fix(config): persist geo-filter saves through config symlinks

cmd/server/config.go

@@ -1245,6 +1245,16 @@ func SaveGeoFilter(configDir string, gf *GeoFilterConfig) error {
 	if configPath == "" {
 		return fmt.Errorf("config.json not found in %s", configDir)
 	}
+	// Resolve the selected file before creating its replacement. Containers
+	// can link config.json into a persistent data directory: renaming over
+	// that link would save only in the container layer and leave the mounted
+	// config unchanged. Using the effective path also keeps temp + rename
+	// together on the target filesystem, including relative/chained links.
+	resolvedPath, err := filepath.EvalSymlinks(configPath)
+	if err != nil {
+		return fmt.Errorf("resolve config: %w", err)
+	}
+	configPath = resolvedPath
 
 	src, err := os.Open(configPath)
 	if err != nil {

cmd/server/config_geofilter_symlink_407_test.go

@@ -0,0 +1,252 @@
+package main
+
+import (
+	"errors"
+	"os"
+	"path/filepath"
+	"reflect"
+	"strings"
+	"testing"
+)
+
+func requireGeo407Symlink(t *testing.T, target, link string) {
+	t.Helper()
+	if err := os.Symlink(target, link); err != nil {
+		t.Skipf("symlink unsupported: %v", err)
+	}
+}
+
+func assertGeo407LinkUnchanged(t *testing.T, link, want string) {
+	t.Helper()
+	got, err := os.Readlink(link)
+	if err != nil {
+		t.Fatalf("config link no longer exists as a symlink: %v", err)
+	}
+	if got != want {
+		t.Fatalf("link target = %q, want %q", got, want)
+	}
+}
+
+// A container can expose config.json via a link to its persistent data mount.
+// Both saving and removing the geo-filter must update that target, keeping all
+// link entries intact so the next container start reads the persisted value.
+func TestSaveGeoFilterPersistsThroughConfigSymlinks407(t *testing.T) {
+	for _, kind := range []string{"absolute", "relative", "chained", "symlinked directory"} {
+		t.Run(kind, func(t *testing.T) {
+			dir := t.TempDir()
+			persistedDir := t.TempDir()
+			target := writeGeoPerm340Config(t, filepath.Join(persistedDir, "persistent.json"), 0o640)
+			link := filepath.Join(dir, "config.json")
+			links := map[string]string{}
+			switch kind {
+			case "absolute":
+				links[link] = target
+			case "relative":
+				rel, err := filepath.Rel(dir, target)
+				if err != nil {
+					t.Fatal(err)
+				}
+				links[link] = rel
+			case "chained":
+				middle := filepath.Join(dir, "intermediate.json")
+				links[middle] = target
+				links[link] = "intermediate.json"
+			case "symlinked directory":
+				dataLink := filepath.Join(dir, "data")
+				links[dataLink] = persistedDir
+				links[link] = filepath.Join("data", "persistent.json")
+			}
+			for path, dest := range links {
+				requireGeo407Symlink(t, dest, path)
+			}
+
+			before, err := os.Stat(target)
+			if err != nil {
+				t.Fatal(err)
+			}
+			wantFields := geoPerm340Decode(t, []byte(geoPerm340Config))
+			for _, gf := range []*GeoFilterConfig{geoPerm340Filter(), nil} {
+				if err := SaveGeoFilter(dir, gf); err != nil {
+					t.Fatalf("SaveGeoFilter: %v", err)
+				}
+				for path, dest := range links {
+					assertGeo407LinkUnchanged(t, path, dest)
+				}
+				data, err := os.ReadFile(target)
+				if err != nil {
+					t.Fatal(err)
+				}
