netdev - Re: [PATCHv3 next] blackhole_netdev: fix syzkaller reported issue

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Message-Id: <20191015.103609.86962935874616520.davem@davemloft.net>
Date:   Tue, 15 Oct 2019 10:36:09 -0700 (PDT)
From:   David Miller <davem@...emloft.net>
To:     maheshb@...gle.com
Cc:     netdev@...r.kernel.org, edumazet@...gle.com, weiwan@...gle.com,
        mahesh@...dewar.net
Subject: Re: [PATCHv3 next] blackhole_netdev: fix syzkaller reported issue

From: Mahesh Bandewar <maheshb@...gle.com>
Date: Fri, 11 Oct 2019 18:14:55 -0700

> While invalidating the dst, we assign backhole_netdev instead of
> loopback device. However, this device does not have idev pointer
> and hence no ip6_ptr even if IPv6 is enabled. Possibly this has
> triggered the syzbot reported crash.
> 
> The syzbot report does not have reproducer, however, this is the
> only device that doesn't have matching idev created.
> 
> Crash instruction is :
> 
> static inline bool ip6_ignore_linkdown(const struct net_device *dev)
> {
>         const struct inet6_dev *idev = __in6_dev_get(dev);
> 
>         return !!idev->cnf.ignore_routes_with_linkdown; <= crash
> }
> 
> Also ipv6 always assumes presence of idev and never checks for it
> being NULL (as does the above referenced code). So adding a idev
> for the blackhole_netdev to avoid this class of crashes in the future.
> 
> ---
 ...
> Fixes: 8d7017fd621d ("blackhole_netdev: use blackhole_netdev to invalidate dst entries")
> Signed-off-by: Mahesh Bandewar <maheshb@...gle.com>

Applied and queued up for -stable, thanks.