test: add test for handling invalid sizes

Signed-off-by: Tonis Tiigi <tonistiigi@gmail.com>

test/sched.go

@@ -114,7 +114,11 @@ func SchedGetAttr(pid int) (SchedAttr, error) {
 
 func SchedSetAttr(pid int, attr SchedAttr, flags SchedFlag) error {
 	attr.Size = uint32(unsafe.Sizeof(attr))
-	_, _, e1 := unix.Syscall(unix.SYS_SCHED_SETATTR, uintptr(pid), uintptr(unsafe.Pointer(&attr)), uintptr(flags))
+	return schedSetAttr(pid, unsafe.Pointer(&attr), flags)
+}
+
+func schedSetAttr(pid int, attr unsafe.Pointer, flags SchedFlag) error {
+	_, _, e1 := unix.Syscall(unix.SYS_SCHED_SETATTR, uintptr(pid), uintptr(attr), uintptr(flags))
 	if e1 != 0 {
 		return syscall.Errno(e1)
 	}

test/sched_test.go

@@ -7,6 +7,7 @@ import (
 	"strconv"
 	"syscall"
 	"testing"
+	"unsafe"
 
 	"github.com/stretchr/testify/require"
 )
@@ -150,3 +151,40 @@ func TestSchedAttr(t *testing.T) {
 		require.Equal(t, 60, int(attr.SchedPriority))
 	}
 }
+
+func TestSchedAttrSize(t *testing.T) {
+	pid := os.Getpid()
+
+	dt := make([]byte, 2)
+	ptr := unsafe.Pointer(&dt[0])
+	err := schedSetAttr(pid, ptr, 0)
+	require.Error(t, err)
+	t.Logf("short read error: %v", err) // this error does not look consistent even with no emulation
+
+	dt = make([]byte, 80)
+	ptr = unsafe.Pointer(&dt[0])
+
+	err = schedSetAttr(pid, ptr, 0)
+	require.NoError(t, err) // empty size is ok for some reason
+
+	ints := (*[20]uint32)(ptr)
+	ints[0] = 8 // too small size
+
+	err = schedSetAttr(pid, ptr, 0)
+	require.Error(t, err)
+	require.True(t, errors.Is(err, syscall.E2BIG))
+	require.Equal(t, uint32(0x38), ints[0]) // expecting kernel 5.3+
+
+	ints[0] = 80 // too big but empty contents is ok
+	err = schedSetAttr(pid, ptr, 0)
+	require.NoError(t, err)
+
+	ints[18] = 0xff // too big and not empty
+
+	err = schedSetAttr(pid, ptr, 0)
+	require.Error(t, err)
+	require.True(t, errors.Is(err, syscall.E2BIG))
+	require.Equal(t, uint32(0x38), ints[0]) // expecting kernel 5.3+
+
+	runtime.KeepAlive(dt)
+}