Re: PROBLEM: IMA xattrs not written on overlayfs

[Mimi Zohar <zohar@linux.ibm.com>]

On Mon, 2018-09-10 at 11:17 +0200, Ignaz Forster wrote:
> Am 07.09.18 um 20:45 schrieb Mimi Zohar:
> >> A small example for reproduction (on a system with IMA appraisal):
> >> # OVERLAYFS_TEST_DIR=`mktemp -d`
> >> # mkdir "${OVERLAYFS_TEST_DIR}/upper"
> >> # mkdir "${OVERLAYFS_TEST_DIR}/work"
> >> # mount -t overlay -o lowerdir=/etc,upperdir="${OVERLAYFS_TEST_DIR}
> >> /upper",workdir="${OVERLAYFS_TEST_DIR}/work" overlay /etc
> >> #
> >> # rm -f /etc/test.txt
> >> # echo Test > /etc/test.txt
> >> # cat /etc/test.txt
> >> cat: /etc/test.txt: Permission denied
> >> # ls -s /etc/test.txt
> >> 4 /etc/test.txt # <- The contents are there
> >> # getfattr -m . -d /etc/test.txt
> >> # # <- The hash isn't
> >>
> > 
> > Thank you for providing the example.  Also on a linux-4.18.0-rcX test
> > kernel, the file hash isn't being written out either.  The builtin
> > "appraise_tcb" policy (eg. specified as "ima_policy=appraise_tcb" on
> > the boot command) has a tmpfs dont_appraise rule.
> 
> Putting the mount point into /tmp may have been a bad example, however 
> at least on my system /tmp is mounted from a btrfs subvolume. Same with 
> /var, which I'm using for my personal tests.

The file size is still 0, when ima_check_last_writer() calls
ima_update_xattr(), which tries to calculate the file hash and write
it out an security.ima.

Mimi