Re: [PATCH v4 0/3] initramfs: add support for xattrs in the initial ram disk

[Alexander Lobakin]

From: Roberto Sassu <roberto.sassu@xxxxxxxxxx>
Date: Thu, 23 May 2019 14:18:00 +0200

> This patch set aims at solving the following use case: appraise files from
> the initial ram disk. To do that, IMA checks the signature/hash from the

Hi,
is this[0] relatable somehow?

> security.ima xattr. Unfortunately, this use case cannot be implemented
> currently, as the CPIO format does not support xattrs.
> 
> This proposal consists in including file metadata as additional files named
> METADATA!!!, for each file added to the ram disk. The CPIO parser in the
> kernel recognizes these special files from the file name, and calls the
> appropriate parser to add metadata to the previously extracted file. It has
> been proposed to use bit 17:16 of the file mode as a way to recognize files
> with metadata, but both the kernel and the cpio tool declare the file mode
> as unsigned short.
> 
> The difference from v2, v3 (https://lkml.org/lkml/2019/5/9/230,
> https://lkml.org/lkml/2019/5/17/466) is that file metadata are stored in
> separate files instead of a single file. Given that files with metadata
> must immediately follow the files metadata will be added to, image
> generators have to be modified in this version.
> 
> The difference from v1 (https://lkml.org/lkml/2018/11/22/1182) is that
> all files have the same name. The file metadata are added to is always the
> previous one, and the image generator in user space will make sure that
> files are in the correct sequence.
> 
> The difference with another proposal
> (https://lore.kernel.org/patchwork/cover/888071/) is that xattrs can be
> included in an image without changing the image format. Files with metadata
> will appear as regular files. It will be task of the parser in the kernel
> to process them.
> 
> This patch set extends the format of data defined in patch 9/15 of the last
> proposal. It adds header version and type, so that new formats can be
> defined and arbitrary metadata types can be processed.
> 
> The changes introduced by this patch set don't cause any compatibility
> issue: kernels without the metadata parser simply extract the special files
> and don't process metadata; kernels with the metadata parser don't process
> metadata if the special files are not included in the image.
> 
> >>From the kernel space perspective, backporting this functionality to older
> kernels should be very easy. It is sufficient to add two calls to the new
> function do_process_metadata() in do_copy(), and to check the file name in
> do_name(). From the user space perspective, unlike the previous version of
> the patch set, it is required to modify the image generators in order to
> include metadata as separate files.
> 
> Changelog
> 
> v3:
> - include file metadata as separate files named METADATA!!!
> - add the possibility to include in the ram disk arbitrary metadata types
> 
> v2:
> - replace ksys_lsetxattr() with kern_path() and vfs_setxattr()
>   (suggested by Jann Horn)
> - replace ksys_open()/ksys_read()/ksys_close() with
>   filp_open()/kernel_read()/fput()
>   (suggested by Jann Horn)
> - use path variable instead of name_buf in do_readxattrs()
> - set last byte of str to 0 in do_readxattrs()
> - call do_readxattrs() in do_name() before replacing an existing
>   .xattr-list
> - pass pathname to do_setxattrs()
> 
> v1:
> - move xattr unmarshaling to CPIO parser
> 
> 
> Mimi Zohar (1):
>   initramfs: add file metadata
> 
> Roberto Sassu (2):
>   initramfs: read metadata from special file METADATA!!!
>   gen_init_cpio: add support for file metadata
> 
>  include/linux/initramfs.h |  21 ++++++
>  init/initramfs.c          | 137 +++++++++++++++++++++++++++++++++++++-
>  usr/Kconfig               |   8 +++
>  usr/Makefile              |   4 +-
>  usr/gen_init_cpio.c       | 137 ++++++++++++++++++++++++++++++++++++--
>  usr/gen_initramfs_list.sh |  10 ++-
>  6 files changed, 305 insertions(+), 12 deletions(-)
>  create mode 100644 include/linux/initramfs.h
> 
> -- 
> 2.17.1

[0] https://lore.kernel.org/all/20210702233727.21301-1-alobakin@xxxxx

Thanks,
Olek