[alsa-devel] [PATCH] ASoC: fsl_spdif: Fix integer overflow when calculating divisors

[Anssi Hannula]

The calculation code does
u64 = (u32 - u32) * 100000;

The 64 bits are of no help here as the type is casted only after the
multiplication, and therefore the result may overflow, possibly causing
inoptimal or wrong clock setup in an unfortunate case (the maximum
result value of the first substraction is currently 47999).

Fix the code to cast before multiplication.

Signed-off-by: Anssi Hannula <anssi.hannula at iki.fi>
Cc: Nicolin Chen <Guangyu.Chen at freescale.com>
---
 sound/soc/fsl/fsl_spdif.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/sound/soc/fsl/fsl_spdif.c b/sound/soc/fsl/fsl_spdif.c
index b912d45a2a4c..0bd9136279a2 100644
--- a/sound/soc/fsl/fsl_spdif.c
+++ b/sound/soc/fsl/fsl_spdif.c
@@ -1076,7 +1076,7 @@ static u32 fsl_spdif_txclk_caldiv(struct fsl_spdif_priv *spdif_priv,
 				goto out;
 			} else if (arate / rate[index] == 1) {
 				/* A little bigger than expect */
-				sub = (arate - rate[index]) * 100000;
+				sub = (u64)(arate - rate[index]) * 100000;
 				do_div(sub, rate[index]);
 				if (sub >= savesub)
 					continue;
@@ -1086,7 +1086,7 @@ static u32 fsl_spdif_txclk_caldiv(struct fsl_spdif_priv *spdif_priv,
 				spdif_priv->txrate[index] = arate;
 			} else if (rate[index] / arate == 1) {
 				/* A little smaller than expect */
-				sub = (rate[index] - arate) * 100000;
+				sub = (u64)(rate[index] - arate) * 100000;
 				do_div(sub, rate[index]);
 				if (sub >= savesub)
 					continue;
-- 
1.8.4.5