# RE: \[PATCH\] net: mana: Prefer struct\_size over open coded arithmetic

- From: Haiyang Zhang \<haiyangz@microsoft.com\>
- Date: 2021-09-11 13:36:13 
- List: netdev
- Page: https://ratatoskr.run/netdev/2021/09/1504224
- Thread: https://ratatoskr.run/linux-hardening/2021/09/1504037/t.md

```text


> -----Original Message-----
> From: Len Baker <redacted>
> Sent: Saturday, September 11, 2021 6:28 AM
> To: KY Srinivasan <redacted>; Haiyang Zhang
> [ref]; Stephen Hemminger [ref];
> Wei Liu [ref]; Dexuan Cui [ref]; David S.
> Miller [ref]; Jakub Kicinski [ref]; Sumit
> Semwal [ref]; Christian König
> [ref]; Kees Cook [ref]
> Cc: Len Baker <redacted>; Colin Ian King
> [ref]; linux-hardening@vger.kernel.org; linux-
> hyperv@vger.kernel.org; netdev@vger.kernel.org; linux-
> kernel@vger.kernel.org; linux-media@vger.kernel.org; dri-
> devel@lists.freedesktop.org; linaro-mm-sig@lists.linaro.org
> Subject: [PATCH] net: mana: Prefer struct_size over open coded
> arithmetic
> 
> [Some people who received this message don't often get email from
> len.baker@gmx.com. Learn why this is important at
> http://aka.ms/LearnAboutSenderIdentification.]
> 
> 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://nam06.safelinks.protection.outlook.com/?url=https%3A%2F%2Fwww.ke
> rnel.org%2Fdoc%2Fhtml%2Fv5.14%2Fprocess%2Fdeprecated.html%23open-coded-
> arithmetic-in-allocator-
> arguments&amp;data=04%7C01%7Chaiyangz%40microsoft.com%7C1bf83c1204a34dae
> a6d308d9750eef16%7C72f988bf86f141af91ab2d7cd011db47%7C1%7C0%7C6376695297
> 12931146%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJ
> BTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000&amp;sdata=PbYpBtyYfVfwwlxWSQx%2FiARc9
> mhb0J7bfD46%2F9q5oTw%3D&amp;reserved=0
> 
> Signed-off-by: Len Baker <redacted>
> ---
>  drivers/net/ethernet/microsoft/mana/hw_channel.c | 4 +---
>  1 file changed, 1 insertion(+), 3 deletions(-)
> 
> diff --git a/drivers/net/ethernet/microsoft/mana/hw_channel.c
> b/drivers/net/ethernet/microsoft/mana/hw_channel.c
> index 1a923fd99990..0efdc6c3c32a 100644
> --- a/drivers/net/ethernet/microsoft/mana/hw_channel.c
> +++ b/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);

Thanks!

Reviewed-by: Haiyang Zhang <haiyangz@microsoft.com>

```