netdev - Re: [PATCH net-next 5/6] netlink: add mask validation

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Message-ID: <20201005122242.48ed17cf@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com>
Date:   Mon, 5 Oct 2020 12:22:42 -0700
From:   Jakub Kicinski <kuba@...nel.org>
To:     Johannes Berg <johannes@...solutions.net>
Cc:     davem@...emloft.net, netdev@...r.kernel.org, kernel-team@...com,
        jiri@...nulli.us, andrew@...n.ch, mkubecek@...e.cz,
        dsahern@...il.com, pablo@...filter.org
Subject: Re: [PATCH net-next 5/6] netlink: add mask validation

On Mon, 05 Oct 2020 21:05:23 +0200 Johannes Berg wrote:
> On Mon, 2020-10-05 at 08:57 -0700, Jakub Kicinski wrote:
> > We don't have good validation policy for existing unsigned int attrs
> > which serve as flags (for new ones we could use NLA_BITFIELD32).
> > With increased use of policy dumping having the validation be
> > expressed as part of the policy is important. Add validation
> > policy in form of a mask of supported/valid bits.  
> 
> Nice, I'll surely use this as well somewhere :)
> 
> >  #define __NLA_ENSURE(condition) BUILD_BUG_ON_ZERO(!(condition))
> > +#define NLA_ENSURE_UINT_TYPE(tp)			\
> > +	(__NLA_ENSURE(tp == NLA_U8 || tp == NLA_U16 ||	\
> > +		      tp == NLA_U32 || tp == NLA_U64) + tp)
> >  #define NLA_ENSURE_UINT_OR_BINARY_TYPE(tp)		\  
> 
> nit: maybe express this (_OR_BINARY_TYPE) in terms of UINT_TYPE() ||
> tp==NLA_BINARY? Doesn't matter much though.

Will do!

> > +static int nla_validate_mask(const struct nla_policy *pt,
> > +			     const struct nlattr *nla,
> > +			     struct netlink_ext_ack *extack)
> > +{
> > +	u64 value;
> > +
> > +	switch (pt->type) {
> > +	case NLA_U8:
> > +		value = nla_get_u8(nla);
> > +		break;
> > +	case NLA_U16:
> > +		value = nla_get_u16(nla);
> > +		break;
> > +	case NLA_U32:
> > +		value = nla_get_u32(nla);
> > +		break;
> > +	case NLA_U64:
> > +		value = nla_get_u64(nla);
> > +		break;
> > +	default:
> > +		return -EINVAL;
> > +	}
> > +
> > +	if (value & ~(u64)pt->mask) {
> > +		NL_SET_ERR_MSG_ATTR(extack, nla, "reserved bit set");
> > +		return -EINVAL;  
> 
> You had an export of the valid bits there in ethtool, using the cookie.
> Just pointing out you lost it now. I'm not sure I like using the cookie,
> that seems a bit strange, but we could easily define a different attr?
> 
> OTOH, one can always query the policy export too (which hopefully got
> wired up) so it wouldn't really matter much.

My thinking is that there are no known uses of the cookie, it'd only
have practical use to test for new flags - and we're adding first new
flag in 5.10.

> Either way is fine with me on both of these points.
> 
> Reviewed-by: Johannes Berg <johannes@...solutions.net>

Thanks!