[lxc-devel] [PATCH 1/1] Fix unprivileged networking
Serge Hallyn
serge.hallyn at ubuntu.com
Wed Feb 19 04:55:12 UTC 2014
Quoting Stéphane Graber (stgraber at ubuntu.com):
> On Tue, Feb 18, 2014 at 04:32:02PM -0600, Serge Hallyn wrote:
> Right, I'd be fine with us just having:
> - lxc discard lxc.network.mtu for unpriv containers
Done implicitly by unpriv users not calling lxc_create_network(),
which calls instantiate_veth() where mtu is set. So unpriv veths
always have mtu set to 1500.
> - lxc-user-nic mirror the bridge mtu to both interfaces of the veth pair
the patch below does that.
> - ensure that privileged lxc will always set the same mtu on both
> interfaces in a veth pair
I was wrong before, that's being done now.
>From 99b3648323a468341f35e84ed9417b344b6fb8a7 Mon Sep 17 00:00:00 2001
From: Serge Hallyn <serge.hallyn at ubuntu.com>
Date: Tue, 18 Feb 2014 22:42:34 -0600
Subject: [PATCH 1/1] network: set mtu of unpriv veth to the bridge's mtu
That's to make sure that if the bridge has a higher than 1500
mtu, the new veth (defaulting to 1500) doesn't lower it.
The netlink get_mtu fn is ugly. If it causes us any problems we should
ditch it in favor of /sys/class/net/$name/mtu.
Signed-off-by: Serge Hallyn <serge.hallyn at ubuntu.com>
---
src/lxc/lxc_user_nic.c | 18 +++++++-
src/lxc/network.c | 110 +++++++++++++++++++++++++++++++++++++++++++++++++
src/lxc/network.h | 1 +
3 files changed, 128 insertions(+), 1 deletion(-)
diff --git a/src/lxc/lxc_user_nic.c b/src/lxc/lxc_user_nic.c
index a67c63d..0e66549 100644
--- a/src/lxc/lxc_user_nic.c
+++ b/src/lxc/lxc_user_nic.c
@@ -226,12 +226,18 @@ static int instanciate_veth(char *n1, char **n2)
return netdev_set_flag(n1, IFF_UP);
}
+static int get_mtu(char *name)
+{
+ int idx = if_nametoindex(name);
+ return netdev_get_mtu(idx);
+}
+
static bool create_nic(char *nic, char *br, int pid, char **cnic)
{
char *veth1buf, *veth2buf;
veth1buf = alloca(IFNAMSIZ);
veth2buf = alloca(IFNAMSIZ);
- int ret;
+ int ret, mtu;
ret = snprintf(veth1buf, IFNAMSIZ, "%s", nic);
if (ret < 0 || ret >= IFNAMSIZ) {
@@ -245,6 +251,16 @@ static bool create_nic(char *nic, char *br, int pid, char **cnic)
return false;
}
+ /* copy the bridge's mtu to both ends */
+ mtu = get_mtu(br);
+ if (mtu != -1) {
+ if (lxc_netdev_set_mtu(veth1buf, mtu) < 0 ||
+ lxc_netdev_set_mtu(veth2buf, mtu) < 0) {
+ fprintf(stderr, "Failed setting mtu\n");
+ goto out_del;
+ }
+ }
+
/* attach veth1 to bridge */
if (lxc_bridge_attach(br, veth1buf) < 0) {
fprintf(stderr, "Error attaching %s to %s\n", veth1buf, br);
diff --git a/src/lxc/network.c b/src/lxc/network.c
index 34845d1..090b9bd 100644
--- a/src/lxc/network.c
+++ b/src/lxc/network.c
@@ -297,6 +297,116 @@ out:
return err;
}
+int netdev_get_mtu(int ifindex)
+{
+ struct nl_handler nlh;
+ struct nlmsg *nlmsg = NULL, *answer = NULL;
+ struct ip_req *ip_req;
+ struct nlmsghdr *msg;
+ int err, res;
+ int recv_len = 0, answer_len;
+ int readmore = 0;
+
