Re: [PATCH 03/34] teach move_mount(2) to work with OPEN_TREE_CLONE [ver #12]

[David Howells]

Eric W. Biederman <ebied...@xmission.com> wrote:

> It should just be a matter of replacing the test
> "if (p->mnt.mnt_sb->s_type == &nsfs)" with "if mnt_ns_loop(p->mnt.mnt_root)"

Okay, the attached seems to work.

Thanks,
David
---
diff --git a/fs/namespace.c b/fs/namespace.c
index e969ded7d54b..5548fb9b7de2 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -2388,6 +2388,27 @@ static inline int tree_contains_unbindable(struct mount 
*mnt)
        return 0;
 }
 
+/*
+ * Object if there are any nsfs mounts in the specified subtree.  These can act
+ * as pins for mount namespaces that aren't checked by the mount-cycle checking
+ * code, thereby allowing cycles to be made.
+ */
+static bool check_for_nsfs_mounts(struct mount *subtree)
+{
+       struct mount *p;
+       bool ret = false;
+
+       lock_mount_hash();
+       for (p = subtree; p; p = next_mnt(p, subtree))
+               if (mnt_ns_loop(p->mnt.mnt_root))
+                       goto out;
+
+       ret = true;
+out:
+       unlock_mount_hash();
+       return ret;
+}
+
 static int do_move_mount(struct path *old_path, struct path *new_path)
 {
        struct path parent_path = {.mnt = NULL, .dentry = NULL};
@@ -2442,6 +2463,8 @@ static int do_move_mount(struct path *old_path, struct 
path *new_path)
        if (IS_MNT_SHARED(p) && tree_contains_unbindable(old))
                goto out1;
        err = -ELOOP;
+       if (!check_for_nsfs_mounts(old))
+               goto out1;
        for (; mnt_has_parent(p); p = p->mnt_parent)
                if (p == old)
                        goto out1;