From 38129a13e6e71f666e0468e99fdd932a687b4d7e Mon Sep 17 00:00:00 2001 From: Al Viro Date: Thu, 20 Mar 2014 21:10:51 -0400 Subject: 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/pnode.c | 26 +++++++++++++++----------- 1 file changed, 15 insertions(+), 11 deletions(-) (limited to 'fs/pnode.c') diff --git a/fs/pnode.c b/fs/pnode.c index c7221bb19801..88396df725b4 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; } -- cgit v1.2.3