nspawn: explicitly remove veth links after use (#3111)

* sd-netlink: permit RTM_DELLINK messages with no ifindex

This is useful for removing network interfaces by name.

* nspawn: explicitly remove veth links we created after use

Sometimes the kernel keeps veth links pinned after the namespace they have been
joined to died. Let's hence explicitly remove veth links after use.

Fixes: #2173

1 files changed, 47 insertions, 0 deletions

diff --git a/src/nspawn/nspawn-network.c b/src/nspawn/nspawn-network.c
index 74a0ae865b..f2b7e4dd79 100644
--- a/src/nspawn/nspawn-network.c
+++ b/src/nspawn/nspawn-network.c
@@ -538,3 +538,50 @@ int veth_extra_parse(char ***l, const char *p) {
         a = b = NULL;
         return 0;
 }
+
+static int remove_one_veth_link(sd_netlink *rtnl, const char *name) {
+        _cleanup_(sd_netlink_message_unrefp) sd_netlink_message *m = NULL;
+        int r;
+
+        if (isempty(name))
+                return 0;
+
+        r = sd_rtnl_message_new_link(rtnl, &m, RTM_DELLINK, 0);
+        if (r < 0)
+                return log_error_errno(r, "Failed to allocate netlink message: %m");
+
+        r = sd_netlink_message_append_string(m, IFLA_IFNAME, name);
+        if (r < 0)
+                return log_error_errno(r, "Failed to add netlink interface name: %m");
+
+        r = sd_netlink_call(rtnl, m, 0, NULL);
+        if (r == -ENODEV) /* Already gone */
+                return 0;
+        if (r < 0)
+                return log_error_errno(r, "Failed to remove veth interface %s: %m", name);
+
+        return 1;
+}
+
+int remove_veth_links(const char *primary, char **pairs) {
+        _cleanup_(sd_netlink_unrefp) sd_netlink *rtnl = NULL;
+        char **a, **b;
+        int r;
+
+        /* In some cases the kernel might pin the veth links between host and container even after the namespace
+         * died. Hence, let's better remove them explicitly too. */
+
+        if (isempty(primary) && strv_isempty(pairs))
+                return 0;
+
+        r = sd_netlink_open(&rtnl);
+        if (r < 0)
+                return log_error_errno(r, "Failed to connect to netlink: %m");
+
+        remove_one_veth_link(rtnl, primary);
+
+        STRV_FOREACH_PAIR(a, b, pairs)
+                remove_one_veth_link(rtnl, *a);
+
+        return 0;
+}