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Add -dict option (like AFL's -x) to replace low-signal string literal list #315

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Add -dict option (like AFL's -x) to replace low-signal string literal list #315

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1b70c6d
go-fuzz: add -dict option
roddux Mar 26, 2021
f01a8e4
Don't log unnecessarily
roddux May 7, 2021
5d957e6
Use %q instead of "%v"
roddux May 7, 2021
2e5342a
Don't include newline at end of log.Printf
roddux May 7, 2021
f8cbffe
Don't capitalise help strings
roddux May 7, 2021
1911501
Log error message if we can't read dict file
roddux May 7, 2021
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19 changes: 19 additions & 0 deletions go-fuzz/hub.go
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Original file line number Diff line number Diff line change
Expand Up @@ -6,6 +6,8 @@ package main
import (
"fmt"
"log"
"io/ioutil"
"strings"
"net/rpc"
"path/filepath"
"sync"
Expand Down Expand Up @@ -116,6 +118,23 @@ func newHub(metadata MetaData) *Hub {
ro.intLits = append(ro.intLits, []byte(lit.Val))
}
}
if *flagDict != "" {
ro.strLits = nil // Discard existing tokens
fileName := *flagDict
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This renaming looks excessive, especially if we remove the log.Printf. Just use *flagDict.

dictData, err := ioutil.ReadFile(fileName)
if err != nil {
log.Fatalf("could not read tokens from %q: %v", fileName, err)
}
textData := string(dictData)
splits := strings.Split(textData,"\n")
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Not that it really matters, but let's not convert to string and then convert back to []byte. Use bytes.Split instead. Or use a bufio.Scanner, which'll be simpler yet.

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+1

for S := range splits {
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Will be shorter with for _, token := range splits.
Or even shorter with for _, token := range strings.Split(textData,"\n").

token := splits[S]
if token == "\n" || token == "" {
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Can it contain "\n" is we split by "\n"?

continue // skip blanks
}
ro.strLits = append(ro.strLits, []byte(token))
}
}
hub.ro.Store(ro)

go hub.loop()
Expand Down
11 changes: 11 additions & 0 deletions go-fuzz/main.go
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Expand Up @@ -42,6 +42,7 @@ var (
flagSonar = flag.Bool("sonar", true, "use sonar hints")
flagV = flag.Int("v", 0, "verbosity level")
flagHTTP = flag.String("http", "", "HTTP server listen address (coordinator mode only)")
flagDict = flag.String("dict", "", "dictionary file containing string tokens (one per line, not quoted)")

shutdown uint32
shutdownC = make(chan struct{})
Expand All @@ -57,6 +58,16 @@ func main() {
log.Fatalf("both -http and -worker are specified")
}

if *flagDict != "" {
dictStat, err := os.Stat(*flagDict)
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Add a comment explaining why we stat here.

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Could we pass *flagDict to workerMain? Or read here and pass contents to workerMain?
It looks like this split stat/size check + reading separately doubles amount of code.

if err != nil {
log.Fatalf("cannot read dictionary file %q: %v", *flagDict, err)
}
if dictStat.Size() == 0 {
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Any reason not to allow an empty dictionary? E.g. I can imagine someone using this to disable dictionaries. (Maybe it'd break something in the mutator code? If so, we could add an early exit when strLits is empty.)

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I feel if the user is manually specifying a dictionary, it would be strange if it was empty -- therefore probably a mistake. Happy to remove the Fatalf call, but I still think it should be logged. Thoughts?

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Sure, we could log.

log.Fatalf("dictionary file %q is empty", *flagDict)
}
}

go func() {
c := make(chan os.Signal, 1)
signal.Notify(c, syscall.SIGINT)
Expand Down