[PATCH net-next v6 0/4] rtnetlink: dump link-layer multicast addresses

[PATCH net-next v6 0/4] rtnetlink: dump link-layer multicast addresses

[Yuyang Huang]

"ip maddr show" prints link-layer, IPv4 and IPv6 entries. The IPv4 and
IPv6 ones come over netlink today, with IFA_MC_USERS for the user count.
The link-layer list, dev->mc, is only exported via /proc/net/dev_mcast,
so iproute2 and other users still parse procfs for it.

This series adds the AF_PACKET family to RTM_GETMULTICAST so that the
link-layer multicast addresses are reported the same way. Patch 2 dumps
dev->mc in the ifaddrmsg format of the IPv4 and IPv6 dumps: IFA_MULTICAST
carries the address, IFA_MC_USERS the reference count and a new
IFA_F_GLOBAL flag marks entries added explicitly, the "static" column of
/proc/net/dev_mcast. ifa_index limits the dump to one device and
IFA_TARGET_NETNSID selects another netns. Patches 1 and 3 update the
rt-addr spec and patch 4 adds a selftest.

AF_PACKET dumps returned -EOPNOTSUPP before, so iproute2 can keep the
procfs fallback for older kernels. The iproute2 side is ready and will
be posted once this is in.

Changes in v6:
- Move the dump to net/core/dev_addr_lists.c next to the dev->mc
  helpers
- Stamp cb->seq from dev_base_seq and check dump consistency
- Let an unexpected dump error propagate instead of skipping
- Check for an address only present in the peer netns in the
  target-netnsid selftest, the peer and local ifindex can be equal
- Document the ifa-index filter and the zero header fields in the spec

Changes in v5:
- Filter the target-netnsid selftest dump by ifa-index, a new netns
  also contains the fallback tunnel devices

Changes in v4:
- Reset the resume offset when the device the dump stopped at is gone
- Use a tracked netns reference (put_net_track)
- Say ifa-family must be set in the spec doc, drop the AF_UNSPEC remark
- Close the netlink socket and guard the checks in the selftest
- Drop the Fixes tag

Changes in v3:
- Report the static bit as a new IFA_F_GLOBAL flag in IFA_FLAGS
  instead of IFA_F_PERMANENT
- Support IFA_TARGET_NETNSID and test it
- Describe global_use accurately, it is also set by dev_mc_add_excl()
- Fix the target-netnsid type in the rt-addr spec, as its own patch

Changes in v2:
- Always validate the request header, not only with strict checking
- Use a single "with" statement in the selftest (ruff)

Yuyang Huang (4):
  netlink: specs: rt-addr: fix the type of target-netnsid
  net: add AF_PACKET multicast dumps
  netlink: specs: rt-addr: document AF_PACKET multicast dumps
  selftests: net: test AF_PACKET multicast dumps

 Documentation/netlink/specs/rt-addr.yaml |  19 ++-
 include/linux/netdevice.h                |   1 +
 include/uapi/linux/if_addr.h             |   1 +
 net/core/dev_addr_lists.c                | 177 +++++++++++++++++++++++
 net/core/rtnetlink.c                     |   2 +
 tools/testing/selftests/net/rtnetlink.py |  73 +++++++++-
 6 files changed, 268 insertions(+), 5 deletions(-)

-- 
2.43.0

[PATCH net-next v6 1/4] netlink: specs: rt-addr: fix the type of target-netnsid

[Yuyang Huang]

The kernel parses IFA_TARGET_NETNSID as NLA_S32 and rt-link.yaml
declares its target-netnsid as s32, but rt-addr.yaml has it as binary.

Signed-off-by: Yuyang Huang <sigefriedhyy@gmail.com>
Reviewed-by: Nicolas Dichtel <nicolas.dichtel@6wind.com>
---
 Documentation/netlink/specs/rt-addr.yaml | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/Documentation/netlink/specs/rt-addr.yaml b/Documentation/netlink/specs/rt-addr.yaml
index 0ecbd24c890c..17ead2203451 100644
--- a/Documentation/netlink/specs/rt-addr.yaml
+++ b/Documentation/netlink/specs/rt-addr.yaml
@@ -119,7 +119,7 @@ attribute-sets:
         type: u32
       -
         name: target-netnsid
-        type: binary
+        type: s32
       -
         name: proto
         type: u8
-- 
2.43.0

[PATCH net-next v6 2/4] net: add AF_PACKET multicast dumps

[Yuyang Huang]

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 next to
the dev->mc helpers in dev_addr_lists.c 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_GLOBAL in IFA_FLAGS reports netdev_hw_addr::global_use, set
    by dev_mc_add_global() (SIOCADDMULTI) and dev_mc_add_excl()
    ("bridge fdb add ... self"), i.e. entries added explicitly rather
    than by a protocol join. This is the static column of
    /proc/net/dev_mcast
  - 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").

