From c9822fad8038870bb690543539c8e9ad5213b12f Mon Sep 17 00:00:00 2001 From: Christian Brauner Date: Wed, 29 Oct 2025 13:20:14 +0100 Subject: libfs: allow to specify s_d_flags Make it possible for pseudo filesystems to specify default dentry flags. Link: https://patch.msgid.link/20251029-work-namespace-nstree-listns-v4-1-2e6f823ebdc0@kernel.org Tested-by: syzbot@syzkaller.appspotmail.com Reviewed-by: Jeff Layton Signed-off-by: Christian Brauner --- include/linux/pseudo_fs.h | 1 + 1 file changed, 1 insertion(+) (limited to 'include') diff --git a/include/linux/pseudo_fs.h b/include/linux/pseudo_fs.h index 2503f7625d65..a651e60d9410 100644 --- a/include/linux/pseudo_fs.h +++ b/include/linux/pseudo_fs.h @@ -9,6 +9,7 @@ struct pseudo_fs_context { const struct xattr_handler * const *xattr; const struct dentry_operations *dops; unsigned long magic; + unsigned int s_d_flags; }; struct pseudo_fs_context *init_pseudo(struct fs_context *fc, -- cgit v1.2.3 From 8627bc8c7d815d929ad59407e13458b564870acf Mon Sep 17 00:00:00 2001 From: Christian Brauner Date: Mon, 3 Nov 2025 17:34:18 +0100 Subject: ns: add missing authorship I authored the files a short while ago. Signed-off-by: Christian Brauner --- include/linux/nstree.h | 1 + 1 file changed, 1 insertion(+) (limited to 'include') diff --git a/include/linux/nstree.h b/include/linux/nstree.h index 8b8636690473..43aa262c0ea1 100644 --- a/include/linux/nstree.h +++ b/include/linux/nstree.h @@ -1,4 +1,5 @@ /* SPDX-License-Identifier: GPL-2.0 */ +/* Copyright (c) 2025 Christian Brauner */ #ifndef _LINUX_NSTREE_H #define _LINUX_NSTREE_H -- cgit v1.2.3 From d915fe20e5cba4bd50e41e792a32dcddc7490e25 Mon Sep 17 00:00:00 2001 From: Christian Brauner Date: Mon, 3 Nov 2025 16:10:10 +0100 Subject: ns: add NS_COMMON_INIT() Add an initializer that can be used for the ns common initialization for static namespace such as most init namespaces. Suggested-by: Thomas Gleixner Link: https://patch.msgid.link/87ecqhy2y5.ffs@tglx Signed-off-by: Christian Brauner --- include/linux/ns_common.h | 10 ++++++++++ 1 file changed, 10 insertions(+) (limited to 'include') diff --git a/include/linux/ns_common.h b/include/linux/ns_common.h index f5b68b8abb54..3a72c3f81eca 100644 --- a/include/linux/ns_common.h +++ b/include/linux/ns_common.h @@ -119,6 +119,16 @@ void __ns_common_free(struct ns_common *ns); struct user_namespace *: CLONE_NEWUSER, \ struct uts_namespace *: CLONE_NEWUTS) +#define NS_COMMON_INIT(nsname, refs) \ +{ \ + .ns_type = ns_common_type(&nsname), \ + .ns_id = 0, \ + .inum = ns_init_inum(&nsname), \ + .ops = to_ns_operations(&nsname), \ + .stashed = NULL, \ + .__ns_ref = REFCOUNT_INIT(refs), \ +} + #define ns_common_init(__ns) \ __ns_common_init(to_ns_common(__ns), \ ns_common_type(__ns), \ -- cgit v1.2.3 From 3dd50c58664e2684bd610a57bf3ab713cbb0ea91 Mon Sep 17 00:00:00 2001 From: Christian Brauner Date: Wed, 29 Oct 2025 13:20:21 +0100 Subject: ns: initialize ns_list_node for initial namespaces Make sure that the list is always initialized for initial namespaces. Link: https://patch.msgid.link/20251029-work-namespace-nstree-listns-v4-8-2e6f823ebdc0@kernel.org Fixes: 885fc8ac0a4d ("nstree: make iterator generic") Tested-by: syzbot@syzkaller.appspotmail.com Reviewed-by: Jeff Layton Signed-off-by: Christian Brauner --- include/linux/ns_common.h | 1 + 1 file changed, 1 insertion(+) (limited to 'include') diff --git a/include/linux/ns_common.h b/include/linux/ns_common.h index 3a72c3f81eca..71a5e28344d1 100644 --- a/include/linux/ns_common.h +++ b/include/linux/ns_common.h @@ -127,6 +127,7 @@ void __ns_common_free(struct ns_common *ns); .ops = to_ns_operations(&nsname), \ .stashed = NULL, \ .