Re: [PATCH iproute2-next] ipmaddr: use RTM_GETMULTICAST to list multicast addresses

[David Ahern <dsahern@kernel.org>]

On 7/10/26 9:07 PM, Yuyang Huang wrote:
> +static int accept_maddr(struct nlmsghdr *n, void *arg)
> +{
> +	struct maddr_dump_ctx *ctx = arg;
> +	struct ifaddrmsg *ifm = NLMSG_DATA(n);
> +	int len = n->nlmsg_len - NLMSG_LENGTH(sizeof(*ifm));
> +	struct rtattr *tb[IFA_MAX + 1];
> +	struct ma_info *ma;
> +
> +	if (n->nlmsg_type != RTM_GETMULTICAST &&
> +	    n->nlmsg_type != RTM_NEWMULTICAST)
> +		return 0;

From claude (and I agree with the finding)

> +static int accept_maddr(struct nlmsghdr *n, void *arg)
> +{
> ...
> +     if (n->nlmsg_type != RTM_GETMULTICAST &&
> +         n->nlmsg_type != RTM_NEWMULTICAST)
> +             return 0;

The kernel replies to a RTM_GETMULTICAST dump request with
RTM_NEWMULTICAST messages — it never sends RTM_GETMULTICAST in a
response.  Including RTM_GETMULTICAST in the guard is dead code and is
confusing; it inverts the usual convention used everywhere else in
iproute2 (e.g. ipaddress.c always checks RTM_NEW* / RTM_DEL*, never
RTM_GET*).

Should be:

        if (n->nlmsg_type != RTM_NEWMULTICAST)
                return 0;