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>

4 files changed, 29 insertions, 55 deletions

diff --git a/fs/dcache.c b/fs/dcache.c
index 8a75e3b0f49d..64c8ce4c147f 100644
--- 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 ec8512478b04..7aad258dcaf6 100644
--- 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 f1cd958b92e5..4d5a06ea57a2 100644
--- 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 7f0c13ae9484..723399e76134 100644
--- 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 */