__ns_ref = REFCOUNT_INIT(refs), \ + .ns_list_node = LIST_HEAD_INIT(nsname.ns.ns_list_node), \ } #define ns_common_init(__ns) \ -- cgit v1.2.3 From 6b053576edb12c7739ea9c7c9900031361922631 Mon Sep 17 00:00:00 2001 From: Christian Brauner Date: Wed, 29 Oct 2025 13:20:22 +0100 Subject: ns: add __ns_ref_read() Implement ns_ref_read() the same way as ns_ref_{get,put}(). No point in making that any more special or different from the other helpers. Link: https://patch.msgid.link/20251029-work-namespace-nstree-listns-v4-9-2e6f823ebdc0@kernel.org Tested-by: syzbot@syzkaller.appspotmail.com Reviewed-by: Jeff Layton Signed-off-by: Christian Brauner --- include/linux/ns_common.h | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-) (limited to 'include') diff --git a/include/linux/ns_common.h b/include/linux/ns_common.h index 71a5e28344d1..5e09facafd93 100644 --- a/include/linux/ns_common.h +++ b/include/linux/ns_common.h @@ -154,7 +154,12 @@ static __always_inline __must_check bool __ns_ref_get(struct ns_common *ns) return refcount_inc_not_zero(&ns->__ns_ref); } -#define ns_ref_read(__ns) refcount_read(&to_ns_common((__ns))->__ns_ref) +static __always_inline __must_check int __ns_ref_read(const struct ns_common *ns) +{ + return refcount_read(&ns->__ns_ref); +} + +#define ns_ref_read(__ns) __ns_ref_read(to_ns_common((__ns))) #define ns_ref_inc(__ns) refcount_inc(&to_ns_common((__ns))->__ns_ref) #define ns_ref_get(__ns) __ns_ref_get(to_ns_common((__ns))) #define ns_ref_put(__ns) __ns_ref_put(to_ns_common((__ns))) -- cgit v1.2.3 From 4b06b70c8244b442d58ae0fb59870cf31fdb422e Mon Sep 17 00:00:00 2001 From: Christian Brauner Date: Wed, 29 Oct 2025 13:20:23 +0100 Subject: ns: rename to exit_nsproxy_namespaces() The current naming is very misleading as this really isn't exiting all of the task's namespaces. It is only exiting the namespaces that hang of off nsproxy. Reflect that in the name. Link: https://patch.msgid.link/20251029-work-namespace-nstree-listns-v4-10-2e6f823ebdc0@kernel.org Reviewed-by: Jeff Layton Signed-off-by: Christian Brauner --- include/linux/nsproxy.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'include') diff --git a/include/linux/nsproxy.h b/include/linux/nsproxy.h index bd118a187dec..538ba8dba184 100644 --- a/include/linux/nsproxy.h +++ b/include/linux/nsproxy.h @@ -93,7 +93,7 @@ static inline struct cred *nsset_cred(struct nsset *set) */ int copy_namespaces(u64 flags, struct task_struct *tsk); -void exit_task_namespaces(struct task_struct *tsk); +void exit_nsproxy_namespaces(struct task_struct *tsk); void switch_task_namespaces(struct task_struct *tsk, struct nsproxy *new); int exec_task_namespaces(void); void free_nsproxy(struct nsproxy *ns); -- cgit v1.2.3 From 3a18f809184bc5a1cfad7cde5b8b026e2ff61587 Mon Sep 17 00:00:00 2001 From: Christian Brauner Date: Wed, 29 Oct 2025 13:20:24 +0100 Subject: ns: add active reference count The namespace tree is, among other things, currently used to support file handles for namespaces. When a namespace is created it is placed on the namespace trees and when it is destroyed it is removed from the namespace trees. 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. Link: https://patch.msgid.link/20251029-work-namespace-nstree-listns-v4-11-2e6f823ebdc0@kernel.org Signed-off-by: Christian Brauner --- include/linux/ns_common.h | 141 +++++++++++++++++++++++++++++++++++++++++++++- include/linux/nsfs.h | 3 + include/linux/nsproxy.h | 3 + 3 files changed, 145 insertions(+), 2 deletions(-) (limited to 'include') diff --git a/include/linux/ns_common.h b/include/linux/ns_common.h index 5e09facafd93..bdd0df15ad9c 100644 --- a/include/linux/ns_common.h +++ b/include/linux/ns_common.h @@ -4,7 +4,9 @@ #include #include +#include #include +#include struct proc_ns_operations; @@ -37,6 +39,67 @@ extern const struct proc_ns_operations cgroupns_operations; extern const struct proc_ns_operations timens_operations; extern const struct proc_ns_operations