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Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Simon Horman , Yuyang Huang , Nicolas Dichtel , netdev@vger.kernel.org, linux-kernel@vger.kernel.org, 1342116488@qq.com Subject: Re: [PATCH net] ipv4: igmp: report IFA_TARGET_NETNSID in multicast address dumps Message-ID: References: <20261111082222.327963-1-sunwenbo@cmss.chinamobile.com> X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20261111082222.327963-1-sunwenbo@cmss.chinamobile.com> On Wed, Nov 11, 2026 at 04:22:22PM +0800, Wenbo Sun wrote: > Commit eb4e17a1d915 ("netlink: support dumping IPv4 multicast addresses") > extended RTM_GETMULTICAST to support dumping IPv4 multicast addresses. > While inet_valid_dump_ifaddr_req() accepts IFA_TARGET_NETNSID in dump > requests and dumps addresses from the target network namespace, > inet_fill_ifmcaddr() never puts IFA_TARGET_NETNSID in the netlink > replies. > > As a result, userspace applications querying multicast addresses in a > target netns receive entries without IFA_TARGET_NETNSID, which may lead > them to conclude that the kernel does not support netns-targeted dumps > or to misattribute the returned addresses. In contrast, IPv4 unicast > address dumps (inet_fill_ifaddr()), IPv6 multicast address dumps > (inet6_fill_ifmcaddr()), and AF_PACKET multicast address dumps all > report IFA_TARGET_NETNSID. > > Add IFA_TARGET_NETNSID to inet_fill_ifmcaddr() when requested, and > explicitly set fillargs.netnsid = -1 in inet_ifmcaddr_notify() to > prevent notification messages from exceeding their preallocated skb > size. > > This issue was identified with the assistance of an LLM-based code > review tool, confirmed by reproducing in a User-Mode Linux (UML) > environment where AF_INET RTM_GETMULTICAST dumps with IFA_TARGET_NETNSID > omitted the attribute, and verified in UML that AF_INET multicast dumps > now report IFA_TARGET_NETNSID, normal dumps without netnsid continue to > work, and socket multicast join/leave notifications succeed without > warning. > > Fixes: eb4e17a1d915 ("netlink: support dumping IPv4 multicast addresses") I don't think this should be fix. Maybe consider this as a new feature and target to net-next? Thanks Hangbin > Signed-off-by: Wenbo Sun > --- > net/ipv4/igmp.c | 7 +++++++ > 1 file changed, 7 insertions(+) > > diff --git a/net/ipv4/igmp.c b/net/ipv4/igmp.c > index 144fca158adc..831d003677ba 100644 > --- a/net/ipv4/igmp.c > +++ b/net/ipv4/igmp.c > @@ -1517,6 +1517,12 @@ int inet_fill_ifmcaddr(struct sk_buff *skb, struct net_device *dev, > ifm->ifa_scope = RT_SCOPE_UNIVERSE; > ifm->ifa_index = dev->ifindex; > > + if (args->netnsid >= 0 && > + nla_put_s32(skb, IFA_TARGET_NETNSID, args->netnsid)) { > + nlmsg_cancel(skb, nlh); > + return -EMSGSIZE; > + } > + > ci.cstamp = (READ_ONCE(im->mca_cstamp) - INITIAL_JIFFIES) * 100UL / HZ; > ci.tstamp = ci.cstamp; > ci.ifa_prefered = INFINITY_LIFE_TIME; > @@ -1538,6 +1544,7 @@ static void inet_ifmcaddr_notify(struct net_device *dev, > { > struct inet_fill_args fillargs = { > .event = event, > + .netnsid = -1, > }; > struct net *net = dev_net(dev); > struct sk_buff *skb; > -- > 2.33.0 >