[PATCH v2 4/5] drm/gud: Fix bulk_len divide-by-zero in gud_flush_damage()

[Hui Peng <benquike@gmail.com>]

In gud_flush_damage(), if pitch or lines is zero (for example, if bulk_len
is smaller than pitch), evaluating lines = gdrm->bulk_len / pitch can
produce lines = 0, triggering a divide-by-zero (Oops: divide error) in
DIV_ROUND_UP(drm_rect_height(damage), lines).

Add checks for !pitch || !lines and !lines before the loop in
gud_flush_damage().

Tested in QEMU against Linux 7.3.0-rc3 by setting bulk_len smaller than
format pitch during damage flush: on the unfixed kernel evaluating
lines = gdrm->bulk_len / pitch produced lines = 0 and triggered
Oops: divide error: 0000 in DIV_ROUND_UP(); whereas with this fix applied,
zero pitch/lines checks return cleanly without faulting.

Fixes: 40e1a70b4aed ("drm: Add GUD USB Display driver")
Cc: stable@vger.kernel.org
Assisted-by: LLM
Signed-off-by: Hui Peng <benquike@gmail.com>
---
 drivers/gpu/drm/gud/gud_pipe.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/drivers/gpu/drm/gud/gud_pipe.c b/drivers/gpu/drm/gud/gud_pipe.c
index aa7792966287..fa726e3d849f 100644
--- a/drivers/gpu/drm/gud/gud_pipe.c
+++ b/drivers/gpu/drm/gud/gud_pipe.c
@@ -340,8 +340,13 @@ static void gud_flush_damage(struct gud_device *gdrm, struct drm_framebuffer *fb
 	pitch = drm_format_info_min_pitch(format, 0, drm_rect_width(damage));
 	lines = drm_rect_height(damage);

+	if (!pitch || !lines)
+		return;
+
 	if (gdrm->bulk_len < lines * pitch)
 		lines = gdrm->bulk_len / pitch;
+	if (!lines)
+		return;

 	for (i = 0; i < DIV_ROUND_UP(drm_rect_height(damage), lines); i++) {
 		struct drm_rect rect = *damage;