timens_for_children_operations; +/* + * Namespace lifetimes are managed via a two-tier reference counting model: + * + * (1) __ns_ref (refcount_t): Main reference count tracking memory + * lifetime. Controls when the namespace structure itself is freed. + * It also pins the namespace on the namespace trees whereas (2) + * only regulates their visibility to userspace. + * + * (2) __ns_ref_active (atomic_t): Reference count tracking active users. + * Controls visibility of the namespace in the namespace trees. + * Any live task that uses the namespace (via nsproxy or cred) holds + * an active reference. Any open file descriptor or bind-mount of + * the namespace holds an active reference. Once all tasks have + * called exited their namespaces and all file descriptors and + * bind-mounts have been released the active reference count drops + * to zero and the namespace becomes inactive. IOW, the namespace + * cannot be listed or opened via file handles anymore. + * + * Note that it is valid to transition from active to inactive and + * back from inactive to active e.g., when resurrecting an inactive + * namespace tree via the SIOCGSKNS ioctl(). + * + * Relationship and lifecycle states: + * + * - Active (__ns_ref_active > 0): + * Namespace is actively used and visible to userspace. The namespace + * can be reopened via /proc//ns/, via namespace file + * handles, or discovered via listns(). + * + * - Inactive (__ns_ref_active == 0, __ns_ref > 0): + * No tasks are actively using the namespace and it isn't pinned by + * any bind-mounts or open file descriptors anymore. But the namespace + * is still kept alive by internal references. For example, the user + * namespace could be pinned by an open file through file->f_cred + * references when one of the now defunct tasks had opened a file and + * handed the file descriptor off to another process via a UNIX + * sockets. Such references keep the namespace structure alive through + * __ns_ref but will not hold an active reference. + * + * - Destroyed (__ns_ref == 0): + * No references remain. The namespace is removed from the tree and freed. + * + * State transitions: + * + * Active -> Inactive: + * When the last task using the namespace exits it drops its active + * references to all namespaces. However, user and pid namespaces + * remain accessible until the task has been reaped. + * + * Inactive -> Active: + * An inactive namespace tree might be resurrected due to e.g., the + * SIOCGSKNS ioctl() on a socket. + * + * Inactive -> Destroyed: + * When __ns_ref drops to zero the namespace is removed from the + * namespaces trees and the memory is freed (after RCU grace period). + * + * Initial namespaces: + * Boot-time namespaces (init_net, init_pid_ns, etc.) start with + * __ns_ref_active = 1 and remain active forever. + */ struct ns_common { u32 ns_type; struct dentry *stashed; @@ -48,6 +111,7 @@ struct ns_common { u64 ns_id; struct rb_node ns_tree_node; struct list_head ns_list_node; + atomic_t __ns_ref_active; /* do not use directly */ }; struct rcu_head ns_rcu; }; @@ -56,6 +120,13 @@ struct ns_common { int __ns_common_init(struct ns_common *ns, u32 ns_type, const struct proc_ns_operations *ops, int inum); void __ns_common_free(struct ns_common *ns); +static __always_inline bool is_initial_namespace(struct ns_common *ns) +{ + VFS_WARN_ON_ONCE(ns->inum == 0); + return unlikely(in_range(ns->inum, MNT_NS_INIT_INO, + IPC_NS_INIT_INO - MNT_NS_INIT_INO + 1)); +} + #define to_ns_common(__ns) \ _Generic((__ns), \ struct cgroup_namespace *: &(__ns)->ns, \ @@ -127,6 +198,7 @@ void __ns_common_free(struct ns_common *ns); .ops = to_ns_operations(&nsname), \ .stashed = NULL, \ .__ns_ref = REFCOUNT_INIT(refs), \ + .