From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To: stable@vger.kernel.org
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	patches@lists.linux.dev,
	Babanpreet Singh <bbnpreetsingh@gmail.com>,
	Joshua Crofts <joshua.crofts1@gmail.com>,
	William Breathitt Gray <wbg@kernel.org>,
	Sasha Levin <sashal@kernel.org>
Subject: [PATCH 6.12 029/181] counter: microchip-tcb-capture: Fix DT channel validation
Date: Mon, 17 Aug 2026 15:32:03 +0200
Message-ID: <20260817132536.523676987@linuxfoundation.org>
In-Reply-To: <20260817132535.394764707@linuxfoundation.org>
References: <20260817132535.394764707@linuxfoundation.org>
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6.12-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Babanpreet Singh <bbnpreetsingh@gmail.com>

[ Upstream commit f1a3a9946aab611dd2200c01ff122f64b033dad2 ]

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>
Reviewed-by: Joshua Crofts <joshua.crofts1@gmail.com>
Link: https://lore.kernel.org/r/20260714042910.7-1-bbnpreetsingh@gmail.com
Signed-off-by: William Breathitt Gray <wbg@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 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 461f57f66631c..fbd1afe178a36 100644
--- a/drivers/counter/microchip-tcb-capture.c
+++ b/drivers/counter/microchip-tcb-capture.c
@@ -309,7 +309,7 @@ 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));
@@ -343,7 +343,7 @@ 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])) {
-- 
2.53.0