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 global_use bit. Extending it would change "bridge fdb show"
output and add NDA_* attributes.

Requests are always validated, there are no legacy users: prefixlen,
flags and scope must be zero, ifa_index selects one device and
IFA_TARGET_NETNSID is the only attribute accepted. The dump runs under
RCU and netif_addr_lock_bh() without RTNL, and stamps cb->seq from
dev_base_seq so a device added or removed between dump rounds sets
NLM_F_DUMP_INTR.

Signed-off-by: Yuyang Huang <sigefriedhyy@gmail.com>
Reviewed-by: Nicolas Dichtel <nicolas.dichtel@6wind.com>
---
 include/linux/netdevice.h    |   1 +
 include/uapi/linux/if_addr.h |   1 +
 net/core/dev_addr_lists.c    | 177 +++++++++++++++++++++++++++++++++++
 net/core/rtnetlink.c         |   2 +
 4 files changed, 181 insertions(+)

diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
index 1f0710eef185..d469aba057c7 100644
--- a/include/linux/netdevice.h
+++ b/include/linux/netdevice.h
@@ -5169,6 +5169,7 @@ int dev_mc_sync_multiple(struct net_device *to, struct net_device *from);
 void dev_mc_unsync(struct net_device *to, struct net_device *from);
 void dev_mc_flush(struct net_device *dev);
 void dev_mc_init(struct net_device *dev);
+int dev_mc_dump(struct sk_buff *skb, struct netlink_callback *cb);
 
 /**
  *  __dev_mc_sync - Synchronize device's multicast list
diff --git a/include/uapi/linux/if_addr.h b/include/uapi/linux/if_addr.h
index 7fb630b7fe31..0a1ad9ebb47b 100644
--- a/include/uapi/linux/if_addr.h
+++ b/include/uapi/linux/if_addr.h
@@ -57,6 +57,7 @@ enum {
 #define IFA_F_NOPREFIXROUTE	0x200
 #define IFA_F_MCAUTOJOIN	0x400
 #define IFA_F_STABLE_PRIVACY	0x800
+#define IFA_F_GLOBAL		0x1000
 
 struct ifa_cacheinfo {
 	__u32	ifa_prefered;
diff --git a/net/core/dev_addr_lists.c b/net/core/dev_addr_lists.c
index 08528ca0a8b3..b69565f8ff05 100644
--- a/net/core/dev_addr_lists.c
+++ b/net/core/dev_addr_lists.c
@@ -10,8 +10,12 @@
 #include <linux/netdevice.h>
 #include <linux/rtnetlink.h>
 #include <linux/export.h>
+#include <linux/if_addr.h>
 #include <linux/list.h>
 #include <linux/spinlock.h>
+#include <net/netlink.h>
+#include <net/rtnetlink.h>
+#include <net/sock.h>
 #include <kunit/visibility.h>
 
 #include "dev.h"
@@ -1180,6 +1184,179 @@ void dev_mc_init(struct net_device *dev)
 }
 EXPORT_SYMBOL(dev_mc_init);
 
