netdev - [PATCH iproute2-next] bridge: fdb: Fix filtering with strict checking enabled / disabled

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Date:   Tue, 1 Jan 2019 07:18:48 +0000
From:   Ido Schimmel <idosch@...lanox.com>
To:     "netdev@...r.kernel.org" <netdev@...r.kernel.org>
CC:     "dsahern@...il.com" <dsahern@...il.com>,
        "stephen@...workplumber.org" <stephen@...workplumber.org>,
        Ido Schimmel <idosch@...lanox.com>
Subject: [PATCH iproute2-next] bridge: fdb: Fix filtering with strict checking
 enabled / disabled

When strict checking is enabled the kernel expects to receive the
ifindex of the bridge device using 'NDA_MASTER', but iproute2 currently
uses 'IFLA_MASTER' which the kernel expects when strict checking is
disabled. Therefore, using iproute2 on current kernels while filtering
on bridge results in the following error:

# bridge fdb show br br0
Error: Unsupported attribute in fdb dump request.
Dump terminated

Additionally, when strict checking is disabled and the bridge is
specified via 'IFLA_MASTER', we need to make sure that the message
length actually corresponds to 'struct ifinfomsg' and a potential
attribute.

Fix this by adding a new flag to the RTNL handle which indicates whether
strict checking is enabled on the socket or not. If it is enabled,
specify 'NDA_MASTER'. Otherwise, specify 'IFLA_MASTER' and set the
message length accordingly.

Tested with and without strict checking on net-next and on older kernels
(v4.18, v4.17, v4.9).

Fixes: 66e8e73edc65 ("bridge: fdb: Use 'struct ndmsg' for FDB dumping")
Fixes: aea41afcfd6d ("ip bridge: Set NETLINK_GET_STRICT_CHK on socket")
Signed-off-by: Ido Schimmel <idosch@...lanox.com>
---
 bridge/fdb.c         | 11 ++++++++++-
 include/libnetlink.h |  1 +
 lib/libnetlink.c     |  6 ++++--
 3 files changed, 15 insertions(+), 3 deletions(-)

diff --git a/bridge/fdb.c b/bridge/fdb.c
index a7a0d8052307..f898b20918fb 100644
--- a/bridge/fdb.c
+++ b/bridge/fdb.c
@@ -271,6 +271,11 @@ static int fdb_show(int argc, char **argv)
 	char *br = NULL;
 	int msg_size = sizeof(struct ndmsg);
 
+	if (!(rth.flags & RTNL_HANDLE_F_STRICT_CHK)) {
+		req.n.nlmsg_len = NLMSG_LENGTH(sizeof(struct ifinfomsg));
+		msg_size = sizeof(struct ifinfomsg);
+	}
+
 	while (argc > 0) {
 		if ((strcmp(*argv, "brport") == 0) || strcmp(*argv, "dev") == 0) {
 			NEXT_ARG();
@@ -304,7 +309,11 @@ static int fdb_show(int argc, char **argv)
 			fprintf(stderr, "Cannot find bridge device \"%s\"\n", br);
 			return -1;
 		}
-		addattr32(&req.n, sizeof(req), IFLA_MASTER, br_ifindex);
+
+		if (rth.flags & RTNL_HANDLE_F_STRICT_CHK)
+			addattr32(&req.n, sizeof(req), NDA_MASTER, br_ifindex);
+		else
+			addattr32(&req.n, sizeof(req), IFLA_MASTER, br_ifindex);
 		msg_size += RTA_LENGTH(4);
 	}
 
diff --git a/include/libnetlink.h b/include/libnetlink.h
index dc0c9c4eb3f5..5c3ef4025d81 100644
--- a/include/libnetlink.h
+++ b/include/libnetlink.h
@@ -23,6 +23,7 @@ struct rtnl_handle {
 	FILE		       *dump_fp;
 #define RTNL_HANDLE_F_LISTEN_ALL_NSID		0x01
 #define RTNL_HANDLE_F_SUPPRESS_NLERR		0x02
+#define RTNL_HANDLE_F_STRICT_CHK		0x04
 	int			flags;
 };
 
diff --git a/lib/libnetlink.c b/lib/libnetlink.c
index 4d7d081054fd..c43efaa8c55b 100644
--- a/lib/libnetlink.c
+++ b/lib/libnetlink.c
@@ -166,8 +166,10 @@ void rtnl_set_strict_dump(struct rtnl_handle *rth)
 {
 	int one = 1;
 
-	setsockopt(rth->fd, SOL_NETLINK, NETLINK_GET_STRICT_CHK,
-		   &one, sizeof(one));
+	if (setsockopt(rth->fd, SOL_NETLINK, NETLINK_GET_STRICT_CHK,
+		       &one, sizeof(one)) < 0)
+		return;
+	rth->flags |= RTNL_HANDLE_F_STRICT_CHK;
 }
 
 void rtnl_close(struct rtnl_handle *rth)
-- 
2.20.1