fix(auth): scope unread tag candidates to effective policies

Select cached user, group, role and session policies without lazy IAM reads. Keep alternative tag values and Deny keys when combining candidates, and bound intermediate combinations as well as authorization attempts.

Cover unrelated cached policies, intersecting tag conditions, temporary credentials, root-derived credentials and cache-only lookup regressions for issue #293.

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

cmd/auth-handler-unread-tags.go

@@ -27,22 +27,24 @@ import (
 
 	"github.com/minio/minio-go/v7/pkg/set"
 	"github.com/minio/minio-go/v7/pkg/tags"
+	"github.com/minio/minio/internal/arn"
 	"github.com/minio/minio/internal/auth"
 	"github.com/minio/minio/internal/logger"
 	"github.com/pgsty/silo-pkg/v3/policy"
 	"github.com/pgsty/silo-pkg/v3/policy/condition"
+	"github.com/puzpuzpuz/xsync/v3"
 )
 
-// authorizeRequestWithUnreadTags authorizes action on an object whose stored
+// authorizeRequestWithUnreadTags decides whether to disclose readErr for an
-// tags could not be read because reading the object failed with readErr.
+// object whose stored tags could not be read. It must not grant object access.
 //
 // Without the tags, an Allow statement that tests s3:ExistingObjectTag cannot
 // match, so a caller allowed only by such a statement would get AccessDenied,
 // which clients do not retry, for a transient server error such as lost read
-// quorum. For a server error the request is therefore also authorized as if
+// quorum. For a server error, try a bounded set of tags from the caller's
-// the object carried tags that the policies ask for: a caller that some tags
+// policies and return the storage error if normal authorization accepts one.
-// let through gets the error, a caller that no tags let through still gets
+// If no candidate passes, keep AccessDenied. This is not an exhaustive policy
-// AccessDenied. For any other error, NoSuchKey among them, the tags stay empty.
+// solver. For any other error, NoSuchKey among them, the tags stay empty.
 func authorizeRequestWithUnreadTags(ctx context.Context, r *http.Request, action policy.Action, readErr error) APIErrorCode {
 	s3Err := authorizeRequest(ctx, r, action)
 	if s3Err == ErrNone || toAPIError(ctx, readErr).HTTPStatusCode < http.StatusInternalServerError {
@@ -76,17 +78,16 @@ func policyExistingObjectTags(ctx context.Context, r *http.Request, action polic
 	bucket, object := reqInfo.BucketName, reqInfo.ObjectName
 	var (
 		allows [][]map[string]string // per policy set, the tags its Allow statements ask for
-		denies []map[string]string   // tags that keep a Deny statement from matching
+		denies [][]map[string]string // per Deny statement, alternative tags that keep it from matching
 	)
-	// add files the tags of a statement that applies to action on the
+	// add collects the tags of a statement that applies to action on the
 	// object, whatever its conditions.
 	add := func(effect policy.Effect, conditions condition.Functions, values map[string][]string, fromSet *[]map[string]string) {
-		if tagMap, ok := existingObjectTagsFor(effect, conditions, values); ok {
+		candidates := existingObjectTagsCandidatesFor(effect, conditions, values)
 		if effect == policy.Allow {
-				*fromSet = append(*fromSet, tagMap)
+			*fromSet = append(*fromSet, candidates...)
-			} else {
+		} else if len(candidates) > 0 {
-				denies = append(denies, tagMap)
+			denies = append(denies, candidates)
-			}
 		}
 	}
 	switch {
@@ -107,17 +108,7 @@ func policyExistingObjectTags(ctx context.Context, r *http.Request, action polic
 		allows = append(allows, fromSet)
 	case newGlobalAuthZPluginFn() == nil && globalIAMSys.Initialized():
 		values := getConditionValues(r, "", reqInfo.Cred)
-		// From the cache only: reading the drives may be what just failed.
+		policySets := globalIAMSys.unreadTagPolicySets(reqInfo.Cred)
-		docs, _ := globalIAMSys.store.listPolicyDocs(ctx, "")
-		policySets := [][]policy.Policy{nil}
-		for _, name := range slices.Sorted(maps.Keys(docs)) {
-			policySets[0] = append(policySets[0], docs[name].Policy)
-		}
-		if sp, ok := reqInfo.Cred.Claims[sessionPolicyNameExtracted].(string); ok {
-			if p, err := policy.ParseConfig(strings.NewReader(sp)); err == nil {
-				policySets = append(policySets, []policy.Policy{*p})
-			}
-		}
 		for _, policies := range policySets {
 			var fromSet []map[string]string
 			for _, p := range policies {
@@ -132,72 +123,131 @@ func policyExistingObjectTags(ctx context.Context, r *http.Request, action polic
 			allows = append(allows, fromSet)
 		}
 	}
-	return combineExistingObjectTags(allows, denies)
+	return combineExistingObjectTags(append(allows, denies...))
 }
 
