[PATCH net-next v4 4/5] netns: enable to specify a nsid for a get request

[Nicolas Dichtel <nicolas.dichtel@6wind.com>]

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>
---
 net/core/net_namespace.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/net/core/net_namespace.c b/net/core/net_namespace.c
index 885c54197e31..dd25fb22ad45 100644
--- 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;
-- 
2.18.0