linux-kernel - Re: [PATCH 04/13] overlay filesystem

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Date:	Wed, 15 Aug 2012 23:24:48 -0700
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	Miklos Szeredi <miklos@...redi.hu>
Cc:	viro@...IV.linux.org.uk, linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org, hch@...radead.org,
	torvalds@...ux-foundation.org, akpm@...ux-foundation.org,
	apw@...onical.com, nbd@...nwrt.org, neilb@...e.de,
	hramrach@...trum.cz, jordipujolp@...il.com, ezk@....cs.sunysb.edu,
	ricwheeler@...il.com, dhowells@...hat.com, hpj@...la.net,
	sedat.dilek@...glemail.com, penberg@...nel.org,
	goran.cetusic@...il.com, romain@...bokech.com, mszeredi@...e.cz
Subject: Re: [PATCH 04/13] overlay filesystem

Miklos Szeredi <miklos@...redi.hu> writes:

Minor nits below.

> diff --git a/fs/overlayfs/dir.c b/fs/overlayfs/dir.c
> new file mode 100644
> index 0000000..6b50823
> --- /dev/null
> +++ b/fs/overlayfs/dir.c
> @@ -0,0 +1,598 @@
> +/*
> + *
> + * Copyright (C) 2011 Novell Inc.
> + *
> + * This program is free software; you can redistribute it and/or modify it
> + * under the terms of the GNU General Public License version 2 as published by
> + * the Free Software Foundation.
> + */
> +
> +#include <linux/fs.h>
> +#include <linux/namei.h>
> +#include <linux/xattr.h>
> +#include <linux/security.h>
> +#include <linux/cred.h>
> +#include "overlayfs.h"
> +
> +static const char *ovl_whiteout_symlink = "(overlay-whiteout)";
> +
> +static int ovl_whiteout(struct dentry *upperdir, struct dentry *dentry)
> +{
> +	int err;
> +	struct dentry *newdentry;
> +	const struct cred *old_cred;
> +	struct cred *override_cred;
> +
> +	/* FIXME: recheck lower dentry to see if whiteout is really
>  	needed */

Is that FIXME still valid?

> +	err = -ENOMEM;
> +	override_cred = prepare_creds();
> +	if (!override_cred)
> +		goto out;
> +
> +	/*
> +	 * CAP_SYS_ADMIN for setxattr
> +	 * CAP_DAC_OVERRIDE for symlink creation
> +	 * CAP_FOWNER for unlink in sticky directory
> +	 */
> +	cap_raise(override_cred->cap_effective, CAP_SYS_ADMIN);
> +	cap_raise(override_cred->cap_effective, CAP_DAC_OVERRIDE);
> +	cap_raise(override_cred->cap_effective, CAP_FOWNER);
> +	override_cred->fsuid = 0;
> +	override_cred->fsgid = 0;

Could you please make these GLOBAL_ROOT_UID and GLOBAL_ROOT_GID
instead of 0?  Otherwise this code won't compile with the usernamespace
bits enabled.

> +	old_cred = override_creds(override_cred);

Eric
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