[PATCH] ASoC: tlv320aic32x4: Prevent division by zero in divider callbacks

[Alex Kazinsky]

A zero rate requested through clk_set_rate() or clk_round_rate() reaches
clk_aic32x4_div_determine_rate() when the minimum rate is zero. Clamping
the requested rate to the allowed range leaves it unchanged, causing
division by zero when calculating the divisor.

A zero parent rate can also cause division by zero in determine_rate().
For example, if reading a parent divider's register fails,
clk_aic32x4_div_recalc_rate() returns zero, which the clock framework
caches as the parent's rate. A subsequent rate request for a child
divider receives this value in best_parent_rate. With a nonzero requested
rate, the calculated divisor is zero. It passes the existing upper-bound
check and causes division by zero in the resulting rate calculation.

The set_rate callback can receive a zero rate when an ancestor's rate
changes. clk_calc_subtree() calculates descendant rates through
recalc_rate() without calling their determine_rate callbacks. If reading
a descendant divider's register fails, clk_aic32x4_div_recalc_rate()
returns zero. This becomes the descendant's new_rate, which
clk_change_rate() passes to clk_aic32x4_div_set_rate(), causing division
by zero.

Reject zero rates in both callbacks and reject a zero divisor in
clk_aic32x4_div_determine_rate().

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

Fixes: a51b50062091 ("ASoC: tlv320aic32x4: Model DAC/ADC dividers in CCF")
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Alex Kazinsky <a.kazinsky@xxxxxxxx>
---
 sound/soc/codecs/tlv320aic32x4-clk.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/sound/soc/codecs/tlv320aic32x4-clk.c b/sound/soc/codecs/tlv320aic32x4-clk.c
index deed61650e09..8fa8e69f1f72 100644
--- a/sound/soc/codecs/tlv320aic32x4-clk.c
+++ b/sound/soc/codecs/tlv320aic32x4-clk.c
@@ -318,6 +318,9 @@ static int clk_aic32x4_div_set_rate(struct clk_hw *hw, unsigned long rate,
 	struct clk_aic32x4 *div = to_clk_aic32x4(hw);
 	u8 divisor;
 
+	if (!rate)
+		return -EINVAL;
+
 	divisor = DIV_ROUND_UP(parent_rate, rate);
 	if (divisor > AIC32X4_DIV_MAX)
 		return -EINVAL;
@@ -331,8 +334,11 @@ static int clk_aic32x4_div_determine_rate(struct clk_hw *hw,
 {
 	unsigned long divisor;
 
+	if (!req->rate)
+		return -EINVAL;
+
 	divisor = DIV_ROUND_UP(req->best_parent_rate, req->rate);
-	if (divisor > AIC32X4_DIV_MAX)
+	if (!divisor || divisor > AIC32X4_DIV_MAX)
 		return -EINVAL;
 
 	req->rate = DIV_ROUND_UP(req->best_parent_rate, divisor);
-- 
2.56.0