__ns_ref_active = ATOMIC_INIT(1), \ .ns_list_node = LIST_HEAD_INIT(nsname.ns.ns_list_node), \ } @@ -144,14 +216,26 @@ void __ns_common_free(struct ns_common *ns); #define ns_common_free(__ns) __ns_common_free(to_ns_common((__ns))) +static __always_inline __must_check int __ns_ref_active_read(const struct ns_common *ns) +{ + return atomic_read(&ns->__ns_ref_active); +} + static __always_inline __must_check bool __ns_ref_put(struct ns_common *ns) { - return refcount_dec_and_test(&ns->__ns_ref); + if (refcount_dec_and_test(&ns->__ns_ref)) { + VFS_WARN_ON_ONCE(__ns_ref_active_read(ns)); + return true; + } + return false; } static __always_inline __must_check bool __ns_ref_get(struct ns_common *ns) { - return refcount_inc_not_zero(&ns->__ns_ref); + if (refcount_inc_not_zero(&ns->__ns_ref)) + return true; + VFS_WARN_ON_ONCE(__ns_ref_active_read(ns)); + return false; } static __always_inline __must_check int __ns_ref_read(const struct ns_common *ns) @@ -166,4 +250,57 @@ static __always_inline __must_check int __ns_ref_read(const struct ns_common *ns #define ns_ref_put_and_lock(__ns, __lock) \ refcount_dec_and_lock(&to_ns_common((__ns))->__ns_ref, (__lock)) +#define ns_ref_active_read(__ns) \ + ((__ns) ? __ns_ref_active_read(to_ns_common(__ns)) : 0) + +void __ns_ref_active_get_owner(struct ns_common *ns); + +static __always_inline void __ns_ref_active_get(struct ns_common *ns) +{ + WARN_ON_ONCE(atomic_add_negative(1, &ns->__ns_ref_active)); + VFS_WARN_ON_ONCE(is_initial_namespace(ns) && __ns_ref_active_read(ns) <= 0); +} +#define ns_ref_active_get(__ns) \ + do { if (__ns) __ns_ref_active_get(to_ns_common(__ns)); } while (0) + +static __always_inline bool __ns_ref_active_get_not_zero(struct ns_common *ns) +{ + if (atomic_inc_not_zero(&ns->__ns_ref_active)) { + VFS_WARN_ON_ONCE(!__ns_ref_read(ns)); + return true; + } + return false; +} + +#define ns_ref_active_get_owner(__ns) \ + do { if (__ns) __ns_ref_active_get_owner(to_ns_common(__ns)); } while (0) + +void __ns_ref_active_put_owner(struct ns_common *ns); + +static __always_inline void __ns_ref_active_put(struct ns_common *ns) +{ + if (atomic_dec_and_test(&ns->__ns_ref_active)) { + VFS_WARN_ON_ONCE(is_initial_namespace(ns)); + VFS_WARN_ON_ONCE(!__ns_ref_read(ns)); + __ns_ref_active_put_owner(ns); + } +} +#define ns_ref_active_put(__ns) \ + do { if (__ns) __ns_ref_active_put(to_ns_common(__ns)); } while (0) + +static __always_inline struct ns_common *__must_check ns_get_unless_inactive(struct ns_common *ns) +{ + VFS_WARN_ON_ONCE(__ns_ref_active_read(ns) && !__ns_ref_read(ns)); + if (!__ns_ref_active_read(ns)) + return NULL; + if (!__ns_ref_get(ns)) + return NULL; + return ns; +} + +void __ns_ref_active_resurrect(struct ns_common *ns); + +#define ns_ref_active_resurrect(__ns) \ + do { if (__ns) __ns_ref_active_resurrect(to_ns_common(__ns)); } while (0) + #endif diff --git a/include/linux/nsfs.h b/include/linux/nsfs.h index e5a5fa83d36b..731b67fc2fec 100644 --- a/include/linux/nsfs.h +++ b/include/linux/nsfs.h @@ -37,4 +37,7 @@ void nsfs_init(void); #define current_in_namespace(__ns) (__current_namespace_from_type(__ns) == __ns) +void nsproxy_ns_active_get(struct nsproxy *ns); +void nsproxy_ns_active_put(struct nsproxy *ns); + #endif /* _LINUX_NSFS_H */ diff --git a/include/linux/nsproxy.h b/include/linux/nsproxy.h index 538ba8dba184..ac825eddec59 100644 --- a/include/linux/nsproxy.h +++ b/include/linux/nsproxy.h @@ -93,7 +93,10 @@ static inline struct cred *nsset_cred(struct nsset *set) */ int copy_namespaces(u64 flags, struct task_struct *tsk); +void switch_cred_namespaces(const struct cred *old, const struct cred *new); void exit_nsproxy_namespaces(struct task_struct *tsk); +void get_cred_namespaces(struct task_struct *tsk); +void exit_cred_namespaces(struct task_struct *tsk); void switch_task_namespaces(struct task_struct *tsk, struct nsproxy *new); int exec_task_namespaces(void); void free_nsproxy(struct nsproxy *ns); -- cgit