netns: enable to specify a nsid for a get request

Combined with NETNSA_TARGET_NSID, it enables to "translate" a nsid from one
netns to a nsid of another netns.
This is useful when using NETLINK_F_LISTEN_ALL_NSID because it helps the
user to interpret a nsid received from an other netns.

Signed-off-by: Nicolas Dichtel <nicolas.dichtel@6wind.com>
Reviewed-by: David Ahern <dsahern@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/core/net_namespace.c b/net/core/net_namespace.c
index 885c541..dd25fb2 100644 (file)
--- a/net/core/net_namespace.c
+++ b/net/core/net_namespace.c
@@ -797,6 +797,11 @@ static int rtnl_net_getid(struct sk_buff *skb, struct nlmsghdr *nlh,
        } else if (tb[NETNSA_FD]) {
                peer = get_net_ns_by_fd(nla_get_u32(tb[NETNSA_FD]));
                nla = tb[NETNSA_FD];
+       } else if (tb[NETNSA_NSID]) {
+               peer = get_net_ns_by_id(net, nla_get_u32(tb[NETNSA_NSID]));
+               if (!peer)
+                       peer = ERR_PTR(-ENOENT);
+               nla = tb[NETNSA_NSID];
        } else {
                NL_SET_ERR_MSG(extack, "Peer netns reference is missing");
                return -EINVAL;