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Message-Id: <20251021-work-namespace-nstree-listns-v1-32-ad44261a8a5b@kernel.org>
Date: Tue, 21 Oct 2025 13:43:38 +0200
From: Christian Brauner <brauner@...nel.org>
To: linux-fsdevel@...r.kernel.org, Josef Bacik <josef@...icpanda.com>,
Jeff Layton <jlayton@...nel.org>
Cc: Jann Horn <jannh@...gle.com>, Mike Yuan <me@...dnzj.com>,
Zbigniew Jędrzejewski-Szmek <zbyszek@...waw.pl>,
Lennart Poettering <mzxreary@...inter.de>,
Daan De Meyer <daan.j.demeyer@...il.com>, Aleksa Sarai <cyphar@...har.com>,
Amir Goldstein <amir73il@...il.com>, Tejun Heo <tj@...nel.org>,
Johannes Weiner <hannes@...xchg.org>, Thomas Gleixner <tglx@...utronix.de>,
Alexander Viro <viro@...iv.linux.org.uk>, Jan Kara <jack@...e.cz>,
linux-kernel@...r.kernel.org, cgroups@...r.kernel.org, bpf@...r.kernel.org,
Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>,
netdev@...r.kernel.org, Arnd Bergmann <arnd@...db.de>,
Christian Brauner <brauner@...nel.org>
Subject: [PATCH RFC DRAFT 32/50] selftests/namespaces: fourteenth active
reference count tests
Test that user namespace as a child also propagates correctly.
Create user_A -> user_B, verify when user_B is active that user_A
is also active. This is different from non-user namespace children.
Signed-off-by: Christian Brauner <brauner@...nel.org>
---
.../selftests/namespaces/ns_active_ref_test.c | 138 +++++++++++++++++++++
1 file changed, 138 insertions(+)
diff --git a/tools/testing/selftests/namespaces/ns_active_ref_test.c b/tools/testing/selftests/namespaces/ns_active_ref_test.c
index 4c077223b05c..1eb4dc07e924 100644
--- a/tools/testing/selftests/namespaces/ns_active_ref_test.c
+++ b/tools/testing/selftests/namespaces/ns_active_ref_test.c
@@ -1914,4 +1914,142 @@ TEST(ns_parent_multiple_children_refcount)
}
}
+/*
+ * Test that user namespace as a child also propagates correctly.
+ * Create user_A -> user_B, verify when user_B is active that user_A
+ * is also active. This is different from non-user namespace children.
+ */
+TEST(ns_userns_child_propagation)
+{
+ struct file_handle *ua_handle, *ub_handle;
+ int ret, pipefd[2];
+ pid_t pid;
+ int status;
+ __u64 ua_id, ub_id;
+ char ua_buf[sizeof(*ua_handle) + MAX_HANDLE_SZ];
+ char ub_buf[sizeof(*ub_handle) + MAX_HANDLE_SZ];
+
+ ASSERT_EQ(pipe(pipefd), 0);
+ pid = fork();
+ ASSERT_GE(pid, 0);
+
+ if (pid == 0) {
+ close(pipefd[0]);
+
+ /* Create user_A */
+ if (setup_userns() < 0) {
+ close(pipefd[1]);
+ exit(1);
+ }
+
+ int ua_fd = open("/proc/self/ns/user", O_RDONLY);
+ if (ua_fd < 0) {
+ close(pipefd[1]);
+ exit(1);
+ }
+ if (ioctl(ua_fd, NS_GET_ID, &ua_id) < 0) {
+ close(ua_fd);
+ close(pipefd[1]);
+ exit(1);
+ }
+ close(ua_fd);
+
+ /* Create user_B (child of user_A) */
+ if (setup_userns() < 0) {
+ close(pipefd[1]);
+ exit(1);
+ }
+
+ int ub_fd = open("/proc/self/ns/user", O_RDONLY);
+ if (ub_fd < 0) {
+ close(pipefd[1]);
+ exit(1);
+ }
+ if (ioctl(ub_fd, NS_GET_ID, &ub_id) < 0) {
+ close(ub_fd);
+ close(pipefd[1]);
+ exit(1);
+ }
+ close(ub_fd);
+
+ /* Send both namespace IDs */
+ write(pipefd[1], &ua_id, sizeof(ua_id));
+ write(pipefd[1], &ub_id, sizeof(ub_id));
+ close(pipefd[1]);
+ exit(0);
+ }
+
+ close(pipefd[1]);
+
+ /* Read both namespace IDs - fixed size, no parsing needed */
+ ret = read(pipefd[0], &ua_id, sizeof(ua_id));
+ if (ret != sizeof(ua_id)) {
+ close(pipefd[0]);
+ waitpid(pid, NULL, 0);
+ SKIP(return, "Failed to read user_A namespace ID");
+ }
+
+ ret = read(pipefd[0], &ub_id, sizeof(ub_id));
+ close(pipefd[0]);
+ if (ret != sizeof(ub_id)) {
+ waitpid(pid, NULL, 0);
+ SKIP(return, "Failed to read user_B namespace ID");
+ }
+
+ /* Construct file handles from namespace IDs */
+ ua_handle = (struct file_handle *)ua_buf;
+ ua_handle->handle_bytes = sizeof(struct nsfs_file_handle);
+ ua_handle->handle_type = FILEID_NSFS;
+ struct nsfs_file_handle *ua_fh = (struct nsfs_file_handle *)ua_handle->f_handle;
+ ua_fh->ns_id = ua_id;
+ ua_fh->ns_type = 0;
+ ua_fh->ns_inum = 0;
+
+ ub_handle = (struct file_handle *)ub_buf;
+ ub_handle->handle_bytes = sizeof(struct nsfs_file_handle);
+ ub_handle->handle_type = FILEID_NSFS;
+ struct nsfs_file_handle *ub_fh = (struct nsfs_file_handle *)ub_handle->f_handle;
+ ub_fh->ns_id = ub_id;
+ ub_fh->ns_type = 0;
+ ub_fh->ns_inum = 0;
+
+ /* Open user_B before child exits */
+ int ub_fd = open_by_handle_at(FD_NSFS_ROOT, ub_handle, O_RDONLY);
+ if (ub_fd < 0) {
+ waitpid(pid, NULL, 0);
+ SKIP(return, "Failed to open user_B");
+ }
+
+ waitpid(pid, &status, 0);
+ ASSERT_TRUE(WIFEXITED(status));
+ if (WEXITSTATUS(status) != 0) {
+ close(ub_fd);
+ SKIP(return, "Child failed");
+ }
+
+ /* With user_B active, user_A should also be active */
+ TH_LOG("Testing user_A active when child user_B is active");
+ int ua_fd = open_by_handle_at(FD_NSFS_ROOT, ua_handle, O_RDONLY);
+ ASSERT_GE(ua_fd, 0);
+
+ /* Close user_B */
+ TH_LOG("Closing user_B");
+ close(ub_fd);
+
+ /* user_A should remain active (we hold direct ref) */
+ int ua_fd2 = open_by_handle_at(FD_NSFS_ROOT, ua_handle, O_RDONLY);
+ ASSERT_GE(ua_fd2, 0);
+ close(ua_fd2);
+
+ /* Close user_A - should become inactive */
+ TH_LOG("Closing user_A - should become inactive");
+ close(ua_fd);
+
+ ua_fd = open_by_handle_at(FD_NSFS_ROOT, ua_handle, O_RDONLY);
+ if (ua_fd >= 0) {
+ close(ua_fd);
+ TH_LOG("Warning: user_A still active");
+ }
+}
+
TEST_HARNESS_MAIN
--
2.47.3
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