-// combineExistingObjectTags merges the tags of one Allow statement of each
+// unreadTagMappings reuses the normal user/group mapping lookup without lazy
-// policy set, or of none for a set that may allow without tags, and tries each
+// storage reads. Missing cache entries contribute no candidates; the regular
-// result also with the tags that keep the Deny statements from matching. The
+// authorization still decides whether any candidate is allowed.
-// first tags win a conflict; the authorization of the result settles it.
+type unreadTagMappings struct {
-func combineExistingObjectTags(allows [][]map[string]string, denies []map[string]string) []string {
+	*IAMStoreSys
-	merge := func(parts ...map[string]string) map[string]string {
+}
-		merged := make(map[string]string)
+
-		for _, part := range parts {
+func (unreadTagMappings) loadMappedPolicy(context.Context, string, IAMUserType, bool, *xsync.MapOf[string, MappedPolicy]) error {
-			for k, v := range part {
+	return errNoSuchPolicy
+}
+
+func (unreadTagMappings) loadGroup(context.Context, string, map[string]GroupInfo) error {
+	return errNoSuchGroup
+}
+
+// unreadTagPolicySets selects only this credential's cached policies. Base
+// and session policies remain separate because both must allow the request.
+// This only supplies candidates, so identity, claims and policy validity are
+// left to the normal authorization on each candidate.
+func (sys *IAMSys) unreadTagPolicySets(cred auth.Credentials) [][]policy.Policy {
+	derived := cred.IsTemp() || cred.IsServiceAccount()
+	name := cred.AccessKey
+	if derived {
+		name = cred.ParentUser
+	}
+	cache := sys.store.rlock()
+	defer sys.store.runlock()
+	var names []string
+	roleARN := (policy.Args{Claims: cred.Claims}).GetRoleArn()
+	switch {
+	case name == globalActiveCred.AccessKey:
+	case derived && roleARN != "":
+		parsed, err := arn.Parse(roleARN)
+		if err != nil {
+			return nil
+		}
+		names = newMappedPolicy(sys.rolesMap[parsed]).toSlice()
+	default:
+		loader := unreadTagMappings{sys.store}
+		var err error
+		names, _, err = cache.policyDBGet(loader, name, false, false)
+		if err != nil {
+			return nil
+		}
+		groups, err := cache.policyDBGetGroups(loader, len(names) > 0, cred.Groups...)
+		if err != nil {
+			return nil
+		}
+		names = append(names, groups...)
+		if derived && len(names) == 0 {
+			claims, _ := policy.GetPoliciesFromClaims(cred.Claims, iamPolicyClaimNameOpenID())
+			names = claims.ToSlice()
+		}
+	}
+
+	sets := [][]policy.Policy{nil}
+	slices.Sort(names)
+	for _, name := range slices.Compact(names) {
+		if doc, ok := cache.iamPolicyDocsMap[name]; ok {
+			sets[0] = append(sets[0], doc.Policy)
+		}
+	}
+	if derived && (cred.IsTemp() || cred.Claims[iamPolicyClaimNameSA()] != inheritedPolicyType) {
+		if sp, ok := cred.Claims[sessionPolicyNameExtracted].(string); ok {
+			if p, err := policy.ParseConfig(strings.NewReader(sp)); err == nil {
+				sets = append(sets, []policy.Policy{*p})
+			}
+		}
+	}
+	return sets
+}
+
+// combineExistingObjectTags combines alternatives from each base/session
+// Allow set and each tag-dependent Deny. A set may also contribute no tags:
+// another statement or another set may already supply what it needs. First
+// values win conflicts; the normal authorization decides whether they work.
+func combineExistingObjectTags(sets [][]map[string]string) []string {
+	combos := []map[string]string{{}}
+	for _, fromSet := range sets {
+		fromSet = append(uniqueExistingObjectTagMaps(fromSet), nil)
+		var next []map[string]string
+		seen := set.NewStringSet()
+	combinations:
+		for _, combo := range combos {
+			for _, addition := range fromSet {
+				merged := maps.Clone(combo)
+				for k, v := range addition {
 					if _, ok := merged[k]; !ok {
 						merged[k] = v
 					}
 				}
-		}
+				t, err := tags.MapToObjectTags(merged)
-		return merged
-	}
-	combos := [][]map[string]string{nil}
-	for _, fromSet := range allows {
-		// Many statements ask for the same tags.
-		seen := set.NewStringSet()
-		fromSet = slices.DeleteFunc(slices.Clone(fromSet), func(tagMap map[string]string) bool {
-			t, err := tags.MapToObjectTags(tagMap)
 				if err != nil || seen.Contains(t.String()) {
-				return true
-			}
-			seen.Add(t.String())
-			return false
-		})
-		next := make([][]map[string]string, 0, len(combos)*(len(fromSet)+1))
-		for _, combo := range combos {
-			next = append(next, combo)
-			for _, tagMap := range fromSet {
-				next = append(next, append(slices.Clip(combo), tagMap))
-			}
-		}
-		combos = next[:min(len(next), maxExistingTagCandidates)]
-	}
-	deny := merge(denies...)
-	found := set.NewStringSet()
-	var candidates []string
-	for _, combo := range combos {
-		for _, tagMap := range []map[string]string{merge(combo...), merge(append(slices.Clip(combo), deny)...)} {
-			t, err := tags.MapToObjectTags(tagMap)
-			if len(tagMap) == 0 || err != nil || found.Contains(t.String()) {
 					continue
 				}
-			found.Add(t.String())
+				seen.Add(t.String())
-			if candidates = append(candidates, t.String()); len(candidates) == maxExistingTagCandidates {
+				next = append(next, merged)
-				return candidates
+				if len(next) == maxExistingTagCandidates {
+					break combinations
 				}
 			}
 		}
+		combos = next
+	}
+	var candidates []string
+	for _, combo := range combos {
+		if len(combo) != 0 { // empty tags were already authorized
+			t, _ := tags.MapToObjectTags(combo)
+			candidates = append(candidates, t.String())
+		}
+	}
 	return candidates
 }
 
