[yocto] [meta-selinux][PATCHv2 0/8] Label file system in build.

Philip Tricca flihp at twobit.us
Wed Jun 17 15:30:50 PDT 2015

This is the second version of a patch series that allows the file system
of SELinux images to be labeled as part of the build process. This will
allow SELinux images to boot read only file systems and remove the need to
label the file system on first boot.

To do this we must label the file system in the build as well as add
support for extended attributes to the mke2fs utility in the e2fsprogs
package. The first version of this patch series is here:
The approach described in this previous RFC remains the same.

Changes in v2:
This second version has two significant changes: First I've done a bunch
of cleanup. This includes work to make the descriptions in the patch
headers / commit messages more exact as well as combining some commits
with related functionality. Secondly I've reimplemented the xattr cache
so that it actually works.

I've made the patch headers as descriptive as possible and kept the git
commit messages minimal. If the preference is for more verbose commit
messages I'm happy to oblige if advised.

The cache is just a single linked list that's searched for duplicates after
the creation of each new xattr block. The previous implementation was similar
but, aside from not working properly, it was overly complex in its attempt to
keep the list sorted.

To test this new implementation I used the core-image-selinux-minimal image
from the unmodified master branch as a control. This image has 2536 unique
file system objects including the root fs directory. The ext4 file system
produced by the build has 71492 blocks with 13621 free.

As an additional test I added the patches from this set WITHOUT the cache
patches. This causes each file system object with an associated extended
attribute to use up an additional block for the xattr. This should cause
(hypothesis) the output file system to have 13621 - 2536 = 11085 free
blocks. The build producing an ext4 file system with 71492 blocks and 11088
free. That's an additional 2533 blocks used instead of the 2536 expected.
These 3 missing xattr blocks can be accounted for in that there are 3
unlabeled files in the file system.

Introducing the cache allows files with identical xattr blocks to share
them to reduce the number of used blocks. Since we're only storing SELinux
labels in the xattrs we can say that every file with the same SELinux label
should share an xattr block. Counting the unique SELinux labels on file
objects we know that there are 83 in total. The second hypothesis we have
to test then is that using the cache will reduce the number of used blocks
from 2533 down to 83.

Applying the patch that enables the cache produces a third and final ext4
file system. This one again report 71492 total blocks but this time 13538
free. This is 83 blocks fewer than the unlabled file system from the
initial test as we expected. The code added by this patch set is also
instrumented to count the objects in the cache when they're freed. With
this debug output enabled it reports the same number of objects in the

>From the test results I'm pretty confident that the cache functions as
expected. It's still a very basic implementation but given the small
number of unique SELinux labels in the reference file systems it's
likely sufficient for a first version. Feedback / comments on both the
implementation and testing approach would be appreciated.


Philip Tricca (8):
  policycoreutils: Patch setfiles to add FTS_NOCHDIR to fts_flags.
  selinux-image: Add new image class to label the rootfs, use it for
    selinux images.
  e2fsprogs: Add bbappend and stub for xattr module.
  e2fsprogs: Insert calls to xattr module into mke2fs and build xattr
  e2fsprogs: Add xattr security prefix data to
  e2fsprogs: Copy xattr block from source file.
  e2fsprogs: Add stub functions for an xattr cache and struct to hold
    the header and block data.
  e2fsprogs: Implement xattr block cache with simple linked list.

 classes/selinux-image.bbclass                      |   8 +
 ...ib-ext2fs-ext2_ext_attr.h-add-xattr-index.patch |  20 ++
 .../misc-xattr-add-xattr-module-stub.patch         |  57 ++++
 .../misc-xattr-create-xattr-block-node.patch       | 175 +++++++++++
 .../e2fsprogs/misc-xattr-create-xattr-block.patch  | 341 +++++++++++++++++++++
 .../e2fsprogs/misc-xattr-create-xattr-cache.patch  | 181 +++++++++++
 .../mke2fs.c-create_inode.c-copy-xattrs.patch      | 164 ++++++++++
 .../e2fsprogs/e2fsprogs_1.42.9.bbappend            |  10 +
 .../images/core-image-selinux-minimal.bb           |   2 +-
 recipes-security/images/core-image-selinux.bb      |   2 +-
 .../policycoreutils-fts_flags-FTS_NOCHDIR.patch    |  25 ++
 recipes-security/selinux/policycoreutils_2.3.bb    |   1 +
 12 files changed, 984 insertions(+), 2 deletions(-)
 create mode 100644 classes/selinux-image.bbclass
 create mode 100644 recipes-devtools/e2fsprogs/e2fsprogs/lib-ext2fs-ext2_ext_attr.h-add-xattr-index.patch
 create mode 100644 recipes-devtools/e2fsprogs/e2fsprogs/misc-xattr-add-xattr-module-stub.patch
 create mode 100644 recipes-devtools/e2fsprogs/e2fsprogs/misc-xattr-create-xattr-block-node.patch
 create mode 100644 recipes-devtools/e2fsprogs/e2fsprogs/misc-xattr-create-xattr-block.patch
 create mode 100644 recipes-devtools/e2fsprogs/e2fsprogs/misc-xattr-create-xattr-cache.patch
 create mode 100644 recipes-devtools/e2fsprogs/e2fsprogs/mke2fs.c-create_inode.c-copy-xattrs.patch
 create mode 100644 recipes-devtools/e2fsprogs/e2fsprogs_1.42.9.bbappend
 create mode 100644 recipes-security/selinux/policycoreutils/policycoreutils-fts_flags-FTS_NOCHDIR.patch


More information about the yocto mailing list