tree 4ca7931e6ae9d3e2d3d115d01b0fda824a9ca97e
parent 9cb0aec9ad370163b4cb038d9538baceadb345de
author Mahesh Bandewar <maheshb@google.com> 1570842895 -0700
committer David S. Miller <davem@davemloft.net> 1571160923 -0700

blackhole_netdev: fix syzkaller reported issue

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.

Signed-off-by: David S. Miller <davem@davemloft.net>