[PATCH] platform/chrome: cros_ec: fix read overflow in cros_ec_lpc_readmem()

[Dan Carpenter <dan.carpenter@oracle.com>]

If bytes is larger than EC_MEMMAP_SIZE (255) then "EC_MEMMAP_SIZE -
bytes" is a very high unsigned value and basically offset is
accepted.  The second problem is that it uses >= instead of > so this
means that we are not able to read the very last byte.

Fixes: ec2f33ab582b ("platform/chrome: Add cros_ec_lpc driver for x86 devices")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
---
 drivers/platform/chrome/cros_ec_lpc.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/platform/chrome/cros_ec_lpc.c b/drivers/platform/chrome/cros_ec_lpc.c
index d6306d2a096f..7e1d175def9f 100644
--- a/drivers/platform/chrome/cros_ec_lpc.c
+++ b/drivers/platform/chrome/cros_ec_lpc.c
@@ -290,7 +290,8 @@ static int cros_ec_lpc_readmem(struct cros_ec_device *ec, unsigned int offset,
 	char *s = dest;
 	int cnt = 0;
 
-	if (offset >= EC_MEMMAP_SIZE - bytes)
+	if (offset > EC_MEMMAP_SIZE ||
+	    bytes > EC_MEMMAP_SIZE - offset)
 		return -EINVAL;
 
 	/* fixed length */
-- 
2.20.1