linux-kernel - [PATCH RFC DRAFT 45/50] selftests/namespaces: second listns() permission test

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Message-Id: <20251021-work-namespace-nstree-listns-v1-45-ad44261a8a5b@kernel.org>
Date: Tue, 21 Oct 2025 13:43:51 +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 45/50] selftests/namespaces: second listns()
 permission test

Test that users with CAP_SYS_ADMIN in a user namespace can see
all namespaces owned by that user namespace.

Signed-off-by: Christian Brauner <brauner@...nel.org>
---
 .../selftests/namespaces/listns_permissions_test.c | 103 +++++++++++++++++++++
 1 file changed, 103 insertions(+)

diff --git a/tools/testing/selftests/namespaces/listns_permissions_test.c b/tools/testing/selftests/namespaces/listns_permissions_test.c
index 87ec71560d99..803c42fc76ec 100644
--- a/tools/testing/selftests/namespaces/listns_permissions_test.c
+++ b/tools/testing/selftests/namespaces/listns_permissions_test.c
@@ -131,4 +131,107 @@ TEST(listns_unprivileged_current_only)
 			unexpected_count);
 }
 
+/*
+ * Test that users with CAP_SYS_ADMIN in a user namespace can see
+ * all namespaces owned by that user namespace.
+ */
+TEST(listns_cap_sys_admin_in_userns)
+{
+	struct ns_id_req req = {
+		.size = sizeof(req),
+		.spare = 0,
+		.ns_id = 0,
+		.ns_type = 0,  /* All types */
+		.spare2 = 0,
+		.user_ns_id = 0,  /* Will be set to our created user namespace */
+	};
+	__u64 ns_ids[100];
+	int pipefd[2];
+	pid_t pid;
+	int status;
+	bool success;
+	ssize_t count;
+
+	ASSERT_EQ(pipe(pipefd), 0);
+
+	pid = fork();
+	ASSERT_GE(pid, 0);
+
+	if (pid == 0) {
+		int fd;
+		__u64 userns_id;
+		ssize_t ret;
+		int min_expected;
+		bool success;
+
+		close(pipefd[0]);
+
+		/* Create user namespace - we'll have CAP_SYS_ADMIN in it */
+		if (setup_userns() < 0) {
+			close(pipefd[1]);
+			exit(1);
+		}
+
+		/* Get the 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, &userns_id) < 0) {
+			close(fd);
+			close(pipefd[1]);
+			exit(1);
+		}
+		close(fd);
+
+		/* Create several namespaces owned by this user namespace */
+		unshare(CLONE_NEWNET);
+		unshare(CLONE_NEWUTS);
+		unshare(CLONE_NEWIPC);
+
+		/* List namespaces owned by our user namespace */
+		req.user_ns_id = userns_id;
+		ret = sys_listns(&req, ns_ids, ARRAY_SIZE(ns_ids), 0);
+		if (ret < 0) {
+			close(pipefd[1]);
+			exit(1);
+		}
+
+		/*
+		 * We have CAP_SYS_ADMIN in this user namespace,
+		 * so we should see all namespaces owned by it.
+		 * That includes: net, uts, ipc, and the user namespace itself.
+		 */
+		min_expected = 4;
+		success = (ret >= min_expected);
+
+		write(pipefd[1], &success, sizeof(success));
+		write(pipefd[1], &ret, sizeof(ret));
+		close(pipefd[1]);
+		exit(0);
+	}
+
+	/* Parent */
+	close(pipefd[1]);
+
+	success = false;
+	count = 0;
+	read(pipefd[0], &success, sizeof(success));
+	read(pipefd[0], &count, sizeof(count));
+	close(pipefd[0]);
+
+	waitpid(pid, &status, 0);
+	ASSERT_TRUE(WIFEXITED(status));
+
+	if (WEXITSTATUS(status) != 0) {
+		SKIP(return, "Child failed to setup namespaces");
+	}
+
+	ASSERT_TRUE(success);
+	TH_LOG("User with CAP_SYS_ADMIN saw %zd namespaces owned by their user namespace",
+			count);
+}
+
 TEST_HARNESS_MAIN

-- 
2.47.3