genirq/generic_chip: Use struct_size() in kzalloc()

Make use of the struct_size() helper instead of an open-coded version,
in order to avoid any potential type mistakes or integer overflows
that, in the worst scenario, could lead to heap overflows.

This code was detected with the help of Coccinelle and, audited and
fixed manually.
Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/r/20210513212729.GA214145@embeddedor

kernel/irq/generic-chip.c

@@ -240,9 +240,8 @@ irq_alloc_generic_chip(const char *name, int num_ct, unsigned int irq_base,
 		       void __iomem *reg_base, irq_flow_handler_t handler)
 {
 	struct irq_chip_generic *gc;
-	unsigned long sz = sizeof(*gc) + num_ct * sizeof(struct irq_chip_type);
 
-	gc = kzalloc(sz, GFP_KERNEL);
+	gc = kzalloc(struct_size(gc, chip_types, num_ct), GFP_KERNEL);
 	if (gc) {
 		irq_init_generic_chip(gc, name, num_ct, irq_base, reg_base,
 				      handler);
@@ -288,8 +287,11 @@ int __irq_alloc_domain_generic_chips(struct irq_domain *d, int irqs_per_chip,
 {
 	struct irq_domain_chip_generic *dgc;
 	struct irq_chip_generic *gc;
-	int numchips, sz, i;
 	unsigned long flags;
+	int numchips, i;
+	size_t dgc_sz;
+	size_t gc_sz;
+	size_t sz;
 	void *tmp;
 
 	if (d->gc)
@@ -300,8 +302,9 @@ int __irq_alloc_domain_generic_chips(struct irq_domain *d, int irqs_per_chip,
 		return -EINVAL;
 
 	/* Allocate a pointer, generic chip and chiptypes for each chip */
-	sz = sizeof(*dgc) + numchips * sizeof(gc);
-	sz += numchips * (sizeof(*gc) + num_ct * sizeof(struct irq_chip_type));
+	gc_sz = struct_size(gc, chip_types, num_ct);
+	dgc_sz = struct_size(dgc, gc, numchips);
+	sz = dgc_sz + numchips * gc_sz;
 
 	tmp = dgc = kzalloc(sz, GFP_KERNEL);
 	if (!dgc)
@@ -314,7 +317,7 @@ int __irq_alloc_domain_generic_chips(struct irq_domain *d, int irqs_per_chip,
 	d->gc = dgc;
 
 	/* Calc pointer to the first generic chip */
-	tmp += sizeof(*dgc) + numchips * sizeof(gc);
+	tmp += dgc_sz;
 	for (i = 0; i < numchips; i++) {
 		/* Store the pointer to the generic chip */
 		dgc->gc[i] = gc = tmp;
@@ -331,7 +334,7 @@ int __irq_alloc_domain_generic_chips(struct irq_domain *d, int irqs_per_chip,
 		list_add_tail(&gc->list, &gc_list);
 		raw_spin_unlock_irqrestore(&gc_lock, flags);
 		/* Calc pointer to the next generic chip */
-		tmp += sizeof(*gc) + num_ct * sizeof(struct irq_chip_type);
+		tmp += gc_sz;
 	}
 	return 0;
 }