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Date:   Mon, 13 May 2019 17:18:28 +0200
From:   Nicolas Dichtel <nicolas.dichtel@...nd.com>
To:     David Ahern <dsahern@...il.com>,
        Sabrina Dubroca <sd@...asysnail.net>, netdev@...r.kernel.org
Cc:     Dan Winship <danw@...hat.com>
Subject: Re: [PATCH net v2] rtnetlink: always put ILFA_LINK for links with a
 link-netnsid

Le 13/05/2019 à 17:07, David Ahern a écrit :
> On 5/13/19 7:47 AM, Sabrina Dubroca wrote:
>> Currently, nla_put_iflink() doesn't put the IFLA_LINK attribute when
>> iflink == ifindex.
>>
>> In some cases, a device can be created in a different netns with the
>> same ifindex as its parent. That device will not dump its IFLA_LINK
>> attribute, which can confuse some userspace software that expects it.
>> For example, if the last ifindex created in init_net and foo are both
>> 8, these commands will trigger the issue:
>>
>>     ip link add parent type dummy                   # ifindex 9
>>     ip link add link parent netns foo type macvlan  # ifindex 9 in ns foo
>>
>> So, in case a device puts the IFLA_LINK_NETNSID attribute in a dump,
>> always put the IFLA_LINK attribute as well.
>>
>> Thanks to Dan Winship for analyzing the original OpenShift bug down to
>> the missing netlink attribute.
>>
>> Analyzed-by: Dan Winship <danw@...hat.com>
>> Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
>> Signed-off-by: Sabrina Dubroca <sd@...asysnail.net>
>> Acked-by: Nicolas Dichtel <nicolas.dichtel@...nd.com>
>> ---
>> v2: change Fixes tag, it's been here forever as Nicolas said, and add his Ack
>>
>>  net/core/rtnetlink.c | 16 ++++++++++------
>>  1 file changed, 10 insertions(+), 6 deletions(-)
>>
>> diff --git a/net/core/rtnetlink.c b/net/core/rtnetlink.c
>> index 2bd12afb9297..adcc045952c2 100644
>> --- a/net/core/rtnetlink.c
>> +++ b/net/core/rtnetlink.c
>> @@ -1496,14 +1496,15 @@ static int put_master_ifindex(struct sk_buff *skb, struct net_device *dev)
>>  	return ret;
>>  }
>>  
>> -static int nla_put_iflink(struct sk_buff *skb, const struct net_device *dev)
>> +static int nla_put_iflink(struct sk_buff *skb, const struct net_device *dev,
>> +			  bool force)
>>  {
>>  	int ifindex = dev_get_iflink(dev);
>>  
>> -	if (dev->ifindex == ifindex)
>> -		return 0;
>> +	if (force || dev->ifindex != ifindex)
>> +		return nla_put_u32(skb, IFLA_LINK, ifindex);
>>  
>> -	return nla_put_u32(skb, IFLA_LINK, ifindex);
>> +	return 0;
>>  }
>>  
>>  static noinline_for_stack int nla_put_ifalias(struct sk_buff *skb,
> 
> why not always adding the attribute?
> 
Adding this attribute may change the output of 'ip link'.
See this patch for example:
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=95ec655bc465


Nicolas

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