Re: [PATCH] ipv6: Prevent access to uninitialized fib_table_hash via /proc/net/ipv6_route

[David Miller <davem@davemloft.net>]

From: David Miller <davem@davemloft.net>
Date: Fri, 15 Jun 2012 15:32:40 -0700 (PDT)

> From: Neil Horman <nhorman@tuxdriver.com>
> Date: Fri, 15 Jun 2012 06:56:55 -0400
> 
>> On Fri, Jun 15, 2012 at 11:00:17AM +0200, Thomas Graf wrote:
>>> /proc/net/ipv6_route reflects the contents of fib_table_hash. The proc
>>> handler is installed in ip6_route_net_init() whereas fib_table_hash is
>>> allocated in fib6_net_init() _after_ the proc handler has been installed.
>>> 
>>> This opens up a short time frame to access fib_table_hash with its pants
>>> down.
>>> 
>>> fib6_init() as a whole can't be moved to an earlier position as it also
>>> registers the rtnetlink message handlers which should be registered at
>>> the end. Therefore split it into fib6_init() which is run early and
>>> fib6_init_late() to register the rtnetlink message handlers.
>>> 
>>> Signed-off-by: Thomas Graf <tgraf@suug.ch>
>> Reviewed-by: Neil Horman <nhorman@tuxdriver.com>
> 
> Applied.
> 
> Since you're snooping around in here, you might notice that on network
> namespace shutdown, we leak all user configured ipv6 FIB rules.

Thomas, this patch is buggy.

We will now initialize fib6_init() before ip6_net_route_net_ops is registerd.

This causes fib6_net_init() to run before net->ipv6.ip6_null_entry it
initialized.

Any route lookup will crash when we dereference a root's ->leaf
because it will be NULL.

Please test your changes more thoroughly.