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

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Date:   Mon, 20 Sep 2021 19:11:17 -0500
From:   "Gustavo A. R. Silva" <gustavo@...eddedor.com>
To:     Len Baker <len.baker@....com>, Benjamin LaHaise <bcrl@...ck.org>,
        Alexander Viro <viro@...iv.linux.org.uk>
Cc:     Kees Cook <keescook@...omium.org>,
        "Gustavo A. R. Silva" <gustavoars@...nel.org>, linux-aio@...ck.org,
        linux-fsdevel@...r.kernel.org, linux-hardening@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] aio: Prefer struct_size over open coded arithmetic



On 9/19/21 04:45, 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 + size * count" in the kzalloc() function.
> 
> [1] https://www.kernel.org/doc/html/latest/process/deprecated.html#open-coded-arithmetic-in-allocator-arguments
> 
> Signed-off-by: Len Baker <len.baker@....com>

Reviewed-by: Gustavo A. R. Silva <gustavoars@...nel.org>

Thanks
--
Gustavo

> ---
>  fs/aio.c | 3 +--
>  1 file changed, 1 insertion(+), 2 deletions(-)
> 
> diff --git a/fs/aio.c b/fs/aio.c
> index 51b08ab01dff..c2978c0b872c 100644
> --- a/fs/aio.c
> +++ b/fs/aio.c
> @@ -659,8 +659,7 @@ static int ioctx_add_table(struct kioctx *ctx, struct mm_struct *mm)
>  		new_nr = (table ? table->nr : 1) * 4;
>  		spin_unlock(&mm->ioctx_lock);
> 
> -		table = kzalloc(sizeof(*table) + sizeof(struct kioctx *) *
> -				new_nr, GFP_KERNEL);
> +		table = kzalloc(struct_size(table, table, new_nr), GFP_KERNEL);
>  		if (!table)
>  			return -ENOMEM;
> 
> --
> 2.25.1
>