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route-table: Avoid routes from non-standard routing tables.
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Currently, ovs-vswitchd is subscribed to all the routing changes in the
kernel.  On each change, it marks the internal routing table cache as
invalid, then resets it and dumps all the routes from the kernel from
scratch.  The reason for that is kernel routing updates not being
reliable in a sense that it's hard to tell which route is getting
removed or modified.  Userspace application has to track the order in
which route entries are dumped from the kernel.  Updates can get lost
or even duplicated and the kernel doesn't provide a good mechanism to
distinguish one route from another.  To my knowledge, dumping all the
routes from a kernel after each change is the only way to keep the
cache consistent.  Some more info can be found in the following never
addressed issues:
  https://bugzilla.redhat.com/1337860
  https://bugzilla.redhat.com/1337855

It seems to be believed that NetworkManager "mostly" does incremental
updates right.  But it is still not completely correct, will re-dump
the whole table in certain cases, and it takes a huge amount of very
complicated code to do the accounting and route comparisons.

Going back to ovs-vswitchd, it currently dumps routes from all the
routing tables.  If it will get conflicting routes from multiple
tables, the cache will not be useful.  The routing cache in userspace
is primarily used for checking the egress port for tunneled traffic
and this way also detecting link state changes for a tunnel port.
For userspace datapath it is used for actual routing of the packet
after sending to a native tunnel.
With kernel datapath we don't really have a mechanism to know which
routing table will actually be used by the kernel after encapsulation,
so our lookups on a cache may be incorrect because of this as well.

So, unless all the relevant routes are in the standard tables, the
lookup in userspace route cache is unreliable.

Luckily, most setups are not using any complicated routing in
non-standard tables that OVS has to be aware of.

It is possible, but unlikely, that standard routing tables are
completely empty while some other custom table is not, and all the OVS
tunnel traffic is directed to that table.  That would be the only
scenario where dumping non-standard tables would make sense.  But it
seems like this kind of setup will likely need a way to tell OVS from
which table the routes should be taken, or we'll need to dump routing
rules and keep a separate cache for each table, so we can first match
on rules and then lookup correct routes in a specific table.  I'm not
sure if trying to implement all that is justified.

For now, stop considering routes from non-standard tables to avoid
mixing different tables together and also wasting CPU resources.

This fixes a high CPU usage in ovs-vswitchd in case a BGP daemon is
running on a same host and in a same network namespace with OVS using
its own custom routing table.

Unfortunately, there seems to be no way to tell the kernel to send
updates only for particular tables.  So, we'll still receive and parse
all of them.  But they will not result in a full cache invalidation in
most cases.

Linux kernel v4.20 introduced filtering support for RTM_GETROUTE dumps.
So, we can make use of it and dump only standard tables when we get a
relevant route update.  NETLINK_GET_STRICT_CHK has to be enabled on
the socket for filtering to work.  There is no reason to not enable it
by default, if supported.  It is not used outside of NETLINK_ROUTE.

Fixes: f0e167f ("route-table: Handle route updates more robustly.")
Fixes: ea83a2f ("lib: Show tunnel egress interface in ovsdb")
Reported-at: openvswitch/ovs-issues#185
Reported-at: https://mail.openvswitch.org/pipermail/ovs-discuss/2022-October/052091.html
Acked-by: Aaron Conole <aconole@redhat.com>
Signed-off-by: Ilya Maximets <i.maximets@ovn.org>
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@igsilya
igsilya committed Mar 22, 2024
1 parent 2ecb466 commit dcaae48
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Showing 4 changed files with 147 additions and 16 deletions.
10 changes: 10 additions & 0 deletions lib/netlink-protocol.h
View file
Expand Up @@ -155,6 +155,11 @@ enum {
#define NLA_TYPE_MASK ~(NLA_F_NESTED | NLA_F_NET_BYTEORDER)
#endif

