netdev - Re: [PATCH 1/2] ipv6: avoid blackhole and prohibited entries upon prefix purge [v2]

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Date:	Mon, 7 Jan 2013 12:30:18 +0100
From:	Romain KUNTZ <r.kuntz@...lavors.com>
To:	nicolas.dichtel@...nd.com
Cc:	netdev@...r.kernel.org, Eric Dumazet <eric.dumazet@...il.com>,
	yoshfuji@...ux-ipv6.org, davem@...emloft.net,
	Romain KUNTZ <r.kuntz@...lavors.com>
Subject: Re: [PATCH 1/2] ipv6: avoid blackhole and prohibited entries upon prefix purge [v2]

Hello Nicolas,

On Jan 7, 2013, at 11:25 , Nicolas Dichtel <nicolas.dichtel@...nd.com> wrote:

> Le 05/01/2013 22:44, Romain KUNTZ a écrit :
>> Mobile IPv6 provokes a kernel Oops since commit 64c6d08e (ipv6:
>> del unreachable route when an addr is deleted on lo), because
>> ip6_route_lookup() may also return blackhole and prohibited
>> entry. However, these entries have a NULL rt6i_table argument,
>> which provokes an Oops in __ip6_del_rt() when trying to lock
>> rt6i_table->tb6_lock.
>> 
>> Beside, when purging a prefix, blakhole and prohibited entries
>> should not be selected because they are not what we are looking
>> for.
>> 
>> We fix this by adding two new lookup flags (RT6_LOOKUP_F_NO_BLK_HOLE
>> and RT6_LOOKUP_F_NO_PROHIBIT) in order to ensure that such entries
>> are skipped during lookup and that the correct entry is returned.
>> 
>> [v2]: use 'goto out;' instead of 'goto again;' to avoid unnecessary
>> oprations on rt (as suggested by Eric Dumazet).
>> 
>> Signed-off-by: Romain Kuntz <r.kuntz@...lavors.com>
>> ---
>>  include/net/ip6_route.h |    2 ++
>>  net/ipv6/addrconf.c     |    4 +++-
>>  net/ipv6/fib6_rules.c   |    4 ++++
>>  3 files changed, 9 insertions(+), 1 deletions(-)
>> 
>> diff --git a/include/net/ip6_route.h b/include/net/ip6_route.h
>> index 27d8318..3c93743 100644
>> --- a/include/net/ip6_route.h
>> +++ b/include/net/ip6_route.h
>> @@ -30,6 +30,8 @@ struct route_info {
>>  #define RT6_LOOKUP_F_SRCPREF_TMP	0x00000008
>>  #define RT6_LOOKUP_F_SRCPREF_PUBLIC	0x00000010
>>  #define RT6_LOOKUP_F_SRCPREF_COA	0x00000020
>> +#define RT6_LOOKUP_F_NO_BLK_HOLE	0x00000040
>> +#define RT6_LOOKUP_F_NO_PROHIBIT	0x00000080
>> 
>>  /*
>>   * rt6_srcprefs2flags() and rt6_flags2srcprefs() translate
>> diff --git a/net/ipv6/addrconf.c b/net/ipv6/addrconf.c
>> index 408cac4a..1891e23 100644
>> --- a/net/ipv6/addrconf.c
>> +++ b/net/ipv6/addrconf.c
>> @@ -948,7 +948,9 @@ static void ipv6_del_addr(struct inet6_ifaddr *ifp)
>>  		fl6.flowi6_oif = ifp->idev->dev->ifindex;
>>  		fl6.daddr = prefix;
>>  		rt = (struct rt6_info *)ip6_route_lookup(net, &fl6,
>> -							 RT6_LOOKUP_F_IFACE);
>> +						RT6_LOOKUP_F_IFACE |
>> +						RT6_LOOKUP_F_NO_BLK_HOLE |
>> +						RT6_LOOKUP_F_NO_PROHIBIT);
>> 
>>  		if (rt != net->ipv6.ip6_null_entry &&
> Is it not simpler to test the result here (net->ipv6.ip6_blk_hole_entry and
> net->ipv6.ip6_prohibit_entry) like for the null_entry?
> It will also avoid adding more flags.

Your proposal would only solve part of the problem (the Oops in __ip6_del_rt()). Another problem here is that blackhole and prohibited rules should not be selected when trying to purge a prefix (correct me if I'm wrong) because they are not what we are looking for. This can prevent the targeted prefix from being purged. 

Thank you,
Romain


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