From 7d70afc937ac0125496c5bde2f0e5b1029b704d1 Mon Sep 17 00:00:00 2001
From: Harshavardhana <harsha@minio.io>
Date: Mon, 6 Dec 2021 15:55:29 -0800
Subject: [PATCH] fix: potential crash in diskCache when fileScorer is empty
 (#13850)

```
goroutine 115 [running]:
github.com/minio/minio/cmd.(*diskCache).purge.func3({0xc007a10a40, 0x40}, 0x40)
   github.com/minio/minio/cmd/disk-cache-backend.go:430 +0x90d
```
---
 cmd/disk-cache-backend.go | 14 +++++++-------
 cmd/disk-cache-utils.go   |  3 +++
 2 files changed, 10 insertions(+), 7 deletions(-)

diff --git a/cmd/disk-cache-backend.go b/cmd/disk-cache-backend.go
index e3730866f..10db2f555 100644
--- a/cmd/disk-cache-backend.go
+++ b/cmd/disk-cache-backend.go
@@ -325,7 +325,11 @@ func (c *diskCache) purge(ctx context.Context) {
 	expiry := UTCNow().Add(-cacheExpiryDays)
 	// defaulting max hits count to 100
 	// ignore error we know what value we are passing.
-	scorer, _ := newFileScorer(toFree, time.Now().Unix(), 100)
+	scorer, err := newFileScorer(toFree, time.Now().Unix(), 100)
+	if err != nil {
+		logger.LogIf(ctx, err)
+		return
+	}
 
 	// this function returns FileInfo for cached range files.
 	fiStatRangesFn := func(ranges map[string]string, pathPrefix string) map[string]os.FileInfo {
@@ -388,9 +392,7 @@ func (c *diskCache) purge(ctx context.Context) {
 		switch {
 		case cc != nil:
 			if cc.isStale(objInfo.ModTime) {
-				if err = removeAll(cacheDir); err != nil {
-					logger.LogIf(ctx, err)
-				}
+				removeAll(cacheDir)
 				scorer.adjustSaveBytes(-objInfo.Size)
 				// break early if sufficient disk space reclaimed.
 				if c.diskUsageLow() {
@@ -408,9 +410,7 @@ func (c *diskCache) purge(ctx context.Context) {
 		for fname, fi := range cachedRngFiles {
 			if cc != nil {
 				if cc.isStale(objInfo.ModTime) {
-					if err = removeAll(fname); err != nil {
-						logger.LogIf(ctx, err)
-					}
+					removeAll(fname)
 					scorer.adjustSaveBytes(-fi.Size())
 
 					// break early if sufficient disk space reclaimed.
diff --git a/cmd/disk-cache-utils.go b/cmd/disk-cache-utils.go
index d1f1f435e..2b184a042 100644
--- a/cmd/disk-cache-utils.go
+++ b/cmd/disk-cache-utils.go
@@ -419,6 +419,9 @@ func (f *fileScorer) addFileWithObjInfo(objInfo ObjectInfo, hits int) {
 // Returns true if there still is a need to delete files (n+saveBytes >0),
 // false if no more bytes needs to be saved.
 func (f *fileScorer) adjustSaveBytes(n int64) bool {
+	if f == nil {
+		return false
+	}
 	if int64(f.saveBytes)+n <= 0 {
 		f.saveBytes = 0
 		f.trimQueue()