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/namespace.c b/fs/namespace.c
index ec85124..7aad258 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -1876,8 +1876,7 @@
/*
* 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 @@
}
/*
+ * 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 @@
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 @@
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);