+static int dev_mc_fill_addr(struct sk_buff *skb, const struct net_device *dev,
+			    const struct netdev_hw_addr *ha, u32 portid,
+			    u32 seq, unsigned int flags, int netnsid)
+{
+	u32 ifa_flags = ha->global_use ? IFA_F_GLOBAL : 0;
+	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 holds 8 bits, the full value is in IFA_FLAGS */
+	ifm->ifa_flags = (__u8)ifa_flags;
+	ifm->ifa_scope = RT_SCOPE_LINK;
+	ifm->ifa_index = dev->ifindex;
+
+	if ((netnsid >= 0 &&
+	     nla_put_s32(skb, IFA_TARGET_NETNSID, netnsid)) ||
+	    nla_put(skb, IFA_MULTICAST, dev->addr_len, ha->addr) ||
+	    nla_put_u32(skb, IFA_MC_USERS, ha->refcount) ||
+	    nla_put_u32(skb, IFA_FLAGS, ifa_flags)) {
+		nlmsg_cancel(skb, nlh);
+		return -EMSGSIZE;
+	}
+
+	nlmsg_end(skb, nlh);
+	return 0;
+}
+
+static int dev_mc_dump_dev(struct net_device *dev, struct sk_buff *skb,
+			   struct netlink_callback *cb, int *s_addr_idx,
+			   unsigned int flags, int netnsid)
+{
+	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 = dev_mc_fill_addr(skb, dev, ha, NETLINK_CB(cb->skb).portid,
+				       cb->nlh->nlmsg_seq, flags, netnsid);
+		if (err < 0)
+			break;
+		nl_dump_check_consistent(cb, nlmsg_hdr(skb));
+		addr_idx++;
+	}
+	netif_addr_unlock_bh(dev);
+
+	*s_addr_idx = err < 0 ? addr_idx : 0;
+
+	return err;
+}
+
+struct dev_mc_dump_filter {
+	struct net *tgt_net;
+	netns_tracker ns_tracker;
+	int netnsid;
+	int ifindex;
+};
+
+static const struct nla_policy dev_mc_dump_policy[IFA_MAX + 1] = {
+	[IFA_TARGET_NETNSID]	= { .type = NLA_S32 },
+};
+
+static int dev_mc_valid_dump_req(const struct nlmsghdr *nlh, struct sock *sk,
+				 struct dev_mc_dump_filter *filter,
+				 struct netlink_ext_ack *extack)
+{
+	struct nlattr *tb[IFA_MAX + 1];
+	struct ifaddrmsg *ifm;
+	int err;
+
+	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;
+	}
+
+	err = nlmsg_parse(nlh, sizeof(*ifm), tb, IFA_MAX,
+			  dev_mc_dump_policy, extack);
+	if (err < 0)
+		return err;
+
+	if (tb[IFA_TARGET_NETNSID]) {
+		struct net *net;
+
+		filter->netnsid = nla_get_s32(tb[IFA_TARGET_NETNSID]);
+		net = rtnl_get_net_ns_capable(sk, filter->netnsid);
+		if (IS_ERR(net)) {
+			NL_SET_ERR_MSG(extack,
+				       "Invalid target network namespace id");
+			return PTR_ERR(net);
+		}
+		netns_tracker_alloc(net, &filter->ns_tracker, GFP_KERNEL);
+		filter->tgt_net = net;
+	}
+
+	filter->ifindex = ifm->ifa_index;
+
+	return 0;
+}
+
+int dev_mc_dump(struct sk_buff *skb, struct netlink_callback *cb)
+{
+	struct dev_mc_dump_filter filter = {
+		.tgt_net = sock_net(skb->sk),
+		.netnsid = -1,
+	};
+	unsigned int flags = NLM_F_MULTI;
+	struct {
+		unsigned long ifindex;
+		int addr_idx;
+	} *ctx = (void *)cb->ctx;
+	unsigned long s_ifindex;
+	struct net_device *dev;
+	int err;
+
+	err = dev_mc_valid_dump_req(cb->nlh, skb->sk, &filter, cb->extack);
+	if (err < 0)
+		return err;
+
+	cb->seq = READ_ONCE(filter.tgt_net->dev_base_seq);
+
+	rcu_read_lock();
+
+	if (filter.ifindex) {
+		cb->answer_flags |= NLM_F_DUMP_FILTERED;
+		flags |= NLM_F_DUMP_FILTERED;
+		dev = dev_get_by_index_rcu(filter.tgt_net, filter.ifindex);
+		if (!dev) {
+			err = -ENODEV;
+			goto out;
+		}
+		err = dev_mc_dump_dev(dev, skb, cb, &ctx->addr_idx, flags,
+				      filter.netnsid);
+		goto out;
+	}
+
+	s_ifindex = ctx->ifindex;
+	for_each_netdev_dump(filter.tgt_net, dev, ctx->ifindex) {
+		/* The device the dump stopped at is gone, do not skip
+		 * entries of the next one.
+		 */
+		if (dev->ifindex != s_ifindex)
+			ctx->addr_idx = 0;
+		err = dev_mc_dump_dev(dev, skb, cb, &ctx->addr_idx, flags,
+				      filter.netnsid);
+		if (err < 0)
+			break;
+	}
+out:
+	rcu_read_unlock();
+	if (filter.netnsid >= 0)
+		put_net_track(filter.tgt_net, &filter.ns_tracker);
+	return err;
+}
+
 static int netif_addr_lists_snapshot(struct net_device *dev,
 				     struct netdev_hw_addr_list *uc_snap,
 				     struct netdev_hw_addr_list *mc_snap,
diff --git a/net/core/rtnetlink.c b/net/core/rtnetlink.c
index e3444fd24061..204dc9040e3c 100644
--- a/net/core/rtnetlink.c
+++ b/net/core/rtnetlink.c
@@ -7278,6 +7278,8 @@ 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 = dev_mc_dump, .flags = RTNL_FLAG_DUMP_UNLOCKED},
 	{.protocol = PF_BRIDGE, .msgtype = RTM_GETLINK,
 	 .dumpit = rtnl_bridge_getlink},
 	{.protocol = PF_BRIDGE, .msgtype = RTM_DELLINK,
-- 
2.43.0

