vfs: more mnt_parent cleanups

a) mount --move is checking that ->mnt_parent is non-NULL before
looking if that parent happens to be shared; ->mnt_parent is never
NULL and it's not even an misspelled !mnt_has_parent()

b) pivot_root open-codes is_path_reachable(), poorly.

c) so does path_is_under(), while we are at it.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

diff --git a/fs/dcache.c b/fs/dcache.c
index 8a75e3b..64c8ce4 100644 (file)
--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -2853,31 +2853,6 @@ int is_subdir(struct dentry *new_dentry, struct dentry *old_dentry)
        return result;
 }
 
-int path_is_under(struct path *path1, struct path *path2)
-{
-       struct vfsmount *mnt = path1->mnt;
-       struct dentry *dentry = path1->dentry;
-       int res;
-
-       br_read_lock(vfsmount_lock);
-       if (mnt != path2->mnt) {
-               for (;;) {
-                       if (!mnt_has_parent(mnt)) {
-                               br_read_unlock(vfsmount_lock);
-                               return 0;
-                       }
-                       if (mnt->mnt_parent == path2->mnt)
-                               break;
-                       mnt = mnt->mnt_parent;
-               }
-               dentry = mnt->mnt_mountpoint;
-       }
-       res = is_subdir(dentry, path2->dentry);
-       br_read_unlock(vfsmount_lock);
-       return res;
-}
-EXPORT_SYMBOL(path_is_under);
-
 void d_genocide(struct dentry *root)
 {
        struct dentry *this_parent;

diff --git a/fs/namespace.c b/fs/namespace.c
index ec85124..7aad258 100644 (file)
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -1876,8 +1876,7 @@ static int do_move_mount(struct path *path, char *old_name)
        /*
         * Don't move a mount residing in a shared parent.
         */
-       if (old_path.mnt->mnt_parent &&
-           IS_MNT_SHARED(old_path.mnt->mnt_parent))
+       if (IS_MNT_SHARED(old_path.mnt->mnt_parent))
                goto out1;
        /*
         * Don't move a mount tree containing unbindable mounts to a destination
@@ -2534,6 +2533,31 @@ out_type:
 }
 
 /*
+ * Return true if path is reachable from root
+ *
+ * namespace_sem or vfsmount_lock is held
+ */
+bool is_path_reachable(struct vfsmount *mnt, struct dentry *dentry,
+                        const struct path *root)
+{
+       while (mnt != root->mnt && mnt_has_parent(mnt)) {
+               dentry = mnt->mnt_mountpoint;
+               mnt = mnt->mnt_parent;
+       }
+       return mnt == root->mnt && is_subdir(dentry, root->dentry);
+}
+
+int path_is_under(struct path *path1, struct path *path2)
+{
+       int res;
+       br_read_lock(vfsmount_lock);
+       res = is_path_reachable(path1->mnt, path1->dentry, path2);
+       br_read_unlock(vfsmount_lock);
+       return res;
+}
+EXPORT_SYMBOL(path_is_under);
+
+/*
  * pivot_root Semantics:
  * Moves the root file system of the current process to the directory put_old,
  * makes new_root as the new root file system of the current process, and sets
@@ -2561,7 +2585,6 @@ out_type:
 SYSCALL_DEFINE2(pivot_root, const char __user *, new_root,
                const char __user *, put_old)
 {
-       struct vfsmount *tmp;
        struct path new, old, parent_path, root_parent, root;
        int error;
 
@@ -2611,18 +2634,7 @@ SYSCALL_DEFINE2(pivot_root, const char __user *, new_root,
        if (!mnt_has_parent(new.mnt))
                goto out4; /* not attached */
        /* make sure we can reach put_old from new_root */
-       tmp = old.mnt;
-       if (tmp != new.mnt) {
-               for (;;) {
-                       if (!mnt_has_parent(tmp))
-                               goto out4; /* already mounted on put_old */
-                       if (tmp->mnt_parent == new.mnt)
-                               break;
-                       tmp = tmp->mnt_parent;
-               }
-               if (!is_subdir(tmp->mnt_mountpoint, new.dentry))
-                       goto out4;
-       } else if (!is_subdir(old.dentry, new.dentry))
+       if (!is_path_reachable(old.mnt, old.dentry, &new))
                goto out4;
        br_write_lock(vfsmount_lock);
        detach_mnt(new.mnt, &parent_path);

diff --git a/fs/pnode.c b/fs/pnode.c
index f1cd958..4d5a06e 100644 (file)
--- a/fs/pnode.c
+++ b/fs/pnode.c
@@ -28,21 +28,6 @@ static inline struct vfsmount *next_slave(struct vfsmount *p)
        return list_entry(p->mnt_slave.next, struct vfsmount, mnt_slave);
 }
 
-/*
- * Return true if path is reachable from root
- *
- * namespace_sem is held, and mnt is attached
- */
-static bool is_path_reachable(struct vfsmount *mnt, struct dentry *dentry,
-                        const struct path *root)
-{
-       while (mnt != root->mnt && mnt_has_parent(mnt)) {
-               dentry = mnt->mnt_mountpoint;
-               mnt = mnt->mnt_parent;
-       }
-       return mnt == root->mnt && is_subdir(dentry, root->dentry);
-}
-
 static struct vfsmount *get_peer_under_root(struct vfsmount *mnt,
                                            struct mnt_namespace *ns,
                                            const struct path *root)

diff --git a/fs/pnode.h b/fs/pnode.h
index 7f0c13a..723399e 100644 (file)
--- a/fs/pnode.h
+++ b/fs/pnode.h
@@ -42,4 +42,6 @@ void mnt_set_mountpoint(struct vfsmount *, struct dentry *,
 void release_mounts(struct list_head *);
 void umount_tree(struct vfsmount *, int, struct list_head *);
 struct vfsmount *copy_tree(struct vfsmount *, struct dentry *, int);
+bool is_path_reachable(struct vfsmount *, struct dentry *,
+                        const struct path *root);
 #endif /* _LINUX_PNODE_H */