wireguard: allowedips: add WGALLOWEDIP_F_REMOVE_ME flag

The current netlink API for WireGuard does not directly support removal
of allowed ips from a peer. A user can remove an allowed ip from a peer
in one of two ways:

1. By using the WGPEER_F_REPLACE_ALLOWEDIPS flag and providing a new
   list of allowed ips which omits the allowed ip that is to be removed.
2. By reassigning an allowed ip to a "dummy" peer then removing that
   peer with WGPEER_F_REMOVE_ME.

With the first approach, the driver completely rebuilds the allowed ip
list for a peer. If my current configuration is such that a peer has
allowed ips 192.168.0.2 and 192.168.0.3 and I want to remove 192.168.0.2
the actual transition looks like this.

[192.168.0.2, 192.168.0.3] <-- Initial state
[]                         <-- Step 1: Allowed ips removed for peer
[192.168.0.3]              <-- Step 2: Allowed ips added back for peer

This is true even if the allowed ip list is small and the update does
not need to be batched into multiple WG_CMD_SET_DEVICE requests, as the
removal and subsequent addition of ips is non-atomic within a single
request. Consequently, wg_allowedips_lookup_dst and
wg_allowedips_lookup_src may return NULL while reconfiguring a peer even
for packets bound for ips a user did not intend to remove leading to
unintended interruptions in connectivity. This presents in userspace as
failed calls to sendto and sendmsg for UDP sockets. In my case, I ran
netperf while repeatedly reconfiguring the allowed ips for a peer with
wg.

/usr/local/bin/netperf -H 10.102.73.72 -l 10m -t UDP_STREAM -- -R 1 -m 1024
send_data: data send error: No route to host (errno 113)
netperf: send_omni: send_data failed: No route to host

While this may not be of particular concern for environments where peers
and allowed ips are mostly static, systems like Cilium manage peers and
allowed ips in a dynamic environment where peers (i.e. Kubernetes nodes)
and allowed ips (i.e. pods running on those nodes) can frequently
change making WGPEER_F_REPLACE_ALLOWEDIPS problematic.

The second approach avoids any possible connectivity interruptions
but is hacky and less direct, requiring the creation of a temporary
peer just to dispose of an allowed ip.

Introduce a new flag called WGALLOWEDIP_F_REMOVE_ME which in the same
way that WGPEER_F_REMOVE_ME allows a user to remove a single peer from
a WireGuard device's configuration allows a user to remove an ip from a
peer's set of allowed ips. This enables incremental updates to a
device's configuration without any connectivity blips or messy
workarounds.

A corresponding patch for wg extends the existing `wg set` interface to
leverage this feature.

$ wg set wg0 peer <PUBKEY> allowed-ips +192.168.88.0/24,-192.168.0.1/32

When '+' or '-' is prepended to any ip in the list, wg clears
WGPEER_F_REPLACE_ALLOWEDIPS and sets the WGALLOWEDIP_F_REMOVE_ME flag on
any ip prefixed with '-'.

Signed-off-by: Jordan Rife <jordan@jrife.io>
[Jason: minor style nits, fixes to selftest, bump of wireguard-tools version]
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
Link: https://patch.msgid.link/20250521212707.1767879-5-Jason@zx2c4.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

1 files changed, 48 insertions, 0 deletions

diff --git a/drivers/net/wireguard/selftest/allowedips.c b/drivers/net/wireguard/selftest/allowedips.c
index 25de7058701a..41837efa70cb 100644
--- a/drivers/net/wireguard/selftest/allowedips.c
+++ b/drivers/net/wireguard/selftest/allowedips.c
@@ -460,6 +460,10 @@ static __init struct wg_peer *init_peer(void)
 	wg_allowedips_insert_v##version(&t, ip##version(ipa, ipb, ipc, ipd), \
 					cidr, mem, &mutex)
 
