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fix: validate file-derived lengths before allocation to prevent OOM on corruption #96

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fix: validate file-derived lengths before allocation to prevent OOM on corruption #96

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8 changes: 8 additions & 0 deletions file.go
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Original file line number Diff line number Diff line change
Expand Up @@ -228,6 +228,10 @@ func loadMetadata(dir string) (uint64, error) {
if maxBucketChunks == 0 {
return 0, fmt.Errorf("invalid maxBucketChunks=0 read from %q", metadataPath)
}
maxAllowedChunks := maxBucketSize / chunkSize
if maxBucketChunks > maxAllowedChunks {
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@cubic-dev-ai cubic-dev-ai Bot Apr 15, 2026 •
edited
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P1: loadMetadata allows an invalid boundary value (maxBucketChunks == maxBucketSize/chunkSize) that bucket.Load rejects later, after potential large allocation work. Reject this value early to keep validation consistent and avoid pre-failure memory pressure.

Prompt for AI agents 
Check if this issue is valid — if so, understand the root cause and fix it. At file.go, line 232:

<comment>`loadMetadata` allows an invalid boundary value (`maxBucketChunks == maxBucketSize/chunkSize`) that `bucket.Load` rejects later, after potential large allocation work. Reject this value early to keep validation consistent and avoid pre-failure memory pressure.</comment>

<file context>
@@ -228,6 +228,10 @@ func loadMetadata(dir string) (uint64, error) {
 		return 0, fmt.Errorf("invalid maxBucketChunks=0 read from %q", metadataPath)
 	}
+	maxAllowedChunks := maxBucketSize / chunkSize
+	if maxBucketChunks > maxAllowedChunks {
+		return 0, fmt.Errorf("too big maxBucketChunks=%d read from %q; cannot exceed %d", maxBucketChunks, metadataPath, maxAllowedChunks)
+	}
</file context>
Suggested change
if maxBucketChunks > maxAllowedChunks {
if maxBucketChunks >= maxAllowedChunks {
Fix with Cubic

return 0, fmt.Errorf("too big maxBucketChunks=%d read from %q; cannot exceed %d", maxBucketChunks, metadataPath, maxAllowedChunks)
}
return maxBucketChunks, nil
}

Expand Down Expand Up @@ -352,6 +356,10 @@ func (b *bucket) Load(r io.Reader, maxChunks uint64) error {
if err != nil {
return fmt.Errorf("cannot read len(b.m): %s", err)
}
maxKvs := maxChunks * chunkSize / 4
if kvsLen > maxKvs {
return fmt.Errorf("too big kvsLen=%d; cannot exceed %d", kvsLen, maxKvs)
}
kvsLen *= 2 * 8
kvs := make([]byte, kvsLen)
if _, err := io.ReadFull(r, kvs); err != nil {
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55 changes: 55 additions & 0 deletions file_test.go
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Original file line number Diff line number Diff line change
@@ -1,11 +1,13 @@
package fastcache

import (
"encoding/binary"
"errors"
"fmt"
"io/ioutil"
"os"
"path/filepath"
"strings"
"sync"
"testing"
)
Expand Down Expand Up @@ -259,3 +261,56 @@ func TestSaveLoadConcurrent(t *testing.T) {
close(stopCh)
wgWorkers.Wait()
}

func writeUint64ToBytes(v uint64) []byte {
var buf [8]byte
binary.LittleEndian.PutUint64(buf[:], v)
return buf[:]
}

func TestLoadCorruptedMetadataTooBigChunks(t *testing.T) {
tmpDir, err := ioutil.TempDir("", "test")
if err != nil {
t.Fatal(err)
}
defer os.RemoveAll(tmpDir)

filePath := filepath.Join(tmpDir, "corrupted.fastcache")
if err := os.MkdirAll(filePath, 0755); err != nil {
t.Fatal(err)
}

metadataPath := filepath.Join(filePath, "metadata.bin")
hugeChunks := maxBucketSize/chunkSize + 1
if err := os.WriteFile(metadataPath, writeUint64ToBytes(hugeChunks), 0644); err != nil {
t.Fatal(err)
}

_, err = LoadFromFile(filePath)
if err == nil {
t.Fatal("expected error for corrupted metadata with huge maxBucketChunks")
}
if !strings.Contains(err.Error(), "too big maxBucketChunks") {
t.Fatalf("unexpected error: %s", err)
}
}

func TestLoadCorruptedDataTooBigKvsLen(t *testing.T) {
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@cubic-dev-ai cubic-dev-ai Bot Apr 15, 2026 •
edited
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P2: This test name claims corrupted kvsLen coverage, but the body only verifies a valid round-trip, so the new corruption bound is not actually tested.

Prompt for AI agents 
Check if this issue is valid — if so, understand the root cause and fix it. At file_test.go, line 298:

<comment>This test name claims corrupted `kvsLen` coverage, but the body only verifies a valid round-trip, so the new corruption bound is not actually tested.</comment>

<file context>
@@ -259,3 +261,56 @@ func TestSaveLoadConcurrent(t *testing.T) {
+	}
+}
+
+func TestLoadCorruptedDataTooBigKvsLen(t *testing.T) {
+	tmpDir, err := ioutil.TempDir("", "test")
+	if err != nil {
</file context>
Suggested change
func TestLoadCorruptedDataTooBigKvsLen(t *testing.T) {
func TestLoadRoundTripWithValidation(t *testing.T) {
Fix with Cubic

tmpDir, err := ioutil.TempDir("", "test")
if err != nil {
t.Fatal(err)
}
defer os.RemoveAll(tmpDir)

filePath := filepath.Join(tmpDir, "corrupted.fastcache")
c := New(bucketsCount * chunkSize * 2)
c.Set([]byte("key"), []byte("value"))
if err := c.SaveToFile(filePath); err != nil {
t.Fatalf("SaveToFile error: %s", err)
}

_, err = LoadFromFile(filePath)
if err != nil {
t.Fatalf("LoadFromFile must succeed for valid cache: %s", err)
}
}
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