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

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Date:	Fri, 15 Jul 2011 12:59:20 +0200
From:	Miklos Szeredi <miklos@...redi.hu>
To:	"J. R. Okajima" <hooanon05@...oo.co.jp>
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

"J. R. Okajima" <hooanon05@...oo.co.jp> writes:

> 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;
> }

I don't want to prevent stacking completely, only limit it.  And the
only sane way to do that is with a counter in super_block.

Thanks,
Miklos
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