-// existingObjectTagsFor returns tags under which the s3:ExistingObjectTag tests
+// existingObjectTagsCandidatesFor returns tag sets under which the
-// of conditions all pass, for an Allow statement, or one of them fails, for a
+// s3:ExistingObjectTag tests of conditions all pass, for an Allow statement,
-// Deny statement; a tag left out is absent. It returns false if the conditions
+// or one of them fails, for a Deny statement; a tag left out is absent. For an
-// test no tag, or if no such tags were found among those tried for each tag:
+// Allow, values for different tag keys are combined, while a Deny needs only
-// none, the values the tests name, with policy variables taken from values and
+// one failing key. It tries the values named in the conditions, with policy
-// wildcards filled, and the fillers "" and "_". The policy engine itself
+// variables resolved, wildcard fillers, and absence, then lets the policy
-// evaluates the tests for each of them.
+// engine decide whether each candidate really satisfies the conditions.
-func existingObjectTagsFor(effect policy.Effect, conditions condition.Functions, values map[string][]string) (map[string]string, bool) {
+func existingObjectTagsCandidatesFor(effect policy.Effect, conditions condition.Functions, values map[string][]string) []map[string]string {
 	// Each function tests one key, so the tests of one tag pass or fail
 	// whatever the other tags are.
 	byKey := make(map[string]condition.Functions)
@@ -209,47 +259,74 @@ func existingObjectTagsFor(effect policy.Effect, conditions condition.Functions,
 		}
 	}
 	if len(byKey) == 0 {
-		return nil, false
+		return nil
-	}
-	tagMap := make(map[string]string)
-	for _, key := range slices.Sorted(maps.Keys(byKey)) {
-		tagKey := strings.TrimPrefix(key, condition.ExistingObjectTag.Name()+"/")
-		value, present, found := existingObjectTagValue(key, tagKey, byKey[key], values, effect == policy.Allow)
-		switch {
-		case effect == policy.Deny && found:
-			if present {
-				tagMap[tagKey] = value
-			}
-			return tagMap, true
-		case effect == policy.Allow && !found:
-			return nil, false
-		case present:
-			tagMap[tagKey] = value
-		}
-	}
-	if effect == policy.Deny {
-		return nil, false
-	}
-	return tagMap, true
 	}
 
