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

[Ido Schimmel]

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 <ido...@mellanox.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