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

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Date:	Sat, 09 Jul 2011 21:18:10 +0900
From:	"J. R. Okajima" <hooanon05@...oo.co.jp>
To:	Miklos Szeredi <miklos@...redi.hu>
Cc:	Erez Zadok <ezk@....cs.sunysb.edu>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"viro\@ZenIV.linux.org.uk Viro" <viro@...IV.linux.org.uk>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
	apw@...onical.com, nbd@...nwrt.org, neilb@...e.de,
	hramrach@...trum.cz, jordipujolp@...il.com
Subject: Re: [PATCH 0/7] overlay filesystem: request for inclusion


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
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