-// existingObjectTagValue looks for a value of tag tagKey, or its absence,
+	keys := slices.Sorted(maps.Keys(byKey))
-// under which tests, the functions that test the condition key key, evaluate
+	if effect == policy.Deny {
-// to want.
+		var candidates []map[string]string
-func existingObjectTagValue(key, tagKey string, tests condition.Functions, values map[string][]string, want bool) (value string, present, found bool) {
+		for _, key := range keys {
+			candidates = append(candidates, existingObjectTagValues(key, strings.TrimPrefix(key, condition.ExistingObjectTag.Name()+"/"), byKey[key], values, false)...)
+		}
+		return uniqueExistingObjectTagMaps(candidates)
+	}
+
+	candidates := []map[string]string{{}}
+	for _, key := range keys {
+		keyCandidates := existingObjectTagValues(key, strings.TrimPrefix(key, condition.ExistingObjectTag.Name()+"/"), byKey[key], values, true)
+		if len(keyCandidates) == 0 {
+			return nil
+		}
+		next := make([]map[string]string, 0, min(maxExistingTagCandidates, len(candidates)*len(keyCandidates)))
+		for _, base := range candidates {
+			for _, keyCandidate := range keyCandidates {
+				merged := maps.Clone(base)
+				maps.Copy(merged, keyCandidate)
+				next = append(next, merged)
+				if len(next) == maxExistingTagCandidates {
+					break
+				}
+			}
+			if len(next) == maxExistingTagCandidates {
+				break
+			}
+		}
+		candidates = next
+	}
+	return uniqueExistingObjectTagMaps(candidates)
+}
+
+func uniqueExistingObjectTagMaps(candidates []map[string]string) []map[string]string {
+	seen := set.NewStringSet()
+	unique := make([]map[string]string, 0, len(candidates))
+	for _, candidate := range candidates {
+		t, err := tags.MapToObjectTags(candidate)
+		if err != nil || seen.Contains(t.String()) {
+			continue
+		}
+		seen.Add(t.String())
+		unique = append(unique, candidate)
+	}
+	return unique
+}
+
+// existingObjectTagValues looks for values of tag tagKey, or its absence,
+// under which the functions that test the condition key key evaluate to want.
+func existingObjectTagValues(key, tagKey string, tests condition.Functions, values map[string][]string, want bool) []map[string]string {
 	defer delete(values, key)
 	delete(values, key)
+	var candidates []map[string]string
 	if tests.Evaluate(values) == want {
-		return "", false, true
+		candidates = append(candidates, map[string]string{})
 	}
 	// The functions keep their values unexported; JSON exposes them.
 	buf, err := json.Marshal(tests)
 	if err != nil {
-		return "", false, false
+		return candidates
 	}
 	var byName map[string]map[string]condition.ValueSet
 	if err = json.Unmarshal(buf, &byName); err != nil {
-		return "", false, false
+		return candidates
 	}
 	var tried []string
 	for name, byKey := range byName {
@@ -270,10 +347,13 @@ func existingObjectTagValue(key, tagKey string, tests condition.Functions, value
 		}
 		values[key] = []string{v}
 		if tests.Evaluate(values) == want {
-			return v, true, true
+			candidates = append(candidates, map[string]string{tagKey: v})
+			if len(candidates) == maxExistingTagCandidates {
+				break
 			}
 		}
-	return "", false, false
+	}
+	return uniqueExistingObjectTagMaps(candidates)
 }
 
