src/internal/zstd/fuzz_test.go

   1 // Copyright 2023 The Go Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style
   3 // license that can be found in the LICENSE file.
   4
   5 package zstd
   6
   7 import (
   8         "bytes"
   9         "io"
  10         "os"
  11         "os/exec"
  12         "testing"
  13 )
  14
  15 // badStrings is some inputs that FuzzReader failed on earlier.
  16 var badStrings = []string{
  17         "(\xb5/\xfdd00,\x05\x00\xc4\x0400000000000000000000000000000000000000000000000000000000000000000000000000000 \xa07100000000000000000000000000000000000000000000000000000000000000000000000000aM\x8a2y0B\b",
  18         "(\xb5/\xfd00$\x05\x0020 00X70000a70000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000",
  19         "(\xb5/\xfd00$\x05\x0020 00B00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000",
  20         "(\xb5/\xfd00}\x00\x0020\x00\x9000000000000",
  21         "(\xb5/\xfd00}\x00\x00&0\x02\x830!000000000",
  22         "(\xb5/\xfd\x1002000$\x05\x0010\xcc0\xa8100000000100000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000",
  23         "(\xb5/\xfd\x1002000$\x05\x0000\xcc0\xa8100d\x0000001000000000000000000000000000000000000000000000000000000000000000000000000\x000000000000000000000000000000000000000000000000000000000000000000000000000000",
  24         "(\xb5/\xfd001\x00\x0000000000000000000",
  25 }
  26
  27 // This is a simple fuzzer to see if the decompressor panics.
  28 func FuzzReader(f *testing.F) {
  29         for _, test := range tests {
  30                 f.Add([]byte(test.compressed))
  31         }
  32         for _, s := range badStrings {
  33                 f.Add([]byte(s))
  34         }
  35         f.Fuzz(func(t *testing.T, b []byte) {
  36                 r := NewReader(bytes.NewReader(b))
  37                 io.Copy(io.Discard, r)
  38         })
  39 }
  40
  41 // Fuzz test to verify that what we decompress is what we compress.
  42 // This isn't a great fuzz test because the fuzzer can't efficiently
  43 // explore the space of decompressor behavior, since it can't see
  44 // what the compressor is doing. But it's better than nothing.
  45 func FuzzDecompressor(f *testing.F) {
  46         if _, err := os.Stat("/usr/bin/zstd"); err != nil {
  47                 f.Skip("skipping because /usr/bin/zstd does not exist")
  48         }
  49
  50         for _, test := range tests {
  51                 f.Add([]byte(test.uncompressed))
  52         }
  53
  54         // Add some larger data, as that has more interesting compression.
  55         f.Add(bytes.Repeat([]byte("abcdefghijklmnop"), 256))
  56         var buf bytes.Buffer
  57         for i := 0; i < 256; i++ {
  58                 buf.WriteByte(byte(i))
  59         }
  60         f.Add(bytes.Repeat(buf.Bytes(), 64))
  61         f.Add(bigData(f))
  62
  63         f.Fuzz(func(t *testing.T, b []byte) {
  64                 cmd := exec.Command("/usr/bin/zstd", "-z")
  65                 cmd.Stdin = bytes.NewReader(b)
  66                 var compressed bytes.Buffer
  67                 cmd.Stdout = &compressed
  68                 cmd.Stderr = os.Stderr
  69                 if err := cmd.Run(); err != nil {
  70                         t.Errorf("running zstd failed: %v", err)
  71                 }
  72
  73                 r := NewReader(bytes.NewReader(compressed.Bytes()))
  74                 got, err := io.ReadAll(r)
  75                 if err != nil {
  76                         t.Fatal(err)
  77                 }
  78                 if !bytes.Equal(got, b) {
  79                         showDiffs(t, got, b)
  80                 }
  81         })
  82 }
  83
  84 // Fuzz test to check that if we can decompress some data,
  85 // so can zstd, and that we get the same result.
  86 func FuzzReverse(f *testing.F) {
  87         if _, err := os.Stat("/usr/bin/zstd"); err != nil {
  88                 f.Skip("skipping because /usr/bin/zstd does not exist")
  89         }
  90
  91         for _, test := range tests {
  92                 f.Add([]byte(test.compressed))
  93         }
  94
  95         // Set a hook to reject some cases where we don't match zstd.
  96         fuzzing = true
  97         defer func() { fuzzing = false }()
  98
  99         f.Fuzz(func(t *testing.T, b []byte) {
 100                 r := NewReader(bytes.NewReader(b))
 101                 goExp, goErr := io.ReadAll(r)
 102
 103                 cmd := exec.Command("/usr/bin/zstd", "-d")
 104                 cmd.Stdin = bytes.NewReader(b)
 105                 var uncompressed bytes.Buffer
 106                 cmd.Stdout = &uncompressed
 107                 cmd.Stderr = os.Stderr
 108                 zstdErr := cmd.Run()
 109                 zstdExp := uncompressed.Bytes()
 110
 111                 if goErr == nil && zstdErr == nil {
 112                         if !bytes.Equal(zstdExp, goExp) {
 113                                 showDiffs(t, zstdExp, goExp)
 114                         }
 115                 } else {
 116                         // Ideally we should check that this package and
 117                         // the zstd program both fail or both succeed,
 118                         // and that if they both fail one byte sequence
 119                         // is an exact prefix of the other.
 120                         // Actually trying this proved to be frustrating,
 121                         // as the zstd program appears to accept invalid
 122                         // byte sequences using rules that are difficult
 123                         // to determine.
 124                         // So we just check the prefix.
 125
 126                         c := len(goExp)
 127                         if c > len(zstdExp) {
 128                                 c = len(zstdExp)
 129                         }
 130                         goExp = goExp[:c]
 131                         zstdExp = zstdExp[:c]
 132                         if !bytes.Equal(goExp, zstdExp) {
 133                                 t.Error("byte mismatch after error")
 134                                 t.Logf("Go error: %v\n", goErr)
 135                                 t.Logf("zstd error: %v\n", zstdErr)
 136                                 showDiffs(t, zstdExp, goExp)
 137                         }
 138                 }
 139         })
 140 }