fix: add error handling and validation

drm/drm_linux.go

@@ -441,6 +441,7 @@ func nullTermString(b []byte) string {
 // "rotation" property to DRM_MODE_ROTATE_180 or DRM_MODE_ROTATE_0.
 // crtcIDs is the ordered list from DRM_IOCTL_MODE_GETRESOURCES; the index
 // of crtcID in that list determines which bit to match in PossibleCrtcs.
+// If rotate is true but rotation cannot be set, logs a warning.
 func setPlaneRotation(fd uintptr, crtcID uint32, crtcIDs []uint32, rotate bool) {
 	crtcBit := uint32(0)
 	for i, id := range crtcIDs {
@@ -526,19 +527,19 @@ func Open(dev string, rotate bool) (*Device, error) {
 	cap := drmSetClientCap{Capability: drmClientCapUniversalPlanes, Value: 1}
 	err = drmIoctl(fd, ioctlSetClientCap, &cap)
 	if err != nil {
-		f.Close()
+		cleanup(&buffers)
 		return nil, fmt.Errorf("DRM_CLIENT_CAP_UNIVERSAL_PLANES: %w", err)
 	}
 
 	// First call: discover how many connectors exist.
 	var res drmModeRes
 	err = drmIoctl(fd, ioctlModeGetResources, &res)
 	if err != nil {
-		f.Close()
+		cleanup(&buffers)
 		return nil, fmt.Errorf("DRM_IOCTL_MODE_GETRESOURCES: %w", err)
 	}
 	if res.CountConnectors == 0 {
-		f.Close()
+		cleanup(&buffers)
 		return nil, fmt.Errorf("no DRM connectors found")
 	}
 
@@ -554,7 +555,7 @@ func Open(dev string, rotate bool) (*Device, error) {
 	res.EncoderIDPtr = 0
 	err = drmIoctl(fd, ioctlModeGetResources, &res)
 	if err != nil {
-		f.Close()
+		cleanup(&buffers)
 		return nil, fmt.Errorf("DRM_IOCTL_MODE_GETRESOURCES (ids): %w", err)
 	}
 
@@ -602,7 +603,7 @@ func Open(dev string, rotate bool) (*Device, error) {
 	enc.EncoderID = encoderID
 	err = drmIoctl(fd, ioctlModeGetEncoder, &enc)
 	if err != nil {
-		f.Close()
+		cleanup(&buffers)
 		return nil, fmt.Errorf("DRM_IOCTL_MODE_GETENCODER: %w", err)
 	}
 	crtcID := enc.CrtcID
@@ -751,6 +752,9 @@ func (d *Device) Flip() {
 		SetConnectorsPtr: uint64(uintptr(unsafe.Pointer(&d.connID))),
 		CountConnectors:  1,
 	}
-	drmIoctl(d.fd, ioctlModeSetCRTC, &crtc)
+	if err := drmIoctl(d.fd, ioctlModeSetCRTC, &crtc); err != nil {
+		slog.Error("DRM flip failed; display not updated", "err", err)
+		return
+	}
 	d.active = next
 }

fb/fb_linux.go

@@ -219,11 +219,15 @@ func Open(dev string, rotate bool) (*Device, error) {
 		}
 	}
 
-	fbSize := stride * height
+	fbSize := int64(stride) * int64(height)
+	if fbSize <= 0 || fbSize > 256*1024*1024 {
+		f.Close()
+		return nil, fmt.Errorf("invalid framebuffer size: %d bytes (stride=%d, height=%d)", fbSize, stride, height)
+	}
 	data, err := syscall.Mmap(
 		int(f.Fd()),
 		0,
-		fbSize,
+		int(fbSize),
 		syscall.PROT_READ|syscall.PROT_WRITE,
 		syscall.MAP_SHARED,
 	)
@@ -282,6 +286,7 @@ func (fb *Device) blitToHardware(img *image.RGBA) {
 		}
 
 		// Cache the bayer row for this y — it is constant across the x loop.
+		// The 4×4 Bayer matrix repeats every 4 pixels, so y&3 selects which row.
 		bayerRow := bayer4x4[y&3]
 
 		// Pack the pixel into the hardware format. The vinfo bitfields
@@ -310,6 +315,7 @@ func (fb *Device) blitToHardware(img *image.RGBA) {
 				// steps of 8 (R/B) or 4 (G), producing a visible staircase.
 				// Adding a position-dependent threshold before the right-shift
 				// spreads the quantisation error across neighbouring pixels.
+				// x&3 selects the column in the 4-wide Bayer row for this pixel.
 				d := bayerRow[x&3]
 				r5 := uint16(clamp8(int(r)+int(d>>3))) >> 3
 				g6 := uint16(clamp8(int(g)+int(d>>2))) >> 2
@@ -329,10 +335,18 @@ func (fb *Device) BackBuffer() *image.RGBA {
 
 // Flip copies the back buffer to the hardware framebuffer.
 func (fb *Device) Flip() {
+	if fb.back.Bounds().Dx() != fb.width || fb.back.Bounds().Dy() != fb.height {
+		slog.Error("back buffer size mismatch; this should not happen", "got", fb.back.Bounds(), "want", image.Rect(0, 0, fb.width, fb.height))
+		return
+	}
 	fb.blitToHardware(fb.back)
 }
 
 // Blit copies img to the framebuffer. Deprecated: use BackBuffer and Flip instead.
 func (fb *Device) Blit(img *image.RGBA) {
+	if img.Bounds().Dx() != fb.width || img.Bounds().Dy() != fb.height {
+		slog.Error("Blit image size mismatch", "got", img.Bounds(), "want", image.Rect(0, 0, fb.width, fb.height))
+		return
+	}
 	fb.blitToHardware(img)
 }