v1.2.3 From 8895d2a3dbf49f23622ab8da9fb3909826edd6dc Mon Sep 17 00:00:00 2001 From: Christian Brauner Date: Wed, 29 Oct 2025 13:20:25 +0100 Subject: ns: use anonymous struct to group list member Make it easier to spot that they belong together conceptually. Link: https://patch.msgid.link/20251029-work-namespace-nstree-listns-v4-12-2e6f823ebdc0@kernel.org Tested-by: syzbot@syzkaller.appspotmail.com Reviewed-by: Jeff Layton Signed-off-by: Christian Brauner --- include/linux/ns_common.h | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-) (limited to 'include') diff --git a/include/linux/ns_common.h b/include/linux/ns_common.h index bdd0df15ad9c..32463203c824 100644 --- a/include/linux/ns_common.h +++ b/include/linux/ns_common.h @@ -109,8 +109,10 @@ struct ns_common { union { struct { u64 ns_id; - struct rb_node ns_tree_node; - struct list_head ns_list_node; + struct /* per type rbtree and list */ { + struct rb_node ns_tree_node; + struct list_head ns_list_node; + }; atomic_t __ns_ref_active; /* do not use directly */ }; struct rcu_head ns_rcu; -- cgit v1.2.3 From 2ccaebc686e9ef7e94b3a8d89706daed6e696667 Mon Sep 17 00:00:00 2001 From: Christian Brauner Date: Wed, 29 Oct 2025 13:20:26 +0100 Subject: nstree: introduce a unified tree This will allow userspace to lookup and stat a namespace simply by its identifier without having to know what type of namespace it is. Link: https://patch.msgid.link/20251029-work-namespace-nstree-listns-v4-13-2e6f823ebdc0@kernel.org Signed-off-by: Christian Brauner --- include/linux/ns_common.h | 3 +++ 1 file changed, 3 insertions(+) (limited to 'include') diff --git a/include/linux/ns_common.h b/include/linux/ns_common.h index 32463203c824..7a3c71b3a76f 100644 --- a/include/linux/ns_common.h +++ b/include/linux/ns_common.h @@ -109,6 +109,9 @@ struct ns_common { union { struct { u64 ns_id; + struct /* global namespace rbtree and list */ { + struct rb_node ns_unified_tree_node; + }; struct /* per type rbtree and list */ { struct rb_node ns_tree_node; struct list_head ns_list_node; -- cgit v1.2.3 From 3760342fd6312416491d536144e39297fa5b1950 Mon Sep 17 00:00:00 2001 From: Christian Brauner Date: Wed, 29 Oct 2025 13:20:28 +0100 Subject: nstree: assign fixed ids to the initial namespaces The initial set of namespace comes with fixed inode numbers making it easy for userspace to identify them solely based on that information. This has long preceeded anything here. Similarly, let's assign fixed namespace ids for the initial namespaces. Kill the cookie and use a sequentially increasing number. This has the nice side-effect that the owning user namespace will always have a namespace id that is smaller than any of it's descendant namespaces. Link: https://patch.msgid.link/20251029-work-namespace-nstree-listns-v4-15-2e6f823ebdc0@kernel.org Signed-off-by: Christian Brauner --- include/linux/ns_common.h | 13 ++++++++++++- include/linux/nstree.h | 15 +++++++++++---- include/uapi/linux/nsfs.h | 14 ++++++++++++++ 3 files changed, 37 insertions(+), 5 deletions(-) (limited to 'include') diff --git a/include/linux/ns_common.h b/include/linux/ns_common.h index 7a3c71b3a76f..009a6dea724f 100644 --- a/include/linux/ns_common.h +++ b/include/linux/ns_common.h @@ -173,6 +173,17 @@ static __always_inline bool is_initial_namespace(struct ns_common *ns) struct user_namespace *: &init_user_ns, \ struct uts_namespace *: &init_uts_ns) +#define ns_init_id(__ns) \ + _Generic((__ns), \ + struct cgroup_namespace *: CGROUP_NS_INIT_ID, \ + struct ipc_namespace *: IPC_NS_INIT_ID, \ + struct mnt_namespace *: MNT_NS_INIT_ID, \ + struct net *: NET_NS_INIT_ID, \ + struct pid_namespace *: PID_NS_INIT_ID, \ + struct time_namespace *: TIME_NS_INIT_ID, \ + struct user_namespace *: USER_NS_INIT_ID, \ + struct uts_namespace *: UTS_NS_INIT_ID) + #define to_ns_operations(__ns) \ _Generic((__ns), \ struct cgroup_namespace *: (IS_ENABLED(CONFIG_CGROUPS) ? &cgroupns_operations : NULL), \ @@ -198,7 +209,7 @@ static __always_inline bool is_initial_namespace(struct ns_common *ns) #define NS_COMMON_INIT(nsname, refs) \ { \ .ns_type = ns_common_type(&nsname), \ - .ns_id = 0, \ + .ns_id = ns_init_id(&nsname), \ .inum = ns_init_inum(&nsname), \ .ops = to_ns_operations(&nsname), \ .stashed = NULL, \ diff --git a/include/linux/nstree.h b/include/linux/nstree.h index 43aa262c0ea1..38674c6fa4f7 100644 --- a/include/linux/nstree.h +++ b/include/linux/nstree.h @@ -9,6 +9,7 @@ #include #include #include +#include extern struct ns_tree cgroup_ns_tree; extern struct ns_tree ipc_ns_tree; @@ -30,7 +31,11 @@ extern struct ns_tree uts_ns_tree; struct user_namespace *: &(user_ns_tree), \ struct uts_namespace *: &(uts_ns_tree)) -u64 ns_tree_gen_id(struct ns_common *ns); +#define ns_tree_gen_id(__ns) \ + __ns_tree_gen_id(to_ns_common(__ns), \ + (((__ns) == ns_init_ns(__ns)) ? ns_init_id(__ns) : 0)) + +u64 __ns_tree_gen_id(struct ns_common *ns, u64 id); void __ns_tree_add_raw(struct ns_common *ns, struct ns_tree *ns_tree); void __ns_tree_remove(struct ns_common *ns, struct ns_tree *ns_tree); struct ns_common *ns_tree_lookup_rcu(u64 ns_id, int ns_type); @@ -38,9 +43,9 @@ struct ns_common *__ns_tree_adjoined_rcu(struct ns_common *ns, struct ns_tree *ns_tree, bool previous); -static inline void __ns_tree_add(struct ns_common *ns, struct ns_tree *ns_tree) +static inline void __ns_tree_add(struct ns_common *ns, struct ns_tree *ns_tree, u64 id) { - ns_tree_gen_id(ns); + __ns_tree_gen_id(ns, id); __ns_tree_add_raw(ns, ns_tree); } @@ -60,7 +65,9 @@ static inline void __ns_tree_add(struct ns_common *ns, struct ns_tree *ns_tree) * This function assigns a new id to the namespace and adds it to the * appropriate namespace tree and list. */ -#define ns_tree_add(__ns) __ns_tree_add(to_ns_common(__ns), to_ns_tree(__ns)) +#define ns_tree_add(__ns) \ + __ns_tree_add(to_ns_common(__ns), to_ns_tree(__ns), \ + (((__ns) == ns_init_ns(__ns)) ? ns_init_id(__ns) : 0)) /** * ns_tree_remove - Remove a namespace from a namespace tree diff --git a/include/uapi/linux/nsfs.h b/include/uapi/linux/nsfs.h index e098759ec917..f8bc2aad74d6 100644 --- a/include/uapi/linux/nsfs.h +++ b/include/uapi/linux/nsfs.h @@ -67,4 +67,18 @@ struct nsfs_file_handle { #define NSFS_FILE_HANDLE_SIZE_VER0 16 /* sizeof first published struct */ #define NSFS_FILE_HANDLE_SIZE_LATEST sizeof(struct nsfs_file_handle) /* sizeof latest published struct */ +enum init_ns_id { + IPC_NS_INIT_ID = 1ULL, + UTS_NS_INIT_ID = 2ULL, + USER_NS_INIT_ID = 3ULL, + PID_NS_INIT_ID = 4ULL, + CGROUP_NS_INIT_ID = 5ULL, + TIME_NS_INIT_ID = 6ULL, + NET_NS_INIT_ID = 7ULL, + MNT_NS_INIT_ID = 8ULL, +#ifdef __KERNEL__ + NS_LAST_INIT_ID = MNT_NS_INIT_ID, +#endif +}; + #endif /* __LINUX_NSFS_H */ -- cgit v1.2.3 From 3c1a52f2a6c865464babe7a85c2796aa31cc9744 Mon Sep 17 00:00:00 2001 From: Christian Brauner Date: Wed, 29 Oct 2025 13:20:29 +0100 Subject: nstree: maintain list of owned namespaces The namespace tree doesn't express the ownership concept of namespace appropriately. Maintain a list of directly owned namespaces per user namespace. This will allow userspace and the kernel to use the listns() system call to walk the namespace tree by owning user namespace. The rbtree is used to find the relevant namespace entry point which allows to continue iteration and the owner list can be used to walk the tree completely lock free. Link: https://patch.msgid.link/20251029-work-namespace-nstree-listns-v4-16-2e6f823ebdc0@kernel.org Signed-off-by: Christian Brauner --- include/linux/ns_common.h | 8 ++++++++ 1 file changed, 8 insertions(+) (limited to 'include') diff --git a/include/linux/ns_common.h b/include/linux/ns_common.h index 