netdev - Re: [PATCH net-next 2/2] net: limit altnames to 64k total

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Message-ID: <20220309193708.340a6af5@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com>
Date:   Wed, 9 Mar 2022 19:37:08 -0800
From:   Jakub Kicinski <kuba@...nel.org>
To:     David Ahern <dsahern@...il.com>
Cc:     davem@...emloft.net, netdev@...r.kernel.org, jiri@...nulli.us,
        George Shuklin <george.shuklin@...il.com>
Subject: Re: [PATCH net-next 2/2] net: limit altnames to 64k total

On Wed, 9 Mar 2022 19:51:07 -0700 David Ahern wrote:
> On 3/9/22 11:29 AM, Jakub Kicinski wrote:
> > diff --git a/net/core/rtnetlink.c b/net/core/rtnetlink.c
> > index aa05e89cc47c..159c9c61e6af 100644
> > --- a/net/core/rtnetlink.c
> > +++ b/net/core/rtnetlink.c
> > @@ -3652,12 +3652,23 @@ static int rtnl_alt_ifname(int cmd, struct net_device *dev, struct nlattr *attr,
> >  			   bool *changed, struct netlink_ext_ack *extack)
> >  {
> >  	char *alt_ifname;
> > +	size_t size;
> >  	int err;
> >  
> >  	err = nla_validate(attr, attr->nla_len, IFLA_MAX, ifla_policy, extack);
> >  	if (err)
> >  		return err;
> >  
> > +	if (cmd == RTM_NEWLINKPROP) {
> > +		size = rtnl_prop_list_size(dev);
> > +		size += nla_total_size(ALTIFNAMSIZ);
> > +		if (size >= U16_MAX) {
> > +			NL_SET_ERR_MSG(extack,
> > +				       "effective property list too long");
> > +			return -EINVAL;
> > +		}
> > +	}
> > +
> >  	alt_ifname = nla_strdup(attr, GFP_KERNEL_ACCOUNT);
> >  	if (!alt_ifname)
> >  		return -ENOMEM;  
> 
> this tests the existing property size. Don't you want to test the size
> with the alt_ifname - does it make the list go over 64kB?

Do you mean counting the exact length of the string?

Or that I'm counting pre-add? That's why I added:

	size += nla_total_size(ALTIFNAMSIZ);

I like coding things up as prepare (validate) + commit,
granted it doesn't exactly look pretty here so I can recode
if you prefer. But there's no bug, right? (other than maybe 
>= could have been > but whatever).