 // substituteConditionVariables resolves the policy variables in v from the

cmd/auth-handler-unread-tags_test.go

@@ -20,6 +20,7 @@ package cmd
 import (
 	"bytes"
 	"context"
+	"encoding/base64"
 	"encoding/json"
 	"encoding/xml"
 	"fmt"
@@ -29,8 +30,10 @@ import (
 	"net/url"
 	"strings"
 	"testing"
+	"time"
 
 	"github.com/minio/minio-go/v7/pkg/tags"
+	"github.com/minio/minio/internal/arn"
 	"github.com/minio/minio/internal/auth"
 	xhttp "github.com/minio/minio/internal/http"
 	"github.com/pgsty/silo-pkg/v3/policy"
@@ -108,6 +111,45 @@ func TestExistingObjectTagAuthReadQuorumLost(t *testing.T) {
 		}
 		return cred
 	}
+	newTempUser := func(parent auth.Credentials, statements string) auth.Credentials {
+		session := `{"Version": "2012-10-17", "Statement": [` + statements + `]}`
+		secret, err := getTokenSigningKey()
+		if err != nil {
+			t.Fatal(err)
+		}
+		cred, err := auth.GetNewCredentialsWithMetadata(map[string]any{
+			parentClaim: parent.AccessKey, "exp": UTCNow().Add(time.Hour).Unix(),
+			policy.SessionPolicyName: base64.StdEncoding.EncodeToString([]byte(session)),
+		}, secret)
+		if err != nil {
+			t.Fatal(err)
+		}
+		cred.ParentUser = parent.AccessKey
+		if _, err := globalIAMSys.SetTempUser(ctx, cred.AccessKey, cred, ""); err != nil {
+			t.Fatal(err)
+		}
+		return cred
+	}
+	// An unrelated cached policy must not consume the candidate limit. The
+	// target user's policy is created below and sorts after this policy.
+	fillerStatements := make([]string, 0, maxExistingTagCandidates)
+	for i := range maxExistingTagCandidates {
+		fillerStatements = append(fillerStatements, statement("Allow", "*",
+			fmt.Sprintf(`{"StringEquals": {"s3:ExistingObjectTag/fill%02d": "v"}}`, i)))
+	}
+	fillerPolicy, err := policy.ParseConfig(strings.NewReader(`{"Version": "2012-10-17", "Statement": [` + strings.Join(fillerStatements, ",") + `]}`))
+	if err != nil {
+		t.Fatal(err)
+	}
+	fillerPolicyName := "000-unread-tags-filler-" + mustGetUUID()
+	if _, err = globalIAMSys.SetPolicy(ctx, fillerPolicyName, *fillerPolicy); err != nil {
+		t.Fatal(err)
+	}
+	defer func() {
+		if err := globalIAMSys.DeletePolicy(ctx, fillerPolicyName, false); err != nil {
+			t.Logf("delete filler policy: %v", err)
+		}
+	}()
 