+				got := geoPerm340Decode(t, data)
+				filter, present := got["geo_filter"]
+				if gf == nil {
+					if present {
+						t.Fatal("geo_filter still present in persistent target after removal")
+					}
+				} else {
+					// Use the same JSON conversion as the pre-existing assertions,
+					// so the saved value, not just its presence, is pinned.
+					wantFilter := geoPerm340Decode(t, []byte(`{"polygon":[[51,4],[51,5],[50.5,4]],"bufferKm":20}`))
+					if !reflect.DeepEqual(filter, wantFilter) {
+						t.Fatalf("geo_filter in persistent target = %#v, want %#v", filter, wantFilter)
+					}
+				}
+				delete(got, "geo_filter")
+				if !reflect.DeepEqual(got, wantFields) {
+					t.Fatal("unrelated config fields changed")
+				}
+				if mode := geoPerm340Mode(t, target); mode != 0o640 {
+					t.Fatalf("persistent target mode = %04o, want 0640", mode)
+				}
+				after, err := os.Stat(target)
+				if err != nil {
+					t.Fatal(err)
+				}
+				wantUID, wantGID, ok := configFileOwnerIDs(before)
+				if gotUID, gotGID, available := configFileOwnerIDs(after); ok && available && (gotUID != wantUID || gotGID != wantGID) {
+					t.Fatalf("target owner changed from %d:%d to %d:%d", wantUID, wantGID, gotUID, gotGID)
+				}
+				entries, err := os.ReadDir(persistedDir)
+				if err != nil {
+					t.Fatal(err)
+				}
+				if len(entries) != 1 || entries[0].Name() != "persistent.json" {
+					t.Fatalf("unexpected target-directory entries: %v", entries)
+				}
+			}
+		})
+	}
+}
+
+func TestSaveGeoFilterSymlinkUsesTargetDirectory407(t *testing.T) {
+	dir := t.TempDir()
+	persistedDir := t.TempDir()
+	target := writeGeoPerm340Config(t, filepath.Join(persistedDir, "persistent.json"), 0o600)
+	link := filepath.Join(dir, "config.json")
+	requireGeo407Symlink(t, target, link)
+	resolvedTarget, err := filepath.EvalSymlinks(target)
+	if err != nil {
+		t.Fatal(err)
+	}
+	resolvedDir := filepath.Dir(resolvedTarget)
+
+	origCreate, origRename := configCreateTemp, configRename
+	t.Cleanup(func() { configCreateTemp, configRename = origCreate, origRename })
+	created, renamed := false, false
+	configCreateTemp = func(d, pattern string) (*os.File, error) {
+		if d != resolvedDir || pattern != "persistent.json.*.tmp" {
+			t.Fatalf("temp destination = %q / %q, want resolved config directory and basename", d, pattern)
+		}
+		created = true
+		return origCreate(d, pattern)
+	}
+	configRename = func(old, dest string) error {
+		if filepath.Dir(old) != resolvedDir || dest != resolvedTarget {
+			t.Fatalf("rename %q -> %q is not confined to the target directory", old, dest)
+		}
+		renamed = true
+		return origRename(old, dest)
+	}
+	if err := SaveGeoFilter(dir, geoPerm340Filter()); err != nil {
+		t.Fatal(err)
+	}
+	if !created || !renamed {
+		t.Fatal("atomic temp/rename path was not exercised")
+	}
+	assertGeo407LinkUnchanged(t, link, target)
+}
+
+func TestSaveGeoFilterSymlinkTargetRenameFailure407(t *testing.T) {
+	dir := t.TempDir()
+	persistedDir := t.TempDir()
+	target := writeGeoPerm340Config(t, filepath.Join(persistedDir, "persistent.json"), 0o600)
+	link := filepath.Join(dir, "config.json")
+	requireGeo407Symlink(t, target, link)
+	resolvedTarget, err := filepath.EvalSymlinks(target)
+	if err != nil {
