Subject: [PATCH v2 iproute2-next 4/4] bridge: fdb: enable FDB blackhole feature

From: Hans Schultz <[email-masked]>
Date: Tue, 4 Oct 2022 17:20:36 +0200

Block traffic to a specific host with the command:
bridge fdb add <MAC> vlan <vid> dev br0 blackhole

Blackhole FDB entries can be added, deleted and replaced with
ordinary FDB entries.

Example with output:

$ bridge fdb add 10:10:10:10:10:10 dev br0 blackhole
$ bridge -d fdb show dev br0
10:10:10:10:10:10 vlan 1 blackhole master br0 permanent
10:10:10:10:10:10 blackhole master br0 permanent
$ bridge -d -j -p fdb show dev br0
[ {
        "mac": "10:10:10:10:10:10",
        "vlan": 1,
        "flags": [ "blackhole" ],
        "master": "br0",
        "state": "permanent"
    },{
        "mac": "10:10:10:10:10:10",
        "flags": [ "blackhole" ],
        "master": "br0",
        "state": "permanent"
    } ]

Signed-off-by: Hans Schultz <[email-masked]>
---
 bridge/fdb.c      | 13 ++++++++++++-
 man/man8/bridge.8 | 12 ++++++++++++
 2 files changed, 24 insertions(+), 1 deletion(-)

diff --git a/bridge/fdb.c b/bridge/fdb.c
index f1f0a5bb..1c8c50a8 100644
--- a/bridge/fdb.c
+++ b/bridge/fdb.c
@@ -38,7 +38,7 @@ static void usage(void)
 	fprintf(stderr,
 		"Usage: bridge fdb { add | append | del | replace } ADDR dev DEV\n"
 		"              [ self ] [ master ] [ use ] [ router ] [ extern_learn ]\n"
-		"              [ sticky ] [ local | static | dynamic ] [ vlan VID ]\n"
+		"              [ sticky ] [ local | static | dynamic ] [ blackhole ] [ vlan VID ]\n"
 		"              { [ dst IPADDR ] [ port PORT] [ vni VNI ] | [ nhid NHID ] }\n"
 		"	       [ via DEV ] [ src_vni VNI ]\n"
 		"       bridge fdb [ show [ br BRDEV ] [ brport DEV ] [ vlan VID ]\n"
@@ -116,6 +116,9 @@ static void fdb_print_flags(FILE *fp, unsigned int flags, __u8 ext_flags)
 	if (flags & NTF_STICKY)
 		print_string(PRINT_ANY, NULL, "%s ", "sticky");
 
+	if (ext_flags & NTF_EXT_BLACKHOLE)
+		print_string(PRINT_ANY, NULL, "%s ", "blackhole");
+
 	if (ext_flags & NTF_EXT_LOCKED)
 		print_string(PRINT_ANY, NULL, "%s ", "locked");
 
@@ -421,6 +424,7 @@ static int fdb_modify(int cmd, int flags, int argc, char **argv)
 	char *endptr;
 	short vid = -1;
 	__u32 nhid = 0;
+	__u32 ext_flags = 0;
 
 	while (argc > 0) {
 		if (strcmp(*argv, "dev") == 0) {
@@ -492,6 +496,8 @@ static int fdb_modify(int cmd, int flags, int argc, char **argv)
 			req.ndm.ndm_flags |= NTF_EXT_LEARNED;
 		} else if (matches(*argv, "sticky") == 0) {
 			req.ndm.ndm_flags |= NTF_STICKY;
+		} else if (matches(*argv, "blackhole") == 0) {
+			ext_flags |= NTF_EXT_BLACKHOLE;
 		} else {
 			if (strcmp(*argv, "to") == 0)
 				NEXT_ARG();
@@ -534,6 +540,11 @@ static int fdb_modify(int cmd, int flags, int argc, char **argv)
 	if (dst_ok)
 		addattr_l(&req.n, sizeof(req), NDA_DST, &dst.data, dst.bytelen);
 
+	if (ext_flags &&
+	    addattr_l(&req.n, sizeof(req), NDA_FLAGS_EXT, &ext_flags,
+		      sizeof(ext_flags)) < 0)
+		return -1;
+
 	if (vid >= 0)
 		addattr16(&req.n, sizeof(req), NDA_VLAN, vid);
 	if (nhid > 0)
diff --git a/man/man8/bridge.8 b/man/man8/bridge.8
index f4f1d807..0119a2a9 100644
--- a/man/man8/bridge.8
+++ b/man/man8/bridge.8
@@ -85,6 +85,13 @@ bridge \- show / manipulate bridge addresses and devices
 .B nhid
 .IR NHID " } "
 
+.ti -8
+.BR "bridge fdb" " { " add " | " del " } "
+.I LLADR
+.B dev
+.IR BRDEV " [ "
+.BR self " ] [ " local " ] [ " blackhole " ] "
+
 .ti -8
 .BR "bridge fdb" " [ [ " show " ] [ "
 .B br
@@ -701,6 +708,11 @@ controller learnt dynamic entry. Kernel will not age such an entry.
 - this entry will not change its port due to learning.
 .sp
 
+.B blackhole
+- this entry will silently discard all matching packets. The entry must
+be added as a local permanent entry.
+.sp
+
 .in -8
 The next command line parameters apply only
 when the specified device
-- 
2.34.1