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([2a01:e0a:ab7:2110:6a1d:efff:fe52:1959]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-49cee7fec25sm634667375e9.13.2026.09.09.01.44.41 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 09 Sep 2026 01:44:41 -0700 (PDT) Message-ID: <175b6b01-2f8e-4b77-8504-6f26d9f8df98@6wind.com> Date: Wed, 9 Sep 2026 10:44:41 +0200 Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Reply-To: nicolas.dichtel@6wind.com Subject: Re: [PATCH net-next v2 1/3] rtnetlink: add AF_PACKET multicast dumps To: Yuyang Huang Cc: "David S. Miller" , David Ahern , Donald Hunter , Eric Dumazet , Ido Schimmel , Jakub Kicinski , Kuniyuki Iwashima , Nikolaos Gkarlis , Paolo Abeni , Sabrina Dubroca , Shuah Khan , Simon Horman , Stanislav Fomichev , linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org, netdev@vger.kernel.org References: <20260909013401.14408-1-sigefriedhyy@gmail.com> <20260909013401.14408-2-sigefriedhyy@gmail.com> From: Nicolas Dichtel Content-Language: en-US Organization: 6WIND In-Reply-To: <20260909013401.14408-2-sigefriedhyy@gmail.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Le 09/09/2026 à 03:33, Yuyang Huang a écrit : > RTM_GETMULTICAST dumps IPv4 and IPv6 multicast group memberships, but > the device multicast list (dev->mc) is only available through > /proc/net/dev_mcast, so "ip maddr show" still has to parse procfs for > its link-layer entries. > > Handle RTM_GETMULTICAST dumps with ifa_family set to AF_PACKET and > report every entry of dev->mc in the existing ifaddrmsg format: > > - IFA_MULTICAST carries the raw link-layer address > - IFA_MC_USERS carries the entry reference count > - IFA_F_PERMANENT marks entries added with SIOCADDMULTI > (netdev_hw_addr::global_use, "static" in "ip maddr") The global flag is also set for addresses added via dev_mc_add_excl(), ie by some drivers. > - ifa_scope is RT_SCOPE_LINK > > This covers every column of /proc/net/dev_mcast. AF_PACKET is the > family iproute2 already uses for link-layer addresses ("ip -0"), and > AF_UNSPEC keeps its "all families" meaning from RTM_GETADDR. > > The default FDB dump also walks dev->mc, but only for Ethernet devices > without an ndo_fdb_dump of their own, so bridge, vxlan or macvlan > devices never show their multicast filter there, and it has no users > count or SIOCADDMULTI bit. Extending it would change "bridge fdb show" > output and add NDA_* attributes, while this dump needs no new uAPI. > > There are no legacy users of AF_PACKET requests, so they are always > validated: prefixlen, flags and scope must be zero, no attributes are > accepted, and a non-zero ifa_index restricts the dump to that device. > The dump runs under RCU and netif_addr_lock_bh() and does not need > RTNL. > > Signed-off-by: Yuyang Huang > --- > net/core/rtnetlink.c | 129 +++++++++++++++++++++++++++++++++++++++++++ > 1 file changed, 129 insertions(+) > > diff --git a/net/core/rtnetlink.c b/net/core/rtnetlink.c > index 81c5a6104dea..b2febdb6915e 100644 > --- a/net/core/rtnetlink.c > +++ b/net/core/rtnetlink.c > @@ -4566,6 +4566,133 @@ static int rtnl_dump_all(struct sk_buff *skb, struct netlink_callback *cb) > return skb->len ? : ret; > } > > +static int rtnl_fill_mcaddr(struct sk_buff *skb, const struct net_device *dev, > + const struct netdev_hw_addr *ha, u32 portid, > + u32 seq, unsigned int flags) > +{ > + struct ifaddrmsg *ifm; > + struct nlmsghdr *nlh; > + > + nlh = nlmsg_put(skb, portid, seq, RTM_GETMULTICAST, sizeof(*ifm), > + flags); > + if (!nlh) > + return -EMSGSIZE; > + > + ifm = nlmsg_data(nlh); > + ifm->ifa_family = AF_PACKET; > + ifm->ifa_prefixlen = 0; > + ifm->ifa_flags = ha->global_use ? IFA_F_PERMANENT : 0; I wonder if adding a new attribute IFA_F_GLOBAL would not make the API more understandable. > + ifm->ifa_scope = RT_SCOPE_LINK; > + ifm->ifa_index = dev->ifindex; > + > + if (nla_put(skb, IFA_MULTICAST, dev->addr_len, ha->addr) || > + nla_put_u32(skb, IFA_MC_USERS, ha->refcount)) { > + nlmsg_cancel(skb, nlh); > + return -EMSGSIZE; > + } > + > + nlmsg_end(skb, nlh); > + return 0; > +} > + > +static int rtnl_dump_mcaddr_dev(struct net_device *dev, struct sk_buff *skb, > + struct netlink_callback *cb, int *s_addr_idx, > + unsigned int flags) > +{ > + struct netdev_hw_addr *ha; > + int addr_idx = 0; > + int err = 0; > + > + netif_addr_lock_bh(dev); > + netdev_for_each_mc_addr(ha, dev) { > + if (addr_idx < *s_addr_idx) { > + addr_idx++; > + continue; > + } > + err = rtnl_fill_mcaddr(skb, dev, ha, NETLINK_CB(cb->skb).portid, > + cb->nlh->nlmsg_seq, flags); > + if (err < 0) > + break; > + addr_idx++; > + } > + netif_addr_unlock_bh(dev); > + > + *s_addr_idx = err < 0 ? addr_idx : 0; > + > + return err; > +} > + > +static int rtnl_valid_dump_mcaddr_req(const struct nlmsghdr *nlh, > + struct netlink_ext_ack *extack, > + int *pifindex) > +{ > + struct ifaddrmsg *ifm; > + > + ifm = nlmsg_payload(nlh, sizeof(*ifm)); > + if (!ifm) { > + NL_SET_ERR_MSG(extack, > + "Invalid header for multicast dump request"); > + return -EINVAL; > + } > + > + if (ifm->ifa_prefixlen || ifm->ifa_flags || ifm->ifa_scope) { > + NL_SET_ERR_MSG(extack, > + "Invalid values in multicast dump header"); > + return -EINVAL; > + } > + > + if (nlmsg_attrlen(nlh, sizeof(*ifm))) { > + NL_SET_ERR_MSG(extack, > + "Invalid data after multicast dump header"); > + return -EINVAL; > + } > + > + *pifindex = ifm->ifa_index; > + > + return 0; > +} > + > +static int rtnl_dump_mcaddr(struct sk_buff *skb, struct netlink_callback *cb) > +{ > + struct net *net = sock_net(skb->sk); For consistency with ipv4/ipv6, it would be nice to handle IFA_TARGET_NETNSID. > + unsigned int flags = NLM_F_MULTI; > + struct { > + unsigned long ifindex; > + int addr_idx; > + } *ctx = (void *)cb->ctx; > + struct net_device *dev; > + int ifindex; > + int err; > + > + err = rtnl_valid_dump_mcaddr_req(cb->nlh, cb->extack, &ifindex); > + if (err < 0) > + return err; > + > + rcu_read_lock(); > + > + if (ifindex) { > + cb->answer_flags |= NLM_F_DUMP_FILTERED; > + flags |= NLM_F_DUMP_FILTERED; > + dev = dev_get_by_index_rcu(net, ifindex); > + if (!dev) { > + err = -ENODEV; > + goto out; > + } > + err = rtnl_dump_mcaddr_dev(dev, skb, cb, &ctx->addr_idx, flags); > + goto out; > + } > + > + for_each_netdev_dump(net, dev, ctx->ifindex) { > + err = rtnl_dump_mcaddr_dev(dev, skb, cb, &ctx->addr_idx, > + flags); > + if (err < 0) > + break; > + } > +out: > + rcu_read_unlock(); > + return err; > +} > + > struct sk_buff *rtmsg_ifinfo_build_skb(int type, struct net_device *dev, > unsigned int change, > u32 event, gfp_t flags, int *new_nsid, > @@ -7251,6 +7378,8 @@ static const struct rtnl_msg_handler rtnetlink_rtnl_msg_handlers[] __initconst = > {.msgtype = RTM_SETSTATS, .doit = rtnl_stats_set}, > {.msgtype = RTM_NEWLINKPROP, .doit = rtnl_newlinkprop}, > {.msgtype = RTM_DELLINKPROP, .doit = rtnl_dellinkprop}, > + {.protocol = PF_PACKET, .msgtype = RTM_GETMULTICAST, > + .dumpit = rtnl_dump_mcaddr, .flags = RTNL_FLAG_DUMP_UNLOCKED}, > {.protocol = PF_BRIDGE, .msgtype = RTM_GETLINK, > .dumpit = rtnl_bridge_getlink}, > {.protocol = PF_BRIDGE, .msgtype = RTM_DELLINK,