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 security.ima xattr. Unfortunately, this use case cannot be implemented currently, as the CPIO format does not support xattrs.
This proposal consists in marshaling pathnames and xattrs in a file called .xattr-list. They are unmarshaled by the CPIO parser after all files have been extracted, or before the next ram disk is processed. The difference from v1 (https://lkml.org/lkml/2018/11/22/1182) is that all xattrs are stored in a single file and not per file (solves the file name limitation issue, as it is not necessary to add a suffix to files containing xattrs). 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, as opposed to defining a new one. As seen from the discussion, if a new format has to be defined, it should fix the issues of the existing format, which requires more time. To fulfill both requirements, adding support for xattrs in a short time and defining a new image format properly, this patch set takes an incremental approach: it introduces a parser of xattrs that can be used either if xattrs are in a regular file or directly added to the image (this patch set reuses patch 9/15 of the existing proposal); in addition, it introduces a wrapper of the xattr parser, to read xattrs from a file. The changes introduced by this patch set don't cause any compatibility issue: kernels without the xattr parser simply extracts .xattr-list and don't unmarshal xattrs; kernels with the xattr parser don't unmarshal xattrs if .xattr-list is not found 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_readxattrs(). From the user space perspective, no change is required for the use case. A new dracut module (module-setup.sh) will execute: getfattr --absolute-names -d -h -R -e hex -m security.ima \ <file list> | xattr.awk -b > ${initdir}/.xattr-list where xattr.awk is the script that marshals xattrs (see patch 3/3). The same can be done with the initramfs-tools ram disk generator. Changelog 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() Mimi Zohar (1): initramfs: set extended attributes Roberto Sassu (1): initramfs: introduce do_readxattrs() init/initramfs.c | 170 ++++++++++++++++++++++++++++++++++++++++++++++- 1 file changed, 168 insertions(+), 2 deletions(-) -- 2.17.1
