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

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Date:   Wed, 2 Jan 2019 21:34:28 -0700
From:   David Ahern <dsahern@...il.com>
To:     Ido Schimmel <idosch@...lanox.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>
Cc:     "stephen@...workplumber.org" <stephen@...workplumber.org>
Subject: Re: [PATCH iproute2-next] bridge: fdb: Fix filtering with strict
 checking enabled / disabled

On 1/1/19 12:18 AM, Ido Schimmel wrote:
> 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 I
> --- 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);
>  	}
>  

I like the addition of the flag to rth as a way for commands to know if
the kernel supports strict checking.

Couple of things. first, the patch (at least when I saved it to file)
has html codes in it. New for a patch from you so not sure what
happened. An example:

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 =3D NULL;
        int msg_size =3D sizeof(struct ndmsg);
=20
+       if (!(rth.flags & RTNL_HANDLE_F_STRICT_CHK)) {
+               req.n.nlmsg_len =3D NLMSG_LENGTH(sizeof(struct ifinfomsg));
+               msg_size =3D sizeof(struct ifinfomsg);
+       }
+
        while (argc > 0) {
                if ((strcmp(*argv, "brport") =3D=3D 0) || strcmp(*argv,
"dev") =3D=3D 0)=
 {
                        NEXT_ARG();


Second, the current code after your last patch sets the ifindex in the
ancillary header based on ndmsg versus ifinfomsg. While the offset is
the same, it seems odd and a challenge for future readers that the
master attribute toggles between IFLA and NDA but the struct entry does
not matter.

I think long term the code should be consistent with other dump
commands. I missed neigh and fdb dumps in my first round. Specifically,
removing the req from the list functions and instead using the type
specific dump functions with a filter function that can append to the
request when it makes sense. I have that coded and seems to work fine on
latest kernel and older (4.1). If you have some time another
verification would be great. Thanks,