[net-next,06/20] net/ipv4: Update inet_dump_ifaddr for strict data checking

From: David Ahern <dsahern@gmail.com>

Update inet_dump_ifaddr for strict data checking. 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 supported 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 can support for other fields
(e.g., honor ifa_index and only return data for the given device index).

Signed-off-by: David Ahern <dsahern@gmail.com>
---
 net/ipv4/devinet.c | 53 +++++++++++++++++++++++++++++++++++++++++++----------
 1 file changed, 43 insertions(+), 10 deletions(-)

On Thu, Oct 04, 2018 at 02:33:41PM -0700, David Ahern wrote:
> From: David Ahern <dsahern@gmail.com>
> 
> Update inet_dump_ifaddr for strict data checking. 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 supported 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 can support for other fields
> (e.g., honor ifa_index and only return data for the given device index).
> 
> Signed-off-by: David Ahern <dsahern@gmail.com>
> ---
>  net/ipv4/devinet.c | 53 +++++++++++++++++++++++++++++++++++++++++++----------
>  1 file changed, 43 insertions(+), 10 deletions(-)
> 
> diff --git a/net/ipv4/devinet.c b/net/ipv4/devinet.c
> index ab2b11df5ea4..af968d4fe4fc 100644
> --- a/net/ipv4/devinet.c
> +++ b/net/ipv4/devinet.c
> @@ -1662,15 +1662,16 @@ 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;
> @@ -1684,15 +1685,47 @@ 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, cb->extack) >= 0) {
> -		if (tb[IFA_TARGET_NETNSID]) {
> -			fillargs.netnsid = nla_get_s32(tb[IFA_TARGET_NETNSID]);
> +	if (cb->strict_check) {
> +		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 = nlmsg_data(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(nlh, sizeof(struct ifaddrmsg), tb, IFA_MAX,
> +				  ifa_ipv4_policy, extack);
> +		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 (!tb[i])
> +				continue;
> +			if (i == IFA_TARGET_NETNSID) {

Nit: For the sake of readability there could be an additional newline between the 
"continue" and the next if () condition.

> +				fillargs.netnsid = nla_get_s32(tb[i]);
> +
> +				tgt_net = rtnl_get_net_ns_capable(skb->sk,
> +								  fillargs.netnsid);
> +				if (IS_ERR(tgt_net)) {
> +					NL_SET_ERR_MSG(extack, "Invalid target namespace id");

Nit: Hm, maybe "Invalid target network namespace id" would be better.
You never know what namespace comes along some time later. :)

> +					return PTR_ERR(tgt_net);
> +				}
> +			} else {
> +				NL_SET_ERR_MSG(extack, "Unsupported attribute in dump request");
> +				return -EINVAL;
> +			}
>  		}
>  	}
>  
> -- 
> 2.11.0
>

On 10/5/18 12:02 PM, Christian Brauner wrote:
>> +
>> +		err = nlmsg_parse(nlh, sizeof(struct ifaddrmsg), tb, IFA_MAX,
>> +				  ifa_ipv4_policy, extack);
>> +		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 (!tb[i])
>> +				continue;
>> +			if (i == IFA_TARGET_NETNSID) {
> 
> Nit: For the sake of readability there could be an additional newline between the 
> "continue" and the next if () condition.
> 
>> +				fillargs.netnsid = nla_get_s32(tb[i]);
>> +
>> +				tgt_net = rtnl_get_net_ns_capable(skb->sk,
>> +								  fillargs.netnsid);
>> +				if (IS_ERR(tgt_net)) {
>> +					NL_SET_ERR_MSG(extack, "Invalid target namespace id");
> 
> Nit: Hm, maybe "Invalid target network namespace id" would be better.
> You never know what namespace comes along some time later. :)
> 

done.