In order to allow for listmount() to be used on different namespaces we
need a way to lookup a mount ns by its id. Keep a rbtree of the current
!anonymous mount name spaces indexed by ID that we can use to look up
the namespace.
Co-developed-by: Christian Brauner <brauner@xxxxxxxxxx>
Signed-off-by: Josef Bacik <josef@xxxxxxxxxxxxxx>
Signed-off-by: Christian Brauner <brauner@xxxxxxxxxx>
---
fs/mount.h | 2 +
fs/namespace.c | 113 ++++++++++++++++++++++++++++++++++++++++++++++++-
2 files changed, 113 insertions(+), 2 deletions(-)
diff --git a/fs/mount.h b/fs/mount.h
index 4adce73211ae..ad4b1ddebb54 100644
--- a/fs/mount.h
+++ b/fs/mount.h
@@ -16,6 +16,8 @@ struct mnt_namespace {
u64 event;
unsigned int nr_mounts; /* # of mounts in the namespace */
unsigned int pending_mounts;
+ struct rb_node mnt_ns_tree_node; /* node in the mnt_ns_tree */
+ refcount_t passive; /* number references not pinning @mounts */
} __randomize_layout;
struct mnt_pcp {
diff --git a/fs/namespace.c b/fs/namespace.c
index 45df82f2a059..babdebdb0a9c 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -78,6 +78,8 @@ static struct kmem_cache *mnt_cache __ro_after_init;
static DECLARE_RWSEM(namespace_sem);
static HLIST_HEAD(unmounted); /* protected by namespace_sem */
static LIST_HEAD(ex_mountpoints); /* protected by namespace_sem */
+static DEFINE_RWLOCK(mnt_ns_tree_lock);
+static struct rb_root mnt_ns_tree = RB_ROOT; /* protected by namespace_sem */
struct mount_kattr {
unsigned int attr_set;
@@ -103,6 +105,109 @@ EXPORT_SYMBOL_GPL(fs_kobj);
*/
__cacheline_aligned_in_smp DEFINE_SEQLOCK(mount_lock);
+static int mnt_ns_cmp(u64 seq, const struct mnt_namespace *ns)
+{
+ u64 seq_b = ns->seq;
+
+ if (seq < seq_b)
+ return -1;
+ if (seq > seq_b)
+ return 1;
+ return 0;
+}
+
+static inline struct mnt_namespace *node_to_mnt_ns(const struct rb_node *node)
+{
+ if (!node)
+ return NULL;
+ return rb_entry(node, struct mnt_namespace, mnt_ns_tree_node);
+}
+
+static bool mnt_ns_less(struct rb_node *a, const struct rb_node *b)
+{
+ struct mnt_namespace *ns_a = node_to_mnt_ns(a);
+ struct mnt_namespace *ns_b = node_to_mnt_ns(b);
+ u64 seq_a = ns_a->seq;
+
+ return mnt_ns_cmp(seq_a, ns_b) < 0;
+}
+
+static void mnt_ns_tree_add(struct mnt_namespace *ns)
+{
+ guard(write_lock)(&mnt_ns_tree_lock);
+ rb_add(&ns->mnt_ns_tree_node, &mnt_ns_tree, mnt_ns_less);
+}
+
+static void mnt_ns_release(struct mnt_namespace *ns)
+{
+ lockdep_assert_not_held(&mnt_ns_tree_lock);
+
+ /* keep alive for {list,stat}mount() */
+ if (refcount_dec_and_test(&ns->passive)) {
+ put_user_ns(ns->user_ns);
+ kfree(ns);
+ }
+}
+DEFINE_FREE(mnt_ns_release, struct mnt_namespace *, if (_T) mnt_ns_release(_T))
+
+static void mnt_ns_tree_remove(struct mnt_namespace *ns)
+{
+ /* remove from global mount namespace list */
+ if (!is_anon_ns(ns)) {
+ guard(write_lock)(&mnt_ns_tree_lock);
+ rb_erase(&ns->mnt_ns_tree_node, &mnt_ns_tree);
+ }
+
+ mnt_ns_release(ns);
+}
+
+/*
+ * Returns the mount namespace which either has the specified id, or has the
+ * next smallest id afer the specified one.
+ */
+static struct mnt_namespace *mnt_ns_find_id_at(u64 mnt_ns_id)
+{
+ struct rb_node *node = mnt_ns_tree.rb_node;
+ struct mnt_namespace *ret = NULL;
+
+ lockdep_assert_held(&mnt_ns_tree_lock);
+
+ while (node) {
+ struct mnt_namespace *n = node_to_mnt_ns(node);
+
+ if (mnt_ns_id <= n->seq) {
+ ret = node_to_mnt_ns(node);
+ if (mnt_ns_id == n->seq)
+ break;
+ node = node->rb_left;
+ } else {
+ node = node->rb_right;
+ }
+ }
+ return ret;
+}
+
+/*
+ * Lookup a mount namespace by id and take a passive reference count. Taking a
+ * passive reference means the mount namespace can be emptied if e.g., the last
+ * task holding an active reference exits. To access the mounts of the
+ * namespace the @namespace_sem must first be acquired. If the namespace has
+ * already shut down before acquiring @namespace_sem, {list,stat}mount() will
+ * see that the mount rbtree of the namespace is empty.
+ */
+static struct mnt_namespace *lookup_mnt_ns(u64 mnt_ns_id)
+{
+ struct mnt_namespace *ns;
+
+ guard(read_lock)(&mnt_ns_tree_lock);
+ ns = mnt_ns_find_id_at(mnt_ns_id);
+ if (!ns || ns->seq != mnt_ns_id)
+ return NULL;
+
+ refcount_inc(&ns->passive);
+ return ns;
+}
+
static inline void lock_mount_hash(void)
{
write_seqlock(&mount_lock);
@@ -3736,8 +3841,7 @@ static void free_mnt_ns(struct mnt_namespace *ns)
if (!is_anon_ns(ns))
ns_free_inum(&ns->ns);
dec_mnt_namespaces(ns->ucounts);
- put_user_ns(ns->user_ns);
- kfree(ns);
+ mnt_ns_tree_remove(ns);
}
/*
@@ -3776,7 +3880,9 @@ static struct mnt_namespace *alloc_mnt_ns(struct user_namespace *user_ns, bool a
if (!anon)
new_ns->seq = atomic64_add_return(1, &mnt_ns_seq);
refcount_set(&new_ns->ns.count, 1);
+ refcount_set(&new_ns->passive, 1);
new_ns->mounts = RB_ROOT;
+ RB_CLEAR_NODE(&new_ns->mnt_ns_tree_node);
init_waitqueue_head(&new_ns->poll);
new_ns->user_ns = get_user_ns(user_ns);
new_ns->ucounts = ucounts;
@@ -3853,6 +3959,7 @@ struct mnt_namespace *copy_mnt_ns(unsigned long flags, struct mnt_namespace *ns,
while (p->mnt.mnt_root != q->mnt.mnt_root)
p = next_mnt(skip_mnt_tree(p), old);
}
+ mnt_ns_tree_add(new_ns);
namespace_unlock();
if (rootmnt)
@@ -5208,6 +5315,8 @@ static void __init init_mount_tree(void)
set_fs_pwd(current->fs, &root);
set_fs_root(current->fs, &root);
+
+ mnt_ns_tree_add(ns);
}
void __init mnt_init(void)
--
2.43.0