/* Introduced in v4.4. */
#ifndef NLM_F_DUMP_FILTERED
#define NLM_F_DUMP_FILTERED 0x20
#endif

/* These were introduced all together in 2.6.14. (We want our programs to
* support the newer kernel features even if compiled with older headers.) */
#ifndef NETLINK_ADD_MEMBERSHIP
Expand All @@ -168,6 +173,11 @@ enum {
#define NETLINK_LISTEN_ALL_NSID 8
#endif

/* Strict checking of netlink arguments introduced in Linux kernel v4.20. */
#ifndef NETLINK_GET_STRICT_CHK
#define NETLINK_GET_STRICT_CHK 12
#endif

/* These were introduced all together in 2.6.23. (We want our programs to
* support the newer kernel features even if compiled with older headers.) */
#ifndef CTRL_ATTR_MCAST_GRP_MAX
Expand Down
9 changes: 9 additions & 0 deletions lib/netlink-socket.c
View file
Expand Up @@ -205,6 +205,15 @@ nl_sock_create(int protocol, struct nl_sock **sockp)
}
}

/* Strict checking only supported for NETLINK_ROUTE. */
if (protocol == NETLINK_ROUTE
&& setsockopt(sock->fd, SOL_NETLINK, NETLINK_GET_STRICT_CHK,
&one, sizeof one) < 0) {
VLOG_RL(&rl, errno == ENOPROTOOPT ? VLL_DBG : VLL_WARN,
"netlink: could not enable strict checking (%s)",
ovs_strerror(errno));
}

retval = get_socket_rcvbuf(sock->fd);
if (retval < 0) {
retval = -retval;
Expand Down
80 changes: 64 additions & 16 deletions lib/route-table.c
View file
Expand Up @@ -26,6 +26,7 @@
#include <linux/rtnetlink.h>
#include <net/if.h>

#include "coverage.h"
#include "hash.h"
#include "netdev.h"
#include "netlink.h"
Expand All @@ -44,6 +45,8 @@

VLOG_DEFINE_THIS_MODULE(route_table);

COVERAGE_DEFINE(route_table_dump);

struct route_data {
/* Copied from struct rtmsg. */
unsigned char rtm_dst_len;
Expand Down Expand Up @@ -80,7 +83,7 @@ static struct nln_notifier *name_notifier = NULL;

static bool route_table_valid = false;

static int route_table_reset(void);
static void route_table_reset(void);
static void route_table_handle_msg(const struct route_table_msg *);
static int route_table_parse(struct ofpbuf *, struct route_table_msg *);
static void route_table_change(const struct route_table_msg *, void *);
Expand Down Expand Up @@ -153,26 +156,22 @@ route_table_wait(void)
ovs_mutex_unlock(&route_table_mutex);
}

static int
route_table_reset(void)
static bool
route_table_dump_one_table(unsigned char id)
{
struct nl_dump dump;
struct rtgenmsg *rtgenmsg;
uint64_t reply_stub[NL_DUMP_BUFSIZE / 8];
struct ofpbuf request, reply, buf;

route_map_clear();
netdev_get_addrs_list_flush();
route_table_valid = true;
rt_change_seq++;
struct rtmsg *rq_msg;
bool filtered = true;
struct nl_dump dump;

ofpbuf_init(&request, 0);

nl_msg_put_nlmsghdr(&request, sizeof *rtgenmsg, RTM_GETROUTE,
NLM_F_REQUEST);
nl_msg_put_nlmsghdr(&request, sizeof *rq_msg, RTM_GETROUTE, NLM_F_REQUEST);

rtgenmsg = ofpbuf_put_zeros(&request, sizeof *rtgenmsg);
rtgenmsg->rtgen_family = AF_UNSPEC;
rq_msg = ofpbuf_put_zeros(&request, sizeof *rq_msg);
rq_msg->rtm_family = AF_UNSPEC;
rq_msg->rtm_table = id;

nl_dump_start(&dump, NETLINK_ROUTE, &request);
ofpbuf_uninit(&request);
Expand All @@ -182,12 +181,43 @@ route_table_reset(void)
struct route_table_msg msg;

if (route_table_parse(&reply, &msg)) {
struct nlmsghdr *nlmsghdr = nl_msg_nlmsghdr(&reply);

