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 <brauner@kernel.org>

diff --git a/include/linux/ns_common.h b/include/linux/ns_common.h
index 009a6dea724f1c277204a75d6293407b72790ab5..698aa2f7f4867345c68ef7bed38d3d750f1a95c6 100644 (file)
--- 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)                     \

diff --git a/kernel/nscommon.c b/kernel/nscommon.c
index 17a6ea44f054041d7c5d408018aa09ef45c118ca..f0b7971392d2ed3434cc99318d5f35224cb5fbbb 100644 (file)
--- a/kernel/nscommon.c
+++ b/kernel/nscommon.c
@@ -63,7 +63,11 @@ int __ns_common_init(struct ns_common *ns, u32 ns_type, const struct proc_ns_ope
        ns->ns_type = ns_type;
        RB_CLEAR_NODE(&ns->ns_tree_node);
        RB_CLEAR_NODE(&ns->ns_unified_tree_node);
+       RB_CLEAR_NODE(&ns->ns_owner_tree_node);
        INIT_LIST_HEAD(&ns->ns_list_node);
+       ns->ns_owner_tree = RB_ROOT;
+       INIT_LIST_HEAD(&ns->ns_owner);
+       INIT_LIST_HEAD(&ns->ns_owner_entry);
 
 #ifdef CONFIG_DEBUG_VFS
        ns_debug(ns, ops);

diff --git a/kernel/nstree.c b/kernel/nstree.c
index cf102c5bb849f344c7a4fd5779b96083e2f4ee0b..1f54f914e30c8f1e7c8353464ff4d7466a40db7d 100644 (file)
--- a/kernel/nstree.c
+++ b/kernel/nstree.c
@@ -3,7 +3,9 @@
 
 #include <linux/nstree.h>
 #include <linux/proc_ns.h>
+#include <linux/rculist.h>
 #include <linux/vfsdebug.h>
+#include <linux/user_namespace.h>
 
 static __cacheline_aligned_in_smp DEFINE_SEQLOCK(ns_tree_lock);
 static struct rb_root ns_unified_tree = RB_ROOT; /* protected by ns_tree_lock */
@@ -83,6 +85,13 @@ static inline struct ns_common *node_to_ns_unified(const struct rb_node *node)
        return rb_entry(node, struct ns_common, ns_unified_tree_node);
 }
 
+static inline struct ns_common *node_to_ns_owner(const struct rb_node *node)
+{
+       if (!node)
+               return NULL;
+       return rb_entry(node, struct ns_common, ns_owner_tree_node);
+}
+
 static inline int ns_cmp(struct rb_node *a, const struct rb_node *b)
 {
        struct ns_common *ns_a = node_to_ns(a);
@@ -111,11 +120,27 @@ static inline int ns_cmp_unified(struct rb_node *a, const struct rb_node *b)
        return 0;
 }
 
+static inline int ns_cmp_owner(struct rb_node *a, const struct rb_node *b)
+{
+       struct ns_common *ns_a = node_to_ns_owner(a);
+       struct ns_common *ns_b = node_to_ns_owner(b);
+       u64 ns_id_a = ns_a->ns_id;
+       u64 ns_id_b = ns_b->ns_id;
+
+       if (ns_id_a < ns_id_b)
+               return -1;
+       if (ns_id_a > ns_id_b)
+               return 1;
+       return 0;
+}
+
 void __ns_tree_add_raw(struct ns_common *ns, struct ns_tree *ns_tree)
 {
        struct rb_node *node, *prev;
+       const struct proc_ns_operations *ops = ns->ops;
 
        VFS_WARN_ON_ONCE(!ns->ns_id);
+       VFS_WARN_ON_ONCE(ns->ns_type != ns_tree->type);
 
        write_seqlock(&ns_tree_lock);
 
@@ -131,6 +156,30 @@ void __ns_tree_add_raw(struct ns_common *ns, struct ns_tree *ns_tree)
                list_add_rcu(&ns->ns_list_node, &node_to_ns(prev)->ns_list_node);
 
        rb_find_add_rcu(&ns->ns_unified_tree_node, &ns_unified_tree, ns_cmp_unified);
+
+       if (ops) {
+               struct user_namespace *user_ns;
+
+               VFS_WARN_ON_ONCE(!ops->owner);
+               user_ns = ops->owner(ns);
+               if (user_ns) {
+                       struct ns_common *owner = &user_ns->ns;
+                       VFS_WARN_ON_ONCE(owner->ns_type != CLONE_NEWUSER);
+
+                       /* Insert into owner's rbtree */
+                       rb_find_add_rcu(&ns->ns_owner_tree_node, &owner->ns_owner_tree, ns_cmp_owner);
+
+                       /* Insert into owner's list in sorted order */
+                       prev = rb_prev(&ns->ns_owner_tree_node);
+                       if (!prev)
+                               list_add_rcu(&ns->ns_owner_entry, &owner->ns_owner);
+                       else
+                               list_add_rcu(&ns->ns_owner_entry, &node_to_ns_owner(prev)->ns_owner_entry);
+               } else {
+                       /* Only the initial user namespace doesn't have an owner. */
+                       VFS_WARN_ON_ONCE(ns != to_ns_common(&init_user_ns));
+               }
+       }
        write_sequnlock(&ns_tree_lock);
 
        VFS_WARN_ON_ONCE(node);
@@ -146,6 +195,9 @@ 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)
 {
+       const struct proc_ns_operations *ops = ns->ops;
+       struct user_namespace *user_ns;
+
        VFS_WARN_ON_ONCE(RB_EMPTY_NODE(&ns->ns_tree_node));
        VFS_WARN_ON_ONCE(list_empty(&ns->ns_list_node));
        VFS_WARN_ON_ONCE(ns->ns_type != ns_tree->type);
@@ -153,8 +205,22 @@ void __ns_tree_remove(struct ns_common *ns, struct ns_tree *ns_tree)
        write_seqlock(&ns_tree_lock);
        rb_erase(&ns->ns_tree_node, &ns_tree->ns_tree);
        rb_erase(&ns->ns_unified_tree_node, &ns_unified_tree);
-       list_bidir_del_rcu(&ns->ns_list_node);
        RB_CLEAR_NODE(&ns->ns_tree_node);
+
+       list_bidir_del_rcu(&ns->ns_list_node);
+
+       /* Remove from owner's rbtree if this namespace has an owner */
+       if (ops) {
+               user_ns = ops->owner(ns);
+               if (user_ns) {
+                       struct ns_common *owner = &user_ns->ns;
+                       rb_erase(&ns->ns_owner_tree_node, &owner->ns_owner_tree);
+                       RB_CLEAR_NODE(&ns->ns_owner_tree_node);
+               }
+
+               list_bidir_del_rcu(&ns->ns_owner_entry);
+       }
+
        write_sequnlock(&ns_tree_lock);
 }
 EXPORT_SYMBOL_GPL(__ns_tree_remove);