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.

Link: https://patch.msgid.link/20251029-work-namespace-nstree-listns-v4-56-2e6f823ebdc0@kernel.org
Tested-by: syzbot@syzkaller.appspotmail.com
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Christian Brauner <brauner@kernel.org>

diff --git a/tools/testing/selftests/namespaces/siocgskns_test.c b/tools/testing/selftests/namespaces/siocgskns_test.c
index 0c9098624cd4ef912a68391cc538ef30d04856a8..0ad5e39b7e1686d3185e146d1a4db0288514f2b5 100644 (file)
--- 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