[dev.fuzz] internal/fuzz: fix bug for -fuzzminimizetime of zero

Updates golang/go#48321

Change-Id: Ib35388f17580f1244a6eae4e5879f8329b6b44ce
Reviewed-on: https://go-review.googlesource.com/c/go/+/349090
Trust: Katie Hockman <katie@golang.org>
Run-TryBot: Katie Hockman <katie@golang.org>
Reviewed-by: Jay Conrod <jayconrod@google.com>

src/cmd/go/testdata/script/test_fuzz_minimize.txt

@@ -6,18 +6,6 @@
 # We clean the fuzz cache during this test. Don't clean the user's cache.
 env GOCACHE=$WORK/gocache
 
-# Test that fuzzminimizetime can be zero seconds
-! go test -fuzz=FuzzMinimizerRecoverable -run=FuzzMinimizerRecoverable -fuzztime=10000x -fuzzminimizetime=0s minimizer_test.go
-! stdout '^ok'
-stdout 'contains a non-zero byte'
-stdout FAIL
-
-# Test that fuzzminimizetime can be zero times
-! go test -fuzz=FuzzMinimizerRecoverable -run=FuzzMinimizerRecoverable -fuzztime=10000x -fuzzminimizetime=0x minimizer_test.go
-! stdout '^ok'
-stdout 'contains a non-zero byte'
-stdout FAIL
-
 # Test that fuzzminimizetime cannot be negative seconds
 ! go test -fuzz=FuzzMinimizerRecoverable -run=FuzzMinimizerRecoverable -fuzztime=10000x -fuzzminimizetime=-1ms minimizer_test.go
 ! stdout '^ok'
@@ -32,6 +20,20 @@ stdout FAIL
 stdout 'invalid count'
 stdout FAIL
 
+# Test that fuzzminimizetime can be zero seconds, and minimization is disabled
+! go test -fuzz=FuzzMinimizeZeroDurationSet -run=FuzzMinimizeZeroDurationSet -fuzztime=10000x -fuzzminimizetime=0s minimizer_test.go
+! stdout '^ok'
+! stdout 'found a crash, minimizing...'
+stdout 'there was an Error'
+stdout FAIL
+
+# Test that fuzzminimizetime can be zero times, and minimization is disabled
+! go test -fuzz=FuzzMinimizeZeroLimitSet -run=FuzzMinimizeZeroLimitSet -fuzztime=10000x -fuzzminimizetime=0x minimizer_test.go
+! stdout '^ok'
+! stdout 'found a crash, minimizing...'
+stdout 'there was an Error'
+stdout FAIL
+
 # Test that minimization is working for recoverable errors.
 ! go test -fuzz=FuzzMinimizerRecoverable -run=FuzzMinimizerRecoverable -fuzztime=10000x minimizer_test.go
 ! stdout '^ok'
@@ -87,6 +89,22 @@ import (
 	"testing"
 )
 
+func FuzzMinimizeZeroDurationSet(f *testing.F) {
+	f.Fuzz(func(t *testing.T, b []byte) {
+		if len(b) > 5 {
+			t.Errorf("there was an Error")
+		}
+	})
+}
+
+func FuzzMinimizeZeroLimitSet(f *testing.F) {
+	f.Fuzz(func(t *testing.T, b []byte) {
+		if len(b) > 5 {
+			t.Errorf("there was an Error")
+		}
+	})
+}
+
 func FuzzMinimizerRecoverable(f *testing.F) {
 	f.Add(make([]byte, 100))
 	f.Fuzz(func(t *testing.T, b []byte) {

src/internal/fuzz/fuzz.go

@@ -40,13 +40,16 @@ type CoordinateFuzzingOpts struct {
 	Limit int64
 
 	// MinimizeTimeout is the amount of wall clock time to spend minimizing
-	// after discovering a crasher. If zero, there will be no time limit.
+	// after discovering a crasher. If zero, there will be no time limit. If
+	// MinimizeTimeout and MinimizeLimit are both zero, then minimization will
+	// be disabled.
 	MinimizeTimeout time.Duration
 
 	// MinimizeLimit is the maximum number of calls to the fuzz function to be
-	// made while minimizing after finding a crash. If zero, there will be
+	// made while minimizing after finding a crash. If zero, there will be no
-	// no limit. Calls to the fuzz function made when minimizing also count
+	// limit. Calls to the fuzz function made when minimizing also count toward
-	// toward Limit.
+	// Limit. If MinimizeTimeout and MinimizeLimit are both zero, then
+	// minimization will be disabled.
 	MinimizeLimit int64
 
 	// parallel is the number of worker processes to run in parallel. If zero,
@@ -552,9 +555,10 @@ type coordinator struct {
 	// generated values that workers reported as interesting.
 	corpus corpus
 
-	// typesAreMinimizable is true if one or more of the types of fuzz function's
+	// minimizationAllowed is true if one or more of the types of fuzz
-	// parameters can be minimized.
+	// function's parameters can be minimized, and either the limit or duration
-	typesAreMinimizable bool
+	// for minimization is non-zero.
+	minimizationAllowed bool
 
 	// inputQueue is a queue of inputs that workers should try fuzzing. This is
 	// initially populated from the seed corpus and cached inputs. More inputs
@@ -604,12 +608,14 @@ func newCoordinator(opts CoordinateFuzzingOpts) (*coordinator, error) {
 		resultC:   make(chan fuzzResult),
 		corpus:    corpus,
 	}
+	if opts.MinimizeLimit > 0 || opts.MinimizeTimeout > 0 {
 		for _, t := range opts.Types {
 			if isMinimizable(t) {
-			c.typesAreMinimizable = true
+				c.minimizationAllowed = true
 				break
 			}
 		}
+	}
 
 	covSize := len(coverage())
 	if covSize == 0 {
@@ -736,7 +742,7 @@ func (c *coordinator) queueForMinimization(result fuzzResult, keepCoverage []byt
 // peekMinimizeInput returns the next input that should be sent to workers for
 // minimization.
 func (c *coordinator) peekMinimizeInput() (fuzzMinimizeInput, bool) {
-	if c.opts.Limit > 0 && c.count+c.countWaiting >= c.opts.Limit {
+	if !c.canMinimize() {
 		// Already making the maximum number of calls to the fuzz function.
 		// Don't send more inputs right now.
 		return fuzzMinimizeInput{}, false
@@ -810,7 +816,7 @@ func (c *coordinator) updateCoverage(newCoverage []byte) int {
 // canMinimize returns whether the coordinator should attempt to find smaller
 // inputs that reproduce a crash or new coverage.
 func (c *coordinator) canMinimize() bool {
-	return c.typesAreMinimizable &&
+	return c.minimizationAllowed &&
 		(c.opts.Limit == 0 || c.count+c.countWaiting < c.opts.Limit)
 }