From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 17D1D1D6AA; Fri, 24 Oct 2025 10:53:01 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1761303182; cv=none; b=gNE15AX7myqD1mAtmX8d61uw/i4BqaKzwhX7CYX/auAD04FBMSEGnYiMCjC3K6kEjhHUcKa3KFo17MVOHkjGgrXyMeVgl7Q84oLuA3pn8qyo3NRiPNKzV9U3lfegeDhVVLpZsSOtp4N6sU57UNvosLYrXa1HWk9xBPEq6G0MKuE= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1761303182; c=relaxed/simple; bh=s4jA6uysR5hfK8fmn92d6JgvaQ+NRgfCNf08Y3dBEy8=; h=From:Subject:Date:Message-Id:MIME-Version:Content-Type:To:Cc; b=ZuUmCa63wnLarHzfC/WuqO0plyXZhbS3uKd6XAg4rjo+I5/Qfm88ttwYHGID4mhOJK1mVMfylZU/kl6uhRlB2HZ4Ypn2NQ8dhnwFfH1WxJN0fOKo8LNH4mNMakAFUCrCoSqkO3QPO4ZVtVGmXp62pwe3pN4dbVV8lynwmonAirU= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=r8LYVSCJ; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="r8LYVSCJ" Received: by smtp.kernel.org (Postfix) with ESMTPSA id D0BFDC4CEF1; Fri, 24 Oct 2025 10:52:56 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1761303181; bh=s4jA6uysR5hfK8fmn92d6JgvaQ+NRgfCNf08Y3dBEy8=; h=From:Subject:Date:To:Cc:From; b=r8LYVSCJf04pdbeJ83Tx7yiGtO6QtpwDHjYP/bjziHc9E/k2nH0Clbv+glufrcQmk 7y8G6JbUCLb3Ujubaau7aNRkLHaatTX+Z9tQ10L2/PC7/Z0YcMwnflG/J6hImVyz7L 6WfDC6XCyRGStdu3upVOp93WSvOxkRYxwii9nmD5ZHDuFURI2tjr/q5wo9dz2vL812 uVB4DGqS7m0dCpVLa9fKfvwkkDBJTv6DgJwprNhI+WAPbc1sw32BtzcXn+LzPoBmcH vGCfMpIJtGlO/sWF8x/FwKJskhamEzZjDAnwlZV31hLn3afA+WEpCjXtoy1x2hE3fP R36Nf3o/YkILA== From: Christian Brauner Subject: [PATCH v3 00/70] nstree: listns() Date: Fri, 24 Oct 2025 12:52:29 +0200 Message-Id: <20251024-work-namespace-nstree-listns-v3-0-b6241981b72b@kernel.org> Precedence: bulk X-Mailing-List: cgroups@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit X-B4-Tracking: v=1; b=H4sIAG1a+2gC/4XOwW7CMBAE0F9BPnejrMHE5dT/qDhsnIVYgBPtR gaE8u91kCrBpT3OYd7MwyhLZDW71cMI56hxSCWsP1Ym9JSODLEr2djaOqxtDddBTpDowjpSYEg 6CTOco05J4fPQNejQO3TBFGIUPsTbk//el9ySMrRCKfQLeiGdWKq8rdCDBFwqfZEGuT8PZVyKv 9v493ZGqIG6zcZukTy59uvEkvhcDXI0y3i2r5r9R7NFa5Cc966x6wbftHmefwBfG/8GOgEAAA= = X-Change-ID: 20251020-work-namespace-nstree-listns-9fd71518515c To: linux-fsdevel@vger.kernel.org, Josef Bacik , Jeff Layton Cc: Jann Horn , Mike Yuan , =?utf-8?q?Zbigniew_J=C4=99drzejewski-Szmek?= , Lennart Poettering , Daan De Meyer , Aleksa Sarai , Amir Goldstein , Tejun Heo , Johannes Weiner , Thomas Gleixner , Alexander Viro , Jan Kara , linux-kernel@vger.kernel.org, cgroups@vger.kernel.org, bpf@vger.kernel.org, Eric Dumazet , Jakub Kicinski , netdev@vger.kernel.org, Arnd Bergmann , Christian Brauner X-Mailer: b4 0.15-dev-96507 X-Developer-Signature: v=1; a=openpgp-sha256; l=21184; i=brauner@kernel.org; h=from:subject:message-id; bh=s4jA6uysR5hfK8fmn92d6JgvaQ+NRgfCNf08Y3dBEy8=; b=owGbwMvMwCU28Zj0gdSKO4sYT6slMWT8jmqR7z+3fRLTcbfs3/+rDwsVG0kUdX31yfxoYtT73 romTlm0o4SFQYyLQVZMkcWh3SRcbjlPxWajTA2YOaxMIEMYuDgFYCIzfjIyNHt7bOmWCTlw3VG/ KOWv6OQ/rWu8FD/9l32umCzDe/zBa4bv1Ud9dJvC50d8y8w+Ertamkk//fzRCRp714d6/yk8Wcw DAA== X-Developer-Key: i=brauner@kernel.org; a=openpgp; fpr=4880B8C9BD0E5106FC070F4F7B3C391EFEA93624 Hey, As announced a while ago this is the next step building on the nstree work from prior cycles. There's a bunch of fixes and semantic cleanups in here and a ton of tests. Currently listns() is relying on active namespace reference counts which are introduced alongside this series. While a namespace is on the namespace trees with a valid reference count it is possible to reopen it through a namespace file handle. This is all fine but has some issues that should be addressed. On current kernels a namespace is visible to userspace in the following cases: (1) The namespace is in use by a task. (2) The namespace is persisted through a VFS object (namespace file descriptor or bind-mount). Note that (2) only cares about direct persistence of the namespace itself not indirectly via e.g., file->f_cred file references or similar. (3) The namespace is a hierarchical namespace type and is the parent of a single or multiple child namespaces. Case (3) is interesting because it is possible that a parent namespace might not fulfill any of (1) or (2), i.e., is invisible to userspace but it may still be resurrected through the NS_GET_PARENT ioctl(). Currently namespace file handles allow much broader access