container_test: fix data race with ForEach read.

pkg/sentry/kernel/fd_table.go

@@ -93,7 +93,7 @@ func (f *FDTable) saveDescriptorTable() map[int32]descriptor {
 	m := make(map[int32]descriptor)
 	f.mu.Lock()
 	defer f.mu.Unlock()
-	f.ForEach(context.Background(), func(fd int32, file *vfs.FileDescription, flags FDFlags) bool {
+	f.forEach(context.Background(), func(fd int32, file *vfs.FileDescription, flags FDFlags) bool {
 		m[fd] = descriptor{
 			file:  file,
 			flags: flags,
@@ -172,10 +172,19 @@ func (f *FDTable) forEachUpTo(ctx context.Context, maxFd int32, fn func(fd int32
 	})
 }
 
-// ForEach iterates over all non-nil files upto maxFd in sorted order.
+// ForEach acquires f.mu and iterates over all non-nil files upto maxFd in sorted order.
+func (f *FDTable) ForEach(ctx context.Context, fn func(fd int32, file *vfs.FileDescription, flags FDFlags) bool) {
+	f.mu.Lock()
+	defer f.mu.Unlock()
+	f.forEach(ctx, fn)
+}
+
+// forEach iterates over all non-nil files upto maxFd in sorted order.
 //
 // It is the caller's responsibility to acquire an appropriate lock.
-func (f *FDTable) ForEach(ctx context.Context, fn func(fd int32, file *vfs.FileDescription, flags FDFlags) bool) {
+//
+// +checklocks:f.mu
+func (f *FDTable) forEach(ctx context.Context, fn func(fd int32, file *vfs.FileDescription, flags FDFlags) bool) {
 	f.forEachUpTo(ctx, MaxFdLimit, fn)
 }
 
@@ -187,7 +196,7 @@ func (f *FDTable) String() string {
 	f.mu.Lock()
 	// Can't release f.mu from defer, because vfsObj.PathnameWithDeleted
 	// should not be called under the fdtable mutex.
-	f.ForEach(ctx, func(fd int32, file *vfs.FileDescription, flags FDFlags) bool {
+	f.forEach(ctx, func(fd int32, file *vfs.FileDescription, flags FDFlags) bool {
 		if file != nil {
 			file.IncRef()
 			files[fd] = file
@@ -427,7 +436,7 @@ func (f *FDTable) GetFDs(ctx context.Context) []int32 {
 	f.mu.Lock()
 	defer f.mu.Unlock()
 	fds := make([]int32, 0, int(f.fdBitmap.GetNumOnes()))
-	f.ForEach(ctx, func(fd int32, _ *vfs.FileDescription, _ FDFlags) bool {
+	f.forEach(ctx, func(fd int32, _ *vfs.FileDescription, _ FDFlags) bool {
 		fds = append(fds, fd)
 		return true
 	})
@@ -489,7 +498,7 @@ func (f *FDTable) RemoveIf(ctx context.Context, cond func(*vfs.FileDescription,
 	var files []*vfs.FileDescription
 
 	f.mu.Lock()
-	f.ForEach(ctx, func(fd int32, file *vfs.FileDescription, flags FDFlags) bool {
+	f.forEach(ctx, func(fd int32, file *vfs.FileDescription, flags FDFlags) bool {
 		if cond(file, flags) {
 			// Clear from table.
 			if df := f.set(fd, nil, FDFlags{}); df != nil {

pkg/sentry/kernel/kernel.go

@@ -1668,7 +1668,7 @@ func (k *Kernel) pauseTimeLocked(ctx context.Context) {
 		// This means we'll iterate FDTables shared by multiple tasks repeatedly,
 		// but ktime.Timer.Pause is idempotent so this is harmless.
 		if t.fdTable != nil {
-			t.fdTable.ForEach(ctx, func(_ int32, fd *vfs.FileDescription, _ FDFlags) bool {
+			t.fdTable.forEach(ctx, func(_ int32, fd *vfs.FileDescription, _ FDFlags) bool { // +checklocksignore
 				if tfd, ok := fd.Impl().(*timerfd.TimerFileDescription); ok {
 					tfd.PauseTimer()
 				}
@@ -1699,7 +1699,7 @@ func (k *Kernel) resumeTimeLocked(ctx context.Context) {
 			}
 		}
 		if t.fdTable != nil {
-			t.fdTable.ForEach(ctx, func(_ int32, fd *vfs.FileDescription, _ FDFlags) bool {
+			t.fdTable.forEach(ctx, func(_ int32, fd *vfs.FileDescription, _ FDFlags) bool { // +checklocksignore
 				if tfd, ok := fd.Impl().(*timerfd.TimerFileDescription); ok {
 					tfd.ResumeTimer()
 				}