net: mana: 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-argumentsSigned-off-by: Len Baker <len.baker@gmx.com>
Reviewed-by: Haiyang Zhang <haiyangz@microsoft.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/microsoft/mana/hw_channel.c

@@ -398,9 +398,7 @@ static int mana_hwc_alloc_dma_buf(struct hw_channel_context *hwc, u16 q_depth,
 	int err;
 	u16 i;
 
-	dma_buf = kzalloc(sizeof(*dma_buf) +
-			  q_depth * sizeof(struct hwc_work_request),
-			  GFP_KERNEL);
+	dma_buf = kzalloc(struct_size(dma_buf, reqs, q_depth), GFP_KERNEL);
 	if (!dma_buf)
 		return -ENOMEM;