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f675d2e955
All namespace types now share the same ns_common infrastructure. Extend this to include a security blob so LSMs can start managing namespaces uniformly without having to add one-off hooks or security fields to every individual namespace type. Add a ns_security pointer to ns_common and the corresponding lbs_ns blob size to lsm_blob_sizes. Allocation and freeing hooks are called from the common __ns_common_init() and __ns_common_free() paths so every namespace type gets covered in one go. All information about the namespace type and the appropriate casting helpers to get at the containing namespace are available via ns_common making it straightforward for LSMs to differentiate when they need to. A namespace_install hook is called from validate_ns() during setns(2) giving LSMs a chance to enforce policy on namespace transitions. The LSM check runs before ns->ops->install() so the security module can deny the operation before any type-specific installation effects. Individual namespace types can still have their own specialized security hooks when needed. This is just the common baseline that makes it easy to track and manage namespaces from the security side without requiring every namespace type to reinvent the wheel. Cc: Günther Noack <gnoack@google.com> Cc: Paul Moore <paul@paul-moore.com> Cc: Serge E. Hallyn <serge@hallyn.com> Signed-off-by: Christian Brauner <brauner@kernel.org> Link: https://lore.kernel.org/r/20260216-work-security-namespace-v1-1-075c28758e1f@kernel.org Signed-off-by: Mickaël Salaün <mic@digikod.net> [PM: subject tweak] Signed-off-by: Paul Moore <paul@paul-moore.com>
333 lines
9.2 KiB
C
333 lines
9.2 KiB
C
// SPDX-License-Identifier: GPL-2.0-only
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/* Copyright (c) 2025 Christian Brauner <brauner@kernel.org> */
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#include <linux/ns_common.h>
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#include <linux/nstree.h>
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#include <linux/proc_ns.h>
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#include <linux/security.h>
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#include <linux/user_namespace.h>
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#include <linux/vfsdebug.h>
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#ifdef CONFIG_DEBUG_VFS
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static void ns_debug(struct ns_common *ns, const struct proc_ns_operations *ops)
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{
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switch (ns->ns_type) {
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#ifdef CONFIG_CGROUPS
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case CLONE_NEWCGROUP:
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VFS_WARN_ON_ONCE(ops != &cgroupns_operations);
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break;
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#endif
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#ifdef CONFIG_IPC_NS
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case CLONE_NEWIPC:
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VFS_WARN_ON_ONCE(ops != &ipcns_operations);
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break;
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#endif
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case CLONE_NEWNS:
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VFS_WARN_ON_ONCE(ops != &mntns_operations);
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break;
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#ifdef CONFIG_NET_NS
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case CLONE_NEWNET:
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VFS_WARN_ON_ONCE(ops != &netns_operations);
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break;
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#endif
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#ifdef CONFIG_PID_NS
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case CLONE_NEWPID:
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VFS_WARN_ON_ONCE(ops != &pidns_operations);
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break;
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#endif
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#ifdef CONFIG_TIME_NS
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case CLONE_NEWTIME:
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VFS_WARN_ON_ONCE(ops != &timens_operations);
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break;
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#endif
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#ifdef CONFIG_USER_NS
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case CLONE_NEWUSER:
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VFS_WARN_ON_ONCE(ops != &userns_operations);
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break;
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#endif
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#ifdef CONFIG_UTS_NS
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case CLONE_NEWUTS:
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VFS_WARN_ON_ONCE(ops != &utsns_operations);
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break;
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#endif
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}
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}
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#endif
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int __ns_common_init(struct ns_common *ns, u32 ns_type, const struct proc_ns_operations *ops, int inum)
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{
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int ret = 0;
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refcount_set(&ns->__ns_ref, 1);
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ns->stashed = NULL;
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#ifdef CONFIG_SECURITY
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ns->ns_security = NULL;
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#endif
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ns->ops = ops;
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ns->ns_id = 0;
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ns->ns_type = ns_type;
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ns_tree_node_init(&ns->ns_tree_node);
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ns_tree_node_init(&ns->ns_unified_node);
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ns_tree_node_init(&ns->ns_owner_node);
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ns_tree_root_init(&ns->ns_owner_root);
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#ifdef CONFIG_DEBUG_VFS
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ns_debug(ns, ops);
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#endif
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if (inum)
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ns->inum = inum;
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else
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ret = proc_alloc_inum(&ns->inum);
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if (ret)
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return ret;
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ret = security_namespace_init(ns);
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if (ret) {
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if (!inum)
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proc_free_inum(ns->inum);
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return ret;
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}
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/*
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* Tree ref starts at 0. It's incremented when namespace enters
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* active use (installed in nsproxy) and decremented when all
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* active uses are gone. Initial namespaces are always active.
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*/
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if (is_ns_init_inum(ns))
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atomic_set(&ns->__ns_ref_active, 1);
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else
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atomic_set(&ns->__ns_ref_active, 0);
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return 0;
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}
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void __ns_common_free(struct ns_common *ns)
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{
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security_namespace_free(ns);
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if (ns->inum > MNT_NS_INO_SPECIAL_MAX)
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proc_free_inum(ns->inum);
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}
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struct ns_common *__must_check ns_owner(struct ns_common *ns)
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{
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struct user_namespace *owner;
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if (unlikely(!ns->ops))
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return NULL;
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VFS_WARN_ON_ONCE(!ns->ops->owner);
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owner = ns->ops->owner(ns);
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VFS_WARN_ON_ONCE(!owner && ns != to_ns_common(&init_user_ns));
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if (!owner)
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return NULL;
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/* Skip init_user_ns as it's always active */
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if (owner == &init_user_ns)
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return NULL;
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return to_ns_common(owner);
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}
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/*
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* The active reference count works by having each namespace that gets
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* created take a single active reference on its owning user namespace.
