netdev - Re: [PATCH][next] seg6: fix unintentional integer overflow on left shift

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Date:   Mon, 7 Dec 2020 20:59:26 +0100
From:   Andrea Mayer <andrea.mayer@...roma2.it>
To:     Colin King <colin.king@...onical.com>
Cc:     "David S . Miller" <davem@...emloft.net>,
        Alexey Kuznetsov <kuznet@....inr.ac.ru>,
        Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
        Jakub Kicinski <kuba@...nel.org>, netdev@...r.kernel.org,
        kernel-janitors@...r.kernel.org, linux-kernel@...r.kernel.org,
        Stefano Salsano <stefano.salsano@...roma2.it>,
        Paolo Lungaroni <paolo.lungaroni@...t.it>,
        Ahmed Abdelsalam <ahabdels.dev@...il.com>,
        Andrea Mayer <andrea.mayer@...roma2.it>
Subject: Re: [PATCH][next] seg6: fix unintentional integer overflow on left
 shift

On Mon,  7 Dec 2020 14:45:03 +0000
Colin King <colin.king@...onical.com> wrote:

> From: Colin Ian King <colin.king@...onical.com>
> 
> Shifting the integer value 1 is evaluated using 32-bit arithmetic
> and then used in an expression that expects a unsigned long value
> leads to a potential integer overflow. Fix this by using the BIT
> macro to perform the shift to avoid the overflow.
> 
> Addresses-Coverity: ("Uninitentional integer overflow")
> Fixes: 964adce526a4 ("seg6: improve management of behavior attributes")
> Signed-off-by: Colin Ian King <colin.king@...onical.com>
> ---
>  net/ipv6/seg6_local.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/net/ipv6/seg6_local.c b/net/ipv6/seg6_local.c
> index b07f7c1c82a4..d68de8cd1207 100644
> --- a/net/ipv6/seg6_local.c
> +++ b/net/ipv6/seg6_local.c
> @@ -1366,7 +1366,7 @@ static void __destroy_attrs(unsigned long parsed_attrs, int max_parsed,
>  	 * attribute; otherwise, we call the destroy() callback.
>  	 */
>  	for (i = 0; i < max_parsed; ++i) {
> -		if (!(parsed_attrs & (1 << i)))
> +		if (!(parsed_attrs & BIT(i)))
>  			continue;
>  
>  		param = &seg6_action_params[i];
> -- 
> 2.29.2
>

Hi Colin,
thanks for the fix. I've just given a look a the whole seg6_local.c code and I
found that such issues is present in other parts of the code.

If we agree, I can make a fix which explicitly eliminates the several (1 << i)
in favor of BIT(i).

Andrea