fix(pgdriver): guard protocol message sizes against overflow and invalid lengths

driver/pgdriver/column.go

@@ -61,6 +61,13 @@ func readColumnValue(rd *reader, dataType int32, dataLen int) (any, error) {
 		return readBytesCol(rd, dataLen)
 	}
 
+	if dataLen < 0 {
+		// dataLen == -1 signals SQL NULL; any other negative value is invalid
+		// and must not reach make([]byte, dataLen) (would panic). dataLen == 0
+		// is fine and keeps its previous behavior (empty value).
+		return nil, nil
+	}
+
 	b := make([]byte, dataLen)
 	if _, err := io.ReadFull(rd, b); err != nil {
 		return nil, err

driver/pgdriver/driver.go

@@ -174,6 +174,14 @@ func (cn *Conn) reader(ctx context.Context, timeout time.Duration) *reader {
 }
 
 func (cn *Conn) write(ctx context.Context, wb *writeBuffer) error {
+	// Refuse to send a message that failed to build (e.g. it exceeded the
+	// protocol size limit); sending it would desync the connection.
+	if wb.err != nil {
+		err := wb.err
+		wb.Reset()
+		return err
+	}
+
 	cn.setWriteDeadline(ctx, -1)
 
 	n, err := cn.netConn.Write(wb.Bytes)

driver/pgdriver/error.go

@@ -84,4 +84,15 @@ func isBadConn(err error, allowTimeout bool) bool {
 
 var (
 	errRequiresParameter = errors.New("pgdriver: requires that standard_conforming_strings=on and client_encoding=UTF8")
+
+	// errMessageTooLarge is returned instead of sending a message whose length
+	// prefix would overflow the protocol's 32-bit size field. Without this guard
+	// the length wraps and the server desyncs, which can be abused for SQL
+	// injection (cf. jackc/pgx CVE-2024-27304).
+	errMessageTooLarge = errors.New("pgdriver: message size exceeds the maximum of 4 GiB")
+
+	// errInvalidMessageLength is returned when the server sends a message whose
+	// length field is smaller than the 4-byte length prefix itself (which would
+	// otherwise lead to a negative-length slice/allocation panic).
+	errInvalidMessageLength = errors.New("pgdriver: server sent a message with an invalid length")
 )

driver/pgdriver/message_size_test.go

@@ -0,0 +1,84 @@
+package pgdriver
+
+import (
+	"bytes"
+	"context"
+	"database/sql/driver"
+	"encoding/binary"
+	"errors"
+	"math"
+	"testing"
+)
+
+func TestFinishMessage_TooLargeSetsError(t *testing.T) {
+	orig := maxMessageSize
+	maxMessageSize = 8
+	defer func() { maxMessageSize = orig }()
+
+	wb := newWriteBuffer()
+	wb.StartMessage(queryMsg)
+	wb.WriteString("some query that exceeds the tiny test limit")
+	wb.FinishMessage()
+
+	if !errors.Is(wb.err, errMessageTooLarge) {
+		t.Fatalf("wb.err = %v, want errMessageTooLarge", wb.err)
+	}
+}
+
+func TestConnWrite_RefusesOversizedMessage(t *testing.T) {
+	wb := newWriteBuffer()
+	wb.setErr(errMessageTooLarge)
+
+	// wb.err is set, so write must return it without touching the (nil) netConn.
+	if err := (&Conn{}).write(context.Background(), wb); !errors.Is(err, errMessageTooLarge) {
+		t.Fatalf("write() = %v, want errMessageTooLarge", err)
+	}
+}
+
+func TestFinishParam_TooLargeSetsError(t *testing.T) {
+	orig := maxMessageSize
+	maxMessageSize = 4
+	defer func() { maxMessageSize = orig }()
+
+	wb := newWriteBuffer()
+	wb.StartParam()
+	wb.Write([]byte("larger than the limit"))
+	wb.FinishParam()
+
+	if !errors.Is(wb.err, errMessageTooLarge) {
+		t.Fatalf("wb.err = %v, want errMessageTooLarge", wb.err)
+	}
+}
+
+func TestWriteBindExecute_TooManyParams(t *testing.T) {
+	args := make([]driver.NamedValue, math.MaxInt16+1)
+	err := writeBindExecute(context.Background(), &Conn{}, "", args)
+	if err == nil {
+		t.Fatal("writeBindExecute with > MaxInt16 params: got nil error, want an error")
+	}
+}
+
+func TestReadMessageType_RejectsShortLength(t *testing.T) {
+	// type byte + 4-byte length field of 0 (< 4, invalid).
+	buf := []byte{'X', 0, 0, 0, 0}
+	rd := newReader(bytes.NewReader(buf), 1024)
+	if _, _, err := readMessageType(rd); !errors.Is(err, errInvalidMessageLength) {
+		t.Fatalf("readMessageType short length: err = %v, want errInvalidMessageLength", err)
+	}
+
+	// A valid length (>= 4) is accepted and the body length is length-4.
+	valid := []byte{'X', 0, 0, 0, 0}
+	binary.BigEndian.PutUint32(valid[1:], 10)
+	rd = newReader(bytes.NewReader(valid), 1024)
+	c, n, err := readMessageType(rd)
+	if err != nil || c != 'X' || n != 6 {
+		t.Fatalf("readMessageType valid: (%q, %d, %v), want ('X', 6, nil)", c, n, err)
+	}
+}
+
+func TestReadTemp_RejectsNegative(t *testing.T) {
+	rd := newReader(bytes.NewReader(nil), 1024)
+	if _, err := rd.ReadTemp(-1); !errors.Is(err, errInvalidMessageLength) {
+		t.Fatalf("ReadTemp(-1) = %v, want errInvalidMessageLength", err)
+	}
+}