009a6dea724f..698aa2f7f486 100644 --- a/include/linux/ns_common.h +++ b/include/linux/ns_common.h @@ -116,6 +116,12 @@ struct ns_common { struct rb_node ns_tree_node; struct list_head ns_list_node; }; + struct /* namespace ownership rbtree and list */ { + struct rb_root ns_owner_tree; /* rbtree of namespaces owned by this namespace */ + struct list_head ns_owner; /* list of namespaces owned by this namespace */ + struct rb_node ns_owner_tree_node; /* node in the owner namespace's rbtree */ + struct list_head ns_owner_entry; /* node in the owner namespace's ns_owned list */ + }; atomic_t __ns_ref_active; /* do not use directly */ }; struct rcu_head ns_rcu; @@ -216,6 +222,8 @@ static __always_inline bool is_initial_namespace(struct ns_common *ns) .__ns_ref = REFCOUNT_INIT(refs), \ .__ns_ref_active = ATOMIC_INIT(1), \ .ns_list_node = LIST_HEAD_INIT(nsname.ns.ns_list_node), \ + .ns_owner_entry = LIST_HEAD_INIT(nsname.ns.ns_owner_entry), \ + .ns_owner = LIST_HEAD_INIT(nsname.ns.ns_owner), \ } #define ns_common_init(__ns) \ -- cgit v1.2.3 From 560e25e70fa40ec69f97f14207bde9bc18bec9b8 Mon Sep 17 00:00:00 2001 From: Christian Brauner Date: Wed, 29 Oct 2025 13:20:31 +0100 Subject: nstree: add unified namespace list Allow to walk the unified namespace list completely locklessly. Link: https://patch.msgid.link/20251029-work-namespace-nstree-listns-v4-18-2e6f823ebdc0@kernel.org Signed-off-by: Christian Brauner --- include/linux/ns_common.h | 2 ++ 1 file changed, 2 insertions(+) (limited to 'include') diff --git a/include/linux/ns_common.h b/include/linux/ns_common.h index 698aa2f7f486..3f05dd7d40c7 100644 --- a/include/linux/ns_common.h +++ b/include/linux/ns_common.h @@ -111,6 +111,7 @@ struct ns_common { u64 ns_id; struct /* global namespace rbtree and list */ { struct rb_node ns_unified_tree_node; + struct list_head ns_unified_list_node; }; struct /* per type rbtree and list */ { struct rb_node ns_tree_node; @@ -224,6 +225,7 @@ static __always_inline bool is_initial_namespace(struct ns_common *ns) .ns_list_node = LIST_HEAD_INIT(nsname.ns.ns_list_node), \ .ns_owner_entry = LIST_HEAD_INIT(nsname.ns.ns_owner_entry), \ .ns_owner = LIST_HEAD_INIT(nsname.ns.ns_owner), \ + .ns_unified_list_node = LIST_HEAD_INIT(nsname.ns.ns_unified_list_node), \ } #define ns_common_init(__ns) \ -- cgit v1.2.3 From 76b6f5dfb3fda76fce1f9990d6fa58adc711122b Mon Sep 17 00:00:00 2001 From: Christian Brauner Date: Wed, 29 Oct 2025 13:20:32 +0100 Subject: nstree: add listns() Add 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); } Permission Model 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() Link: https://patch.msgid.link/20251029-work-namespace-nstree-listns-v4-19-2e6f823ebdc0@kernel.org Signed-off-by: Christian Brauner --- include/linux/ns_common.h | 2 ++ include/linux/syscalls.h | 4 ++++ include/linux/user_namespace.h | 4 ++-- include/uapi/linux/nsfs.h | 44 ++++++++++++++++++++++++++++++++++++++++++ 4 files changed, 52 insertions(+), 2 deletions(-) (limited to 'include') diff --git a/include/linux/ns_common.h b/include/linux/ns_common.h index 3f05dd7d40c7..bd4492ef6ffc 100644 --- a/include/linux/ns_common.h +++ b/include/linux/ns_common.h @@ -129,8 +129,10 @@ struct ns_common { }; }; +bool is_current_namespace(struct ns_common *ns); int __ns_common_init(struct ns_common *ns, u32 ns_type, const struct proc_ns_operations *ops, int inum); void __ns_common_free(struct ns_common *ns); +struct ns_common *__must_check ns_owner(struct ns_common *ns); static __always_inline bool is_initial_namespace(struct ns_common *ns) { diff --git a/include/linux/syscalls.h b/include/linux/syscalls.h index 66c06fcdfe19..cf84d98964b2 100644 --- a/include/linux/syscalls.h +++ b/include/linux/syscalls.h @@ -77,6 +77,7 @@ struct cachestat_range; struct cachestat; struct statmount; struct mnt_id_req; +struct