[PATCH net-next v6 3/4] netlink: specs: rt-addr: document AF_PACKET multicast dumps

[Yuyang Huang]

Add the global flag, list the attributes the AF_PACKET dump uses and
describe how ifa-family selects IPv4, IPv6 or link-layer output for
RTM_GETMULTICAST.

Signed-off-by: Yuyang Huang <sigefriedhyy@gmail.com>
Reviewed-by: Nicolas Dichtel <nicolas.dichtel@6wind.com>
---
 Documentation/netlink/specs/rt-addr.yaml | 17 +++++++++++++++--
 1 file changed, 15 insertions(+), 2 deletions(-)

diff --git a/Documentation/netlink/specs/rt-addr.yaml b/Documentation/netlink/specs/rt-addr.yaml
index 17ead2203451..dc5c0ce259ba 100644
--- a/Documentation/netlink/specs/rt-addr.yaml
+++ b/Documentation/netlink/specs/rt-addr.yaml
@@ -77,6 +77,8 @@ definitions:
         name: mcautojoin
       -
         name: stable-privacy
+      -
+        name: global
 
 attribute-sets:
   -
@@ -168,7 +170,15 @@ operations:
           attributes: *ifaddr-all
     -
       name: getmulticast
-      doc: Get / dump IPv4/IPv6 multicast addresses.
+      doc: |
+        Get / dump multicast addresses. ifa-family must select the address
+        family: AF_INET or AF_INET6 for the IP multicast groups joined on
+        a device, AF_PACKET for the link-layer multicast addresses in the
+        device filter. Link-layer entries added explicitly, e.g. with
+        SIOCADDMULTI or "bridge fdb add ... self", rather than by a
+        protocol join are reported with the global flag set. A non-zero
+        ifa-index restricts the dump to that device, ifa-prefixlen,
+        ifa-flags and ifa-scope must be zero.
       attribute-set: addr-attrs
       fixed-header: ifaddrmsg
       do:
@@ -181,10 +191,13 @@ operations:
             - multicast
             - mc-users
             - cacheinfo
+            - flags
+            - target-netnsid
       dump:
         request:
           value: 58
-          attributes: []
+          attributes:
+            - target-netnsid
         reply:
           value: 58
           attributes: *mcaddr-attrs
-- 
2.43.0

[PATCH net-next v6 4/4] selftests: net: test AF_PACKET multicast dumps

[Yuyang Huang]

Dump the link-layer multicast addresses of a dummy device and verify
that ifa_index restricts the dump to that device, that the all-hosts
address joined on link up is listed without IFA_F_GLOBAL, that an
address added with SIOCADDMULTI is listed with IFA_F_GLOBAL and
IFA_MC_USERS, and that IFA_TARGET_NETNSID dumps another netns.

