From 38129a13e6e71f666e0468e99fdd932a687b4d7e Mon Sep 17 00:00:00 2001 From: Al Viro Date: Thu, 20 Mar 2014 21:10:51 -0400 Subject: [PATCH] switch mnt_hash to hlist fixes RCU bug - walking through hlist is safe in face of element moves, since it's self-terminating. Cyclic lists are not - if we end up jumping to another hash chain, we'll loop infinitely without ever hitting the original list head. [fix for dumb braino folded] Spotted by: Max Kellermann Cc: stable@vger.kernel.org Signed-off-by: Al Viro --- fs/mount.h | 2 +- fs/namespace.c | 79 ++++++++++++++++++++++++++++++++-------------------------- fs/pnode.c | 26 +++++++++++-------- fs/pnode.h | 4 +-- 4 files changed, 61 insertions(+), 50 deletions(-) diff --git a/fs/mount.h b/fs/mount.h index acdb428..b29e42f 100644 --- a/fs/mount.h +++ b/fs/mount.h @@ -25,7 +25,7 @@ struct mountpoint { }; struct mount { - struct list_head mnt_hash; + struct hlist_node mnt_hash; struct mount *mnt_parent; struct dentry *mnt_mountpoint; struct vfsmount mnt; diff --git a/fs/namespace.c b/fs/namespace.c index d3fb9f0..2ffc5a2 100644 --- a/fs/namespace.c +++ b/fs/namespace.c @@ -59,7 +59,7 @@ static DEFINE_SPINLOCK(mnt_id_lock); static int mnt_id_start = 0; static int mnt_group_start = 1; -static struct list_head *mount_hashtable __read_mostly; +static struct hlist_head *mount_hashtable __read_mostly; static struct hlist_head *mountpoint_hashtable __read_mostly; static struct kmem_cache *mnt_cache __read_mostly; static DECLARE_RWSEM(namespace_sem); @@ -78,7 +78,7 @@ EXPORT_SYMBOL_GPL(fs_kobj); */ __cacheline_aligned_in_smp DEFINE_SEQLOCK(mount_lock); -static inline struct list_head *m_hash(struct vfsmount *mnt, struct dentry *dentry) +static inline struct hlist_head *m_hash(struct vfsmount *mnt, struct dentry *dentry) { unsigned long tmp = ((unsigned long)mnt / L1_CACHE_BYTES); tmp += ((unsigned long)dentry / L1_CACHE_BYTES); @@ -217,7 +217,7 @@ static struct mount *alloc_vfsmnt(const char *name) mnt->mnt_writers = 0; #endif - INIT_LIST_HEAD(&mnt->mnt_hash); + INIT_HLIST_NODE(&mnt->mnt_hash); INIT_LIST_HEAD(&mnt->mnt_child); INIT_LIST_HEAD(&mnt->mnt_mounts); INIT_LIST_HEAD(&mnt->mnt_list); @@ -605,10 +605,10 @@ bool legitimize_mnt(struct vfsmount *bastard, unsigned seq) */ struct mount *__lookup_mnt(struct vfsmount *mnt, struct dentry *dentry) { - struct list_head *head = m_hash(mnt, dentry); + struct hlist_head *head = m_hash(mnt, dentry); struct mount *p; - list_for_each_entry_rcu(p, head, mnt_hash) + hlist_for_each_entry_rcu(p, head, mnt_hash) if (&p->mnt_parent->mnt == mnt && p->mnt_mountpoint == dentry) return p; return NULL; @@ -620,20 +620,16 @@ struct mount *__lookup_mnt(struct vfsmount *mnt, struct dentry *dentry) */ struct mount *__lookup_mnt_last(struct vfsmount *mnt, struct dentry *dentry) { - struct list_head *head = m_hash(mnt, dentry); - struct mount *p, *res = NULL; - - list_for_each_entry(p, head, mnt_hash) - if (&p->mnt_parent->mnt == mnt && p->mnt_mountpoint == dentry) - goto found; - return res; -found: - res = p; - list_for_each_entry_continue(p, head, mnt_hash) { + struct mount *p, *res; + res = p = __lookup_mnt(mnt, dentry); + if (!p) + goto out; + hlist_for_each_entry_continue(p, mnt_hash) { if (&p->mnt_parent->mnt != mnt || p->mnt_mountpoint != dentry) break; res = p; } +out: return res; } @@ -750,7 +746,7 @@ static void detach_mnt(struct mount *mnt, struct path *old_path) mnt->mnt_parent = mnt; mnt->mnt_mountpoint = mnt->mnt.mnt_root; list_del_init(&mnt->mnt_child); - list_del_init(&mnt->mnt_hash); + hlist_del_init_rcu(&mnt->mnt_hash); put_mountpoint(mnt->mnt_mp); mnt->mnt_mp = NULL; } @@ -777,7 +773,7 @@ static void attach_mnt(struct mount *mnt, struct mountpoint *mp) { mnt_set_mountpoint(parent, mp, mnt); - list_add(&mnt->mnt_hash, m_hash(&parent->mnt, mp->m_dentry)); + hlist_add_head_rcu(&mnt->mnt_hash, m_hash(&parent->mnt, mp->m_dentry)); list_add_tail(&mnt->mnt_child, &parent->mnt_mounts); } @@ -800,9 +796,9 @@ static void commit_tree(struct mount *mnt, struct mount *shadows) list_splice(&head, n->list.prev); if (shadows) - list_add(&mnt->mnt_hash, &shadows->mnt_hash); + hlist_add_after_rcu(&shadows->mnt_hash, &mnt->mnt_hash); else - list_add(&mnt->mnt_hash, + hlist_add_head_rcu(&mnt->mnt_hash, m_hash(&parent->mnt, mnt->mnt_mountpoint)); list_add_tail(&mnt->mnt_child, &parent->mnt_mounts); touch_mnt_namespace(n); @@ -1193,26 +1189,28 @@ int may_umount(struct vfsmount *mnt) EXPORT_SYMBOL(may_umount); -static LIST_HEAD(unmounted); /* protected by namespace_sem */ +static HLIST_HEAD(unmounted); /* protected by namespace_sem */ static void namespace_unlock(void) { struct mount *mnt; - LIST_HEAD(head); + struct hlist_head head = unmounted; - if (likely(list_empty(&unmounted))) { + if (likely(hlist_empty(&head))) { up_write(&namespace_sem); return; } - list_splice_init(&unmounted, &head); + head.first->pprev = &head.first; + INIT_HLIST_HEAD(&unmounted); + up_write(&namespace_sem); synchronize_rcu(); - while (!list_empty(&head)) { - mnt = list_first_entry(&head, struct mount, mnt_hash); - list_del_init(&mnt->mnt_hash); + while (!hlist_empty(&head)) { + mnt = hlist_entry(head.first, struct mount, mnt_hash); + hlist_del_init(&mnt->mnt_hash); if (mnt->mnt_ex_mountpoint.mnt) path_put(&mnt->mnt_ex_mountpoint); mntput(&mnt->mnt); @@ -1233,16 +1231,19 @@ static inline void namespace_lock(void) */ void umount_tree(struct mount *mnt, int how) { - LIST_HEAD(tmp_list); + HLIST_HEAD(tmp_list); struct mount *p; + struct mount *last = NULL; - for (p = mnt; p; p = next_mnt(p, mnt)) - list_move(&p->mnt_hash, &tmp_list); + for (p = mnt; p; p = next_mnt(p, mnt)) { + hlist_del_init_rcu(&p->mnt_hash); + hlist_add_head(&p->mnt_hash, &tmp_list); + } if (how) propagate_umount(&tmp_list); - list_for_each_entry(p, &tmp_list, mnt_hash) { + hlist_for_each_entry(p, &tmp_list, mnt_hash) { list_del_init(&p->mnt_expire); list_del_init(&p->mnt_list); __touch_mnt_namespace(p->mnt_ns); @@ -1260,8 +1261,13 @@ void umount_tree(struct mount *mnt, int how) p->mnt_mp = NULL; } change_mnt_propagation(p, MS_PRIVATE); + last = p; + } + if (last) { + last->mnt_hash.next = unmounted.first; + unmounted.first = tmp_list.first; + unmounted.first->pprev = &unmounted.first; } - list_splice(&tmp_list, &unmounted); } static void shrink_submounts(struct mount *mnt); @@ -1645,8 +1651,9 @@ static int attach_recursive_mnt(struct mount *source_mnt, struct mountpoint *dest_mp, struct path *parent_path) { - LIST_HEAD(tree_list); + HLIST_HEAD(tree_list); struct mount *child, *p; + struct hlist_node *n; int err; if (IS_MNT_SHARED(dest_mnt)) { @@ -1671,9 +1678,9 @@ static int attach_recursive_mnt(struct mount *source_mnt, commit_tree(source_mnt, NULL); } - list_for_each_entry_safe(child, p, &tree_list, mnt_hash) { + hlist_for_each_entry_safe(child, n, &tree_list, mnt_hash) { struct mount *q; - list_del_init(&child->mnt_hash); + hlist_del_init(&child->mnt_hash); q = __lookup_mnt_last(&child->mnt_parent->mnt, child->mnt_mountpoint); commit_tree(child, q); @@ -2818,7 +2825,7 @@ void __init mnt_init(void) 0, SLAB_HWCACHE_ALIGN | SLAB_PANIC, NULL); mount_hashtable = alloc_large_system_hash("Mount-cache", - sizeof(struct list_head), + sizeof(struct hlist_head), mhash_entries, 19, 0, &m_hash_shift, &m_hash_mask, 0, 0); @@ -2832,7 +2839,7 @@ void __init mnt_init(void) panic("Failed to allocate mount hash table\n"); for (u = 0; u <= m_hash_mask; u++) - INIT_LIST_HEAD(&mount_hashtable[u]); + INIT_HLIST_HEAD(&mount_hashtable[u]); for (u = 0; u <= mp_hash_mask; u++) INIT_HLIST_HEAD(&mountpoint_hashtable[u]); diff --git a/fs/pnode.c b/fs/pnode.c index c7221bb..88396df 100644 --- a/fs/pnode.c +++ b/fs/pnode.c @@ -220,14 +220,14 @@ static struct mount *get_source(struct mount *dest, * @tree_list : list of heads of trees to be attached. */ int propagate_mnt(struct mount *dest_mnt, struct mountpoint *dest_mp, - struct mount *source_mnt, struct list_head *tree_list) + struct mount *source_mnt, struct hlist_head *tree_list) { struct user_namespace *user_ns = current->nsproxy->mnt_ns->user_ns; struct mount *m, *child; int ret = 0; struct mount *prev_dest_mnt = dest_mnt; struct mount *prev_src_mnt = source_mnt; - LIST_HEAD(tmp_list); + HLIST_HEAD(tmp_list); for (m = propagation_next(dest_mnt, dest_mnt); m; m = propagation_next(m, dest_mnt)) { @@ -246,27 +246,29 @@ int propagate_mnt(struct mount *dest_mnt, struct mountpoint *dest_mp, child = copy_tree(source, source->mnt.mnt_root, type); if (IS_ERR(child)) { ret = PTR_ERR(child); - list_splice(tree_list, tmp_list.prev); + tmp_list = *tree_list; + tmp_list.first->pprev = &tmp_list.first; + INIT_HLIST_HEAD(tree_list); goto out; } if (is_subdir(dest_mp->m_dentry, m->mnt.mnt_root)) { mnt_set_mountpoint(m, dest_mp, child); - list_add_tail(&child->mnt_hash, tree_list); + hlist_add_head(&child->mnt_hash, tree_list); } else { /* * This can happen if the parent mount was bind mounted * on some subdirectory of a shared/slave mount. */ - list_add_tail(&child->mnt_hash, &tmp_list); + hlist_add_head(&child->mnt_hash, &tmp_list); } prev_dest_mnt = m; prev_src_mnt = child; } out: lock_mount_hash(); - while (!list_empty(&tmp_list)) { - child = list_first_entry(&tmp_list, struct mount, mnt_hash); + while (!hlist_empty(&tmp_list)) { + child = hlist_entry(tmp_list.first, struct mount, mnt_hash); umount_tree(child, 0); } unlock_mount_hash(); @@ -338,8 +340,10 @@ static void __propagate_umount(struct mount *mnt) * umount the child only if the child has no * other children */ - if (child && list_empty(&child->mnt_mounts)) - list_move_tail(&child->mnt_hash, &mnt->mnt_hash); + if (child && list_empty(&child->mnt_mounts)) { + hlist_del_init_rcu(&child->mnt_hash); + hlist_add_before_rcu(&child->mnt_hash, &mnt->mnt_hash); + } } } @@ -350,11 +354,11 @@ static void __propagate_umount(struct mount *mnt) * * vfsmount lock must be held for write */ -int propagate_umount(struct list_head *list) +int propagate_umount(struct hlist_head *list) { struct mount *mnt; - list_for_each_entry(mnt, list, mnt_hash) + hlist_for_each_entry(mnt, list, mnt_hash) __propagate_umount(mnt); return 0; } diff --git a/fs/pnode.h b/fs/pnode.h index 59e7eda..fc28a27 100644 --- a/fs/pnode.h +++ b/fs/pnode.h @@ -36,8 +36,8 @@ static inline void set_mnt_shared(struct mount *mnt) void change_mnt_propagation(struct mount *, int); int propagate_mnt(struct mount *, struct mountpoint *, struct mount *, - struct list_head *); -int propagate_umount(struct list_head *); + struct hlist_head *); +int propagate_umount(struct hlist_head *); int propagate_mount_busy(struct mount *, int); void mnt_release_group_id(struct mount *); int get_dominating_id(struct mount *mnt, const struct path *root); -- 2.7.4