Re: [Patch net] ipv4: restore rt->fi for reference counting

[David Miller <davem@davemloft.net>]

From: Cong Wang <xiyou.wangcong@gmail.com>
Date: Thu,  4 May 2017 14:54:17 -0700

> IPv4 dst could use fi->fib_metrics to store metrics but fib_info
> itself is refcnt'ed, so without taking a refcnt fi and
> fi->fib_metrics could be freed while dst metrics still points to
> it. This triggers use-after-free as reported by Andrey twice.
> 
> This patch reverts commit 2860583fe840 ("ipv4: Kill rt->fi") to
> restore this reference counting. It is a quick fix for -net and
> -stable, for -net-next, as Eric suggested, we can consider doing
> reference counting for metrics itself instead of relying on fib_info.
> 
> IPv6 is very different, it copies or steals the metrics from mx6_config
> in fib6_commit_metrics() so probably doesn't need a refcnt.
> 
> Decnet has already done the refcnt'ing, see dn_fib_semantic_match().
> 
> Fixes: 2860583fe840 ("ipv4: Kill rt->fi")
> Reported-by: Andrey Konovalov <andreyknvl@google.com>
> Tested-by: Andrey Konovalov <andreyknvl@google.com>
> Signed-off-by: Cong Wang <xiyou.wangcong@gmail.com>

Applied and queued up for -stable, thanks.