to namespaces than what is currently possible via (1)-(3). The reason is that namespaces may remain pinned for completely internal reasons yet are inaccessible to userspace. For example, a user namespace my remain pinned by get_cred() calls to stash the opener's credentials into file->f_cred. As it stands file handles allow to resurrect such a users namespace even though this should not be possible via (1)-(3). This is a fundamental uapi change that we shouldn't do if we don't have to. Consider the following insane case: Various architectures support the CONFIG_MMU_LAZY_TLB_REFCOUNT option which uses lazy TLB destruction. When this option is set a userspace task's struct mm_struct may be used for kernel threads such as the idle task and will only be destroyed once the cpu's runqueue switches back to another task. But because of ptrace() permission checks struct mm_struct stashes the user namespace of the task that struct mm_struct originally belonged to. The kernel thread will take a reference on the struct mm_struct and thus pin it. So on an idle system user namespaces can be persisted for arbitrary amounts of time which also means that they can be resurrected using namespace file handles. That makes no sense whatsoever. The problem is of course excarabted on large systems with a huge number of cpus. To handle this nicely we introduce an active reference count which tracks (1)-(3). This is easy to do as all of these things are already managed centrally. Only (1)-(3) will count towards the active reference count and only namespaces which are active may be opened via namespace file handles. The problem is that namespaces may be resurrected. Which means that they can become temporarily inactive and will be reactived some time later. Currently the only example of this is the SIOGCSKNS socket ioctl. The SIOCGSKNS ioctl allows to open a network namespace file descriptor based on a socket file descriptor. If a socket is tied to a network namespace that subsequently becomes inactive but that socket is persisted by another process in another network namespace (e.g., via SCM_RIGHTS of pidfd_getfd()) then the SIOCGSKNS ioctl will resurrect this network namespace. So calls to open_related_ns() and open_namespace() will end up resurrecting the corresponding namespace tree. Note that the active reference count does not regulate the lifetime of the namespace itself. This is still done by the normal reference count. The active reference count can only be elevated if the regular reference count is elevated. The active reference count also doesn't regulate the presence of a namespace on the namespace trees. It only regulates its visiblity to namespace file handles (and in later patches to listns()). A namespace remains on the namespace trees from creation until its actual destruction. This will allow the kernel to always reach any namespace trivially and it will also enable subsystems like bpf to walk the namespace lists on the system for tracing or general introspection purposes. Note that different namespaces have different visibility lifetimes on current kernels. While most namespace are immediately released when the last task using them exits, the user- and pid namespace are persisted and thus both remain accessible via /proc//ns/. The user namespace lifetime is aliged with struct cred and is only released through exit_creds(). However, it becomes inaccessible to userspace once the last task using it is reaped, i.e., when release_task() is called and all proc entries are flushed. Similarly, the pid namespace is also visible until the last task using it has been reaped and the associated pid numbers are freed. The active reference counts of the user- and pid namespace are decremented once the task is reaped. Based on the namespace trees and the active reference count, a new listns() system call that allows userspace to iterate through namespaces in the system. This provides a programmatic interface to discover and inspect namespaces, enhancing existing namespace apis. Currently, there is no direct way for userspace to enumerate namespaces in the system. Applications must resort to scanning /proc//ns/ across all processes, which is: 1. Inefficient - requires iterating over all processes 2. Incomplete - misses inactive namespaces that aren't attached to any running process but are kept alive by file descriptors, bind mounts, or parent namespace references 3. Permission-heavy - requires access to /proc for many processes 4. No ordering or ownership. 