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Message-Id: <20251021-work-namespace-nstree-listns-v1-49-ad44261a8a5b@kernel.org>
Date: Tue, 21 Oct 2025 13:43:55 +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 49/50] selftests/namespaces: sixth listns()
permission test
Test that we can see user namespaces we have CAP_SYS_ADMIN inside of.
This is different from seeing namespaces owned by a user namespace.
Signed-off-by: Christian Brauner <brauner@...nel.org>
---
.../selftests/namespaces/listns_permissions_test.c | 90 ++++++++++++++++++++++
1 file changed, 90 insertions(+)
diff --git a/tools/testing/selftests/namespaces/listns_permissions_test.c b/tools/testing/selftests/namespaces/listns_permissions_test.c
index 07c0c2be0aa5..709250ce1542 100644
--- a/tools/testing/selftests/namespaces/listns_permissions_test.c
+++ b/tools/testing/selftests/namespaces/listns_permissions_test.c
@@ -573,4 +573,94 @@ TEST(listns_parent_userns_cap_sys_admin)
count);
}
+/*
+ * Test that we can see user namespaces we have CAP_SYS_ADMIN inside of.
+ * This is different from seeing namespaces owned by a user namespace.
+ */
+TEST(listns_cap_sys_admin_inside_userns)
+{
+ int pipefd[2];
+ pid_t pid;
+ int status;
+ bool found_ours;
+
+ ASSERT_EQ(pipe(pipefd), 0);
+
+ pid = fork();
+ ASSERT_GE(pid, 0);
+
+ if (pid == 0) {
+ int fd;
+ __u64 our_userns_id;
+ struct ns_id_req req;
+ __u64 ns_ids[100];
+ ssize_t ret;
+ bool found_ours;
+
+ close(pipefd[0]);
+
+ /* Create user namespace - we have CAP_SYS_ADMIN inside it */
+ if (setup_userns() < 0) {
+ close(pipefd[1]);
+ exit(1);
+ }
+
+ /* Get our user namespace ID */
+ fd = open("/proc/self/ns/user", O_RDONLY);
+ if (fd < 0) {
+ close(pipefd[1]);
+ exit(1);
+ }
+
+ if (ioctl(fd, NS_GET_ID, &our_userns_id) < 0) {
+ close(fd);
+ close(pipefd[1]);
+ exit(1);
+ }
+ close(fd);
+
+ /* List all user namespaces globally */
+ req.size = sizeof(req);
+ req.spare = 0;
+ req.ns_id = 0;
+ req.ns_type = CLONE_NEWUSER;
+ req.spare2 = 0;
+ req.user_ns_id = 0;
+
+ ret = sys_listns(&req, ns_ids, ARRAY_SIZE(ns_ids), 0);
+
+ /* We should be able to see our own user namespace */
+ found_ours = false;
+ if (ret > 0) {
+ for (ssize_t i = 0; i < ret; i++) {
+ if (ns_ids[i] == our_userns_id) {
+ found_ours = true;
+ break;
+ }
+ }
+ }
+
+ write(pipefd[1], &found_ours, sizeof(found_ours));
+ close(pipefd[1]);
+ exit(0);
+ }
+
+ /* Parent */
+ close(pipefd[1]);
+
+ found_ours = false;
+ read(pipefd[0], &found_ours, sizeof(found_ours));
+ close(pipefd[0]);
+
+ waitpid(pid, &status, 0);
+ ASSERT_TRUE(WIFEXITED(status));
+
+ if (WEXITSTATUS(status) != 0) {
+ SKIP(return, "Child failed to setup namespace");
+ }
+
+ ASSERT_TRUE(found_ours);
+ TH_LOG("Process can see user namespace it has CAP_SYS_ADMIN inside of");
+}
+
TEST_HARNESS_MAIN
--
2.47.3
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