-version", tags: []string{"false"}, cred: tagAllow, readStatus: http.StatusNotFound, wantStatus: http.StatusForbidden},
+				{name: "tag-allow-lagging-first", tags: []string{"false", "false"}, cred: tagAllow, firstReadStatus: http.StatusNotFound, wantWrites: 1},
+				{name: "tag-allow-lagging-second", tags: []string{"false", "false"}, cred: tagAllow, firstReadStatus: http.StatusOK, readStatus: http.StatusNotFound, wantWrites: 1},
+				{name: "tag-allow-present-untagged", tags: []string{"false", ""}, cred: tagAllow, wantStatus: http.StatusForbidden},
+				{name: "tag-allow-unreadable-first", tags: []string{"false", "false"}, cred: tagAllow, firstReadStatus: http.StatusServiceUnavailable, wantStatus: http.StatusServiceUnavailable},
+				{name: "tag-allow-unreadable-second", tags: []string{"false", "false"}, cred: tagAllow, firstReadStatus: http.StatusOK, readStatus: http.StatusServiceUnavailable, wantStatus: http.StatusServiceUnavailable},
 				{name: "disabled-target", tags: []string{"true", "false"}, cred: conditional, disabledFirst: true, wantWrites: 1},
+				{name: "no-available-target", tags: []string{"false"}, cred: tagAllow, disabledFirst: true, wantStatus: http.StatusServiceUnavailable, noReads: true},
 				{name: "skipped-target-cannot-mask-failure", tags: []string{"false", "false"}, cred: root, disabledFirst: true, writeStatus: http.StatusServiceUnavailable, wantStatus: http.StatusServiceUnavailable, wantWrites: 1},
 			} {
+				if method == http.MethodGet && tc.writeStatus != 0 {
+					continue // This case only exercises a remote mutation failure.
+				}
 				t.Run(backend+"/"+method+"/"+tc.name, func(t *testing.T) {
 					var reads, writes atomic.Int32
 					globalBucketTargetSys.Lock()
@@ -63,6 +85,10 @@ func TestAPITaggingProxyAuthorization(t *testing.T) {
 					globalBucketTargetSys.Unlock()
 					cfg := replication.Config{}
 					for i, value := range tc.tags {
+						readStatus := tc.readStatus
+						if i == 0 && tc.firstReadStatus != 0 {
+							readStatus = tc.firstReadStatus
+						}
 						target := newILMTestTarget(t)
 						registerILMTestTarget(t, obj, bucket, target, func(w http.ResponseWriter, r *http.Request) {
 							if r.URL.Query().Get("versionId") != versionID || !r.URL.Query().Has("tagging") || r.Header.Get(xhttp.MinIOSourceProxyRequest) != "true" {
@@ -71,12 +97,15 @@ func TestAPITaggingProxyAuthorization(t *testing.T) {
 							status := tc.writeStatus
 							if r.Method == http.MethodGet {
 								reads.Add(1)
-								status = tc.readStatus
+								status = readStatus
 							} else {
 								writes.Add(1)
+								if readStatus == http.StatusNotFound {
+									t.Error("tagging write reached a missing replica")
+								}
 							}
 							w.Header().Set("Content-Type", "application/xml")
-							if status != 0 {
+							if status != 0 && status != http.StatusOK {
 								w.WriteHeader(status)
 								code := "ServiceUnavailable"
 								if status == http.StatusNotFound {
@@ -87,7 +116,11 @@ func TestAPITaggingProxyAuthorization(t *testing.T) {
 							}
 							switch r.Method {
 							case http.MethodGet:
-								fmt.Fprintf(w, "<Tagging><TagSet><Tag><Key>secret</Key><Value>%s</Value></Tag></TagSet></Tagging>", value)
+								if value == "" {
+									fmt.Fprint(w, "<Tagging><TagSet></TagSet></Tagging>")
+								} else {
+									fmt.Fprintf(w, "<Tagging><TagSet><Tag><Key>secret</Key><Value>%s</Value></Tag></TagSet></Tagging>", value)
+								}
 							case http.MethodDelete:
 								w.WriteHeader(http.StatusNoContent)
 							}
@@ -130,11 +163,15 @@ func TestAPITaggingProxyAuthorization(t *testing.T) {
 							wantStatus = http.StatusNoContent
 						}
 					}
-					if rec.Code != wantStatus || writes.Load() != tc.wantWrites {
-						t.Errorf("status=%d writes=%d, want status=%d writes=%d: %s", rec.Code, writes.Load(), wantStatus, tc.wantWrites, rec.Body.String())
+					wantWrites := tc.wantWrites
+					if method == http.MethodGet {
+						wantWrites = 0
 					}
-					if tc.name == "invalid-credentials" && reads.Load() != 0 {
-						t.Errorf("invalid credentials reached %d remote reads", reads.Load())
+					if rec.Code != wantStatus || writes.Load() != wantWrites {
+						t.Errorf("status=%d writes=%d, want status=%d writes=%d: %s", rec.Code, writes.Load(), wantStatus, wantWrites, rec.Body.String())
+					}
+					if tc.noReads && reads.Load() != 0 {
+						t.Errorf("unauthorized request reached %d remote reads", reads.Load())
 					}
 				})
 			}