+		t.Fatal(err)
+	}
+	sentinel := errors.New("target rename refused")
+	orig := configRename
+	t.Cleanup(func() { configRename = orig })
+	configRename = func(_, dest string) error {
+		if dest != resolvedTarget {
+			t.Fatalf("rename destination = %q, want target %q", dest, resolvedTarget)
+		}
+		return sentinel
+	}
+	if err := SaveGeoFilter(dir, geoPerm340Filter()); !errors.Is(err, sentinel) {
+		t.Fatalf("save error = %v, want wrapped rename error", err)
+	}
+	assertGeo407LinkUnchanged(t, link, target)
+	data, err := os.ReadFile(target)
+	if err != nil || string(data) != geoPerm340Config {
+		t.Fatalf("target changed on failed save: %q, %v", data, err)
+	}
+	entries, err := os.ReadDir(persistedDir)
+	if err != nil || len(entries) != 1 || entries[0].Name() != "persistent.json" {
+		t.Fatalf("failed save left temporary files: %v, %v", entries, err)
+	}
+}
+
+func TestSaveGeoFilterSymlinkUnwritableTargetDirectory407(t *testing.T) {
+	if os.Geteuid() == 0 {
+		t.Skip("root bypasses directory permission checks")
+	}
+	dir := t.TempDir()
+	persistedDir := t.TempDir()
+	target := writeGeoPerm340Config(t, filepath.Join(persistedDir, "persistent.json"), 0o600)
+	link := filepath.Join(dir, "config.json")
+	requireGeo407Symlink(t, target, link)
+	if err := os.Chmod(persistedDir, 0o500); err != nil {
+		t.Fatal(err)
+	}
+	t.Cleanup(func() { _ = os.Chmod(persistedDir, 0o700) })
+	if err := SaveGeoFilter(dir, geoPerm340Filter()); !errors.Is(err, os.ErrPermission) {
+		t.Fatalf("save error = %v, want target directory permission error", err)
+	}
+	assertGeo407LinkUnchanged(t, link, target)
+	data, err := os.ReadFile(target)
+	if err != nil || string(data) != geoPerm340Config {
+		t.Fatalf("target changed despite read-only directory: %q, %v", data, err)
+	}
+}
+
+func TestSaveGeoFilterDanglingAndLoopSymlinks407(t *testing.T) {
+	for _, kind := range []string{"dangling", "loop"} {
+		t.Run(kind, func(t *testing.T) {
+			dir := t.TempDir()
+			link := filepath.Join(dir, "config.json")
+			dest := "missing.json"
+			if kind == "loop" {
+				dest = "config.json"
+			}
+			requireGeo407Symlink(t, dest, link)
+			if err := SaveGeoFilter(dir, geoPerm340Filter()); err == nil {
+				t.Fatal("expected invalid symlink to fail, got nil")
+			}
+			assertGeo407LinkUnchanged(t, link, dest)
+			entries, err := os.ReadDir(dir)
+			if err != nil || len(entries) != 1 || entries[0].Name() != "config.json" {
+				t.Fatalf("invalid link save created files: %v, %v", entries, err)
+			}
+		})
+	}
+}
+
+func TestSaveGeoFilterDanglingSymlinkKeepsDataFallback407(t *testing.T) {
+	dir := t.TempDir()
+	link := filepath.Join(dir, "config.json")
+	requireGeo407Symlink(t, "missing.json", link)
+	target := writeGeoPerm340Config(t, filepath.Join(dir, "data", "config.json"), 0o600)
+	if err := SaveGeoFilter(dir, geoPerm340Filter()); err != nil {
+		t.Fatal(err)
+	}
+	assertGeo407LinkUnchanged(t, link, "missing.json")
+	data, err := os.ReadFile(target)
+	if err != nil || !strings.Contains(string(data), "geo_filter") {
+		t.Fatalf("data fallback was not updated: %q, %v", data, err)
+	}
+	if _, err := os.Stat(filepath.Join(dir, "missing.json")); !errors.Is(err, os.ErrNotExist) {
+		t.Fatalf("missing target was created: %v", err)
+	}
+}