Signed-off-by: Yuyang Huang <sigefriedhyy@gmail.com>
Reviewed-by: Nicolas Dichtel <nicolas.dichtel@6wind.com>
---
 tools/testing/selftests/net/rtnetlink.py | 73 +++++++++++++++++++++++-
 1 file changed, 71 insertions(+), 2 deletions(-)

diff --git a/tools/testing/selftests/net/rtnetlink.py b/tools/testing/selftests/net/rtnetlink.py
index dc8c77db4897..5534ade056a5 100755
--- a/tools/testing/selftests/net/rtnetlink.py
+++ b/tools/testing/selftests/net/rtnetlink.py
@@ -5,13 +5,18 @@ import socket
 import struct
 import time
 from lib.py import bkg, ip, ksft_exit, ksft_run, ksft_eq, ksft_ge, ksft_true, KsftSkipEx
-from lib.py import ksft_not_in, ksft_not_none
+from lib.py import ksft_in, ksft_not_in, ksft_not_none
 from lib.py import CmdExitFailure, NetNS, NetNSEnter, RtnlAddrFamily, RtnlRouteFamily
 from lib.py import defer
 
 IPV4_ALL_HOSTS_MULTICAST = b'\xe0\x00\x00\x01'
 IPV4_TEST_MULTICAST = b'\xef\x01\x01\x01'
 IPV6_TEST_MULTICAST = bytes.fromhex('ff020000000000000000000000000123')
+ETH_ALL_HOSTS_MULTICAST = bytes.fromhex('01005e000001')
+ETH_TEST_MULTICAST_STR = '01:00:5e:01:01:01'
+ETH_TEST_MULTICAST = bytes.fromhex(ETH_TEST_MULTICAST_STR.replace(':', ''))
+ETH_PEER_MULTICAST_STR = '01:00:5e:02:02:02'
+ETH_PEER_MULTICAST = bytes.fromhex(ETH_PEER_MULTICAST_STR.replace(':', ''))
 
 
 def _users_for(rtnl: RtnlAddrFamily, family: int, grp: bytes, ifindex: int):
@@ -105,6 +110,69 @@ def dump_mcaddr6_check() -> None:
                 s2.close()
 
 
+def dump_mcaddr_l2_check() -> None:
+    """
+    Verify link-layer multicast addresses in an AF_PACKET RTM_GETMULTICAST
+    dump: the ifa-index filter, mc-users, the global flag and
+    target-netnsid.
+    """
+
+    with NetNS() as ns, NetNSEnter(str(ns)):
+        for ifname in ("dummy1", "dummy2"):
+            ip(f"link add name {ifname} type dummy")
+            ip(f"link set {ifname} up")
+        dev_idx = socket.if_nametoindex("dummy1")
+        ip(f"maddr add {ETH_TEST_MULTICAST_STR} dev dummy1")
+
+        rtnl = RtnlAddrFamily()
+        defer(rtnl.close)
+        addresses = rtnl.getmulticast(
+            {"ifa-family": socket.AF_PACKET, "ifa-index": dev_idx},
+            dump=True)
+
+        # dummy2 has entries as well, only dummy1 may be listed
+        ksft_eq({addr['ifa-index'] for addr in addresses}, {dev_idx},
+                "AF_PACKET multicast dump ignored ifa-index filter")
+
+        entries = {addr['multicast']: addr for addr in addresses}
+
+        # Bringing an Ethernet device up joins 224.0.0.1, which maps
+        # to 01:00:5e:00:00:01 in the device multicast list.
+        all_hosts = entries.get(ETH_ALL_HOSTS_MULTICAST)
+        ksft_not_none(all_hosts,
+                      "dummy1 does not have the all-hosts link-layer address")
+        if all_hosts is not None:
+            ksft_not_in('global', all_hosts['flags'],
+                        "protocol entry is global")
+
+        static = entries.get(ETH_TEST_MULTICAST)
+        ksft_not_none(static, "dummy1 does not have the SIOCADDMULTI address")
+        if static is not None:
+            ksft_eq(static['mc-users'], 1,
+                    "unexpected mc-users for the SIOCADDMULTI address")
+            ksft_in('global', static['flags'],
+                    "SIOCADDMULTI entry is not global")
+
+        # target-netnsid dumps another netns, ifa-index is relative to it
+        with NetNS() as peer:
+            ip(f"netns set {peer} 5")
+            ip("link add name dummy3 type dummy", ns=peer)
+            ip("link set dummy3 up", ns=peer)
+            ip(f"maddr add {ETH_PEER_MULTICAST_STR} dev dummy3", ns=peer)
+            peer_idx = ip("link show dummy3", json=True, ns=peer)[0]['ifindex']
+
+            addresses = rtnl.getmulticast(
+                {"ifa-family": socket.AF_PACKET, "target-netnsid": 5,
+                 "ifa-index": peer_idx}, dump=True)
+            ksft_eq({(addr['ifa-index'], addr['target-netnsid'])
+                     for addr in addresses}, {(peer_idx, 5)},
+                    "target-netnsid did not dump the peer netns")
+            # dummy1 in this netns can have the same ifindex as dummy3
+            ksft_in(ETH_PEER_MULTICAST,
+                    {addr['multicast'] for addr in addresses},
+                    "target-netnsid did not dump the peer device")
+
+
 def ipv4_devconf_notify() -> None:
     """
     Configure an interface and set ipv4-devconf values through netlink
@@ -424,7 +492,8 @@ def ipv6_verify_inter_scope_addr_order() -> None:
 
