netdev - Re: [net PATCH] net: route dump netlink NLM_F

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Date:   Sat, 24 Aug 2019 16:50:27 -0700 (PDT)
From:   David Miller <davem@...emloft.net>
To:     john.fastabend@...il.com
Cc:     sbrivio@...hat.com, dsahern@...il.com, netdev@...r.kernel.org
Subject: Re: [net PATCH] net: route dump netlink NLM_F_MULTI flag missing

From: John Fastabend <john.fastabend@...il.com>
Date: Fri, 23 Aug 2019 17:11:38 -0700

> An excerpt from netlink(7) man page,
> 
>   In multipart messages (multiple nlmsghdr headers with associated payload
>   in one byte stream) the first and all following headers have the
>   NLM_F_MULTI flag set, except for the last  header  which  has the type
>   NLMSG_DONE.
> 
> but, after (ee28906) there is a missing NLM_F_MULTI flag in the middle of a
> FIB dump. The result is user space applications following above man page
> excerpt may get confused and may stop parsing msg believing something went
> wrong.
> 
> In the golang netlink lib [0] the library logic stops parsing believing the
> message is not a multipart message. Found this running Cilium[1] against
> net-next while adding a feature to auto-detect routes. I noticed with
> multiple route tables we no longer could detect the default routes on net
> tree kernels because the library logic was not returning them.
> 
> Fix this by handling the fib_dump_info_fnhe() case the same way the
> fib_dump_info() handles it by passing the flags argument through the
> call chain and adding a flags argument to rt_fill_info().
> 
> Tested with Cilium stack and auto-detection of routes works again. Also
> annotated libs to dump netlink msgs and inspected NLM_F_MULTI and
> NLMSG_DONE flags look correct after this.
> 
> Note: In inet_rtm_getroute() pass rt_fill_info() '0' for flags the same
> as is done for fib_dump_info() so this looks correct to me.
> 
> [0] https://github.com/vishvananda/netlink/
> [1] https://github.com/cilium/
> 
> Fixes: ee28906fd7a14 ("ipv4: Dump route exceptions if requested")
> Signed-off-by: John Fastabend <john.fastabend@...il.com>

Applied, thanks John.