linux-kernel - [PATCH] auxdisplay: ht16k33: don't access uninitialized data

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Message-Id: <20170328101203.4121922-1-arnd@arndb.de>
Date:   Tue, 28 Mar 2017 12:11:49 +0200
From:   Arnd Bergmann <arnd@...db.de>
To:     Robin van der Gracht <robin@...tonic.nl>,
        Miguel Ojeda Sandonis <miguel.ojeda.sandonis@...il.com>
Cc:     Arnd Bergmann <arnd@...db.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Dmitry Torokhov <dmitry.torokhov@...il.com>,
        Rob Herring <robh@...nel.org>,
        Linus Walleij <linus.walleij@...aro.org>,
        linux-kernel@...r.kernel.org
Subject: [PATCH] auxdisplay: ht16k33: don't access uninitialized data

gcc-7.0.1 points out that we copy uninitialized data from the stack
into a per-device structure:

drivers/auxdisplay/ht16k33.c: In function 'ht16k33_keypad_irq_thread':
arch/x86/include/asm/string_32.h:78:16: error: 'new_state' may be used uninitialized in this function [-Werror=maybe-uninitialized]
arch/x86/include/asm/string_32.h:79:22: error: '*((void *)&new_state+4)' may be used uninitialized in this function [-Werror=maybe-uninitialized]

The access is harmless because we never read the data, but we are better
off not doing this, so this changes the code to only copy the data
that was actually initialized. To make sure we don't overflow the
stack with an incorrect DT, we also need to add a sanity checkin the
probe function.

Signed-off-by: Arnd Bergmann <arnd@...db.de>
---
 drivers/auxdisplay/ht16k33.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/drivers/auxdisplay/ht16k33.c b/drivers/auxdisplay/ht16k33.c
index f66b45b235b0..ba6370974574 100644
--- a/drivers/auxdisplay/ht16k33.c
+++ b/drivers/auxdisplay/ht16k33.c
@@ -278,7 +278,7 @@ static bool ht16k33_keypad_scan(struct ht16k33_keypad *keypad)
 		}
 	}
 	input_sync(keypad->dev);
-	memcpy(keypad->last_key_state, new_state, sizeof(new_state));
+	memcpy(keypad->last_key_state, new_state, sizeof(u16) * keypad->cols);
 
 	return pressed;
 }
@@ -353,6 +353,12 @@ static int ht16k33_keypad_probe(struct i2c_client *client,
 	err = matrix_keypad_parse_of_params(&client->dev, &rows, &cols);
 	if (err)
 		return err;
+	if (rows > HT16K33_MATRIX_KEYPAD_MAX_ROWS ||
+	    cols > HT16K33_MATRIX_KEYPAD_MAX_COLS) {
+		dev_err(&client->dev, "%u rows or %u cols out of range in DT\n",
+			rows, cols);
+		return -ERANGE;
+	}
 
 	keypad->rows = rows;
 	keypad->cols = cols;
-- 
2.9.0