[PATCH v2] drm/log: Fix division by zero when scale module parameter is 0

[oushixiong1025]

From: Shixiong Ou <oushixiong@xxxxxxxxxx>

The scale module parameter can be set to 0 via kernel command line or
sysfs. When scale is 0, scaled_font_h and scaled_font_w become 0,
causing a division by zero in the rows/columns calculation.

Introduce a drm_log_scale() helper that returns scale ?: 1, and use it
at all read sites. This avoids a race that a setter-based clamp would
have between param_set_uint() and the subsequent check, where another
CPU could observe scale == 0.

Signed-off-by: Shixiong Ou <oushixiong@xxxxxxxxxx>
---
v1->v2:
   Introduce a drm_log_scale() helper.

 drivers/gpu/drm/clients/drm_log.c | 15 ++++++++++-----
 1 file changed, 10 insertions(+), 5 deletions(-)

diff --git a/drivers/gpu/drm/clients/drm_log.c b/drivers/gpu/drm/clients/drm_log.c
index 294b3be1a6b3..9522c1344123 100644
--- a/drivers/gpu/drm/clients/drm_log.c
+++ b/drivers/gpu/drm/clients/drm_log.c
@@ -29,6 +29,11 @@ static unsigned int scale = 1;
 module_param(scale, uint, 0444);
 MODULE_PARM_DESC(scale, "Integer scaling factor for drm_log, default is 1");
 
+static inline unsigned int drm_log_scale(void)
+{
+	return scale ?: 1;
+}
+
 /**
  * DOC: overview
  *
@@ -76,13 +81,13 @@ static void drm_log_blit(struct iosys_map *dst, unsigned int dst_pitch,
 {
 	switch (px_width) {
 	case 2:
-		drm_draw_blit16(dst, dst_pitch, src, src_pitch, height, width, scale, color);
+		drm_draw_blit16(dst, dst_pitch, src, src_pitch, height, width, drm_log_scale(), color);
 		break;
 	case 3:
-		drm_draw_blit24(dst, dst_pitch, src, src_pitch, height, width, scale, color);
+		drm_draw_blit24(dst, dst_pitch, src, src_pitch, height, width, drm_log_scale(), color);
 		break;
 	case 4:
-		drm_draw_blit32(dst, dst_pitch, src, src_pitch, height, width, scale, color);
+		drm_draw_blit32(dst, dst_pitch, src, src_pitch, height, width, drm_log_scale(), color);
 		break;
 	default:
 		WARN_ONCE(1, "Can't blit with pixel width %d\n", px_width);
@@ -216,8 +221,8 @@ static int drm_log_setup_modeset(struct drm_client_dev *client,
 		return -ENOMEM;
 	}
 	mode_set->fb = scanout->buffer->fb;
-	scanout->scaled_font_h = scanout->font->height * scale;
-	scanout->scaled_font_w = scanout->font->width * scale;
+	scanout->scaled_font_h = scanout->font->height * drm_log_scale();
+	scanout->scaled_font_w = scanout->font->width * drm_log_scale();
 	scanout->rows = height / scanout->scaled_font_h;
 	scanout->columns = width / scanout->scaled_font_w;
 	scanout->front_color = drm_draw_color_from_xrgb8888(0xffffff, format);
-- 
2.25.1


No virus found
		Checked by Hillstone Network AntiVirus