/* Older kernels do not support filtering. */
if (!(nlmsghdr->nlmsg_flags & NLM_F_DUMP_FILTERED)) {
filtered = false;
}
route_table_handle_msg(&msg);
}
}
ofpbuf_uninit(&buf);
nl_dump_done(&dump);

return filtered;
}

static void
route_table_reset(void)
{
unsigned char tables[] = {
RT_TABLE_DEFAULT,
RT_TABLE_MAIN,
RT_TABLE_LOCAL,
};

return nl_dump_done(&dump);
route_map_clear();
netdev_get_addrs_list_flush();
route_table_valid = true;
rt_change_seq++;

COVERAGE_INC(route_table_dump);

for (size_t i = 0; i < ARRAY_SIZE(tables); i++) {
if (!route_table_dump_one_table(tables[i])) {
/* Got unfiltered reply, no need to dump further. */
break;
}
}
}

/* Return RTNLGRP_IPV4_ROUTE or RTNLGRP_IPV6_ROUTE on success, 0 on parse
Expand All @@ -203,6 +233,7 @@ route_table_parse(struct ofpbuf *buf, struct route_table_msg *change)
[RTA_GATEWAY] = { .type = NL_A_U32, .optional = true },
[RTA_MARK] = { .type = NL_A_U32, .optional = true },
[RTA_PREFSRC] = { .type = NL_A_U32, .optional = true },
[RTA_TABLE] = { .type = NL_A_U32, .optional = true },
};

static const struct nl_policy policy6[] = {
Expand All @@ -211,6 +242,7 @@ route_table_parse(struct ofpbuf *buf, struct route_table_msg *change)
[RTA_MARK] = { .type = NL_A_U32, .optional = true },
[RTA_GATEWAY] = { .type = NL_A_IPV6, .optional = true },
[RTA_PREFSRC] = { .type = NL_A_IPV6, .optional = true },
[RTA_TABLE] = { .type = NL_A_U32, .optional = true },
};

struct nlattr *attrs[ARRAY_SIZE(policy)];
Expand All @@ -232,6 +264,7 @@ route_table_parse(struct ofpbuf *buf, struct route_table_msg *change)

if (parsed) {
const struct nlmsghdr *nlmsg;
uint32_t table_id;
int rta_oif; /* Output interface index. */

nlmsg = buf->data;
Expand All @@ -247,6 +280,19 @@ route_table_parse(struct ofpbuf *buf, struct route_table_msg *change)
rtm->rtm_type != RTN_LOCAL) {
change->relevant = false;
}

table_id = rtm->rtm_table;
if (attrs[RTA_TABLE]) {
table_id = nl_attr_get_u32(attrs[RTA_TABLE]);
}
/* Do not consider changes in non-standard routing tables. */
if (table_id
&& table_id != RT_TABLE_DEFAULT
&& table_id != RT_TABLE_MAIN
&& table_id != RT_TABLE_LOCAL) {
change->relevant = false;
}

change->nlmsg_type = nlmsg->nlmsg_type;
change->rd.rtm_dst_len = rtm->rtm_dst_len + (ipv4 ? 96 : 0);
change->rd.local = rtm->rtm_type == RTN_LOCAL;
Expand Down Expand Up @@ -312,7 +358,9 @@ static void
route_table_change(const struct route_table_msg *change OVS_UNUSED,
void *aux OVS_UNUSED)
{
route_table_valid = false;
if (!change || change->relevant) {
route_table_valid = false;
}
}

static void
Expand Down
64 changes: 64 additions & 0 deletions tests/system-route.at
View file
Expand Up @@ -64,3 +64,67 @@ Cached: fc00:db8:beef::13/128 dev br0 GW fc00:db8:cafe::1 SRC fc00:db8:cafe::2])

