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Add a test suite for the CLONE_EMPTY_MNTNS flag exercising the empty mount namespace functionality through the clone3() syscall. The clone3() code path is distinct from the unshare() path already tested in empty_mntns_test.c. With clone3(), CLONE_EMPTY_MNTNS (0x400000000ULL) is a 64-bit flag that implies CLONE_NEWNS. The implication happens in kernel_clone() before copy_process(), unlike unshare() where it goes through UNSHARE_EMPTY_MNTNS to CLONE_EMPTY_MNTNS conversion in unshare_nsproxy_namespaces(). The tests cover: - basic functionality: clone3 child gets empty mount namespace with exactly one mount, root and cwd point to the same mount - CLONE_NEWNS implication: CLONE_EMPTY_MNTNS works without explicit CLONE_NEWNS, also works with redundant CLONE_NEWNS - flag interactions: combines correctly with CLONE_NEWUSER, CLONE_NEWPID, CLONE_NEWUTS, CLONE_NEWIPC, CLONE_PIDFD - mutual exclusion: CLONE_EMPTY_MNTNS | CLONE_FS returns EINVAL because the implied CLONE_NEWNS conflicts with CLONE_FS - error paths: EPERM without capabilities, unknown 64-bit flags rejected - parent isolation: parent mount namespace is unchanged after clone - many parent mounts: child still gets exactly one mount - mount properties: root mount is nullfs, is its own parent, is the only listmount entry - overmount workflow: child can mount tmpfs over nullfs root to build a writable filesystem from scratch - repeated clone3: each child gets a distinct mount namespace - setns: parent can join child's empty mount namespace via setns() - regression: plain CLONE_NEWNS via clone3 still copies the full mount tree Link: https://patch.msgid.link/20260306-work-empty-mntns-consolidated-v1-3-6eb30529bbb0@kernel.org Signed-off-by: Christian Brauner <brauner@kernel.org> |
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