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>

1 files changed, 2 insertions, 0 deletions

diff --git a/src/compat/dst_cache/dst_cache.c b/src/compat/dst_cache/dst_cache.c
index 7ec22f7..f74c43c 100644
--- a/src/compat/dst_cache/dst_cache.c
+++ b/src/compat/dst_cache/dst_cache.c
@@ -27,6 +27,7 @@ static inline u32 rt6_get_cookie(const struct rt6_info *rt)
 #endif
 #include <uapi/linux/in.h>
 
+#ifndef COMPAT_HAS_DEFINED_DST_CACHE_PCPU
 struct dst_cache_pcpu {
 	unsigned long refresh_ts;
 	struct dst_entry *dst;
@@ -36,6 +37,7 @@ struct dst_cache_pcpu {
 		struct in6_addr in6_saddr;
 	};
 };
+#endif
 
 static void dst_cache_per_cpu_dst_set(struct dst_cache_pcpu *dst_cache,
 				      struct dst_entry *dst, u32 cookie)