platform/chrome: cros_ec_dev - double fetch bug in ioctl

We verify "u_cmd.outsize" and "u_cmd.insize" but we need to make sure
that those values have not changed between the two copy_from_user()
calls.  Otherwise it could lead to a buffer overflow.

Additionally, cros_ec_cmd_xfer() can set s_cmd->insize to a lower value.
We should use the new smaller value so we don't copy too much data to
the user.

Reported-by: Pengfei Wang <wpengfeinudt@gmail.com>
Fixes: a841178445bb ('mfd: cros_ec: Use a zero-length array for command data')
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
Tested-by: Gwendal Grignou <gwendal@chromium.org>
Cc: <stable@vger.kernel.org> # v4.2+
Signed-off-by: Olof Johansson <olof@lixom.net>

diff --git a/drivers/platform/chrome/cros_ec_dev.c b/drivers/platform/chrome/cros_ec_dev.c
index 6d8ee3b..8abd80d 100644 (file)
--- a/drivers/platform/chrome/cros_ec_dev.c
+++ b/drivers/platform/chrome/cros_ec_dev.c
@@ -151,13 +151,19 @@ static long ec_device_ioctl_xcmd(struct cros_ec_dev *ec, void __user *arg)
                goto exit;
        }
 
+       if (u_cmd.outsize != s_cmd->outsize ||
+           u_cmd.insize != s_cmd->insize) {
+               ret = -EINVAL;
+               goto exit;
+       }
+
        s_cmd->command += ec->cmd_offset;
        ret = cros_ec_cmd_xfer(ec->ec_dev, s_cmd);
        /* Only copy data to userland if data was received. */
        if (ret < 0)
                goto exit;
 
-       if (copy_to_user(arg, s_cmd, sizeof(*s_cmd) + u_cmd.insize))
+       if (copy_to_user(arg, s_cmd, sizeof(*s_cmd) + s_cmd->insize))
                ret = -EFAULT;
 exit:
        kfree(s_cmd);