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* That single reference is only released once the child namespace's
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* active count itself goes down.
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*
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* A regular namespace tree might look as follow:
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* Legend:
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* + : adding active reference
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* - : dropping active reference
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* x : always active (initial namespace)
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*
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*
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* net_ns pid_ns
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* \ /
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* + +
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* user_ns1 (2)
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* |
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* ipc_ns | uts_ns
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* \ | /
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* + + +
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* user_ns2 (3)
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* |
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* cgroup_ns | mnt_ns
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* \ | /
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* x x x
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* init_user_ns (1)
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*
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* If both net_ns and pid_ns put their last active reference on
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* themselves it will cascade to user_ns1 dropping its own active
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* reference and dropping one active reference on user_ns2:
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*
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* net_ns pid_ns
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* \ /
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* - -
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* user_ns1 (0)
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* |
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* ipc_ns | uts_ns
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* \ | /
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* + - +
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* user_ns2 (2)
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* |
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* cgroup_ns | mnt_ns
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* \ | /
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* x x x
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* init_user_ns (1)
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*
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* The iteration stops once we reach a namespace that still has active
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* references.
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*/
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void __ns_ref_active_put(struct ns_common *ns)
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{
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/* Initial namespaces are always active. */
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if (is_ns_init_id(ns))
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return;
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if (!atomic_dec_and_test(&ns->__ns_ref_active)) {
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VFS_WARN_ON_ONCE(__ns_ref_active_read(ns) < 0);
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return;
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}
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VFS_WARN_ON_ONCE(is_ns_init_id(ns));
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VFS_WARN_ON_ONCE(!__ns_ref_read(ns));
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for (;;) {
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ns = ns_owner(ns);
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if (!ns)
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return;
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VFS_WARN_ON_ONCE(is_ns_init_id(ns));
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if (!atomic_dec_and_test(&ns->__ns_ref_active)) {
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VFS_WARN_ON_ONCE(__ns_ref_active_read(ns) < 0);
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return;
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}
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}
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}
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/*
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* The active reference count works by having each namespace that gets
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* created take a single active reference on its owning user namespace.
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* That single reference is only released once the child namespace's
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* active count itself goes down. This makes it possible to efficiently
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* resurrect a namespace tree:
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*
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* A regular namespace tree might look as follow:
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* Legend:
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* + : adding active reference
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* - : dropping active reference
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* x : always active (initial namespace)
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*
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*
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* net_ns pid_ns
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* \ /
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* + +
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* user_ns1 (2)
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* |
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* ipc_ns | uts_ns
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* \ | /
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* + + +
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* user_ns2 (3)
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* |
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* cgroup_ns | mnt_ns
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* \ | /
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* x x x
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* init_user_ns (1)
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*
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* If both net_ns and pid_ns put their last active reference on
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* themselves it will cascade to user_ns1 dropping its own active
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* reference and dropping one active reference on user_ns2:
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*
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* net_ns pid_ns
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* \ /
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* - -
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* user_ns1 (0)
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* |
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* ipc_ns | uts_ns
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* \ | /
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* + - +
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* user_ns2 (2)
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* |
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* cgroup_ns | mnt_ns
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* \ | /
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* x x x
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* init_user_ns (1)
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*
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* Assume the whole tree is dead but all namespaces are still active:
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*
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* net_ns pid_ns
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* \ /
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* - -
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* user_ns1 (0)
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* |
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* ipc_ns | uts_ns
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* \ | /
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* - - -
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* user_ns2 (0)
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* |
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* cgroup_ns | mnt_ns
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* \ | /
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* x x x
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* init_user_ns (1)
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*
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* Now assume the net_ns gets resurrected (.e.g., via the SIOCGSKNS ioctl()):
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*
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* net_ns pid_ns
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* \ /
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* + -
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* user_ns1 (0)
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* |
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* ipc_ns | uts_ns
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* \ | /
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* - + -
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* user_ns2 (0)
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* |
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* cgroup_ns | mnt_ns
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* \ | /
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* x x x
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* init_user_ns (1)
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*
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* If net_ns had a zero reference count and we bumped it we also need to
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* take another reference on its owning user namespace. Similarly, if
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* pid_ns had a zero reference count it also needs to take another
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* reference on its owning user namespace. So both net_ns and pid_ns
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* will each have their own reference on the owning user namespace.
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*
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* If the owning user namespace user_ns1 had a zero reference count then
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* it also needs to take another reference on its owning user namespace
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* and so on.
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*/
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void __ns_ref_active_get(struct ns_common *ns)
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{
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int prev;
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/* Initial namespaces are always active. */
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if (is_ns_init_id(ns))
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return;
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/* If we didn't resurrect the namespace we're done. */
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prev = atomic_fetch_add(1, &ns->__ns_ref_active);
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VFS_WARN_ON_ONCE(prev < 0);
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if (likely(prev))
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return;
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/*
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* We did resurrect it. Walk the ownership hierarchy upwards
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* until we found an owning user namespace that is active.
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*/
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for (;;) {
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ns = ns_owner(ns);
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if (!ns)
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return;
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VFS_WARN_ON_ONCE(is_ns_init_id(ns));
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prev = atomic_fetch_add(1, &ns->__ns_ref_active);
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VFS_WARN_ON_ONCE(prev < 0);
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if (likely(prev))
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return;
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}
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}
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bool may_see_all_namespaces(void)
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{
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return (task_active_pid_ns(current) == &init_pid_ns) &&
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ns_capable_noaudit(init_pid_ns.user_ns, CAP_SYS_ADMIN);
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}
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