s3: restrict admin gRPC to local callers when no signing key (#11530)

* s3: restrict admin gRPC to local callers when no signing key

The S3 gateway's gRPC port (default 0.0.0.0:19000, always on) serves the
IAM cache and internal lifecycle admin services. checkAdminAuth was a
no-op when jwt.filer_signing.key was unset, so any reachable host could
PutIdentity an admin identity and take over the bucket data.

Without a shared key callers cannot be distinguished, so admin RPCs are
now limited to unix-socket, loopback, and the server's own interface
addresses. Remote filer-to-S3 propagation and lifecycle workers must set
jwt.filer_signing.key; the Bearer-token path is unchanged.

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Co-Authored-By: Devin <158243242+devin-ai-integration[bot]@users.noreply.github.com>

* s3: fail closed on nil guard and refresh local addresses per call

Review feedback: a nil filerGuard bypassed all checks — treat it like a
missing key and require a local peer. The own-address set was cached
forever, so interfaces added later were rejected; enumerate per call
instead since admin RPCs are rare. Nil ctx is denied rather than panics.

Generated with [Devin](https://devin.ai)

Co-Authored-By: Devin <158243242+devin-ai-integration[bot]@users.noreply.github.com>

* s3: read the signing key once and bound interface enumeration

Review feedback: reading SigningKey twice could straddle a SIGHUP reload
— an old nonempty key skipped the local-peer check while the new empty
key verified the token. And enumerating interfaces per no-key call is
wasteful for co-located workers dialing the announced address; cache the
address set for 30s so new interfaces still become usable promptly.

Generated with [Devin](https://devin.ai)

Co-Authored-By: Devin <158243242+devin-ai-integration[bot]@users.noreply.github.com>

* s3: enumerate interface addresses per no-key admin call

A cached address set keeps trusting an IP after it is removed from the
host and reassigned to another machine — that host would then hold
unauthenticated admin access for the cache TTL. Per-call enumeration only
runs for non-loopback TCP peers on the no-key path, which is low-volume
admin traffic, so the freshness is worth the syscall.

Generated with [Devin](https://devin.ai)

Co-Authored-By: Devin <158243242+devin-ai-integration[bot]@users.noreply.github.com>

---------

Co-authored-by: Devin <158243242+devin-ai-integration[bot]@users.noreply.github.com>

weed/s3api/s3api_server_grpc.go

@@ -2,6 +2,7 @@ package s3api
 
 import (
 	"context"
+	"net"
 	"strings"
 
 	"github.com/seaweedfs/seaweedfs/weed/glog"
@@ -9,6 +10,7 @@ import (
 	"github.com/seaweedfs/seaweedfs/weed/security"
 	"google.golang.org/grpc/codes"
 	"google.golang.org/grpc/metadata"
+	"google.golang.org/grpc/peer"
 	"google.golang.org/grpc/status"
 )
 
@@ -19,15 +21,16 @@ import (
 // checkAdminAuth verifies the caller presented a Bearer token signed by the
 // filer write-signing key (jwt.filer_signing.key). It mirrors the filer's
 // IamGrpcServer.checkAdminAuth so the same operator knob that locks down the
-// filer IAM gRPC service also locks down this cache. With no key configured the
-// check is a no-op, matching the rest of SeaweedFS's gRPC surface.
+// filer IAM gRPC service also locks down this cache. With no key configured
+// remote callers cannot be told apart, so only local clients (unix socket,
+// loopback, or the server's own addresses) are allowed.
 func (s3a *S3ApiServer) checkAdminAuth(ctx context.Context) error {
-	if s3a.filerGuard == nil {
-		return nil
+	var signingKey security.SigningKey
+	if s3a.filerGuard != nil {
+		signingKey = s3a.filerGuard.SigningKey()
 	}
-	signingKey := s3a.filerGuard.SigningKey()
 	if len(signingKey) == 0 {
-		return nil
+		return checkLocalPeer(ctx)
 	}
 	md, ok := metadata.FromIncomingContext(ctx)
 	if !ok {
@@ -52,6 +55,49 @@ func (s3a *S3ApiServer) checkAdminAuth(ctx context.Context) error {
 	return nil
 }
 
+func checkLocalPeer(ctx context.Context) error {
+	if ctx == nil {
+		return status.Error(codes.Unauthenticated, "admin gRPC calls require jwt.filer_signing.key or a local client")
+	}
+	pr, ok := peer.FromContext(ctx)
+	if !ok {
+		return status.Error(codes.Unauthenticated, "admin gRPC calls require jwt.filer_signing.key or a local client")
+	}
+	if _, isUnix := pr.Addr.(*net.UnixAddr); isUnix {
+		return nil
+	}
+	var ip net.IP
+	if tcpAddr, ok := pr.Addr.(*net.TCPAddr); ok {
+		ip = tcpAddr.IP
+	} else if h, _, err := net.SplitHostPort(pr.Addr.String()); err == nil {
+		ip = net.ParseIP(h)
+	} else {
+		ip = net.ParseIP(pr.Addr.String())
+	}
+	if ip != nil && (ip.IsLoopback() || isLocalAddress(ip)) {
+		return nil
+	}
+	glog.V(1).Infof("rejected unauthenticated admin gRPC call from %s: no jwt.filer_signing.key configured", pr.Addr)
+	return status.Error(codes.Unauthenticated, "admin gRPC calls require jwt.filer_signing.key or a local client")
+}
+
+// isLocalAddress enumerates interfaces per call: only reachable for
+// non-loopback TCP peers on the no-key admin path, which is low-volume —
+// and a cached set would keep trusting an address after it is removed from
+// the host and reassigned.
+func isLocalAddress(ip net.IP) bool {
+	addrs, err := net.InterfaceAddrs()
+	if err != nil {
+		return false
+	}
+	for _, a := range addrs {
+		if ipNet, ok := a.(*net.IPNet); ok && ipNet.IP.Equal(ip) {
+			return true
+		}
+	}
+	return false
+}
+
 func (s3a *S3ApiServer) PutIdentity(ctx context.Context, req *iam_pb.PutIdentityRequest) (*iam_pb.PutIdentityResponse, error) {
 	if err := s3a.checkAdminAuth(ctx); err != nil {
 		return nil, err