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Message-Id: <20251022-work-namespace-nstree-listns-v2-53-71a588572371@kernel.org>
Date: Wed, 22 Oct 2025 18:06:31 +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 v2 53/63] selftests/namespaces: second inactive namespace
resurrection test
Test that socket file descriptors keep network namespaces active. Create
a network namespace, create a socket in it, then exit the namespace. The
namespace should remain active while the socket FD is held.
Signed-off-by: Christian Brauner <brauner@...nel.org>
---
.../testing/selftests/namespaces/siocgskns_test.c | 126 +++++++++++++++++++++
1 file changed, 126 insertions(+)
diff --git a/tools/testing/selftests/namespaces/siocgskns_test.c b/tools/testing/selftests/namespaces/siocgskns_test.c
index 0c9098624cd4..0ad5e39b7e16 100644
--- a/tools/testing/selftests/namespaces/siocgskns_test.c
+++ b/tools/testing/selftests/namespaces/siocgskns_test.c
@@ -69,4 +69,130 @@ TEST(siocgskns_basic)
close(current_netns_fd);
}
+/*
+ * Test that socket file descriptors keep network namespaces active.
+ * Create a network namespace, create a socket in it, then exit the namespace.
+ * The namespace should remain active while the socket FD is held.
+ */
+TEST(siocgskns_keeps_netns_active)
+{
+ int sock_fd, netns_fd, test_fd;
+ int ipc_sockets[2];
+ pid_t pid;
+ int status;
+ struct stat st;
+
+ EXPECT_EQ(socketpair(AF_LOCAL, SOCK_STREAM | SOCK_CLOEXEC, 0, ipc_sockets), 0);
+
+ pid = fork();
+ ASSERT_GE(pid, 0);
+
+ if (pid == 0) {
+ /* Child: create new netns and socket */
+ close(ipc_sockets[0]);
+
+ if (unshare(CLONE_NEWNET) < 0) {
+ TH_LOG("unshare(CLONE_NEWNET) failed: %s", strerror(errno));
+ close(ipc_sockets[1]);
+ exit(1);
+ }
+
+ /* Create a socket in the new network namespace */
+ sock_fd = socket(AF_INET, SOCK_DGRAM, 0);
+ if (sock_fd < 0) {
+ TH_LOG("socket() failed: %s", strerror(errno));
+ close(ipc_sockets[1]);
+ exit(1);
+ }
+
+ /* Send socket FD to parent via SCM_RIGHTS */
+ struct msghdr msg = {0};
+ struct iovec iov = {0};
+ char buf[1] = {'X'};
+ char cmsg_buf[CMSG_SPACE(sizeof(int))];
+
+ iov.iov_base = buf;
+ iov.iov_len = 1;
+ msg.msg_iov = &iov;
+ msg.msg_iovlen = 1;
+ msg.msg_control = cmsg_buf;
+ msg.msg_controllen = sizeof(cmsg_buf);
+
+ struct cmsghdr *cmsg = CMSG_FIRSTHDR(&msg);
+ cmsg->cmsg_level = SOL_SOCKET;
+ cmsg->cmsg_type = SCM_RIGHTS;
+ cmsg->cmsg_len = CMSG_LEN(sizeof(int));
+ memcpy(CMSG_DATA(cmsg), &sock_fd, sizeof(int));
+
+ if (sendmsg(ipc_sockets[1], &msg, 0) < 0) {
+ close(sock_fd);
+ close(ipc_sockets[1]);
+ exit(1);
+ }
+
+ close(sock_fd);
+ close(ipc_sockets[1]);
+ exit(0);
+ }
+
+ /* Parent: receive socket FD */
+ close(ipc_sockets[1]);
+
+ struct msghdr msg = {0};
+ struct iovec iov = {0};
+ char buf[1];
+ char cmsg_buf[CMSG_SPACE(sizeof(int))];
+
+ iov.iov_base = buf;
+ iov.iov_len = 1;
+ msg.msg_iov = &iov;
+ msg.msg_iovlen = 1;
+ msg.msg_control = cmsg_buf;
+ msg.msg_controllen = sizeof(cmsg_buf);
+
+ ssize_t n = recvmsg(ipc_sockets[0], &msg, 0);
+ close(ipc_sockets[0]);
+ ASSERT_EQ(n, 1);
+
+ struct cmsghdr *cmsg = CMSG_FIRSTHDR(&msg);
+ ASSERT_NE(cmsg, NULL);
+ ASSERT_EQ(cmsg->cmsg_type, SCM_RIGHTS);
+
+ memcpy(&sock_fd, CMSG_DATA(cmsg), sizeof(int));
+
+ /* Wait for child to exit */
+ waitpid(pid, &status, 0);
+ ASSERT_TRUE(WIFEXITED(status));
+ if (WEXITSTATUS(status) != 0)
+ SKIP(close(sock_fd); return, "Child failed to create namespace");
+
+ /* Get network namespace from socket */
+ netns_fd = ioctl(sock_fd, SIOCGSKNS);
+ if (netns_fd < 0) {
+ close(sock_fd);
+ if (errno == ENOTTY || errno == EINVAL)
+ SKIP(return, "SIOCGSKNS not supported");
+ ASSERT_GE(netns_fd, 0);
+ }
+
+ ASSERT_EQ(fstat(netns_fd, &st), 0);
+
+ /*
+ * Namespace should still be active because socket FD keeps it alive.
+ * Try to access it via /proc/self/fd/<fd>.
+ */
+ char path[64];
+ snprintf(path, sizeof(path), "/proc/self/fd/%d", netns_fd);
+ test_fd = open(path, O_RDONLY);
+ ASSERT_GE(test_fd, 0);
+ close(test_fd);
+ close(netns_fd);
+
+ /* Close socket - namespace should become inactive */
+ close(sock_fd);
+
+ /* Try SIOCGSKNS again - should fail since socket is closed */
+ ASSERT_LT(ioctl(sock_fd, SIOCGSKNS), 0);
+}
+
TEST_HARNESS_MAIN
--
2.47.3
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