OVS_TRAFFIC_VSWITCHD_STOP
AT_CLEANUP

dnl Checks that OVS doesn't use routes from non-standard tables.
AT_SETUP([ovs-route - route tables])
AT_KEYWORDS([route])
OVS_TRAFFIC_VSWITCHD_START()

dnl Create tap port.
on_exit 'ip link del p1-route'
AT_CHECK([ip tuntap add name p1-route mode tap])
AT_CHECK([ip link set p1-route up])

dnl Add ip address.
AT_CHECK([ip addr add 10.0.0.17/24 dev p1-route], [0], [stdout])

dnl Check that OVS catches route updates.
OVS_WAIT_UNTIL_EQUAL([ovs-appctl ovs/route/show | grep 'p1-route' | sort], [dnl
Cached: 10.0.0.0/24 dev p1-route SRC 10.0.0.17
Cached: 10.0.0.17/32 dev p1-route SRC 10.0.0.17 local])

dnl Add a route to the main routing table and check that OVS caches
dnl this new route.
AT_CHECK([ip route add 10.0.0.18/32 dev p1-route])
OVS_WAIT_UNTIL_EQUAL([ovs-appctl ovs/route/show | grep 'p1-route' | sort], [dnl
Cached: 10.0.0.0/24 dev p1-route SRC 10.0.0.17
Cached: 10.0.0.17/32 dev p1-route SRC 10.0.0.17 local
Cached: 10.0.0.18/32 dev p1-route SRC 10.0.0.17])

dnl Add a route to a custom routing table and check that OVS doesn't cache it.
AT_CHECK([ip route add 10.0.0.19/32 dev p1-route table 42])
AT_CHECK([ip route show table 42 | grep 'p1-route' | grep -q '10.0.0.19'])
dnl Give the main thread a chance to act.
AT_CHECK([ovs-appctl revalidator/wait])
dnl Check that OVS didn't learn this route.
AT_CHECK([ovs-appctl ovs/route/show | grep 'p1-route' | sort], [0], [dnl
Cached: 10.0.0.0/24 dev p1-route SRC 10.0.0.17
Cached: 10.0.0.17/32 dev p1-route SRC 10.0.0.17 local
Cached: 10.0.0.18/32 dev p1-route SRC 10.0.0.17
])

dnl Delete a route from the main table and check that OVS removes the route
dnl from the cache.
AT_CHECK([ip route del 10.0.0.18/32 dev p1-route])
OVS_WAIT_UNTIL_EQUAL([ovs-appctl ovs/route/show | grep 'p1-route' | sort], [dnl
Cached: 10.0.0.0/24 dev p1-route SRC 10.0.0.17
Cached: 10.0.0.17/32 dev p1-route SRC 10.0.0.17 local])

dnl Delete a route from a custom routing table and check that the cache
dnl dosn't change.
AT_CHECK([ip route del 10.0.0.19/32 dev p1-route table 42])
dnl Give the main thread a chance to act.
AT_CHECK([ovs-appctl revalidator/wait])
dnl Check that the cache is still the same.
AT_CHECK([ovs-appctl ovs/route/show | grep 'p1-route' | sort], [0], [dnl
Cached: 10.0.0.0/24 dev p1-route SRC 10.0.0.17
Cached: 10.0.0.17/32 dev p1-route SRC 10.0.0.17 local
])

dnl Delete ip address.
AT_CHECK([ip addr del 10.0.0.17/24 dev p1-route], [0], [stdout])
dnl Check that routes were removed from OVS.
OVS_WAIT_UNTIL([test $(ovs-appctl ovs/route/show | grep -c 'p1-route') -eq 0 ])

OVS_TRAFFIC_VSWITCHD_STOP
AT_CLEANUP

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