driver/pgdriver/proto.go

@@ -94,6 +94,9 @@ func newReader(r io.Reader, size int) *reader {
 }
 
 func (r *reader) ReadTemp(n int) ([]byte, error) {
+	if n < 0 {
+		return nil, errInvalidMessageLength
+	}
 	if n <= len(r.buf) {
 		b := r.buf[:n]
 		_, err := io.ReadFull(r.Reader, b)
@@ -827,6 +830,10 @@ func writeBindExecute(ctx context.Context, cn *Conn, name string, args []driver.
 	wb := getWriteBuffer()
 	defer putWriteBuffer(wb)
 
+	if len(args) > math.MaxInt16 {
+		return fmt.Errorf("pgdriver: too many bind parameters: %d (max %d)", len(args), math.MaxInt16)
+	}
+
 	wb.StartMessage(bindMsg)
 	wb.WriteString("")
 	wb.WriteString(name)
@@ -1020,6 +1027,12 @@ func readMessageType(rd *reader) (byte, int, error) {
 	if err != nil {
 		return 0, 0, err
 	}
+	if l < 4 {
+		// The length field includes its own 4 bytes, so it can never be < 4.
+		// A smaller value would yield a negative body length and panic callers
+		// that allocate/slice with it.
+		return 0, 0, errInvalidMessageLength
+	}
 	return c, int(l) - 4, nil
 }
 

driver/pgdriver/write_buffer.go

@@ -3,9 +3,16 @@ package pgdriver
 import (
 	"encoding/binary"
 	"io"
+	"math"
 	"sync"
 )
 
+// maxMessageSize is the largest value that fits in the protocol's 32-bit message
+// length field. It is an int64 (so the constant does not overflow int on 32-bit
+// platforms) and a var (not a const) so tests can lower it. Do not mutate it
+// outside of tests.
+var maxMessageSize int64 = math.MaxUint32
+
 var wbPool = sync.Pool{
 	New: func() any {
 		return newWriteBuffer()
@@ -27,6 +34,11 @@ type writeBuffer struct {
 
 	msgStart   int
 	paramStart int
+
+	// err records the first fatal error (e.g. a message that exceeds the
+	// protocol size limit). It is checked before the buffer is sent so an
+	// oversized/overflowing message is never written to the wire.
+	err error
 }
 
 func newWriteBuffer() *writeBuffer {
@@ -37,6 +49,14 @@ func newWriteBuffer() *writeBuffer {
 
 func (b *writeBuffer) Reset() {
 	b.Bytes = b.Bytes[:0]
+	b.err = nil
+}
+
+// setErr records the first error seen while building a message.
+func (b *writeBuffer) setErr(err error) {
+	if b.err == nil {
+		b.err = err
+	}
 }
 
 func (b *writeBuffer) StartMessage(c byte) {
@@ -50,8 +70,12 @@ func (b *writeBuffer) StartMessage(c byte) {
 }
 
 func (b *writeBuffer) FinishMessage() {
-	binary.BigEndian.PutUint32(
-		b.Bytes[b.msgStart:], uint32(len(b.Bytes)-b.msgStart))
+	n := len(b.Bytes) - b.msgStart
+	if int64(n) > maxMessageSize {
+		b.setErr(errMessageTooLarge)
+		return
+	}
+	binary.BigEndian.PutUint32(b.Bytes[b.msgStart:], uint32(n))
 }
 
 func (b *writeBuffer) Query() []byte {
@@ -64,8 +88,12 @@ func (b *writeBuffer) StartParam() {
 }
 
 func (b *writeBuffer) FinishParam() {
-	binary.BigEndian.PutUint32(
-		b.Bytes[b.paramStart:], uint32(len(b.Bytes)-b.paramStart-4))
+	n := len(b.Bytes) - b.paramStart - 4
+	if int64(n) > maxMessageSize {
+		b.setErr(errMessageTooLarge)
+		return
+	}
+	binary.BigEndian.PutUint32(b.Bytes[b.paramStart:], uint32(n))
 }
 
 var nullParamLength = int32(-1)