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Message-Id: <20251021-work-namespace-nstree-listns-v1-46-ad44261a8a5b@kernel.org>
Date: Tue, 21 Oct 2025 13:43:52 +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 46/50] selftests/namespaces: third listns()
permission test
Test that users cannot see namespaces from unrelated user namespaces.
Create two sibling user namespaces, verify they can't see each other's
owned namespaces.
Signed-off-by: Christian Brauner <brauner@...nel.org>
---
.../selftests/namespaces/listns_permissions_test.c | 138 +++++++++++++++++++++
1 file changed, 138 insertions(+)
diff --git a/tools/testing/selftests/namespaces/listns_permissions_test.c b/tools/testing/selftests/namespaces/listns_permissions_test.c
index 803c42fc76ec..4e47b4c82c56 100644
--- a/tools/testing/selftests/namespaces/listns_permissions_test.c
+++ b/tools/testing/selftests/namespaces/listns_permissions_test.c
@@ -234,4 +234,142 @@ TEST(listns_cap_sys_admin_in_userns)
count);
}
+/*
+ * Test that users cannot see namespaces from unrelated user namespaces.
+ * Create two sibling user namespaces, verify they can't see each other's
+ * owned namespaces.
+ */
+TEST(listns_cannot_see_sibling_userns_namespaces)
+{
+ int pipefd[2];
+ pid_t pid1, pid2;
+ int status;
+ __u64 netns_a_id;
+ int pipefd2[2];
+ bool found_sibling_netns;
+
+ ASSERT_EQ(pipe(pipefd), 0);
+
+ /* Fork first child - creates user namespace A */
+ pid1 = fork();
+ ASSERT_GE(pid1, 0);
+
+ if (pid1 == 0) {
+ int fd;
+ __u64 netns_a_id;
+ char buf;
+
+ close(pipefd[0]);
+
+ /* Create user namespace A */
+ if (setup_userns() < 0) {
+ close(pipefd[1]);
+ exit(1);
+ }
+
+ /* Create network namespace owned by user namespace A */
+ if (unshare(CLONE_NEWNET) < 0) {
+ close(pipefd[1]);
+ exit(1);
+ }
+
+ /* Get network namespace ID */
+ fd = open("/proc/self/ns/net", O_RDONLY);
+ if (fd < 0) {
+ close(pipefd[1]);
+ exit(1);
+ }
+
+ if (ioctl(fd, NS_GET_ID, &netns_a_id) < 0) {
+ close(fd);
+ close(pipefd[1]);
+ exit(1);
+ }
+ close(fd);
+
+ /* Send namespace ID to parent */
+ write(pipefd[1], &netns_a_id, sizeof(netns_a_id));
+
+ /* Keep alive for sibling to check */
+ read(pipefd[1], &buf, 1);
+ close(pipefd[1]);
+ exit(0);
+ }
+
+ /* Parent reads namespace A ID */
+ close(pipefd[1]);
+ netns_a_id = 0;
+ read(pipefd[0], &netns_a_id, sizeof(netns_a_id));
+
+ TH_LOG("User namespace A created network namespace with ID %llu",
+ (unsigned long long)netns_a_id);
+
+ /* Fork second child - creates user namespace B */
+ ASSERT_EQ(pipe(pipefd2), 0);
+
+ pid2 = fork();
+ ASSERT_GE(pid2, 0);
+
+ if (pid2 == 0) {
+ struct ns_id_req req = {
+ .size = sizeof(req),
+ .spare = 0,
+ .ns_id = 0,
+ .ns_type = CLONE_NEWNET,
+ .spare2 = 0,
+ .user_ns_id = 0,
+ };
+ __u64 ns_ids[100];
+ ssize_t ret;
+ bool found_sibling_netns;
+
+ close(pipefd[0]);
+ close(pipefd2[0]);
+
+ /* Create user namespace B (sibling to A) */
+ if (setup_userns() < 0) {
+ close(pipefd2[1]);
+ exit(1);
+ }
+
+ /* Try to list all network namespaces */
+ ret = sys_listns(&req, ns_ids, ARRAY_SIZE(ns_ids), 0);
+
+ found_sibling_netns = false;
+ if (ret > 0) {
+ for (ssize_t i = 0; i < ret; i++) {
+ if (ns_ids[i] == netns_a_id) {
+ found_sibling_netns = true;
+ break;
+ }
+ }
+ }
+
+ /* We should NOT see the sibling's network namespace */
+ write(pipefd2[1], &found_sibling_netns, sizeof(found_sibling_netns));
+ close(pipefd2[1]);
+ exit(0);
+ }
+
+ /* Parent reads result from second child */
+ close(pipefd2[1]);
+ found_sibling_netns = false;
+ read(pipefd2[0], &found_sibling_netns, sizeof(found_sibling_netns));
+ close(pipefd2[0]);
+
+ /* Signal first child to exit */
+ close(pipefd[0]);
+
+ /* Wait for both children */
+ waitpid(pid2, &status, 0);
+ ASSERT_TRUE(WIFEXITED(status));
+
+ waitpid(pid1, &status, 0);
+ ASSERT_TRUE(WIFEXITED(status));
+
+ /* Second child should NOT have seen first child's namespace */
+ ASSERT_FALSE(found_sibling_netns);
+ TH_LOG("User namespace B correctly could not see sibling namespace A's network namespace");
+}
+
TEST_HARNESS_MAIN
--
2.47.3
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