From: Taras Kondratiuk <takondra@cisco.com>
To: Arnd Bergmann <arnd@arndb.de>
Cc: "H. Peter Anvin" <hpa@zytor.com>,
Al Viro <viro@zeniv.linux.org.uk>, Rob Landley <rob@landley.net>,
Mimi Zohar <zohar@linux.vnet.ibm.com>,
Jonathan Corbet <corbet@lwn.net>,
James McMechan <james.w.mcmechan@gmail.com>,
initramfs@vger.kernel.org, Victor Kamensky <kamensky@cisco.com>,
linux-doc@vger.kernel.org,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
LSM List <linux-security-module@vger.kernel.org>,
xe-linux-external@cisco.com
Subject: Re: [PATCH v2 01/15] Documentation: add newcx initramfs format description
Date: Thu, 25 Jan 2018 12:26:45 -0800 [thread overview]
Message-ID: <151691200536.5378.11544479301138437367@takondra-t460s> (raw)
In-Reply-To: <CAK8P3a2FqEcq44-sRQrsgJ=_DOanC-qgJ3yFr=J6UrOKO0_3uw@mail.gmail.com>
Quoting Arnd Bergmann (2018-01-25 01:29:12)
> On Thu, Jan 25, 2018 at 4:27 AM, Taras Kondratiuk <takondra@cisco.com> wrote:
> > Many of the Linux security/integrity features are dependent on file
> > metadata, stored as extended attributes (xattrs), for making decisions.
> > These features need to be initialized during initcall and enabled as
> > early as possible for complete security coverage.
> >
> > Initramfs (tmpfs) supports xattrs, but newc CPIO archive format does not
> > support including them into the archive.
> >
> > This patch describes "extended" newc format (newcx) that is based on
> > newc and has following changes:
> > - extended attributes support
> > - increased size of filesize to support files >4GB.
> > - increased mtime field size to have usec precision and more than
> > 32-bit of seconds.
> > - removed unused checksum field.
> >
> > Signed-off-by: Taras Kondratiuk <takondra@cisco.com>
> > Signed-off-by: Mimi Zohar <zohar@linux.vnet.ibm.com>
> > Signed-off-by: Victor Kamensky <kamensky@cisco.com>
>
> Ah nice, I like the extension of the time handling, that certainly
> addresses one of the issues with y2038 that we have previously
> hacked around in an ugly way (interpreting the 32-bit
> number as unsigned).
>
> However, if this is to become a generally supported format
> for cpio files, could we make it use nanosecond resolution
> instead? The issue that I see with microseconds is that
> storing a file in an archive and extracting it again would
> otherwise keep the mtime stamp /almost/ identical on file
> systems that have nanosecond resolution, but most of
> the time a comparison would indicate that the files are
> not the same.
>
> Unfortunately, the range of a 64-bit nanoseconds counter
> is still a bit limited (584 years, or half of that if we make it
> signed). While this is clearly enough for the uses in
> initramfs, it still has a similar problem: someone creating
> a fake timestamp a long time in the past or future on
> a file system would lose information after going though
> cpio.
We can match statx(2) by having 64 bits for seconds plus 32 bits for
nanoseconds. For initramfs nanoseconds field can be ignored during
unpacking.
next prev parent reply other threads:[~2018-01-25 20:26 UTC|newest]
Thread overview: 29+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-01-25 3:27 [PATCH v2 00/15] extend initramfs archive format to support xattrs Taras Kondratiuk
2018-01-25 3:27 ` [PATCH v2 01/15] Documentation: add newcx initramfs format description Taras Kondratiuk
2018-01-25 9:29 ` Arnd Bergmann
2018-01-25 20:26 ` Taras Kondratiuk [this message]
2018-01-25 21:02 ` Arnd Bergmann
2018-01-25 22:13 ` Taras Kondratiuk
2018-01-26 2:39 ` Rob Landley
2018-01-26 9:04 ` Arnd Bergmann
2018-01-26 10:31 ` Henrique de Moraes Holschuh
2018-01-26 15:51 ` Victor Kamensky
2018-01-26 18:15 ` Henrique de Moraes Holschuh
2018-01-26 2:40 ` Rob Landley
2018-01-26 21:02 ` Taras Kondratiuk
2018-01-25 3:27 ` [PATCH v2 02/15] initramfs: replace states with function pointers Taras Kondratiuk
2018-01-25 3:27 ` [PATCH v2 03/15] initramfs: store file name in name_buf Taras Kondratiuk
2018-01-25 3:27 ` [PATCH v2 04/15] initramfs: remove unnecessary symlinks processing shortcut Taras Kondratiuk
2018-01-25 3:27 ` [PATCH v2 05/15] initramfs: move files creation into separate state Taras Kondratiuk
2018-01-25 3:27 ` [PATCH v2 06/15] initramfs: separate reading cpio method from header Taras Kondratiuk
2018-01-25 3:27 ` [PATCH v2 07/15] initramfs: split header layout information from parsing function Taras Kondratiuk
2018-01-25 3:27 ` [PATCH v2 08/15] initramfs: add newcx format Taras Kondratiuk
2018-01-25 3:27 ` [PATCH v2 09/15] initramfs: set extended attributes Taras Kondratiuk
2018-01-25 3:27 ` [PATCH v2 10/15] gen_init_cpio: move header formatting into function Taras Kondratiuk
2018-01-25 3:27 ` [PATCH v2 11/15] gen_init_cpio: add newcx format Taras Kondratiuk
2018-01-26 2:40 ` Rob Landley
2018-01-26 20:37 ` Taras Kondratiuk
2018-01-25 3:27 ` [PATCH v2 12/15] gen_init_cpio: set extended attributes for " Taras Kondratiuk
2018-01-25 3:27 ` [PATCH v2 13/15] gen_initramfs_list.sh: add -x option to enable " Taras Kondratiuk
2018-01-25 3:27 ` [PATCH v2 14/15] selinux: allow setxattr on rootfs so initramfs code can set them Taras Kondratiuk
2018-01-25 3:27 ` [PATCH v2 15/15] selinux: delay sid population for rootfs till init is complete Taras Kondratiuk
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