drm/repaper: fix integer overflows in repeat functions

Commit Message

Nikita Zhandarovich Jan. 16, 2025, 1:48 p.m. UTC

There are conditions, albeit somewhat unlikely, under which right hand
expressions, calculating the end of time period in functions like
repaper_frame_fixed_repeat(), may overflow.

For instance, if 'factor10x' in repaper_get_temperature() is high
enough (170), as is 'epd->stage_time' in repaper_probe(), then the
resulting value of 'end' will not fit in unsigned int expression.

Mitigate this by casting 'epd->factored_stage_time' to wider type before
any multiplication is done.

Found by Linux Verification Center (linuxtesting.org) with static
analysis tool SVACE.

Fixes: 3589211e9b03 ("drm/tinydrm: Add RePaper e-ink driver")
Cc: [e-mail]
Signed-off-by: Nikita Zhandarovich <[e-mail]>
---
 drivers/gpu/drm/tiny/repaper.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

Patch

diff --git a/drivers/gpu/drm/tiny/repaper.c b/drivers/gpu/drm/tiny/repaper.c
index 77944eb17b3c..d76c0e8e05f5 100644
--- a/drivers/gpu/drm/tiny/repaper.c
+++ b/drivers/gpu/drm/tiny/repaper.c
@@ -456,7 +456,7 @@  static void repaper_frame_fixed_repeat(struct repaper_epd *epd, u8 fixed_value,
 				       enum repaper_stage stage)
 {
 	u64 start = local_clock();
-	u64 end = start + (epd->factored_stage_time * 1000 * 1000);
+	u64 end = start + ((u64)epd->factored_stage_time * 1000 * 1000);
 
 	do {
 		repaper_frame_fixed(epd, fixed_value, stage);
@@ -467,7 +467,7 @@  static void repaper_frame_data_repeat(struct repaper_epd *epd, const u8 *image,
 				      const u8 *mask, enum repaper_stage stage)
 {
 	u64 start = local_clock();
-	u64 end = start + (epd->factored_stage_time * 1000 * 1000);
+	u64 end = start + ((u64)epd->factored_stage_time * 1000 * 1000);
 
 	do {
 		repaper_frame_data(epd, image, mask, stage);