[PATCH net-next v15 10/12] selftests/vsock: add namespace tests for CID collisions

Bobby Eshleman
2026-01-16T21:29:13Z

Add tests to verify CID collision rules across different vsock namespace
modes.

1. Two VMs with the same CID cannot start in different global namespaces
(ns_global_same_cid_fails)
2. Two VMs with the same CID can start in different local namespaces
(ns_local_same_cid_ok)
3. VMs with the same CID can coexist when one is in a global namespace
and another is in a local namespace (ns_global_local_same_cid_ok and
ns_local_global_same_cid_ok)

The tests ns_global_local_same_cid_ok and ns_local_global_same_cid_ok
make sure that ordering does not matter.

The tests use a shared helper function namespaces_can_boot_same_cid()
that attempts to start two VMs with identical CIDs in the specified
namespaces and verifies whether VM initialization failed or succeeded.

Reviewed-by: Stefano Garzarella <sgarzare@redhat.com>
Signed-off-by: Bobby Eshleman <bobbyeshleman@meta.com>
---
Changes in v11:
- check vm_start() rc in namespaces_can_boot_same_cid() (Stefano)
- fix ns_local_same_cid_ok() to use local0 and local1 instead of reusing
local0 twice. This check should pass, ensuring local namespaces do not
collide (Stefano)
---
tools/testing/selftests/vsock/vmtest.sh | 78 +++++++++++++++++++++++++++++++++
1 file changed, 78 insertions(+)

diff --git a/tools/testing/selftests/vsock/vmtest.sh b/tools/testing/selftests/vsock/vmtest.sh
index 38785a102236..1bf537410ea6 100755
--- a/tools/testing/selftests/vsock/vmtest.sh
+++ b/tools/testing/selftests/vsock/vmtest.sh
@@ -50,6 +50,10 @@ readonly TEST_NAMES=(
vm_loopback
ns_host_vsock_ns_mode_ok
ns_host_vsock_child_ns_mode_ok
+ ns_global_same_cid_fails
+ ns_local_same_cid_ok
+ ns_global_local_same_cid_ok
+ ns_local_global_same_cid_ok
)
readonly TEST_DESCS=(
# vm_server_host_client
@@ -66,6 +70,18 @@ readonly TEST_DESCS=(

# ns_host_vsock_child_ns_mode_ok
"Check /proc/sys/net/vsock/ns_mode is read-only and child_ns_mode is writable."
+
+ # ns_global_same_cid_fails
+ "Check QEMU fails to start two VMs with same CID in two different global namespaces."
+
+ # ns_local_same_cid_ok
+ "Check QEMU successfully starts two VMs with same CID in two different local namespaces."
+
+ # ns_global_local_same_cid_ok
+ "Check QEMU successfully starts one VM in a global ns and then another VM in a local ns with the same CID."
+
+ # ns_local_global_same_cid_ok
+ "Check QEMU successfully starts one VM in a local ns and then another VM in a global ns with the same CID."
)

readonly USE_SHARED_VM=(
@@ -577,6 +593,68 @@ test_ns_host_vsock_ns_mode_ok() {
return "${KSFT_PASS}"
}

+namespaces_can_boot_same_cid() {
+ local ns0=$1
+ local ns1=$2
+ local pidfile1 pidfile2
+ local rc
+
+ pidfile1="$(create_pidfile)"
+
+ # The first VM should be able to start. If it can't then we have
+ # problems and need to return non-zero.
+ if ! vm_start "${pidfile1}" "${ns0}"; then
+ return 1
+ fi
+
+ pidfile2="$(create_pidfile)"
+ vm_start "${pidfile2}" "${ns1}"
+ rc=$?
+ terminate_pidfiles "${pidfile1}" "${pidfile2}"
+
+ return "${rc}"
+}
+
+test_ns_global_same_cid_fails() {
+ init_namespaces
+
+ if namespaces_can_boot_same_cid "global0" "global1"; then
+ return "${KSFT_FAIL}"
+ fi
+
+ return "${KSFT_PASS}"
+}
+
+test_ns_local_global_same_cid_ok() {
+ init_namespaces
+
+ if namespaces_can_boot_same_cid "local0" "global0"; then
+ return "${KSFT_PASS}"
+ fi
+
+ return "${KSFT_FAIL}"
+}
+
+test_ns_global_local_same_cid_ok() {
+ init_namespaces
+
+ if namespaces_can_boot_same_cid "global0" "local0"; then
+ return "${KSFT_PASS}"
+ fi
+
+ return "${KSFT_FAIL}"
+}
+
+test_ns_local_same_cid_ok() {
+ init_namespaces
+
+ if namespaces_can_boot_same_cid "local0" "local1"; then
+ return "${KSFT_PASS}"
+ fi
+
+ return "${KSFT_FAIL}"
+}
+
test_ns_host_vsock_child_ns_mode_ok() {
local orig_mode
local rc

--
2.47.3