ieee802154: ca8210: fix uninitialised data read

In ca8210_test_int_user_write() a user can request the transfer of a
frame with a length field (command.length) that is longer than the
actual buffer provided (len). In this scenario the driver will copy
the buffer contents into the uninitialised command[] buffer, then
transfer <data.length> bytes over the SPI even though only <len> bytes
had been populated, potentially leaking sensitive kernel memory.

Also the first 6 bytes of the command buffer must be initialised in case
a malformed, short packet is written and the uninitialised bytes are
read in ca8210_test_check_upstream.

Reported-by: Domen Puncer Kugler <domen.puncer@samsung.com>
Signed-off-by: Harry Morris <h.morris@cascoda.com>
Tested-by: Harry Morris <h.morris@cascoda.com>
Signed-off-by: Stefan Schmidt <stefan@osg.samsung.com>

drivers/net/ieee802154/ca8210.c

@@ -2493,13 +2493,14 @@ static ssize_t ca8210_test_int_user_write(
 	struct ca8210_priv *priv = filp->private_data;
 	u8 command[CA8210_SPI_BUF_SIZE];
 
-	if (len > CA8210_SPI_BUF_SIZE) {
+	memset(command, SPI_IDLE, 6);
+	if (len > CA8210_SPI_BUF_SIZE || len < 2) {
 		dev_warn(
 			&priv->spi->dev,
-			"userspace requested erroneously long write (%zu)\n",
+			"userspace requested erroneous write length (%zu)\n",
 			len
 		);
-		return -EMSGSIZE;
+		return -EBADE;
 	}
 
 	ret = copy_from_user(command, in_buf, len);
@@ -2511,6 +2512,13 @@ static ssize_t ca8210_test_int_user_write(
 		);
 		return -EIO;
 	}
+	if (len != command[1] + 2) {
+		dev_err(
+			&priv->spi->dev,
+			"write len does not match packet length field\n"
+		);
+		return -EBADE;
+	}
 
 	ret = ca8210_test_check_upstream(command, priv->spi);
 	if (ret == 0) {