device: reset peer src endpoint when netns exits

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>
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
Change-Id: Ie3c2d3ffbf27c94bdfd3bc37e314d14c306c217a

1 files changed, 31 insertions, 0 deletions

diff --git a/drivers/net/wireguard/compat/compat.h b/drivers/net/wireguard/compat/compat.h
index 9aa767a277fe..0270a288816f 100644
--- a/drivers/net/wireguard/compat/compat.h
+++ b/drivers/net/wireguard/compat/compat.h
@@ -1102,6 +1102,37 @@ static const struct header_ops ip_tunnel_header_ops = { .parse_protocol = ip_tun
 #endif
 #endif
 
+#if LINUX_VERSION_CODE < KERNEL_VERSION(5, 16, 0)
+#include <net/dst_cache.h>
+struct dst_cache_pcpu {
+	unsigned long refresh_ts;
+	struct dst_entry *dst;
+	u32 cookie;
+	union {
+		struct in_addr in_saddr;
+		struct in6_addr in6_saddr;
+	};
+};
+#define COMPAT_HAS_DEFINED_DST_CACHE_PCPU
+static inline 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);
+	}
+}
+#endif
+
 #if defined(ISUBUNTU1604) || defined(ISRHEL7)
 #include <linux/siphash.h>
 #ifndef _WG_LINUX_SIPHASH_H