5. No filtering per namespace type: Must always iterate and check all namespaces. The list goes on. The listns() system call solves these problems by providing direct kernel-level enumeration of namespaces. It is similar to listmount() but obviously tailored to namespaces. /* * @req: Pointer to struct ns_id_req specifying search parameters * @ns_ids: User buffer to receive namespace IDs * @nr_ns_ids: Size of ns_ids buffer (maximum number of IDs to return) * @flags: Reserved for future use (must be 0) */ ssize_t listns(const struct ns_id_req *req, u64 *ns_ids, size_t nr_ns_ids, unsigned int flags); Returns: - On success: Number of namespace IDs written to ns_ids - On error: Negative error code /* * @size: Structure size * @ns_id: Starting point for iteration; use 0 for first call, then * use the last returned ID for subsequent calls to paginate * @ns_type: Bitmask of namespace types to include (from enum ns_type): * 0: Return all namespace types * MNT_NS: Mount namespaces * NET_NS: Network namespaces * USER_NS: User namespaces * etc. Can be OR'd together * @user_ns_id: Filter results to namespaces owned by this user namespace: * 0: Return all namespaces (subject to permission checks) * LISTNS_CURRENT_USER: Namespaces owned by caller's user namespace * Other value: Namespaces owned by the specified user namespace ID */ struct ns_id_req { __u32 size; /* sizeof(struct ns_id_req) */ __u32 spare; /* Reserved, must be 0 */ __u64 ns_id; /* Last seen namespace ID (for pagination) */ __u32 ns_type; /* Filter by namespace type(s) */ __u32 spare2; /* Reserved, must be 0 */ __u64 user_ns_id; /* Filter by owning user namespace */ }; Example 1: List all namespaces void list_all_namespaces(void) { struct ns_id_req req = { .size = sizeof(req), .ns_id = 0, /* Start from beginning */ .ns_type = 0, /* All types */ .user_ns_id = 0, /* All user namespaces */ }; uint64_t ids[100]; ssize_t ret; printf("All namespaces in the system:\n"); do { ret = listns(&req, ids, 100, 0); if (ret < 0) { perror("listns"); break; } for (ssize_t i = 0; i < ret; i++) printf(" Namespace ID: %llu\n", (unsigned long long)ids[i]); /* Continue from last seen ID */ if (ret > 0) req.ns_id = ids[ret - 1]; } while (ret == 100); /* Buffer was full, more may exist */ } Example 2 : List network namespaces only void list_network_namespaces(void) { struct ns_id_req req = { .size = sizeof(req), .ns_id = 0, .ns_type = NET_NS, /* Only network namespaces */ .user_ns_id = 0, }; uint64_t ids[100]; ssize_t ret; ret = listns(&req, ids, 100, 0); if (ret < 0) { perror("listns"); return; } printf("Network namespaces: %zd found\n", ret); for (ssize_t i = 0; i < ret; i++) printf(" netns ID: %llu\n", (unsigned long long)ids[i]); } Example 3 : List namespaces owned by current user namespace void list_owned_namespaces(void) { struct ns_id_req req = { .size = sizeof(req), .ns_id = 0, .ns_type = 0, /* All types */ .user_ns_id = LISTNS_CURRENT_USER, /* Current userns */ }; uint64_t ids[100]; ssize_t ret; ret = listns(&req, ids, 100, 0); if (ret < 0) { perror("listns"); return; } printf("Namespaces owned by my user namespace: %zd\n", ret); for (ssize_t i = 0; i < ret; i++) printf(" ns ID: %llu\n", (unsigned long long)ids[i]); } Example 4 : List multiple namespace types void list_network_and_mount_namespaces(void) { struct ns_id_req req = { .size = sizeof(req), .ns_id = 0, .ns_type = NET_NS | MNT_NS, /* Network and mount */ .user_ns_id = 0, }; uint64_t ids[100]; ssize_t ret; ret = listns(&req, ids, 100, 0); printf("Network and mount namespaces: %zd found\n", ret); } Example 5 : Pagination through large namespace sets void list_all_with_pagination(void) { struct ns_id_req req = { .size = sizeof(req), .ns_id = 0, .ns_type = 0, .user_ns_id = 0, }; uint64_t ids[50]; size_t total = 0; ssize_t ret; printf("Enumerating all namespaces with pagination:\n"); while (1) { ret = listns(&req, ids, 50, 0); if (ret < 0) { perror("listns"); break; } if (ret == 0) break; /* No more namespaces */ total += ret; printf(" Batch: %zd namespaces\n", ret); /* Last ID in this batch becomes start of next batch */ req.ns_id = ids[ret - 1]; if (ret < 50) break; /* Partial batch = end of results */ } printf("Total: %zu namespaces\n", total); } listns() respects namespace isolation and capabilities: (1) Global listing (user_ns_id = 0): - Requires CAP_SYS_ADMIN in the namespace's owning user namespace - OR the namespace must be in the caller's namespace context (e.g., a namespace the caller is currently using) - User namespaces additionally allow listing if the caller has CAP_SYS_ADMIN in that user namespace itself (2) Owner-filtered listing (user_ns_id != 0): - Requires CAP_SYS_ADMIN in the specified owner user namespace - OR the namespace must be in the caller's namespace context - This allows unprivileged processes to enumerate namespaces they own (3) Visibility: - Only "active" namespaces are listed - A namespace is active if it has a non-zero __ns_ref_active count - This includes namespaces used by running processes, held by open file descriptors, or kept active by bind mounts - Inactive namespaces (kept alive only by internal kernel references) are not visible via listns() Signed-off-by: Christian Brauner --- Changes in v3: - Expanded test-suite. - Moved active reference count tracking for task-attached namespaces to dedicated helpers. - Fixed active reference count leaks when creating a new process fails. - Allow to be rescheduled when walking a a long namespace list. - Grab reference count when accessing a namespace when walking the list. - Link to v2: https://patch.msgid.link/20251022-work-namespace-nstree-listns-v2-0-71a588572371@kernel.org Changes in v2: - Fully implement the active reference count. - Fix various minor issues. - Expand the testsuite to test complex resurrection scenarios due to SIOCGSKNS. - Currently each task takes an active reference on the user namespace as credentials can be persisted for a very long time and completely arbitrary reasons but we don't want to tie the lifetime of a user namespace being visible to userspace to the existence of some credentials being stashed somewhere. We want to tie it to it being in-use by actual tasks or vfs objects and then go away. There might be more clever ways of doing this but for now this is good enough. - TODO: Add detailed tests for multi-threaded namespace sharing. - Link to v1: https://patch.msgid.link/20251021-work-namespace-nstree-listns-v1-0-ad44261a8a5b@kernel.org --- Christian Brauner (70): libfs: allow to specify s_d_flags nsfs: use inode_just_drop() nsfs: raise DCACHE_DONTCACHE explicitly pidfs: raise DCACHE_DONTCACHE explicitly nsfs: raise SB_I_NODEV and SB_I_NOEXEC cgroup: add cgroup namespace to tree after owner is set nstree: simplify return ns: initialize ns_list_node for initial namespaces ns: add __ns_ref_read() ns: rename to exit_nsproxy_namespaces() ns: add active reference count ns: use anonymous struct to group list member nstree: introduce a unified tree nstree: allow lookup solely based on inode nstree: assign fixed ids to the initial namespaces ns: maintain list of owned namespaces nstree: add listns() arch: hookup listns() system call nsfs: update tools header selftests/filesystems: remove CLONE_NEWPIDNS from setup_userns() helper selftests/namespaces: first active reference count tests selftests/namespaces: second active reference count tests selftests/namespaces: third active reference count tests selftests/namespaces: fourth active reference count tests selftests/namespaces: fifth active reference count tests selftests/namespaces: sixth active reference count tests selftests/namespaces: seventh active reference count tests selftests/namespaces: eigth active reference count tests selftests/namespaces: ninth active reference count tests selftests/namespaces: tenth active reference count tests selftests/namespaces: eleventh active reference count tests selftests/namespaces: twelth active reference count tests selftests/namespaces: thirteenth active reference count tests selftests/namespaces: fourteenth active reference count tests selftests/namespaces: fifteenth active reference count tests selftests/namespaces: add listns() wrapper selftests/namespaces: first listns() test selftests/namespaces: second listns() test selftests/namespaces: third listns() test selftests/namespaces: fourth listns() test selftests/namespaces: fifth listns() test selftests/namespaces: sixth listns() test selftests/namespaces: seventh listns() test selftests/namespaces: eigth listns() test selftests/namespaces: ninth listns() test selftests/namespaces: first listns() permission test selftests/namespaces: second listns() permission test selftests/namespaces: third listns() permission test selftests/namespaces: fourth listns() permission test selftests/namespaces: fifth listns() permission test selftests/namespaces: sixth listns() permission test selftests/namespaces: seventh listns() permission test selftests/namespaces: first inactive namespace resurrection test selftests/namespaces: second inactive namespace resurrection test selftests/namespaces: third inactive namespace resurrection test selftests/namespaces: fourth inactive namespace resurrection test selftests/namespaces: fifth inactive namespace resurrection test selftests/namespaces: sixth inactive namespace resurrection test selftests/namespaces: seventh inactive namespace resurrection test selftests/namespaces: eigth inactive namespace resurrection test selftests/namespaces: ninth inactive namespace resurrection test selftests/namespaces: tenth inactive namespace resurrection test selftests/namespaces: eleventh inactive namespace resurrection test selftests/namespaces: twelth inactive namespace resurrection test selftests/namespace: first threaded active reference count test selftests/namespace: second threaded active reference count test selftests/namespace: third threaded active reference count test selftests/namespace: commit_creds() active reference tests selftests/namespace: add stress test selftests/namespace: test listns() pagination arch/alpha/kernel/syscalls/syscall.tbl | 1 + arch/arm/tools/syscall.tbl | 1 + arch/arm64/tools/syscall_32.tbl | 1 + arch/m68k/kernel/syscalls/syscall.tbl | 1 + arch/microblaze/kernel/syscalls/syscall.tbl | 1 + arch/mips/kernel/syscalls/syscall_n32.tbl | 1 + arch/mips/kernel/syscalls/syscall_n64.tbl | 1 + arch/mips/kernel/syscalls/syscall_o32.tbl | 1 + arch/parisc/kernel/syscalls/syscall.tbl | 1 + arch/powerpc/kernel/syscalls/syscall.tbl | 1 + arch/s390/kernel/syscalls/syscall.tbl | 1 + arch/sh/kernel/syscalls/syscall.tbl | 1 + arch/sparc/kernel/syscalls/syscall.tbl | 1 + arch/x86/entry/syscalls/syscall_32.tbl | 1 + arch/x86/entry/syscalls/syscall_64.tbl | 1 + arch/xtensa/kernel/syscalls/syscall.tbl | 1 + fs/libfs.c | 1 + fs/namespace.c | 8 +- fs/nsfs.c | 95 +- fs/pidfs.c | 1 + include/linux/ns_common.h | 166 +- include/linux/nsfs.h | 3 + include/linux/nsproxy.h | 5 +- include/linux/nstree.h | 26 +- include/linux/pseudo_fs.h | 1 + include/linux/syscalls.h | 4 + include/linux/user_namespace.h | 4 +- include/uapi/asm-generic/unistd.h | 4 +- include/uapi/linux/nsfs.h | 58 + init/version-timestamp.c | 5 + ipc/msgutil.c | 5 + ipc/namespace.c | 1 + kernel/cgroup/cgroup.c | 11 +- kernel/cgroup/namespace.c | 3 +- kernel/cred.c | 6 + kernel/exit.c | 3 +- kernel/fork.c | 3 +- kernel/nscommon.c | 227 +- kernel/nsproxy.c | 25 +- kernel/nstree.c | 540 +++- kernel/pid.c | 10 + kernel/pid_namespace.c | 1 + kernel/time/namespace.c | 6 + kernel/user.c | 5 + kernel/user_namespace.c | 1 + kernel/utsname.c | 1 + net/core/net_namespace.c | 3 +- scripts/syscall.tbl | 1 + tools/include/uapi/linux/nsfs.h | 70 + tools/testing/selftests/filesystems/utils.c | 2 +- tools/testing/selftests/namespaces/.gitignore | 7 + tools/testing/selftests/namespaces/Makefile | 20 +- .../selftests/namespaces/cred_change_test.c | 814 ++++++ .../selftests/namespaces/listns_pagination_bug.c | 138 + .../selftests/namespaces/listns_permissions_test.c | 759 ++++++ tools/testing/selftests/namespaces/listns_test.c | 679 +++++ .../selftests/namespaces/ns_active_ref_test.c | 2672 ++++++++++++++++++++ .../testing/selftests/namespaces/siocgskns_test.c | 1824 +++++++++++++ tools/testing/selftests/namespaces/stress_test.c | 626 +++++ tools/testing/selftests/namespaces/wrappers.h | 35 + 60 files changed, 8835 insertions(+), 60 deletions(-) --- base-commit: 3a8660878839faadb4f1a6dd72c3179c1df56787 change-id: 20251020-work-namespace-nstree-listns-9fd71518515c