+ err = netlink_open(&nlh, NETLINK_ROUTE);
+ if (err)
+ return err;
+
+ err = -ENOMEM;
+ nlmsg = nlmsg_alloc(NLMSG_GOOD_SIZE);
+ if (!nlmsg)
+ goto out;
+
+ answer = nlmsg_alloc(NLMSG_GOOD_SIZE);
+ if (!answer)
+ goto out;
+
+ /* Save the answer buffer length, since it will be overwritten
+ * on the first receive (and we might need to receive more than
+ * once. */
+ answer_len = answer->nlmsghdr.nlmsg_len;
+
+ ip_req = (struct ip_req *)nlmsg;
+ ip_req->nlmsg.nlmsghdr.nlmsg_len =
+ NLMSG_LENGTH(sizeof(struct ifaddrmsg));
+ ip_req->nlmsg.nlmsghdr.nlmsg_flags = NLM_F_REQUEST|NLM_F_DUMP;
+ ip_req->nlmsg.nlmsghdr.nlmsg_type = RTM_GETLINK;
+ ip_req->ifa.ifa_family = AF_UNSPEC;
+
+ /* Send the request for addresses, which returns all addresses
+ * on all interfaces. */
+ err = netlink_send(&nlh, nlmsg);
+ if (err < 0)
+ goto out;
+
+ do {
+ /* Restore the answer buffer length, it might have been
+ * overwritten by a previous receive. */
+ answer->nlmsghdr.nlmsg_len = answer_len;
+
+ /* Get the (next) batch of reply messages */
+ err = netlink_rcv(&nlh, answer);
+ if (err < 0)
+ goto out;
+
+ recv_len = err;
+ err = 0;
+
+ /* Satisfy the typing for the netlink macros */
+ msg = &answer->nlmsghdr;
+
+ while (NLMSG_OK(msg, recv_len)) {
+
+ /* Stop reading if we see an error message */
+ if (msg->nlmsg_type == NLMSG_ERROR) {
+ struct nlmsgerr *errmsg = (struct nlmsgerr*)NLMSG_DATA(msg);
+ err = errmsg->error;
+ goto out;
+ }
+
+ /* Stop reading if we see a NLMSG_DONE message */
+ if (msg->nlmsg_type == NLMSG_DONE) {
+ readmore = 0;
+ break;
+ }
+
+ struct ifinfomsg *ifi = NLMSG_DATA(msg);
+ if (ifi->ifi_index == ifindex) {
+ struct rtattr *rta = IFLA_RTA(ifi);
+ int attr_len = msg->nlmsg_len - NLMSG_LENGTH(sizeof(*ifi));
+ res = 0;
+ while(RTA_OK(rta, attr_len)) {
+ /* Found a local address for the requested interface,
+ * return it. */
+ if (rta->rta_type == IFLA_MTU) {
+ memcpy(&res, RTA_DATA(rta), sizeof(int));
+ err = res;
+ goto out;
+ }
+ rta = RTA_NEXT(rta, attr_len);
+ }
+
+ }
+
+ /* Keep reading more data from the socket if the
+ * last message had the NLF_F_MULTI flag set */
+ readmore = (msg->nlmsg_flags & NLM_F_MULTI);
+
+ /* Look at the next message received in this buffer */
+ msg = NLMSG_NEXT(msg, recv_len);
+ }
+ } while (readmore);
+
+ /* If we end up here, we didn't find any result, so signal an
+ * error */
+ err = -1;
+
+out:
+ netlink_close(&nlh);
+ nlmsg_free(answer);
+ nlmsg_free(nlmsg);
+ return err;
+}
+
int lxc_netdev_set_mtu(const char *name, int mtu)
{
struct nl_handler nlh;
diff --git a/src/lxc/network.h b/src/lxc/network.h
index 3ea99ac..97f6b4d 100644
--- a/src/lxc/network.h
+++ b/src/lxc/network.h
@@ -138,4 +138,5 @@ extern char *lxc_mkifname(char *template);
extern const char *lxc_net_type_to_str(int type);
extern int setup_private_host_hw_addr(char *veth1);
+extern int netdev_get_mtu(int ifindex);
#endif
--
1.9.rc1
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