Re: [PATCH net-next 09/20] rtnetlink: Update rtnl_bridge_getlink for strict data checking

[Christian Brauner <christian@brauner.io>]

On Thu, Oct 04, 2018 at 02:33:44PM -0700, David Ahern wrote:
> From: David Ahern <dsahern@gmail.com>
> 
> Update rtnl_bridge_getlink for strict data checking. If the flag is set,
> the dump request is expected to have an ifinfomsg 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 IFLA_EXT_MASK
> attribute is supported.
> 
> Signed-off-by: David Ahern <dsahern@gmail.com>
> ---
>  net/core/rtnetlink.c | 50 ++++++++++++++++++++++++++++++++++++++++----------
>  1 file changed, 40 insertions(+), 10 deletions(-)
> 
> diff --git a/net/core/rtnetlink.c b/net/core/rtnetlink.c
> index 4fd27b5db787..d2c8d41a6fbc 100644
> --- a/net/core/rtnetlink.c
> +++ b/net/core/rtnetlink.c
> @@ -4000,27 +4000,57 @@ EXPORT_SYMBOL_GPL(ndo_dflt_bridge_getlink);
>  
>  static int rtnl_bridge_getlink(struct sk_buff *skb, struct netlink_callback *cb)
>  {
> +	struct netlink_ext_ack *extack = cb->extack;
> +	const struct nlmsghdr *nlh = cb->nlh;
>  	struct net *net = sock_net(skb->sk);
> +	struct nlattr *tb[IFLA_MAX+1];
>  	struct net_device *dev;
>  	int idx = 0;
>  	u32 portid = NETLINK_CB(cb->skb).portid;
> -	u32 seq = cb->nlh->nlmsg_seq;
> +	u32 seq = nlh->nlmsg_seq;
>  	u32 filter_mask = 0;
> -	int err;
> +	int err, i;
>  
> -	if (nlmsg_len(cb->nlh) > sizeof(struct ifinfomsg)) {
> -		struct nlattr *extfilt;
> +	if (cb->strict_check) {
> +		struct ifinfomsg *ifm;
>  
> -		extfilt = nlmsg_find_attr(cb->nlh, sizeof(struct ifinfomsg),
> -					  IFLA_EXT_MASK);
> -		if (extfilt) {
> -			if (nla_len(extfilt) < sizeof(filter_mask))
> -				return -EINVAL;
> +		if (nlh->nlmsg_len < nlmsg_msg_size(sizeof(*ifm))) {
> +			NL_SET_ERR_MSG(extack, "Invalid header");
> +			return -EINVAL;
> +		}
> +
> +		ifm = nlmsg_data(nlh);
> +		if (ifm->__ifi_pad || ifm->ifi_type || ifm->ifi_flags ||
> +		    ifm->ifi_change || ifm->ifi_index) {
> +			NL_SET_ERR_MSG(extack, "Invalid values in header for dump request");
> +			return -EINVAL;
> +		}
> +	}
>  
> -			filter_mask = nla_get_u32(extfilt);
> +	err = nlmsg_parse(nlh, sizeof(struct ifinfomsg), tb, IFLA_MAX,
> +			  ifla_policy, extack);
> +	if (err < 0) {
> +		if (cb->strict_check)
> +			return -EINVAL;
> +		goto walk_entries;
> +	}

What's the point of moving this out of the
if (cb->strict_check) {} branch above? This looks like it would cause
the same parse warnings that we're trying to get rid of in inet{4,6}
dumps.
Seems to make more sense to make the nlmsg_parse() itself conditional as
well unless I'm lacking context.

> +
> +	for (i = 0; i <= IFLA_MAX; ++i) {
> +		if (!tb[i])
> +			continue;
> +		switch (i) {

I'm a fan of \n between different conditions etc. so can we please have
one after the continue. :)

> +		case IFLA_EXT_MASK:
> +			filter_mask = nla_get_u32(tb[i]);
> +			break;
> +		default:
> +			if (cb->strict_check) {
> +				NL_SET_ERR_MSG(extack, "Unsupported attribute in dump request");
> +				return -EINVAL;
> +			}
>  		}
>  	}
>  
> +walk_entries:
>  	rcu_read_lock();
>  	for_each_netdev_rcu(net, dev) {
>  		const struct net_device_ops *ops = dev->netdev_ops;
> -- 
> 2.11.0
>