ns_id_req; struct xattr_args; struct file_attr; @@ -437,6 +438,9 @@ asmlinkage long sys_statmount(const struct mnt_id_req __user *req, asmlinkage long sys_listmount(const struct mnt_id_req __user *req, u64 __user *mnt_ids, size_t nr_mnt_ids, unsigned int flags); +asmlinkage long sys_listns(const struct ns_id_req __user *req, + u64 __user *ns_ids, size_t nr_ns_ids, + unsigned int flags); asmlinkage long sys_truncate(const char __user *path, long length); asmlinkage long sys_ftruncate(unsigned int fd, off_t length); #if BITS_PER_LONG == 32 diff --git a/include/linux/user_namespace.h b/include/linux/user_namespace.h index 9a9aebbf96b9..9c3be157397e 100644 --- a/include/linux/user_namespace.h +++ b/include/linux/user_namespace.h @@ -166,13 +166,13 @@ static inline void set_userns_rlimit_max(struct user_namespace *ns, ns->rlimit_max[type] = max <= LONG_MAX ? max : LONG_MAX; } -#ifdef CONFIG_USER_NS - static inline struct user_namespace *to_user_ns(struct ns_common *ns) { return container_of(ns, struct user_namespace, ns); } +#ifdef CONFIG_USER_NS + static inline struct user_namespace *get_user_ns(struct user_namespace *ns) { if (ns) diff --git a/include/uapi/linux/nsfs.h b/include/uapi/linux/nsfs.h index f8bc2aad74d6..a25e38d1c874 100644 --- a/include/uapi/linux/nsfs.h +++ b/include/uapi/linux/nsfs.h @@ -81,4 +81,48 @@ enum init_ns_id { #endif }; +enum ns_type { + TIME_NS = (1ULL << 7), /* CLONE_NEWTIME */ + MNT_NS = (1ULL << 17), /* CLONE_NEWNS */ + CGROUP_NS = (1ULL << 25), /* CLONE_NEWCGROUP */ + UTS_NS = (1ULL << 26), /* CLONE_NEWUTS */ + IPC_NS = (1ULL << 27), /* CLONE_NEWIPC */ + USER_NS = (1ULL << 28), /* CLONE_NEWUSER */ + PID_NS = (1ULL << 29), /* CLONE_NEWPID */ + NET_NS = (1ULL << 30), /* CLONE_NEWNET */ +}; + +/** + * struct ns_id_req - namespace ID request structure + * @size: size of this structure + * @spare: reserved for future use + * @filter: filter mask + * @ns_id: last namespace id + * @user_ns_id: owning user namespace ID + * + * Structure for passing namespace ID and miscellaneous parameters to + * statns(2) and listns(2). + * + * For statns(2) @param represents the request mask. + * For listns(2) @param represents the last listed mount id (or zero). + */ +struct ns_id_req { + __u32 size; + __u32 spare; + __u64 ns_id; + struct /* listns */ { + __u32 ns_type; + __u32 spare2; + __u64 user_ns_id; + }; +}; + +/* + * Special @user_ns_id value that can be passed to listns() + */ +#define LISTNS_CURRENT_USER 0xffffffffffffffff /* Caller's userns */ + +/* List of all ns_id_req versions. */ +#define NS_ID_REQ_SIZE_VER0 32 /* sizeof first published struct */ + #endif /* __LINUX_NSFS_H */ -- cgit v1.2.3 From b36d4b6aa88ef039647228b98c59a875e92f8c8e Mon Sep 17 00:00:00 2001 From: Christian Brauner Date: Wed, 29 Oct 2025 13:20:33 +0100 Subject: arch: hookup listns() system call Add the listns() system call to all architectures. Link: https://patch.msgid.link/20251029-work-namespace-nstree-listns-v4-20-2e6f823ebdc0@kernel.org Tested-by: syzbot@syzkaller.appspotmail.com Reviewed-by: Arnd Bergmann Reviewed-by: Jeff Layton Signed-off-by: Christian Brauner --- include/uapi/asm-generic/unistd.h | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) (limited to 'include') diff --git a/include/uapi/asm-generic/unistd.h b/include/uapi/asm-generic/unistd.h index 04e0077fb4c9..942370b3f5d2 100644 --- a/include/uapi/asm-generic/unistd.h +++ b/include/uapi/asm-generic/unistd.h @@ -857,9 +857,11 @@ __SYSCALL(__NR_open_tree_attr, sys_open_tree_attr) __SYSCALL(__NR_file_getattr, sys_file_getattr) #define __NR_file_setattr 469 __SYSCALL(__NR_file_setattr, sys_file_setattr) +#define __NR_listns 470 +__SYSCALL(__NR_listns, sys_listns) #undef __NR_syscalls -#define __NR_syscalls 470 +#define __NR_syscalls 471 /* * 32 bit systems traditionally used different -- cgit v1.2.3