tifm: 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 + size * count" 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 <len.baker@gmx.com>
Link: https://lore.kernel.org/r/20210905153707.9638-1-len.baker@gmx.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/misc/tifm_core.c

@@ -176,8 +176,7 @@ struct tifm_adapter *tifm_alloc_adapter(unsigned int num_sockets,
 {
 	struct tifm_adapter *fm;
 
-	fm = kzalloc(sizeof(struct tifm_adapter)
-		     + sizeof(struct tifm_dev*) * num_sockets, GFP_KERNEL);
+	fm = kzalloc(struct_size(fm, sockets, num_sockets), GFP_KERNEL);
 	if (fm) {
 		fm->dev.class = &tifm_adapter_class;
 		fm->dev.parent = dev;