Re: [PATCH 0/7] overlay filesystem: request for inclusion

["J. R. Okajima" <hooanon05@yahoo.co.jp>]

Miklos Szeredi:
> Here's a patch to limit stacking overlayfs instances on top of each
> other and on ecryptfs to prevent kernel stack overflow.

I don't think it a good idea to introduce such new member to generic
struct super_block.
- the new member is unrelated to most of other fs.
- ecryptfs already rejects such nests by checking
  (sb->s_type == &ecryptfs_fs_type).
Instead I'd suggest you to introduce a new small test function,
something like
int test_nested(sb)
{
	return sb->s_magic == ECRYPTFS_SUPER_MAGIC
		|| sb->s_type == &ovl_fs_type;
}
Of course "#ifdef CONFIG_ECRYPT_FS" or something should be added too.

If overlayfs had its own SUPER_MAGIC number, it might be better to test it
instead of s_type. But there is no such magic number currently, and I am
afraid intoducing it may affect stat/statfs for overlayfs which you
might dislike.


J. R. Okajima