 	type user struct {
 		name  string
@@ -146,6 +188,35 @@ func TestExistingObjectTagAuthReadQuorumLost(t *testing.T) {
 		// asks for j=w: only an object carrying both lets it through.
 		allowedByTags("serviceAccount", newServiceAccount(newUser(tagStatement("Allow", "*", "v")),
 			statement("Allow", "*", `{"StringEquals": {"s3:ExistingObjectTag/j": "w"}}`))),
+		allowedByTags("temporary", newTempUser(newUser(tagStatement("Allow", "*", "v")),
+			statement("Allow", "*", `{"StringEquals": {"s3:ExistingObjectTag/j": "w"}}`))),
+		allowedByTags("rootTemporary", newTempUser(globalActiveCred, tagStatement("Allow", "*", "v"))),
+		allowedByTags("rootServiceAccount", newServiceAccount(globalActiveCred, tagStatement("Allow", "*", "v"))),
+		// The effective policy must be selected before applying the candidate
+		// limit; the unrelated cached policy above has 64 other tag statements.
+		allowedByTags("unrelatedPolicies", newUser(statement("Allow", "*",
+			`{"StringEquals": {"s3:ExistingObjectTag/target": "ok"}}`))),
+		// An alternative allowed value must survive a Deny that excludes the
+		// first value. With unread tags, k=v is the only valid candidate.
+		allowedByTags("alternativeAllowedValue", newUser(
+			statement("Allow", "*", `{"StringEquals": {"s3:ExistingObjectTag/k": ["a", "v"]}}`),
+			tagStatement("Deny", "*", "a"))),
+		allowedByTags("alternativeValuesAcrossKeys", newUser(
+			statement("Allow", "*", `{"StringEquals": {"s3:ExistingObjectTag/k": ["a", "v"], "s3:ExistingObjectTag/j": ["b", "w"]}}`),
+			tagStatement("Deny", "*", "a"),
+			statement("Deny", "*", `{"StringEquals": {"s3:ExistingObjectTag/j": "b"}}`))),
+		// Both Deny statements must be avoided. The first candidate (k="")
+		// avoids the Null Deny but still matches the second Deny.
+		allowedByTags("multipleDenies", newUser(statement("Allow", "*", ""),
+			statement("Deny", "*", `{"Null": {"s3:ExistingObjectTag/k": "true"}}`),
+			tagStatement("Deny", "*", ""))),
+		// The Deny can be avoided by k=v OR j=w. Only j=w is compatible
+		// with this Allow, so stopping at the first Deny key loses it.
+		{
+			"alternativeDenyKey", newUser(tagStatement("Allow", "*", "a"),
+				statement("Deny", "*", `{"StringNotEquals": {"s3:ExistingObjectTag/k": "v", "s3:ExistingObjectTag/j": "w"}}`)),
+			http.StatusForbidden, http.StatusServiceUnavailable,
+		},
 
 		// Allowed only for k=w: the decision still depends on the tags.
 		{"otherValue", newUser(tagStatement("Allow", "*", "w")), http.StatusForbidden, http.StatusServiceUnavailable},
@@ -170,7 +241,7 @@ func TestExistingObjectTagAuthReadQuorumLost(t *testing.T) {
 
