netdev - Re: [PATCH net] net/ipv6: prevent use after free in ip6_route_mpath

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Date:   Tue, 05 Jun 2018 09:57:03 -0400 (EDT)
From:   David Miller <davem@...emloft.net>
To:     dsahern@...nel.org
Cc:     netdev@...r.kernel.org, dsahern@...il.com, edumazet@...gle.com
Subject: Re: [PATCH net] net/ipv6: prevent use after free in
 ip6_route_mpath_notify

From: dsahern@...nel.org
Date: Mon,  4 Jun 2018 13:41:42 -0700

> From: David Ahern <dsahern@...il.com>
> 
> syzbot reported a use-after-free:
 ...
> The problem is that rt_last can point to a deleted route if the insert
> fails.
> 
> One reproducer is to insert a route and then add a multipath route that
> has a duplicate nexthop.e.g,:
>     $ ip -6 ro add vrf red 2001:db8:101::/64 nexthop via 2001:db8:1::2
>     $ ip -6 ro append vrf red 2001:db8:101::/64 nexthop via 2001:db8:1::4 nexthop via 2001:db8:1::2
> 
> Fix by not setting rt_last until the it is verified the insert succeeded.
> 
> Fixes: 3b1137fe7482 ("net: ipv6: Change notifications for multipath add to RTA_MULTIPATH")
> Cc: Eric Dumazet <edumazet@...gle.com>
> Reported-by: syzbot <syzkaller@...glegroups.com>
> Signed-off-by: David Ahern <dsahern@...il.com>

Applied and queued up for -stable, thanks David.