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Date:   Sun, 7 Oct 2018 12:48:47 +0200
From:   Christian Brauner <christian@...uner.io>
To:     David Ahern <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 net-next 15/20] net/neighbor: Update neightbl_dump_info
 for strict data checking

On Thu, Oct 04, 2018 at 02:33:50PM -0700, David Ahern wrote:
> From: David Ahern <dsahern@...il.com>
> 
> Update neightbl_dump_info for strict data checking. If the flag is set,
> the dump request is expected to have an ndtmsg struct as the header.
> All elements of the struct are expected to be 0 and no attributes can
> be appended.
> 
> Signed-off-by: David Ahern <dsahern@...il.com>
> ---
>  net/core/neighbour.c | 38 +++++++++++++++++++++++++++++++++++---
>  1 file changed, 35 insertions(+), 3 deletions(-)
> 
> diff --git a/net/core/neighbour.c b/net/core/neighbour.c
> index 3130d010b7ad..8e07b92403ab 100644
> --- a/net/core/neighbour.c
> +++ b/net/core/neighbour.c
> @@ -2164,15 +2164,47 @@ static int neightbl_set(struct sk_buff *skb, struct nlmsghdr *nlh,
>  	return err;
>  }
>  
> +static int neightbl_valid_dump_info(const struct nlmsghdr *nlh,
> +				    struct netlink_ext_ack *extack)
> +{
> +	struct ndtmsg *ndtm;
> +
> +	if (nlh->nlmsg_len < nlmsg_msg_size(sizeof(*ndtm))) {
> +		NL_SET_ERR_MSG(extack, "Invalid header");
> +		return -EINVAL;
> +	}
> +
> +	ndtm = nlmsg_data(nlh);
> +	if (ndtm->ndtm_pad1  || ndtm->ndtm_pad2) {
> +		NL_SET_ERR_MSG(extack, "Invalid values in header for dump request");
> +		return -EINVAL;
> +	}
> +
> +	if (nlh->nlmsg_len != nlmsg_msg_size(sizeof(*ndtm))) {
> +		NL_SET_ERR_MSG(extack, "Invalid data after header");
> +		return -EINVAL;
> +	}
> +
> +	return 0;
> +}
> +
>  static int neightbl_dump_info(struct sk_buff *skb, struct netlink_callback *cb)
>  {
> +	const struct nlmsghdr *nlh = cb->nlh;
>  	struct net *net = sock_net(skb->sk);
>  	int family, tidx, nidx = 0;
>  	int tbl_skip = cb->args[0];
>  	int neigh_skip = cb->args[1];
>  	struct neigh_table *tbl;
>  
> -	family = ((struct rtgenmsg *) nlmsg_data(cb->nlh))->rtgen_family;
> +	if (cb->strict_check) {
> +		int err = neightbl_valid_dump_info(nlh, cb->extack);
> +
> +		if (err)
> +			return err;
> +	}
> +
> +	family = ((struct rtgenmsg *)nlmsg_data(nlh))->rtgen_family;

So this already was a problem prior to your patch: what happens when you
pass in the wrong struct? Then this case is not safe to do and might
contain all kinds of crap.

>  
>  	for (tidx = 0; tidx < NEIGH_NR_TABLES; tidx++) {
>  		struct neigh_parms *p;
> @@ -2185,7 +2217,7 @@ static int neightbl_dump_info(struct sk_buff *skb, struct netlink_callback *cb)
>  			continue;
>  
>  		if (neightbl_fill_info(skb, tbl, NETLINK_CB(cb->skb).portid,
> -				       cb->nlh->nlmsg_seq, RTM_NEWNEIGHTBL,
> +				       nlh->nlmsg_seq, RTM_NEWNEIGHTBL,
>  				       NLM_F_MULTI) < 0)
>  			break;
>  
> @@ -2200,7 +2232,7 @@ static int neightbl_dump_info(struct sk_buff *skb, struct netlink_callback *cb)
>  
>  			if (neightbl_fill_param_info(skb, tbl, p,
>  						     NETLINK_CB(cb->skb).portid,
> -						     cb->nlh->nlmsg_seq,
> +						     nlh->nlmsg_seq,
>  						     RTM_NEWNEIGHTBL,
>  						     NLM_F_MULTI) < 0)
>  				goto out;
> -- 
> 2.11.0
> 

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