netdev - Re: [PATCH net-next v2 3/3] genetlink: fit NLMSG

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Message-ID: <bb4d62d9-fbe2-41e3-90ff-02d7c2a05443@linux.dev>
Date: Thu, 21 Mar 2024 17:03:39 +0200
From: Gal Pressman <gal.pressman@...ux.dev>
To: Ido Schimmel <idosch@...sch.org>
Cc: Jakub Kicinski <kuba@...nel.org>, Eric Dumazet <edumazet@...gle.com>,
 Stefano Brivio <sbrivio@...hat.com>, davem@...emloft.net,
 netdev@...r.kernel.org, pabeni@...hat.com, jiri@...nulli.us,
 johannes@...solutions.net, fw@...len.de, pablo@...filter.org,
 Martin Pitt <mpitt@...hat.com>, Paul Holzinger <pholzing@...hat.com>,
 David Gibson <david@...son.dropbear.id.au>
Subject: Re: [PATCH net-next v2 3/3] genetlink: fit NLMSG_DONE into same
 read() as families

On 21/03/2024 15:51, Ido Schimmel wrote:
> On Thu, Mar 21, 2024 at 02:56:41PM +0200, Gal Pressman wrote:
>> We've encountered a new issue recently which I believe is related to
>> this discussion.
>>
>> Following Eric's patch:
>> 9cc4cc329d30 ("ipv6: use xa_array iterator to implement inet6_dump_addr()")
>>
>> Setting the interface mtu to < 1280 results in 'ip addr show eth2'
>> returning an error, because the ipv6 dump fails. This is a degradation
>> from the user's perspective.
>>
>> # ip addr show eth2
>> 4: eth2: <BROADCAST,MULTICAST> mtu 1500 qdisc noop state DOWN group
>> default qlen 1000
>>     link/ether 24:42:53:21:52:44 brd ff:ff:ff:ff:ff:ff
>>     altname enp6s0f0np0
>> # ip link set dev eth2 mtu 1000
>> # ip addr show eth2
>> RTNETLINK answers: No such device
>> Dump terminated
> 
> I don't think it's the same issue. Original issue was about user space
> not knowing how to handle NLMSG_DONE being sent together with dump
> responses. The issue you reported seems to be related to an
> unintentional change in the return code when IPv6 is disabled on an
> interface. Can you please test the following patch?
> 
> diff --git a/net/ipv6/addrconf.c b/net/ipv6/addrconf.c
> index 247bd4d8ee45..92db9b474f2b 100644
> --- a/net/ipv6/addrconf.c
> +++ b/net/ipv6/addrconf.c
> @@ -5416,10 +5416,11 @@ static int inet6_dump_addr(struct sk_buff *skb, struct netlink_callback *cb,
>  
>                 err = 0;
>                 if (fillargs.ifindex) {
> -                       err = -ENODEV;
>                         dev = dev_get_by_index_rcu(tgt_net, fillargs.ifindex);
> -                       if (!dev)
> +                       if (!dev) {
> +                               err = -ENODEV;
>                                 goto done;
> +                       }
>                         idev = __in6_dev_get(dev);
>                         if (idev)
>                                 err = in6_dump_addrs(idev, skb, cb,

This seems to fix it, thanks!
Will you submit a patch?