netdev - Re: [PATCH RFC net-next 4/5] net/ipv4: Update inet_dump_ifaddr to support NLM_F_DUMP_PROPER

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Date:   Fri, 28 Sep 2018 20:41:16 +0200
From:   Christian Brauner <christian@...uner.io>
To:     dsahern@...nel.org
Cc:     netdev@...r.kernel.org, davem@...emloft.net, jbenc@...hat.com,
        stephen@...workplumber.org, David Ahern <dsahern@...il.com>
Subject: Re: [PATCH RFC net-next 4/5] net/ipv4: Update inet_dump_ifaddr to
 support NLM_F_DUMP_PROPER_HDR

On Fri, Sep 28, 2018 at 08:45:01AM -0700, dsahern@...nel.org wrote:
> From: David Ahern <dsahern@...il.com>
> 
> Update inet_dump_ifaddr to check for NLM_F_DUMP_PROPER_HDR in the netlink
> message header. If the flag is set, the dump request is expected to have
> an ifaddrmsg struct as the header potentially followed by one or more
> attributes. Any data passed in the header or as an attribute is taken as
> a request to influence the data returned. Only values suppored by the
> dump handler are allowed to be non-0 or set in the request. At the moment
> only the IFA_TARGET_NETNSID attribute is supported. Follow on patches
> will support for other fields (e.g., honor ifa_index and only return data
> for the given device index).
> 
> Signed-off-by: David Ahern <dsahern@...il.com>
> ---
>  net/ipv4/devinet.c | 52 +++++++++++++++++++++++++++++++++++++++++-----------
>  1 file changed, 41 insertions(+), 11 deletions(-)
> 
> diff --git a/net/ipv4/devinet.c b/net/ipv4/devinet.c
> index 44d931a3cd50..1e06a21cd8f4 100644
> --- a/net/ipv4/devinet.c
> +++ b/net/ipv4/devinet.c
> @@ -1661,15 +1661,15 @@ static int inet_fill_ifaddr(struct sk_buff *skb, struct in_ifaddr *ifa,
>  
>  static int inet_dump_ifaddr(struct sk_buff *skb, struct netlink_callback *cb)
>  {
> +	struct netlink_ext_ack *extack = cb->extack;
> +	const struct nlmsghdr *nlh = cb->nlh;
>  	struct inet_fill_args fillargs = {
>  		.portid = NETLINK_CB(cb->skb).portid,
> -		.seq = cb->nlh->nlmsg_seq,
> +		.seq = nlh->nlmsg_seq,
>  		.event = RTM_NEWADDR,
> -		.flags = NLM_F_MULTI,
>  		.netnsid = -1,
>  	};
>  	struct net *net = sock_net(skb->sk);
> -	struct nlattr *tb[IFA_MAX+1];
>  	struct net *tgt_net = net;
>  	int h, s_h;
>  	int idx, s_idx;
> @@ -1683,15 +1683,45 @@ static int inet_dump_ifaddr(struct sk_buff *skb, struct netlink_callback *cb)
>  	s_idx = idx = cb->args[1];
>  	s_ip_idx = ip_idx = cb->args[2];
>  
> -	if (nlmsg_parse(cb->nlh, sizeof(struct ifaddrmsg), tb, IFA_MAX,
> -			ifa_ipv4_policy, NULL) >= 0) {
> -		if (tb[IFA_TARGET_NETNSID]) {
> -			fillargs.netnsid = nla_get_s32(tb[IFA_TARGET_NETNSID]);
> +	if (nlh->nlmsg_flags & NLM_F_DUMP_PROPER_HDR) {
> +		struct nlattr *tb[IFA_MAX+1];
> +		struct ifaddrmsg *ifm;
> +		int err, i;
> +
> +		if (nlh->nlmsg_len < nlmsg_msg_size(sizeof(*ifm))) {
> +			NL_SET_ERR_MSG(extack, "Invalid header");
> +			return -EINVAL;
> +		}
> +
> +		ifm = (struct ifaddrmsg *) nlmsg_data(cb->nlh);
> +		if (ifm->ifa_prefixlen || ifm->ifa_flags || ifm->ifa_scope) {
> +			NL_SET_ERR_MSG(extack, "Invalid values in header for dump request");
> +			return -EINVAL;
> +		}
> +		if (ifm->ifa_index) {
> +			NL_SET_ERR_MSG(extack, "Filter by device index not supported");
> +			return -EINVAL;
> +		}
> +		err = nlmsg_parse(cb->nlh, sizeof(struct ifaddrmsg), tb, IFA_MAX,
> +				ifa_ipv4_policy, NULL);
> +		if (err < 0)
> +			return err;
>  
> -			tgt_net = rtnl_get_net_ns_capable(skb->sk,
> -							  fillargs.netnsid);
> -			if (IS_ERR(tgt_net))
> -				return PTR_ERR(tgt_net);
> +		for (i = 0; i < IFA_MAX; ++i) {
> +			if (i == IFA_TARGET_NETNSID) {
> +				fillargs.netnsid = nla_get_s32(tb[i]);
> +
> +				tgt_net = rtnl_get_net_ns_capable(skb->sk,
> +								  fillargs.netnsid);
> +				if (IS_ERR(tgt_net))
> +					return PTR_ERR(tgt_net);
> +
> +				fillargs.flags |= NLM_F_DUMP_FILTERED;
> +			}
> +			if (tb[i]) {
> +				NL_SET_ERR_MSG(extack, "Unsupported attribute in dump request");
> +				return -EINVAL;
> +			}

That loop doesn't do what it promises, no? Shouldn't it be:

		for (i = 0; i < IFA_MAX; ++i) {
			if (i == IFA_TARGET_NETNSID && tb[IFA_TARGET_NETNSID]) {
				fillargs.netnsid = nla_get_s32(tb[i]);

				tgt_net = rtnl_get_net_ns_capable(skb->sk,
								  fillargs.netnsid);
				if (IS_ERR(tgt_net))
					return PTR_ERR(tgt_net);

				fillargs.flags |= NLM_F_DUMP_FILTERED;
				continue;
			}

			if (tb[i]) {
				NL_SET_ERR_MSG(extack, "Unsupported attribute in dump request");
				return -EINVAL;
			}
		}

>  	}
>  
> -- 
> 2.11.0
>