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Message-Id: <20200513094419.336724064@linuxfoundation.org>
Date: Wed, 13 May 2020 11:43:57 +0200
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: linux-kernel@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
stable@...r.kernel.org,
Nikolay Aleksandrov <nikolay@...ulusnetworks.com>,
David Ahern <dsahern@...nel.org>,
"David S. Miller" <davem@...emloft.net>
Subject: [PATCH 5.6 018/118] ipv6: Use global sernum for dst validation with nexthop objects
From: David Ahern <dsahern@...nel.org>
[ Upstream commit 8f34e53b60b337e559f1ea19e2780ff95ab2fa65 ]
Nik reported a bug with pcpu dst cache when nexthop objects are
used illustrated by the following:
$ ip netns add foo
$ ip -netns foo li set lo up
$ ip -netns foo addr add 2001:db8:11::1/128 dev lo
$ ip netns exec foo sysctl net.ipv6.conf.all.forwarding=1
$ ip li add veth1 type veth peer name veth2
$ ip li set veth1 up
$ ip addr add 2001:db8:10::1/64 dev veth1
$ ip li set dev veth2 netns foo
$ ip -netns foo li set veth2 up
$ ip -netns foo addr add 2001:db8:10::2/64 dev veth2
$ ip -6 nexthop add id 100 via 2001:db8:10::2 dev veth1
$ ip -6 route add 2001:db8:11::1/128 nhid 100
Create a pcpu entry on cpu 0:
$ taskset -a -c 0 ip -6 route get 2001:db8:11::1
Re-add the route entry:
$ ip -6 ro del 2001:db8:11::1
$ ip -6 route add 2001:db8:11::1/128 nhid 100
Route get on cpu 0 returns the stale pcpu:
$ taskset -a -c 0 ip -6 route get 2001:db8:11::1
RTNETLINK answers: Network is unreachable
While cpu 1 works:
$ taskset -a -c 1 ip -6 route get 2001:db8:11::1
2001:db8:11::1 from :: via 2001:db8:10::2 dev veth1 src 2001:db8:10::1 metric 1024 pref medium
Conversion of FIB entries to work with external nexthop objects
missed an important difference between IPv4 and IPv6 - how dst
entries are invalidated when the FIB changes. IPv4 has a per-network
namespace generation id (rt_genid) that is bumped on changes to the FIB.
Checking if a dst_entry is still valid means comparing rt_genid in the
rtable to the current value of rt_genid for the namespace.
IPv6 also has a per network namespace counter, fib6_sernum, but the
count is saved per fib6_node. With the per-node counter only dst_entries
based on fib entries under the node are invalidated when changes are
made to the routes - limiting the scope of invalidations. IPv6 uses a
reference in the rt6_info, 'from', to track the corresponding fib entry
used to create the dst_entry. When validating a dst_entry, the 'from'
is used to backtrack to the fib6_node and check the sernum of it to the
cookie passed to the dst_check operation.
With the inline format (nexthop definition inline with the fib6_info),
dst_entries cached in the fib6_nh have a 1:1 correlation between fib
entries, nexthop data and dst_entries. With external nexthops, IPv6
looks more like IPv4 which means multiple fib entries across disparate
fib6_nodes can all reference the same fib6_nh. That means validation
of dst_entries based on external nexthops needs to use the IPv4 format
- the per-network namespace counter.
Add sernum to rt6_info and set it when creating a pcpu dst entry. Update
rt6_get_cookie to return sernum if it is set and update dst_check for
IPv6 to look for sernum set and based the check on it if so. Finally,
rt6_get_pcpu_route needs to validate the cached entry before returning
a pcpu entry (similar to the rt_cache_valid calls in __mkroute_input and
__mkroute_output for IPv4).
This problem only affects routes using the new, external nexthops.
Thanks to the kbuild test robot for catching the IS_ENABLED needed
around rt_genid_ipv6 before I sent this out.
Fixes: 5b98324ebe29 ("ipv6: Allow routes to use nexthop objects")
Reported-by: Nikolay Aleksandrov <nikolay@...ulusnetworks.com>
Signed-off-by: David Ahern <dsahern@...nel.org>
Reviewed-by: Nikolay Aleksandrov <nikolay@...ulusnetworks.com>
Tested-by: Nikolay Aleksandrov <nikolay@...ulusnetworks.com>
Signed-off-by: David S. Miller <davem@...emloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
include/net/ip6_fib.h | 4 ++++
include/net/net_namespace.h | 7 +++++++
net/ipv6/route.c | 25 +++++++++++++++++++++++++
3 files changed, 36 insertions(+)
--- a/include/net/ip6_fib.h
+++ b/include/net/ip6_fib.h
@@ -204,6 +204,7 @@ struct fib6_info {
struct rt6_info {
struct dst_entry dst;
struct fib6_info __rcu *from;
+ int sernum;
struct rt6key rt6i_dst;
struct rt6key rt6i_src;
@@ -292,6 +293,9 @@ static inline u32 rt6_get_cookie(const s
struct fib6_info *from;
u32 cookie = 0;
+ if (rt->sernum)
+ return rt->sernum;
+
rcu_read_lock();
from = rcu_dereference(rt->from);
--- a/include/net/net_namespace.h
+++ b/include/net/net_namespace.h
@@ -432,6 +432,13 @@ static inline int rt_genid_ipv4(const st
return atomic_read(&net->ipv4.rt_genid);
}
+#if IS_ENABLED(CONFIG_IPV6)
+static inline int rt_genid_ipv6(const struct net *net)
+{
+ return atomic_read(&net->ipv6.fib6_sernum);
+}
+#endif
+
static inline void rt_genid_bump_ipv4(struct net *net)
{
atomic_inc(&net->ipv4.rt_genid);
--- a/net/ipv6/route.c
+++ b/net/ipv6/route.c
@@ -1388,9 +1388,18 @@ static struct rt6_info *ip6_rt_pcpu_allo
}
ip6_rt_copy_init(pcpu_rt, res);
pcpu_rt->rt6i_flags |= RTF_PCPU;
+
+ if (f6i->nh)
+ pcpu_rt->sernum = rt_genid_ipv6(dev_net(dev));
+
return pcpu_rt;
}
+static bool rt6_is_valid(const struct rt6_info *rt6)
+{
+ return rt6->sernum == rt_genid_ipv6(dev_net(rt6->dst.dev));
+}
+
/* It should be called with rcu_read_lock() acquired */
static struct rt6_info *rt6_get_pcpu_route(const struct fib6_result *res)
{
@@ -1398,6 +1407,19 @@ static struct rt6_info *rt6_get_pcpu_rou
pcpu_rt = this_cpu_read(*res->nh->rt6i_pcpu);
+ if (pcpu_rt && pcpu_rt->sernum && !rt6_is_valid(pcpu_rt)) {
+ struct rt6_info *prev, **p;
+
+ p = this_cpu_ptr(res->nh->rt6i_pcpu);
+ prev = xchg(p, NULL);
+ if (prev) {
+ dst_dev_put(&prev->dst);
+ dst_release(&prev->dst);
+ }
+
+ pcpu_rt = NULL;
+ }
+
return pcpu_rt;
}
@@ -2596,6 +2618,9 @@ static struct dst_entry *ip6_dst_check(s
rt = container_of(dst, struct rt6_info, dst);
+ if (rt->sernum)
+ return rt6_is_valid(rt) ? dst : NULL;
+
rcu_read_lock();
/* All IPV6 dsts are created with ->obsolete set to the value
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