[patch] Input: force feedback - potential integer wrap in input_ff_create()

Smatch complains about max_effects because it's an int and we cap the
maximum size, but we don't check for negative.  A negative value here
could make "ff" smaller than sizeof(struct ff_device) and lead to
memory corruption.

I think max_effects can come from ->ff_effects_max in
uinput_setup_device() and that comes from the user so potentially
it could be negative.  The call path is that uinput_setup_device()
sets the value in the ->private_data struct.  From there it is:
-> uinput_ioctl_handler()
   -> uinput_create_device()
      -> input_ff_create(dev, udev->ff_effects_max);

Signed-off-by: Dan Carpenter <redacted>

diff --git a/drivers/input/ff-core.c b/drivers/input/ff-core.c
index 3367f76..12422ed 100644
--- a/drivers/input/ff-core.c
+++ b/drivers/input/ff-core.c

@@ -319,6 +319,12 @@ int input_ff_create(struct input_dev *dev, int max_effects)
 		return -EINVAL;
 	}
 
+	if (max_effects < 0)
+		return -EINVAL;
+	if (sizeof(struct ff_device) + max_effects * sizeof(struct file *) <
+			max_effects)
+		return -EINVAL;
+
 	ff = kzalloc(sizeof(struct ff_device) +
 		     max_effects * sizeof(struct file *), GFP_KERNEL);
 	if (!ff)