Re: [PATCH net v4 1/8] ipv4/fib_frontend: Rename ip_valid_fib_dump_req, provide non-strict version

[Stefano Brivio <sbrivio@redhat.com>]

On Fri, 14 Jun 2019 20:54:49 -0600
David Ahern <dsahern@gmail.com> wrote:

> On 6/14/19 7:32 PM, Stefano Brivio wrote:
> > ip_valid_fib_dump_req() does two things: performs strict checking on
> > netlink attributes for dump requests, and sets a dump filter if netlink
> > attributes require it.
> > 
> > We might want to just set a filter, without performing strict validation.
> > 
> > Rename it to ip_filter_fib_dump_req(), and add a 'strict' boolean
> > argument that must be set if strict validation is requested.
> > 
> > This patch doesn't introduce any functional changes.
> > 
> > Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
> > ---
> > v4: New patch
> >   
> 
> Can you explain why this patch is needed? The existing function requires
> strict mode and is needed to enable any of the kernel side filtering
> beyond the RTM_F_CLONED setting in rtm_flags.

It's mostly to have proper NLM_F_MATCH support. Let's pick an iproute2
version without strict checking support (< 5.0), that sets NLM_F_MATCH
though. Then we need this check:

	if (nlh->nlmsg_len < nlmsg_msg_size(sizeof(*rtm)))

and to set filter parameters not just based on flags (i.e. RTM_F_CLONED),
but also on table, protocol, etc.

For example one might want to: 'ip route list cache table main', and this
is then taken into account in fn_trie_dump_leaf() and rt6_dump_route().

Reusing this function avoids a nice amount of duplicated code and allows
to have an almost common path with strict checking.

-- 
Stefano