Re: [PATCH net] wireguard: remove peer cache in netns_pre_exit

["Jason A. Donenfeld" <Jason@zx2c4.com>]

Hi Hangbin,

Thanks for the patch and especially for the test. While I see that
you've pointed to a real problem, I don't think that this particular way
of fixing it is correct, because it will cause issues for userspace that
expects to be able to read back the list of peers for, for example,
keeping track of the latest endpoint addresses or rx/tx transfer
quantities.

I think the real solution here is to simply clear the endpoint src cache
and consequently the dst_cache. This is slightly complicated by the fact
that dst_cache releases dsts lazily, so I needed to add a little utility
function for that, but that was pretty easy to do.

Can you take a look at the below patch and let me know if it works for
you and passes other testing you and Toke might be doing with it? (Also,
please CC the wireguard mailing list in addition to netdev next time?)
If the patch looks good to you and works well, I'll include it in the
next series of wireguard patches I send back out to netdev. I'm back
from travels next week and will begin working on the next series then.

Regards,
Jason

---------8<-------------8<-----------------

From f9984a41eeaebfdcef5aba8a71966b77ba0de8c0 Mon Sep 17 00:00:00 2001
From: "Jason A. Donenfeld" <Jason@zx2c4.com>
Date: Wed, 1 Sep 2021 14:53:39 +0200
Subject: [PATCH] wireguard: device: reset peer src endpoint when netns exits
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

Each peer's endpoint contains a dst_cache entry that takes a reference
to another netdev. When the containing namespace exits, we take down the
socket and prevent future sockets from being created (by setting
creating_net to NULL), which removes that potential reference on the
netns. However, it doesn't release references to the netns that a netdev
cached in dst_cache might be taking, so the netns still might fail to
exit. Since the socket is gimped anyway, we can simply clear all the
dst_caches (by way of clearing the endpoint src), which will release all
references.

However, the current dst_cache_reset function only releases those
references lazily. But it turns out that all of our usages of
wg_socket_clear_peer_endpoint_src are called from contexts that are not
exactly high-speed or bottle-necked. For example, when there's
connection difficulty, or when userspace is reconfiguring the interface.
And in particular for this patch, when the netns is exiting. So for
those cases, it makes more sense to call dst_release immediately. For
that, we add a small helper function to dst_cache.

This patch also adds a test to netns.sh from Hangbin Liu to ensure this
doesn't regress.

Test-by: Hangbin Liu <liuhangbin@gmail.com>
Reported-by: Xiumei Mu <xmu@redhat.com>
Cc: Hangbin Liu <liuhangbin@gmail.com>
Cc: Toke Høiland-Jørgensen <toke@redhat.com>
Cc: Paolo Abeni <pabeni@redhat.com>
Fixes: 900575aa33a3 ("wireguard: device: avoid circular netns references")
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
---
 drivers/net/wireguard/device.c             |  3 +++
 drivers/net/wireguard/socket.c             |  2 +-
 include/net/dst_cache.h                    | 11 ++++++++++
 net/core/dst_cache.c                       | 19 +++++++++++++++++
 tools/testing/selftests/wireguard/netns.sh | 24 +++++++++++++++++++++-
 5 files changed, 57 insertions(+), 2 deletions(-)

diff --git a/drivers/net/wireguard/device.c b/drivers/net/wireguard/device.c
index 551ddaaaf540..77e64ea6be67 100644
--- a/drivers/net/wireguard/device.c
+++ b/drivers/net/wireguard/device.c
@@ -398,6 +398,7 @@ static struct rtnl_link_ops link_ops __read_mostly = {
 static void wg_netns_pre_exit(struct net *net)
 {
 	struct wg_device *wg;
+	struct wg_peer *peer;
 
 	rtnl_lock();
 	list_for_each_entry(wg, &device_list, device_list) {
@@ -407,6 +408,8 @@ static void wg_netns_pre_exit(struct net *net)
 			mutex_lock(&wg->device_update_lock);
 			rcu_assign_pointer(wg->creating_net, NULL);
 			wg_socket_reinit(wg, NULL, NULL);
+			list_for_each_entry(peer, &wg->peer_list, peer_list)
+				wg_socket_clear_peer_endpoint_src(peer);
 			mutex_unlock(&wg->device_update_lock);
 		}
 	}
diff --git a/drivers/net/wireguard/socket.c b/drivers/net/wireguard/socket.c
index 8c496b747108..6f07b949cb81 100644
--- a/drivers/net/wireguard/socket.c
+++ b/drivers/net/wireguard/socket.c
@@ -308,7 +308,7 @@ void wg_socket_clear_peer_endpoint_src(struct wg_peer *peer)
 {
 	write_lock_bh(&peer->endpoint_lock);
 	memset(&peer->endpoint.src6, 0, sizeof(peer->endpoint.src6));
-	dst_cache_reset(&peer->endpoint_cache);
+	dst_cache_reset_now(&peer->endpoint_cache);
 	write_unlock_bh(&peer->endpoint_lock);
 }
 
