Input: omap-keypad - prefer struct_size over open coded arithmetic

As noted in the "Deprecated Interfaces, Language Features, Attributes,
and Conventions" documentation [1], size calculations (especially
multiplication) should not be performed in memory allocator (or similar)
function arguments due to the risk of them overflowing. This could lead
to values wrapping around and a smaller allocation being made than the
caller was expecting. Using those allocations could lead to linear
overflows of heap memory and other misbehaviors.

So, use the struct_size() helper to do the arithmetic instead of the
argument "size + count * size" in the kzalloc() function.

[1] https://www.kernel.org/doc/html/v5.14/process/deprecated.html#open-coded-arithmetic-in-allocator-arguments

Signed-off-by: Len Baker <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Dmitry Torokhov <[e-mail]>

drivers/input/keyboard/omap-keypad.c

···
 	row_shift = get_count_order(pdata->cols);
 	keycodemax = pdata->rows << row_shift;
 
-	omap_kp = kzalloc(sizeof(struct omap_kp) +
-			keycodemax * sizeof(unsigned short), GFP_KERNEL);
+	omap_kp = kzalloc(struct_size(omap_kp, keymap, keycodemax), GFP_KERNEL);
 	input_dev = input_allocate_device();
 	if (!omap_kp || !input_dev) {
 		kfree(omap_kp);