Fix invalid conversion between unsafe.Pointer and uintptr

uintptr cannot be stored in variable before conversion back to Pointer.
This is because the variable is an integer with no pointer semantics,
even if a uintptr holds the address of some object, the garbage
collector will not update that uintptr's value if the object moves, nor
will that uintptr keep the object from being reclaimed.

The issue can be detected by checkptr when running unit test with race
detector:

checkptr: pointer arithmetic result points to invalid allocation
```
pFirstRow := uintptr(unsafe.Pointer(&table.Table[0]))
row := *(*MibIPForwardRow)(unsafe.Pointer(pFirstRow + rowSize*uintptr(i)))
```

While it can be fixed by performing both conversions in the same
expression like below, using `unsafe.Slice` to get the slice is much
simpler.
```
row := *(*MibIPForwardRow)(unsafe.Pointer(uintptr(unsafe.Pointer(&table.Table[0])) + rowSize*uintptr(i)))
```

The patch also adds an unit test to validate it.

Signed-off-by: Quan Tian <[email protected]>

pkg/agent/util/syscall/syscall_windows.go

@@ -308,10 +308,17 @@ type NetIOInterface interface {
 
 type netIO struct {
 	syscallN func(trap uintptr, args ...uintptr) (r1, r2 uintptr, err syscall.Errno)
+	// It needs be declared as a variable and replaced during unit tests because the real getIPForwardTable function
+	// converts a Pointer to a uintptr as an argument of syscallN, while converting a uintptr back to a Pointer in the
+	// fake syscallN is not valid.
+	getIPForwardTable func(family uint16, ipForwardTable **MibIPForwardTable) (errcode error)
 }
 
 func NewNetIO() NetIOInterface {
-	return &netIO{syscallN: syscall.SyscallN}
+	return &netIO{
+		syscallN:          syscall.SyscallN,
+		getIPForwardTable: getIPForwardTable,
+	}
 }
 
 func (n *netIO) GetIPInterfaceEntry(ipInterfaceRow *MibIPInterfaceRow) (errcode error) {
@@ -351,8 +358,8 @@ func (n *netIO) freeMibTable(table unsafe.Pointer) {
 	return
 }
 
-func (n *netIO) getIPForwardTable(family uint16, ipForwardTable **MibIPForwardTable) (errcode error) {
-	r0, _, _ := n.syscallN(procGetIPForwardTable.Addr(), uintptr(family), uintptr(unsafe.Pointer(ipForwardTable)))
+func getIPForwardTable(family uint16, ipForwardTable **MibIPForwardTable) (errcode error) {
+	r0, _, _ := syscall.SyscallN(procGetIPForwardTable.Addr(), uintptr(family), uintptr(unsafe.Pointer(ipForwardTable)))
 	if r0 != 0 {
 		errcode = syscall.Errno(r0)
 	}
@@ -362,21 +369,15 @@ func (n *netIO) getIPForwardTable(family uint16, ipForwardTable **MibIPForwardTa
 func (n *netIO) ListIPForwardRows(family uint16) ([]MibIPForwardRow, error) {
 	var table *MibIPForwardTable
 	err := n.getIPForwardTable(family, &table)
-	if table != nil {
-		defer n.freeMibTable(unsafe.Pointer(table))
-	}
 	if err != nil {
 		return nil, os.NewSyscallError("iphlpapi.GetIpForwardTable", err)
 	}
-	rows := make([]MibIPForwardRow, table.NumEntries, table.NumEntries)
+	defer n.freeMibTable(unsafe.Pointer(table))
 
-	pFirstRow := uintptr(unsafe.Pointer(&table.Table[0]))
-	rowSize := unsafe.Sizeof(table.Table[0])
-
-	for i := uint32(0); i < table.NumEntries; i++ {
-		row := *(*MibIPForwardRow)(unsafe.Pointer(pFirstRow + rowSize*uintptr(i)))
-		rows[i] = row
-	}
+	// Copy the rows from the table into a new slice as the table's memory will be freed.
+	// Since MibIPForwardRow contains only value data (no references), the operation performs a deep copy.
+	rows := make([]MibIPForwardRow, 0, table.NumEntries)
+	rows = append(rows, unsafe.Slice(&table.Table[0], table.NumEntries)...)
 	return rows, nil
 }
 

pkg/agent/util/syscall/syscall_windows_test.go

@@ -19,8 +19,10 @@ import (
 	"os"
 	"syscall"
 	"testing"
+	"unsafe"
 