diff --git a/include/net/dst_cache.h b/include/net/dst_cache.h
index 67634675e919..df6622a5fe98 100644
--- a/include/net/dst_cache.h
+++ b/include/net/dst_cache.h
@@ -79,6 +79,17 @@ static inline void dst_cache_reset(struct dst_cache *dst_cache)
 	dst_cache->reset_ts = jiffies;
 }
 
+/**
+ *	dst_cache_reset_now - invalidate the cache contents immediately
+ *	@dst_cache: the cache
+ *
+ *	The caller must be sure there are no concurrent users, as this frees
+ *	all dst_cache users immediately, rather than waiting for the next
+ *	per-cpu usage like dst_cache_reset does. Most callers should use the
+ *	higher speed lazily-freed dst_cache_reset function instead.
+ */
+void dst_cache_reset_now(struct dst_cache *dst_cache);
+
 /**
  *	dst_cache_init - initialize the cache, allocating the required storage
  *	@dst_cache: the cache
diff --git a/net/core/dst_cache.c b/net/core/dst_cache.c
index be74ab4551c2..0ccfd5fa5cb9 100644
--- a/net/core/dst_cache.c
+++ b/net/core/dst_cache.c
@@ -162,3 +162,22 @@ void dst_cache_destroy(struct dst_cache *dst_cache)
 	free_percpu(dst_cache->cache);
 }
 EXPORT_SYMBOL_GPL(dst_cache_destroy);
+
+void dst_cache_reset_now(struct dst_cache *dst_cache)
+{
+	int i;
+
+	if (!dst_cache->cache)
+		return;
+
+	dst_cache->reset_ts = jiffies;
+	for_each_possible_cpu(i) {
+		struct dst_cache_pcpu *idst = per_cpu_ptr(dst_cache->cache, i);
+		struct dst_entry *dst = idst->dst;
+
+		idst->cookie = 0;
+		idst->dst = NULL;
+		dst_release(dst);
+	}
+}
+EXPORT_SYMBOL_GPL(dst_cache_reset_now);
diff --git a/tools/testing/selftests/wireguard/netns.sh b/tools/testing/selftests/wireguard/netns.sh
index 2e5c1630885e..8a9461aa0878 100755
--- a/tools/testing/selftests/wireguard/netns.sh
+++ b/tools/testing/selftests/wireguard/netns.sh
@@ -613,6 +613,28 @@ ip0 link set wg0 up
 kill $ncat_pid
 ip0 link del wg0
 
+# Ensure that dst_cache references don't outlive netns lifetime
+ip1 link add dev wg0 type wireguard
+ip2 link add dev wg0 type wireguard
+configure_peers
+ip1 link add veth1 type veth peer name veth2
+ip1 link set veth2 netns $netns2
+ip1 addr add fd00:aa::1/64 dev veth1
+ip2 addr add fd00:aa::2/64 dev veth2
+ip1 link set veth1 up
+ip2 link set veth2 up
+waitiface $netns1 veth1
+waitiface $netns2 veth2
+ip1 -6 route add default dev veth1 via fd00:aa::2
+ip2 -6 route add default dev veth2 via fd00:aa::1
+n1 wg set wg0 peer "$pub2" endpoint [fd00:aa::2]:2
+n2 wg set wg0 peer "$pub1" endpoint [fd00:aa::1]:1
+n1 ping6 -c 1 fd00::2
+pp ip netns delete $netns1
+pp ip netns delete $netns2
+pp ip netns add $netns1
+pp ip netns add $netns2
+
 # Ensure there aren't circular reference loops
 ip1 link add wg1 type wireguard
 ip2 link add wg2 type wireguard
@@ -631,7 +653,7 @@ while read -t 0.1 -r line 2>/dev/null || [[ $? -ne 142 ]]; do
 done < /dev/kmsg
 alldeleted=1
 for object in "${!objects[@]}"; do
-	if [[ ${objects["$object"]} != *createddestroyed ]]; then
+	if [[ ${objects["$object"]} != *createddestroyed && ${objects["$object"]} != *createdcreateddestroyeddestroyed ]]; then
 		echo "Error: $object: merely ${objects["$object"]}" >&3
 		alldeleted=0
 	fi
-- 
2.32.0