On Fri, Apr 26, 2019 at 11:24:15AM +0200, Johannes Berg wrote: > On Fri, 2019-04-26 at 09:13 +0000, Michal Kubecek wrote: > > > Another observation was that even if NLA_F_NESTED flag was introduced in > > 2007, only few netlink based interfaces set it in kernel generated messages > > and even many recently added APIs omit it. That is unfortunate as without > > the flag, message parsers not familiar with attribute semantics cannot > > recognize nested attributes and do not see message structure; this affects > > e.g. wireshark dissector or mnl_nlmsg_fprintf() from libmnl. > > Indeed. > > I wonder if we should also (start) enforcing that the userspace sender > side sets this, if the policy is strict? I suppose we should, at least the part that attribute with NLA_NESTED policy has NLA_F_NESTED flag. I'm not so sure about the opposite (i.e. that attributes with other policies do not have the flag) as when I was checking where kernel accesses nlattr::nla_type directly rather than with nla_type(), I stumbled upon an attribute NL80211_ATTR_VENDOR_DATA which has policy NLA_BINARY but is sometimes a nest, AFAICS. Michal
