usb: typec: tps6598x: Remove VLA usage

In the quest to remove all stack VLA usage from the kernel[1], this
uses the maximum buffer size and adds a sanity check. While 25 bytes
is the size of the largest current things coming through, Heikki
Krogerus pointed out that the actual max in 64 bytes, as per ch 1.3.2
http://www.ti.com/lit/ug/slvuan1a/slvuan1a.pdf

[1] https://lkml.kernel.org/r/CA+55aFzCG-zNmZwX4A2FQpadafLfEzK6CC=qPXydAacU1RqZWA@mail.gmail.com

Signed-off-by: Kees Cook <keescook@chromium.org>
Acked-by: Heikki Krogerus <heikki.krogerus@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/typec/tps6598x.c

@@ -81,12 +81,21 @@ struct tps6598x {
 	struct typec_capability typec_cap;
 };
 
+/*
+ * Max data bytes for Data1, Data2, and other registers. See ch 1.3.2:
+ * http://www.ti.com/lit/ug/slvuan1a/slvuan1a.pdf
+ */
+#define TPS_MAX_LEN	64
+
 static int
 tps6598x_block_read(struct tps6598x *tps, u8 reg, void *val, size_t len)
 {
-	u8 data[len + 1];
+	u8 data[TPS_MAX_LEN + 1];
 	int ret;
 
+	if (WARN_ON(len + 1 > sizeof(data)))
+		return -EINVAL;
+
 	if (!tps->i2c_protocol)
 		return regmap_raw_read(tps->regmap, reg, val, len);