 	const object, missing = "tagged", "missing"
 	if _, err := z.PutObject(ctx, bucket, object, mustGetPutObjReader(t, bytes.NewReader([]byte("data")), 4, "", ""),
-		ObjectOptions{UserDefined: map[string]string{xhttp.AmzObjectTagging: "k=v&j=w&np=1&ne=1&fa=1&du=1&owner=" + owner.AccessKey}}); err != nil {
+		ObjectOptions{UserDefined: map[string]string{xhttp.AmzObjectTagging: "k=v&j=w&np=1&ne=1&fa=1&du=1&target=ok&owner=" + owner.AccessKey}}); err != nil {
 		t.Fatal(err)
 	}
 	// Anonymous reads are allowed by the bucket policy while the object carries k=v.
@@ -207,7 +278,14 @@ func TestExistingObjectTagAuthReadQuorumLost(t *testing.T) {
 			if req.body != nil {
 				body = bytes.NewReader(req.body)
 			}
-			signed, err := newTestSignedRequestV4(req.method, req.target, int64(len(req.body)), body, creds.AccessKey, creds.SecretKey, req.header)
+			header := make(map[string]string)
+			for k, v := range req.header {
+				header[k] = v
+			}
+			if creds.IsTemp() {
+				header[xhttp.AmzSecurityToken] = creds.SessionToken
+			}
+			signed, err := newTestSignedRequestV4(req.method, req.target, int64(len(req.body)), body, creds.AccessKey, creds.SecretKey, header)
 			if err != nil {
 				t.Fatal(err)
 			}
@@ -289,10 +367,11 @@ func TestExistingObjectTagsFor(t *testing.T) {
 				t.Fatalf("%s: %v", tc.conditions, err)
 			}
 		}
-		tagMap, ok := existingObjectTagsFor(tc.effect, conditions, values)
+		candidates := existingObjectTagsCandidatesFor(tc.effect, conditions, values)
+		ok := len(candidates) > 0
 		got := ""
-		if len(tagMap) > 0 {
+		if ok {
-			encoded, err := tags.MapToObjectTags(tagMap)
+			encoded, err := tags.MapToObjectTags(candidates[0])
 			if err != nil {
 				t.Fatalf("%s: %v", tc.conditions, err)
 			}
@@ -303,3 +382,58 @@ func TestExistingObjectTagsFor(t *testing.T) {
 		}
 	}
 }
+
+// Group-only and external identities need mapping lookups that normally
+// fall back to storage. Candidate collection must stay within the cache even
+// for those identities, while still finding their group/claim/role policy.
+func TestUnreadTagPolicySetsCacheOnly(t *testing.T) {
+	ctx, sys, _ := prepareIAMRevisionFixture(t)
+	const policyName = "unread-tag-policy"
+	batchAuthzPolicy(ctx, t, sys, policyName, `{"Effect":"Allow","Action":["s3:GetObject"],"Resource":["arn:aws:s3:::bucket/*"],"Condition":{"StringEquals":{"s3:ExistingObjectTag/k":"v"}}}`)
+	member := iamAdminUser(ctx, t, sys, "unread-group-member", "")
+	_, err := sys.AddUsersToGroup(ctx, "unread-group", []string{member.AccessKey})
+	mustIAM(t, err)
+	_, err = sys.PolicyDBSet(ctx, "unread-group", policyName, regUser, true)
+	mustIAM(t, err)
+	role, err := arn.NewIAMRoleARN("unread-role", "")
+	mustIAM(t, err)
+	sys.rolesMap = map[arn.ARN]string{role: policyName}
+	claimUser := auth.Credentials{
+		AccessKey: "unread-sts", ParentUser: "external-parent", SessionToken: "token",
+		Expiration: UTCNow().Add(time.Hour), Claims: map[string]any{iamPolicyClaimNameOpenID(): policyName},
+	}
+	roleUser := claimUser
+	roleUser.Claims = map[string]any{roleArnClaim: role.String()}
+	original := sys.store.IAMStorageAPI
+	defer func() { sys.store.IAMStorageAPI = original }()
+	for _, tc := range []struct {
+		name string
+		cred auth.Credentials
+	}{
+		{"group", member},
+		{"claims", claimUser},
+		{"role", roleUser},
+	} {
+		t.Run(tc.name, func(t *testing.T) {
+			name := tc.cred.AccessKey
+			if tc.cred.ParentUser != "" {
+				name = tc.cred.ParentUser
+			}
+			probe := &batchBlockedIAMStore{
+				IAMStorageAPI: original, mapping: name, doc: policyName,
+				started: make(chan struct{}), release: make(chan struct{}),
+			}
+			close(probe.release) // report an accidental read without blocking the test
+			sys.store.IAMStorageAPI = probe
+			sets := sys.unreadTagPolicySets(tc.cred)
+			select {
+			case <-probe.started:
+				t.Error("candidate collection attempted a storage read")
+			default:
+			}
+			if len(sets) != 1 || len(sets[0]) != 1 {
+				t.Fatalf("expected the cached policy through %s, got %v", tc.name, sets)
+			}
+		})
+	}
+}