 
 def main() -> None:
-    ksft_run([dump_mcaddr_check, dump_mcaddr6_check, ipv4_devconf_notify,
+    ksft_run([dump_mcaddr_check, dump_mcaddr6_check, dump_mcaddr_l2_check,
+              ipv4_devconf_notify,
               ipv6_route_del_reason_expired,
               ipv6_route_del_reason_ra_withdrawn,
               ipv6_route_del_reason_absent,
-- 
2.43.0

Re: [PATCH net-next v6 2/4] net: add AF_PACKET multicast dumps

[Nicolas Dichtel]

Le 22/09/2026 à 01:59, 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 next to
> the dev->mc helpers in dev_addr_lists.c 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_GLOBAL in IFA_FLAGS reports netdev_hw_addr::global_use, set
>     by dev_mc_add_global() (SIOCADDMULTI) and dev_mc_add_excl()
>     ("bridge fdb add ... self"), i.e. entries added explicitly rather
>     than by a protocol join. This is the static column of
>     /proc/net/dev_mcast
>   - 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").
> 
> 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 global_use bit. Extending it would change "bridge fdb show"
> output and add NDA_* attributes.
> 
> Requests are always validated, there are no legacy users: prefixlen,
> flags and scope must be zero, ifa_index selects one device and
> IFA_TARGET_NETNSID is the only attribute accepted. The dump runs under
> RCU and netif_addr_lock_bh() without RTNL, and stamps cb->seq from
> dev_base_seq so a device added or removed between dump rounds sets
> NLM_F_DUMP_INTR.
> 
> Signed-off-by: Yuyang Huang <sigefriedhyy@gmail.com>
> Reviewed-by: Nicolas Dichtel <nicolas.dichtel@6wind.com>
> ---
[snip]

> +static int dev_mc_dump_dev(struct net_device *dev, struct sk_buff *skb,
> +			   struct netlink_callback *cb, int *s_addr_idx,
> +			   unsigned int flags, int netnsid)
> +{
> +	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 = dev_mc_fill_addr(skb, dev, ha, NETLINK_CB(cb->skb).portid,
> +				       cb->nlh->nlmsg_seq, flags, netnsid);
> +		if (err < 0)
> +			break;
> +		nl_dump_check_consistent(cb, nlmsg_hdr(skb));
> +		addr_idx++;
> +	}
> +	netif_addr_unlock_bh(dev);
> +
> +	*s_addr_idx = err < 0 ? addr_idx : 0;
> +
> +	return err;
> +}
[snip]

> +int dev_mc_dump(struct sk_buff *skb, struct netlink_callback *cb)
> +{
> +	struct dev_mc_dump_filter filter = {
> +		.tgt_net = sock_net(skb->sk),
> +		.netnsid = -1,
> +	};
> +	unsigned int flags = NLM_F_MULTI;
> +	struct {
> +		unsigned long ifindex;
> +		int addr_idx;
> +	} *ctx = (void *)cb->ctx;
> +	unsigned long s_ifindex;
> +	struct net_device *dev;
> +	int err;
> +
> +	err = dev_mc_valid_dump_req(cb->nlh, skb->sk, &filter, cb->extack);
> +	if (err < 0)
> +		return err;
> +
> +	cb->seq = READ_ONCE(filter.tgt_net->dev_base_seq);
dev_base_seq only indicates whether the netdevice list has changed, not whether
the addr list has changed. It's only a partial consistency check.
See inet_base_seq()/inet6_base_seq().

I don't see an equivalent of dev_addr_genid for the L2 mcaddr list; it should
probably be added.