[PATCH] tsc2007: prevent overflow in pressure calculation

[PATCH] tsc2007: prevent overflow in pressure calculation

[mailinglist1]

From: Johannes Kirchmair <johannes.kirchmair@skidata.com>

The touch resistance calculation in the tsc2007 driver is prone to overflow
if (z2 - z1) is large and also x is reasonably big. As an result the
driver sometimes emit input events even with very little touch pressure
applied. For those events the x and y coordinates can be substantially
off. We fix the overflow problematic by calculating in a bigger int
type.

Signed-off-by: Johannes Kirchmair <johannes.kirchmair@skidata.com>
---
 drivers/input/touchscreen/tsc2007_core.c | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/drivers/input/touchscreen/tsc2007_core.c b/drivers/input/touchscreen/tsc2007_core.c
index 8d832a372b89..80abbccd1feb 100644
--- a/drivers/input/touchscreen/tsc2007_core.c
+++ b/drivers/input/touchscreen/tsc2007_core.c
@@ -68,11 +68,12 @@ static void tsc2007_read_values(struct tsc2007 *tsc, struct ts_event *tc)
 
 u32 tsc2007_calculate_resistance(struct tsc2007 *tsc, struct ts_event *tc)
 {
-	u32 rt = 0;
+	u64 rt = 0;
 
 	/* range filtering */
-	if (tc->x == MAX_12BIT)
+	if (tc->x == MAX_12BIT) {
 		tc->x = 0;
+	}
 
 	if (likely(tc->x && tc->z1)) {
 		/* compute touch resistance using equation #1 */
@@ -83,7 +84,9 @@ u32 tsc2007_calculate_resistance(struct tsc2007 *tsc, struct ts_event *tc)
 		rt = (rt + 2047) >> 12;
 	}
 
-	return rt;
+	if (rt > U32_MAX)
+		return U32_MAX;
+	return (u32) rt;
 }
 
 bool tsc2007_is_pen_down(struct tsc2007 *ts)

---
base-commit: 05dbaf8dd8bf537d4b4eb3115ab42a5fb40ff1f5
change-id: 20250129-fix_tsc_calculation_overflow-90860d4e3492

Best regards,
-- 
Johannes Kirchmair <johannes.kirchmair@skidata.com>

AW: [PATCH] tsc2007: prevent overflow in pressure calculation

[Johannes Kirchmair - SKIDATA]

Hi, 

Did something wrong in this patch. 
So please ignore it :-/
Will send v2 soon.
Sorry for the noise.

Best regards
Johannes


> -----Ursprüngliche Nachricht-----
> Von: mailinglist1@johanneskirchmair.de <mailinglist1@johanneskirchmair.de>
> Gesendet: Mittwoch, 29. Jänner 2025 12:56
> An: Dmitry Torokhov <dmitry.torokhov@gmail.com>
> Cc: linux-input@vger.kernel.org; Johannes Kirchmair - SKIDATA
> <johannes.kirchmair@skidata.com>
> Betreff: [PATCH] tsc2007: prevent overflow in pressure calculation
> 
> Caution: This is an external email, please take care when clicking links or
> opening attachments
> 
> From: Johannes Kirchmair <johannes.kirchmair@skidata.com>
> 
> The touch resistance calculation in the tsc2007 driver is prone to overflow
> if (z2 - z1) is large and also x is reasonably big. As an result the
> driver sometimes emit input events even with very little touch pressure
> applied. For those events the x and y coordinates can be substantially
> off. We fix the overflow problematic by calculating in a bigger int
> type.
> 
> Signed-off-by: Johannes Kirchmair <johannes.kirchmair@skidata.com>
> ---
>  drivers/input/touchscreen/tsc2007_core.c | 9 ++++++---
>  1 file changed, 6 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/input/touchscreen/tsc2007_core.c
> b/drivers/input/touchscreen/tsc2007_core.c
> index 8d832a372b89..80abbccd1feb 100644
> --- a/drivers/input/touchscreen/tsc2007_core.c
> +++ b/drivers/input/touchscreen/tsc2007_core.c
> @@ -68,11 +68,12 @@ static void tsc2007_read_values(struct tsc2007 *tsc,
> struct ts_event *tc)
> 
>  u32 tsc2007_calculate_resistance(struct tsc2007 *tsc, struct ts_event *tc)
>  {
> -       u32 rt = 0;
> +       u64 rt = 0;
> 
>         /* range filtering */
> -       if (tc->x == MAX_12BIT)
> +       if (tc->x == MAX_12BIT) {
>                 tc->x = 0;
> +       }
> 
>         if (likely(tc->x && tc->z1)) {
>                 /* compute touch resistance using equation #1 */
> @@ -83,7 +84,9 @@ u32 tsc2007_calculate_resistance(struct tsc2007 *tsc,
> struct ts_event *tc)
>                 rt = (rt + 2047) >> 12;
>         }
> 
> -       return rt;
> +       if (rt > U32_MAX)
> +               return U32_MAX;
> +       return (u32) rt;
>  }
> 
>  bool tsc2007_is_pen_down(struct tsc2007 *ts)
> 
> ---
> base-commit: 05dbaf8dd8bf537d4b4eb3115ab42a5fb40ff1f5
> change-id: 20250129-fix_tsc_calculation_overflow-90860d4e3492
> 
> Best regards,
> --
> Johannes Kirchmair <johannes.kirchmair@skidata.com>