+#define remove(version, mem, ipa, ipb, ipc, ipd, cidr)                      \
+	wg_allowedips_remove_v##version(&t, ip##version(ipa, ipb, ipc, ipd), \
+					cidr, mem, &mutex)
+
 #define maybe_fail() do {                                               \
 		++i;                                                    \
 		if (!_s) {                                              \
@@ -585,6 +589,50 @@ bool __init wg_allowedips_selftest(void)
 	test_negative(4, a, 192, 0, 0, 0);
 	test_negative(4, a, 255, 0, 0, 0);
 
+	insert(4, a, 1, 0, 0, 0, 32);
+	insert(4, a, 192, 0, 0, 0, 24);
+	insert(6, a, 0x24446801, 0x40e40800, 0xdeaebeef, 0xdefbeef, 128);
+	insert(6, a, 0x24446800, 0xf0e40800, 0xeeaebeef, 0, 98);
+	test(4, a, 1, 0, 0, 0);
+	test(4, a, 192, 0, 0, 1);
+	test(6, a, 0x24446801, 0x40e40800, 0xdeaebeef, 0xdefbeef);
+	test(6, a, 0x24446800, 0xf0e40800, 0xeeaebeef, 0x10101010);
+	/* Must be an exact match to remove */
+	remove(4, a, 192, 0, 0, 0, 32);
+	test(4, a, 192, 0, 0, 1);
+	/* NULL peer should have no effect and return 0 */
+	test_boolean(!remove(4, NULL, 192, 0, 0, 0, 24));
+	test(4, a, 192, 0, 0, 1);
+	/* different peer should have no effect and return 0 */
+	test_boolean(!remove(4, b, 192, 0, 0, 0, 24));
+	test(4, a, 192, 0, 0, 1);
+	/* invalid CIDR should have no effect and return -EINVAL */
+	test_boolean(remove(4, b, 192, 0, 0, 0, 33) == -EINVAL);
+	test(4, a, 192, 0, 0, 1);
+	remove(4, a, 192, 0, 0, 0, 24);
+	test_negative(4, a, 192, 0, 0, 1);
+	remove(4, a, 1, 0, 0, 0, 32);
+	test_negative(4, a, 1, 0, 0, 0);
+	/* Must be an exact match to remove */
+	remove(6, a, 0x24446801, 0x40e40800, 0xdeaebeef, 0xdefbeef, 96);
+	test(6, a, 0x24446801, 0x40e40800, 0xdeaebeef, 0xdefbeef);
+	/* NULL peer should have no effect and return 0 */
+	test_boolean(!remove(6, NULL, 0x24446801, 0x40e40800, 0xdeaebeef, 0xdefbeef, 128));
+	test(6, a, 0x24446801, 0x40e40800, 0xdeaebeef, 0xdefbeef);
+	/* different peer should have no effect and return 0 */
+	test_boolean(!remove(6, b, 0x24446801, 0x40e40800, 0xdeaebeef, 0xdefbeef, 128));
+	test(6, a, 0x24446801, 0x40e40800, 0xdeaebeef, 0xdefbeef);
+	/* invalid CIDR should have no effect and return -EINVAL */
+	test_boolean(remove(6, a, 0x24446801, 0x40e40800, 0xdeaebeef, 0xdefbeef, 129)  == -EINVAL);
+	test(6, a, 0x24446801, 0x40e40800, 0xdeaebeef, 0xdefbeef);
+	remove(6, a, 0x24446801, 0x40e40800, 0xdeaebeef, 0xdefbeef, 128);
+	test_negative(6, a, 0x24446801, 0x40e40800, 0xdeaebeef, 0xdefbeef);
+	/* Must match the peer to remove */
+	remove(6, b, 0x24446800, 0xf0e40800, 0xeeaebeef, 0, 98);
+	test(6, a, 0x24446800, 0xf0e40800, 0xeeaebeef, 0x10101010);
+	remove(6, a, 0x24446800, 0xf0e40800, 0xeeaebeef, 0, 98);
+	test_negative(6, a, 0x24446800, 0xf0e40800, 0xeeaebeef, 0x10101010);
+
 	wg_allowedips_free(&t, &mutex);
 	wg_allowedips_init(&t);
 	insert(4, a, 192, 168, 0, 0, 16);