[PATCH v2] Input: tca8418_keypad - fix potential infinite loop and OOB access on invalid keycodes

[Liang Zhan <liangzhan5dev@gmail.com>]

The current code checks the raw register value against zero to detect an 
empty FIFO. However, the TCA8418 datasheet defines key code 0 as the 
empty-FIFO condition. If the hardware returns garbage data, the loop may 
never terminate and the extracted keycode can cause an out-of-bounds 
access on keymap[].

Move the empty-FIFO check to operate on the extracted key code so that
the loop terminates correctly. Additionally, validate row/column indices
against the configured matrix dimensions before indexing into the
keymap array, skipping invalid events.

Cc: stable@vger.kernel.org
Signed-off-by: Zhian Liang <liangzhan5dev@gmail.com>
---
changes in v2:
- Moved empty-FIFO check to operate on extracted key code instead of
   raw register value.
- Added row/col validation against configured matrix dimensions.
- Dropped explicit 0xFF check as requested.
---
  drivers/input/keyboard/tca8418_keypad.c | 19 ++++++++++++++++---
  1 file changed, 16 insertions(+), 3 deletions(-)

diff --git a/drivers/input/keyboard/tca8418_keypad.c 
b/drivers/input/keyboard/tca8418_keypad.c
index b124e576feca..36d4a7c38bb1 100644
--- a/drivers/input/keyboard/tca8418_keypad.c
+++ b/drivers/input/keyboard/tca8418_keypad.c
@@ -114,6 +114,8 @@ struct tca8418_keypad {
  	struct input_dev *input;

  	unsigned int row_shift;
+	unsigned int rows;
+	unsigned int cols;
  };

  /*
@@ -171,19 +173,28 @@ static void tca8418_read_keypad(struct 
tca8418_keypad *keypad_data)
  			break;
  		}

-		/* Assume that key code 0 signifies empty FIFO */
-		if (reg <= 0)
-			break;

  		state = reg & KEY_EVENT_VALUE;
  		code  = reg & KEY_EVENT_CODE;

+		/* Key code 0 signifies empty FIFO */
+		if (!code)
+			break;
+
  		row = code / TCA8418_MAX_COLS;
  		col = code % TCA8418_MAX_COLS;

  		row = (col) ? row : row - 1;
  		col = (col) ? col - 1 : TCA8418_MAX_COLS - 1;

+		/* Validate against configured matrix size */
+		if (row >= keypad_data->rows || col >= keypad_data->cols) {
+			dev_err(&keypad_data->client->dev,
+				"invalid key code %d (row %d, col %d)\n",
+				code, row, col);
+			continue;
+		}
+
  		code = MATRIX_SCAN_CODE(row, col, keypad_data->row_shift);
  		input_event(input, EV_MSC, MSC_SCAN, code);
  		input_report_key(input, keymap[code], state);
@@ -298,6 +309,8 @@ static int tca8418_keypad_probe(struct i2c_client 
*client)

  	keypad_data->client = client;
  	keypad_data->row_shift = row_shift;
+	keypad_data->rows = rows;
+	keypad_data->cols = cols;

  	/* Read key lock register, if this fails assume device not present */
  	error = tca8418_read_byte(keypad_data, REG_KEY_LCK_EC, &reg);
-- 
2.34.1