Subject: Re: [PATCH net-next 6/8] ipv6: mcast: use min() to simplify the code

From: Simon Horman <[email-masked]>
Date: Sat, 24 Aug 2024 18:57:38 +0100

On Thu, Aug 22, 2024 at 09:39:06PM +0800, Li Zetao wrote:
> When coping sockaddr in ip6_mc_msfget(), the time of copies
> depends on the minimum value between sl_count and gf_numsrc.
> Using min() here is very semantic.
> 
> Signed-off-by: Li Zetao <[email-masked]>
> ---
>  net/ipv6/mcast.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/net/ipv6/mcast.c b/net/ipv6/mcast.c
> index 7ba01d8cfbae..b244dbf61d5f 100644
> --- a/net/ipv6/mcast.c
> +++ b/net/ipv6/mcast.c
> @@ -586,7 +586,8 @@ int ip6_mc_msfget(struct sock *sk, struct group_filter *gsf,
>  	const struct in6_addr *group;
>  	struct ipv6_mc_socklist *pmc;
>  	struct ip6_sf_socklist *psl;
> -	int i, count, copycount;
> +	unsigned int count;
> +	int i, copycount;
>  
>  	group = &((struct sockaddr_in6 *)&gsf->gf_group)->sin6_addr;
>  
> @@ -610,7 +611,7 @@ int ip6_mc_msfget(struct sock *sk, struct group_filter *gsf,
>  	psl = sock_dereference(pmc->sflist, sk);
>  	count = psl ? psl->sl_count : 0;

Both count and psl->sl_count are unsigned int,
so this looks safe (and more correct than what it replaces, IMHO).

>  
> -	copycount = count < gsf->gf_numsrc ? count : gsf->gf_numsrc;
> +	copycount = min(count, gsf->gf_numsrc);

And gsf->gf_numsrc is a __u32, so min operating on it and
count looks safe to me.

Further, the code it replaces seems to be a max() operation in
both intent and function.

Reviewed-by: Simon Horman <[email-masked]>

>  	gsf->gf_numsrc = count;
>  	for (i = 0; i < copycount; i++) {
>  		struct sockaddr_in6 *psin6;
> -- 
> 2.34.1
> 
>