[PATCH] ASoC: rt1011: fix KASAN out-of-bounds bug in find_next_bit()

[Pierre-Louis Bossart]

From: Fred Oh <fred.oh at linux.intel.com>

KASAN throws the following warning in rt1011.c:
[ 170.777603] BUG: KASAN: stack-out-of-bounds in _find_next_bit.constprop.0+0x3e/0xf0

find_next_bit() relies on unsigned long pointer arguments, but this driver
uses a type cast that generates the KASAN warning. Replace find_next_bit()
and find_last_bit() with __ffs() and __fls() to pass the value and avoid
casting pointers to make the warning go away.

Reviewed-by: Guennadi Liakhovetski <guennadi.liakhovetski at linux.intel.com>
Signed-off-by: Fred Oh <fred.oh at linux.intel.com>
Signed-off-by: Pierre-Louis Bossart <pierre-louis.bossart at linux.intel.com>
---
 sound/soc/codecs/rt1011.c | 20 +++++++++++++-------
 1 file changed, 13 insertions(+), 7 deletions(-)

diff --git a/sound/soc/codecs/rt1011.c b/sound/soc/codecs/rt1011.c
index dec5638060c3..098ecf13814d 100644
--- a/sound/soc/codecs/rt1011.c
+++ b/sound/soc/codecs/rt1011.c
@@ -1849,13 +1849,13 @@ static int rt1011_set_tdm_slot(struct snd_soc_dai *dai,
 
 	/* Rx slot configuration */
 	rx_slotnum = hweight_long(rx_mask);
-	first_bit = find_next_bit((unsigned long *)&rx_mask, 32, 0);
-	if (rx_slotnum > 1 || rx_slotnum == 0) {
+	if (rx_slotnum > 1 || !rx_slotnum) {
 		ret = -EINVAL;
-		dev_dbg(component->dev, "too many rx slots or zero slot\n");
+		dev_err(component->dev, "too many rx slots or zero slot\n");
 		goto _set_tdm_err_;
 	}
 
+	first_bit = __ffs(rx_mask);
 	switch (first_bit) {
 	case 0:
 	case 2:
@@ -1892,11 +1892,17 @@ static int rt1011_set_tdm_slot(struct snd_soc_dai *dai,
 
 	/* Tx slot configuration */
 	tx_slotnum = hweight_long(tx_mask);
-	first_bit = find_next_bit((unsigned long *)&tx_mask, 32, 0);
-	last_bit = find_last_bit((unsigned long *)&tx_mask, 32);
-	if (tx_slotnum > 2 || (last_bit-first_bit) > 1) {
+	if (tx_slotnum > 2 || !tx_slotnum) {
 		ret = -EINVAL;
-		dev_dbg(component->dev, "too many tx slots or tx slot location error\n");
+		dev_err(component->dev, "too many tx slots or zero slot\n");
+		goto _set_tdm_err_;
+	}
+
+	first_bit = __ffs(tx_mask);
+	last_bit = __fls(tx_mask);
+	if (last_bit - first_bit > 1) {
+		ret = -EINVAL;
+		dev_err(component->dev, "tx slot location error\n");
 		goto _set_tdm_err_;
 	}
 

base-commit: 39853b1438bf9b07349c8c44b48f6c2eda6f8840
-- 
2.20.1