From 1901c92497bd90caf608a474f1bf4d8795b372a2 Mon Sep 17 00:00:00 2001 From: Josef Bacik Date: Mon, 24 Jun 2024 11:49:46 -0400 Subject: [PATCH] fs: keep an index of current mount namespaces 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 Signed-off-by: Josef Bacik Link: https://lore.kernel.org/r/e5fdd78a90f5b00a75bd893962a70f52a2c015cd.1719243756.git.josef@toxicpanda.com Signed-off-by: Christian Brauner --- 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 4a42fc68f4cc..5b980c262c0c 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 352e8c90b9f7..eebe9d912a71 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 mnt_ns_tree_lock */ 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); @@ -3733,8 +3838,7 @@ 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); } /* @@ -3773,7 +3877,9 @@ 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; @@ -3850,6 +3956,7 @@ 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) @@ -5205,6 +5312,8 @@ 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)