[PATCH v2 00/15] extend initramfs archive format to support xattrs
takondra at cisco.com
Thu Jan 25 03:27:40 UTC 2018
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.
There are several ways to include xattrs for initramfs:
- Add TAR support. Complicated format and big headers looks like too
- Include a file manifest containing the xattrs in the CPIO. Should be
easy for initramfs because we can set xattrs at the end when all files
are extracted, but extracting such archive in userspace will be more
complicated. For example it may be necessary to set SELinux labels for
directories before extracting files into them, so manifest has to be
extracted first and then searched during each file extraction.
- Extend CPIO header to support xattrs. This seem to be the most
straight forward way. It also allows to do other useful changes
to CPIO format at the same time. E.g. increase filesize field to
support files >4GB.
This patch set extends the existing newc CPIO archive format to include
xattrs in the initramfs.
The series is based on v4.15-rc8. cpio_xattr branch is available here:
=== Patch summary ===
[PATCH 01/15] Documentation: add newcx initramfs format description
Refactoring to simplify adding the new format:
[PATCH 02/15] initramfs: replace states with function pointers
[PATCH 03/15] initramfs: store file name in name_buf
[PATCH 04/15] initramfs: remove unnecessary symlinks processing shortcut
[PATCH 05/15] initramfs: move files creation into separate state
[PATCH 06/15] initramfs: separate reading cpio method from header
[PATCH 07/15] initramfs: split header layout information from parsing
Parse newxc format:
[PATCH 08/15] initramfs: add newcx format
[PATCH 09/15] initramfs: set extended attributes
Generate newcx cpio archive:
[PATCH 10/15] gen_init_cpio: move header formatting into function
[PATCH 11/15] gen_init_cpio: add newcx format
[PATCH 12/15] gen_init_cpio: set extended attributes for newcx
[PATCH 13/15] gen_initramfs_list.sh: add -x option to enable newcx
SELinux patches used for testing. They will be sent to SELinux
[PATCH 14/15] selinux: allow setxattr on rootfs so initramfs code can
[PATCH 15/15] selinux: delay sid population for rootfs till init is
=== Testing ===
gen_initramfs_list.sh can be used to generate newcx CPIO archive: if
CONFIG_INITRAMFS_NEWCX is enabled CONFIG_INITRAMFS_SOURCE will be packed
into newcx archive. It is enough for basic testing, but it is not
convenient for more complex setup.
Victor have prepared a test setup with SELinux-labeled initramfs based
on Poky(Yocto) with meta-selinux layer.
Repo manifest and build instructions:
Reference cpio utility patch to support newcx format could be
found as part of poky/meta-selinux testing environment at
=== History ===
The patch set is based on Mimi's series from Jan 2015:
Latest discussion I was able to find is from Dec 2015:
- increased size of filesize to 64 bits to support files >4GB.
- increased mtime field size to 64 bits to get usec precision
and more than 32 bits of seconds. Rob mentioned nsec, but that
will leave only 34 bits for seconds. If nsec precision is needed
then we can add a separate 32 bit nsec field (it will match statx).
- Checksum field is replased by xattrs_size field.
Other fields are left unchanged. See patch format description in the
James suggested to add many other changes, but that will bloat header
and make this new format very similar to tar. To keep format simple no
other fields were added.
- added documentation
- made format more consistent. In previous version a sequence of fields
in newcx header was different for symlinks and regular files (for
symlinks data field was before xattrs). It was caused by a flow
shortcut during symlink entry parsing.
- removed unused checksum field in newcx header
- removed redundant xattrcount at the beginning of xattr section
(xattrs_size is enough to determine the end of section).
- size of xattr entry in xattr section includes both name and value.
This makes format more consistent and allows to jump over an entry
without scanning for the end of name string first.
- streamlined the state machine to address the previous issue and make
it easier to add the new format
- made header parsing data-driven to remove magic numbers and make it
easier to add the new format
- eliminated unnecessary buffer allocation for every file name
- pass xattrs to gen_init_cpio via cpio_list file instead of reading
them from files during packaging. This allows to set xattrs in CPIO
even if they can't be set on a build machine.
- incorporated several bug fixes from Victor Kamensky for v1 series
Mimi Zohar (3):
initramfs: separate reading cpio method from header
initramfs: set extended attributes
gen_initramfs_list.sh: add -x option to enable newcx format
Taras Kondratiuk (10):
Documentation: add newcx initramfs format description
initramfs: replace states with function pointers
initramfs: store file name in name_buf
initramfs: remove unnecessary symlinks processing shortcut
initramfs: move files creation into separate state
initramfs: split header layout information from parsing function
initramfs: add newcx format
gen_init_cpio: move header formatting into function
gen_init_cpio: add newcx format
gen_init_cpio: set extended attributes for newcx format
Victor Kamensky (2):
selinux: allow setxattr on rootfs so initramfs code can set them
selinux: delay sid population for rootfs till init is complete
Documentation/early-userspace/buffer-format.txt | 46 ++-
init/initramfs.c | 401 ++++++++++++++++++------
scripts/gen_initramfs_list.sh | 13 +-
security/selinux/hooks.c | 19 ++
security/selinux/include/security.h | 1 +
usr/Kconfig | 11 +
usr/Makefile | 3 +-
usr/gen_init_cpio.c | 364 ++++++++++++++-------
8 files changed, 626 insertions(+), 232 deletions(-)
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