 	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
 )
 
 func TestRawSockAddrTranslation(t *testing.T) {
@@ -202,16 +204,85 @@ func TestIPForwardEntryOperations(t *testing.T) {
 	}
 }
 
-func TestListIPForwardRows(t *testing.T) {
+func TestListIPForwardRowsFailure(t *testing.T) {
+	testNetIO := &netIO{
+		getIPForwardTable: func(family uint16, ipForwardTable **MibIPForwardTable) (errcode error) {
+			return syscall.Errno(22)
+		},
+		syscallN: func(trap uintptr, args ...uintptr) (r1, r2 uintptr, err syscall.Errno) {
+			assert.Fail(t, "freeMibTable shouldn't be called")
+			return
+		},
+	}
 	wantErr := os.NewSyscallError("iphlpapi.GetIpForwardTable", syscall.Errno(22))
-	testNetIO := NewTestNetIO(22)
-	// Skipping no error case because converting uintptr back to Pointer is not valid in general.
-	gotRow, gotErr := testNetIO.ListIPForwardRows(AF_INET)
-	assert.Nil(t, gotRow)
+	gotRows, gotErr := testNetIO.ListIPForwardRows(AF_INET)
+	assert.Nil(t, gotRows)
 	assert.Equal(t, wantErr, gotErr)
 }
 
-func NewTestNetIO(wantR1 uintptr) NetIOInterface {
+func TestListIPForwardRowsSuccess(t *testing.T) {
+	row1 := MibIPForwardRow{
+		Luid:  10,
+		Index: 11,
+		DestinationPrefix: AddressPrefix{
+			Prefix: RawSockAddrInet{
+				Family: AF_INET,
+				data:   [26]byte{10, 10, 10, 0},
+			},
+			prefixLength: 24,
+		},
+		NextHop: RawSockAddrInet{
+			Family: AF_INET,
+			data:   [26]byte{11, 11, 11, 11},
+		},
+	}
+	row2 := MibIPForwardRow{
+		Luid:  20,
+		Index: 21,
+		DestinationPrefix: AddressPrefix{
+			Prefix: RawSockAddrInet{
+				Family: AF_INET,
+				data:   [26]byte{20, 20, 20, 0},
+			},
+			prefixLength: 24,
+		},
+		NextHop: RawSockAddrInet{
+			Family: AF_INET,
+			data:   [26]byte{21, 21, 21, 21},
+		},
+	}
+	// The table contains two rows. Its memory address will be assigned to ipForwardTable when getIPForwardTable is called.
+	table := struct {
+		NumEntries uint32
+		Table      [2]MibIPForwardRow
+	}{
+		NumEntries: 2,
+		Table:      [2]MibIPForwardRow{row1, row2},
+	}
+	freeMibTableCalled := false
+	testNetIO := &netIO{
+		getIPForwardTable: func(family uint16, ipForwardTable **MibIPForwardTable) (errcode error) {
+			*ipForwardTable = (*MibIPForwardTable)(unsafe.Pointer(&table))
+			return nil
+		},
+		syscallN: func(trap uintptr, args ...uintptr) (r1, r2 uintptr, err syscall.Errno) {
+			freeMibTableCalled = true
+			// Reset the rows.
+			table.Table[0] = MibIPForwardRow{}
+			table.Table[1] = MibIPForwardRow{}
+			return
+		},
+	}
+	gotRows, gotErr := testNetIO.ListIPForwardRows(AF_INET)
+	require.NoError(t, gotErr)
+	assert.True(t, freeMibTableCalled)
+	// It verifies that the returned rows are independent copies, not referencing to the original table's memory, by
+	// asserting they retain the exact same content as the original table whose rows have been reset by freeMibTable.
+	expectedRows := []MibIPForwardRow{row1, row2}
+	assert.Equal(t, expectedRows, gotRows)
+}
+
+func NewTestNetIO(wantR1 uintptr) *netIO {
 	mockSyscallN := func(trap uintptr, args ...uintptr) (r1, r2 uintptr, err syscall.Errno) {
 		return wantR1, 0, 0
 	}