[PATCH v2] media: mali-c55: fix integer overflow in scaler factor calculation

[David Carlier <devnexen@gmail.com>]

The scaling factors are computed by multiplying the crop dimension by
the Q4.20 unit (1 << 20) and dividing by the output dimension. The
results are stored in u64, but both operands are 32-bit, so the product
is evaluated in 32-bit arithmetic and only widened afterwards.

Crop dimensions may be up to 8192. Once a dimension reaches 4096 the
product overflows 32 bits and wraps (zero at exactly 4096), programming
a corrupted scaling increment and corrupting the downscaled output.

Define the fixed-point unit as unsigned long long so the multiplication
is done in 64-bit arithmetic.

Fixes: d5f281f3dd29 ("media: mali-c55: Add Mali-C55 ISP driver")
Cc: stable@vger.kernel.org
Signed-off-by: David Carlier <devnexen@gmail.com>
---
v2: Use the BIT_ULL() macro instead of an open-coded (1ULL << 20)
    (checkpatch).
---
 drivers/media/platform/arm/mali-c55/mali-c55-resizer.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/media/platform/arm/mali-c55/mali-c55-resizer.c b/drivers/media/platform/arm/mali-c55/mali-c55-resizer.c
index c4f46651dcee..6706939b4a90 100644
--- a/drivers/media/platform/arm/mali-c55/mali-c55-resizer.c
+++ b/drivers/media/platform/arm/mali-c55/mali-c55-resizer.c
@@ -15,7 +15,7 @@
 #include "mali-c55-registers.h"
 
 /* Scaling factor in Q4.20 format. */
-#define MALI_C55_RSZ_SCALER_FACTOR	(1U << 20)
+#define MALI_C55_RSZ_SCALER_FACTOR	BIT_ULL(20)
 
 #define MALI_C55_RSZ_COEFS_BANKS	8
 #define MALI_C55_RSZ_COEFS_ENTRIES	64
-- 
2.53.0