[PATCH v2] platform/chrome: cros_ec_dev - Fix security issue

[Gwendal Grignou]

Add a check to prevent memory scribble when sending an ioctl with .insize
set so large that memory allocation argument overflows.

Signed-off-by: Gwendal Grignou <gwendal@xxxxxxxxxxxx>
---
 drivers/platform/chrome/cros_ec_dev.c | 12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

diff --git a/drivers/platform/chrome/cros_ec_dev.c b/drivers/platform/chrome/cros_ec_dev.c
index d45cd25..0b2f730 100644
--- a/drivers/platform/chrome/cros_ec_dev.c
+++ b/drivers/platform/chrome/cros_ec_dev.c
@@ -131,13 +131,23 @@ static ssize_t ec_device_read(struct file *filp, char __user *buffer,
 static long ec_device_ioctl_xcmd(struct cros_ec_dev *ec, void __user *arg)
 {
 	long ret;
+	size_t data_size;
 	struct cros_ec_command u_cmd;
 	struct cros_ec_command *s_cmd;
 
 	if (copy_from_user(&u_cmd, arg, sizeof(u_cmd)))
 		return -EFAULT;
 
-	s_cmd = kmalloc(sizeof(*s_cmd) + max(u_cmd.outsize, u_cmd.insize),
+	/*
+	 * Prevent malicious attack where .insize is so big that amount
+	 * kmalloc'ed rollover, allowing memcpy to write beyond the allocated
+	 * space.
+	 */
+	data_size = max(u_cmd.outsize, u_cmd.insize);
+	if (data_size + sizeof(*s_cmd) < data_size)
+		return -EINVAL;
+
+	s_cmd = kmalloc(sizeof(*s_cmd) + data_size,
 			GFP_KERNEL);
 	if (!s_cmd)
 		return -ENOMEM;
-- 
2.7.0.rc3.207.g0ac5344