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Date:   Sat, 11 Sep 2021 11:46:48 -0400
From:   Alan Stern <stern@...land.harvard.edu>
To:     Len Baker <len.baker@....com>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Kees Cook <keescook@...omium.org>, linux-usb@...r.kernel.org,
        linux-hardening@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] usb: ohci: Prefer struct_size over open coded arithmetic

On Sat, Sep 11, 2021 at 01:26:31PM +0200, Len Baker wrote:
> 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 <len.baker@....com>
> ---

Acked-by: Alan Stern <stern@...land.harvard.edu>

>  drivers/usb/host/ohci-hcd.c | 3 +--
>  1 file changed, 1 insertion(+), 2 deletions(-)
> 
> diff --git a/drivers/usb/host/ohci-hcd.c b/drivers/usb/host/ohci-hcd.c
> index 1f5e69314a17..666b1c665188 100644
> --- a/drivers/usb/host/ohci-hcd.c
> +++ b/drivers/usb/host/ohci-hcd.c
> @@ -191,8 +191,7 @@ static int ohci_urb_enqueue (
>  	}
> 
>  	/* allocate the private part of the URB */
> -	urb_priv = kzalloc (sizeof (urb_priv_t) + size * sizeof (struct td *),
> -			mem_flags);
> +	urb_priv = kzalloc(struct_size(urb_priv, td, size), mem_flags);
>  	if (!urb_priv)
>  		return -ENOMEM;
>  	INIT_LIST_HEAD (&urb_priv->pending);
> --
> 2.25.1
> 

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