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selftests/namespaces: sixth active reference count tests

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Test that an open file descriptor keeps a namespace active.
Even after the creating process exits, the namespace should remain
active as long as an fd is held open.

Link: https://patch.msgid.link/20251029-work-namespace-nstree-listns-v4-28-2e6f823ebdc0@kernel.org
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Christian Brauner <brauner@kernel.org>
This commit is contained in:
Christian Brauner 2025-10-29 13:20:41 +01:00
parent c4803b255f
commit 47a5fd8ce1
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GPG Key ID: 91C61BC06578DCA2
1 changed files with 155 additions and 0 deletions
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155
tools/testing/selftests/namespaces/ns_active_ref_test.c
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@ -448,4 +448,159 @@ TEST(pidns_active_ref_lifecycle)
ASSERT_TRUE(errno == ENOENT || errno == ESTALE);
}
/*
* Test that an open file descriptor keeps a namespace active.
* Even after the creating process exits, the namespace should remain
* active as long as an fd is held open.
*/
TEST(ns_fd_keeps_active)
{
struct file_handle *handle;
int mount_id;
int ret;
int nsfd;
int pipe_child_ready[2];
int pipe_parent_ready[2];
pid_t pid;
int status;
char buf[sizeof(*handle) + MAX_HANDLE_SZ];
char sync_byte;
char proc_path[64];
ASSERT_EQ(pipe(pipe_child_ready), 0);
ASSERT_EQ(pipe(pipe_parent_ready), 0);
pid = fork();
ASSERT_GE(pid, 0);
if (pid == 0) {
/* Child process */
close(pipe_child_ready[0]);
close(pipe_parent_ready[1]);
TH_LOG("Child: creating new network namespace");
/* Create new network namespace */
ret = unshare(CLONE_NEWNET);
if (ret < 0) {
TH_LOG("Child: unshare(CLONE_NEWNET) failed: %s", strerror(errno));
close(pipe_child_ready[1]);
close(pipe_parent_ready[0]);
exit(1);
}
TH_LOG("Child: network namespace created successfully");
/* Get file handle for the namespace */
nsfd = open("/proc/self/ns/net", O_RDONLY);
if (nsfd < 0) {
TH_LOG("Child: failed to open /proc/self/ns/net: %s", strerror(errno));
close(pipe_child_ready[1]);
close(pipe_parent_ready[0]);
exit(1);
}
TH_LOG("Child: opened namespace fd %d", nsfd);
handle = (struct file_handle *)buf;
handle->handle_bytes = MAX_HANDLE_SZ;
ret = name_to_handle_at(nsfd, "", handle, &mount_id, AT_EMPTY_PATH);
close(nsfd);
if (ret < 0) {
TH_LOG("Child: name_to_handle_at failed: %s", strerror(errno));
close(pipe_child_ready[1]);
close(pipe_parent_ready[0]);
exit(1);
}
TH_LOG("Child: got file handle (bytes=%u)", handle->handle_bytes);
/* Send file handle to parent */
ret = write(pipe_child_ready[1], buf, sizeof(*handle) + handle->handle_bytes);
TH_LOG("Child: sent %d bytes of file handle to parent", ret);
close(pipe_child_ready[1]);
/* Wait for parent to open the fd */
TH_LOG("Child: waiting for parent to open fd");
ret = read(pipe_parent_ready[0], &sync_byte, 1);
close(pipe_parent_ready[0]);
TH_LOG("Child: parent signaled (read %d bytes), exiting now", ret);
/* Exit - namespace should stay active because parent holds fd */
exit(0);
}
/* Parent process */
close(pipe_child_ready[1]);
close(pipe_parent_ready[0]);
TH_LOG("Parent: reading file handle from child");
/* Read file handle from child */
ret = read(pipe_child_ready[0], buf, sizeof(buf));
close(pipe_child_ready[0]);
ASSERT_GT(ret, 0);
handle = (struct file_handle *)buf;
TH_LOG("Parent: received %d bytes, handle size=%u", ret, handle->handle_bytes);
/* Open the child's namespace while it's still alive */
snprintf(proc_path, sizeof(proc_path), "/proc/%d/ns/net", pid);
TH_LOG("Parent: opening child's namespace at %s", proc_path);
nsfd = open(proc_path, O_RDONLY);
if (nsfd < 0) {
TH_LOG("Parent: failed to open %s: %s", proc_path, strerror(errno));
close(pipe_parent_ready[1]);
kill(pid, SIGKILL);
waitpid(pid, NULL, 0);
SKIP(return, "Failed to open child's namespace");
}
TH_LOG("Parent: opened child's namespace, got fd %d", nsfd);
/* Signal child that we have the fd */
sync_byte = 'G';
write(pipe_parent_ready[1], &sync_byte, 1);
close(pipe_parent_ready[1]);
TH_LOG("Parent: signaled child that we have the fd");
/* Wait for child to exit */
waitpid(pid, &status, 0);
ASSERT_TRUE(WIFEXITED(status));
ASSERT_EQ(WEXITSTATUS(status), 0);
TH_LOG("Child exited, parent holds fd %d to namespace", nsfd);
/*
* Namespace should still be ACTIVE because we hold an fd.
* We should be able to reopen it via file handle.
*/
TH_LOG("Attempting to reopen namespace via file handle (should succeed - fd held)");
int fd2 = open_by_handle_at(FD_NSFS_ROOT, handle, O_RDONLY);
ASSERT_GE(fd2, 0);
TH_LOG("Successfully reopened namespace via file handle, got fd %d", fd2);
/* Verify it's the same namespace */
struct stat st1, st2;
ASSERT_EQ(fstat(nsfd, &st1), 0);
ASSERT_EQ(fstat(fd2, &st2), 0);
TH_LOG("Namespace inodes: nsfd=%lu, fd2=%lu", st1.st_ino, st2.st_ino);
ASSERT_EQ(st1.st_ino, st2.st_ino);
close(fd2);
/* Now close the fd - namespace should become inactive */
TH_LOG("Closing fd %d - namespace should become inactive", nsfd);
close(nsfd);
/* Now reopening should fail - namespace is inactive */
TH_LOG("Attempting to reopen namespace via file handle (should fail - inactive)");
fd2 = open_by_handle_at(FD_NSFS_ROOT, handle, O_RDONLY);
ASSERT_LT(fd2, 0);
/* Should fail with ENOENT (inactive) or ESTALE (gone) */
TH_LOG("Reopen failed as expected: %s (errno=%d)", strerror(errno), errno);
ASSERT_TRUE(errno == ENOENT || errno == ESTALE);
}
TEST_HARNESS_MAIN