linux-kernel - Re: [PATCH] nfp: Prefer struct_size over open coded arithmetic

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Date:   Mon, 13 Sep 2021 10:31:25 +0200
From:   Simon Horman <simon.horman@...igine.com>
To:     Len Baker <len.baker@....com>
Cc:     Jakub Kicinski <kuba@...nel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Kees Cook <keescook@...omium.org>,
        "Gustavo A. R. Silva" <gustavoars@...nel.org>,
        oss-drivers@...igine.com, netdev@...r.kernel.org,
        linux-hardening@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] nfp: Prefer struct_size over open coded arithmetic

On Sun, Sep 12, 2021 at 03:10:57PM +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>

Reviewed-by: Simon Horman <simon.horman@...igine.com>

> ---
>  drivers/net/ethernet/netronome/nfp/nfp_net_repr.c | 3 +--
>  1 file changed, 1 insertion(+), 2 deletions(-)
> 
> diff --git a/drivers/net/ethernet/netronome/nfp/nfp_net_repr.c b/drivers/net/ethernet/netronome/nfp/nfp_net_repr.c
> index 3b8e675087de..369f6ae700c7 100644
> --- a/drivers/net/ethernet/netronome/nfp/nfp_net_repr.c
> +++ b/drivers/net/ethernet/netronome/nfp/nfp_net_repr.c
> @@ -499,8 +499,7 @@ struct nfp_reprs *nfp_reprs_alloc(unsigned int num_reprs)
>  {
>  	struct nfp_reprs *reprs;
> 
> -	reprs = kzalloc(sizeof(*reprs) +
> -			num_reprs * sizeof(struct net_device *), GFP_KERNEL);
> +	reprs = kzalloc(struct_size(reprs, reprs, num_reprs), GFP_KERNEL);
>  	if (!reprs)
>  		return NULL;
>  	reprs->num_reprs = num_reprs;
> --
> 2.25.1
>