[PATCH] counter: microchip-tcb-capture: Fix DT channel validation

[PATCH] counter: microchip-tcb-capture: Fix DT channel validation

[Babanpreet Singh]

mchp_tc_probe() reads the devicetree "reg" cell - a u32, per the API
contract of of_property_read_u32_index() - into a signed int, so the
bounds check "channel > 2" fails to reject cell values at or above
0x80000000: reinterpreted as a negative int, they compare below 2 and
pass validation.

A malformed devicetree can therefore drive a negative channel into the
ATMEL_TC_REG() offset arithmetic, making the driver access syscon
regmap offsets outside the TC block's register window, and into the
"t%d_clk" clock-name formatting, where it truncates clk_name (sized
for "t0_clk".."t2_clk").

Declare channel as u32, matching the API contract; the unsigned
comparison then rejects everything except channels 0..2. Adjust the
format specifier to %u accordingly, which also resolves the W=1
warning that exposed the gap:

  microchip-tcb-capture.c:520:56: warning: '%d' directive output may
    be truncated writing between 1 and 11 bytes into a region of size
    6 [-Wformat-truncation=]
  note: directive argument in the range [-2147483648, 2]

No behavior change for well-formed devicetrees: channels 0..2 take
identical paths before and after.

Fixes: 106b104137fd ("counter: Add microchip TCB capture counter")
Assisted-by: Claude:claude-fable-5 [gcc W=1]
Signed-off-by: Babanpreet Singh <bbnpreetsingh@gmail.com>
---
Note: struct mchp_tc_data's channel[2] member stays int — after this
fix it can only ever hold 0..2, so converting it (and the QDEC-mode
comparisons reading it) would be churn beyond the minimal fix. Happy
to do that conversion as a follow-up if preferred.

 drivers/counter/microchip-tcb-capture.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/counter/microchip-tcb-capture.c b/drivers/counter/microchip-tcb-capture.c
index 19d457ae4c3b..e53a8390756b 100644
--- a/drivers/counter/microchip-tcb-capture.c
+++ b/drivers/counter/microchip-tcb-capture.c
@@ -483,7 +483,7 @@ static int mchp_tc_probe(struct platform_device *pdev)
 	char clk_name[7];
 	struct regmap *regmap;
 	struct clk *clk[3];
-	int channel;
+	u32 channel;
 	int ret, i;
 
 	counter = devm_counter_alloc(&pdev->dev, sizeof(*priv));
@@ -517,7 +517,7 @@ static int mchp_tc_probe(struct platform_device *pdev)
 
 		priv->channel[i] = channel;
 
-		snprintf(clk_name, sizeof(clk_name), "t%d_clk", channel);
+		snprintf(clk_name, sizeof(clk_name), "t%u_clk", channel);
 
 		clk[i] = of_clk_get_by_name(np->parent, clk_name);
 		if (IS_ERR(clk[i])) {

base-commit: 3b029c035b34bbc693405ddf759f0e9b920c27f1
-- 
2.43.0