On Mon, 2019-07-01 at 16:42 +0300, Roberto Sassu wrote: > On 6/30/2019 6:39 PM, Mimi Zohar wrote: > > On Wed, 2019-06-26 at 10:15 +0200, Roberto Sassu wrote: > >> On 6/3/2019 8:32 PM, Rob Landley wrote: > >>> On 6/3/19 4:31 AM, Roberto Sassu wrote: > >>>>> 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 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. > >>>> > >>>> Any opinion on this patch set? > >>>> > >>>> Thanks > >>>> > >>>> Roberto > >>> > >>> Sorry, I've had the window open since you posted it but haven't gotten around to > >>> it. I'll try to build it later today. > >>> > >>> It does look interesting, and I have no objections to the basic approach. I > >>> should be able to add support to toybox cpio over a weekend once I've got the > >>> kernel doing it to test against. > >> > >> Ok. > >> > >> Let me give some instructions so that people can test this patch set. > >> > >> To add xattrs to the ram disk embedded in the kernel it is sufficient > >> to set CONFIG_INITRAMFS_FILE_METADATA="xattr" and > >> CONFIG_INITRAMFS_SOURCE="<file with xattr>" in the kernel configuration. > >> > >> To add xattrs to the external ram disk, it is necessary to patch cpio: > >> > >> https://github.com/euleros/cpio/commit/531cabc88e9ecdc3231fad6e4856869baa9a91ef > >> (xattr-v1 branch) > >> > >> and dracut: > >> > >> https://github.com/euleros/dracut/commit/a2dee56ea80495c2c1871bc73186f7b00dc8bf3b > >> (digest-lists branch) > >> > >> The same modification can be done for mkinitramfs (add '-e xattr' to the > >> cpio command line). > >> > >> To simplify the test, it would be sufficient to replace only the cpio > >> binary and the dracut script with the modified versions. For dracut, the > >> patch should be applied to the local dracut (after it has been renamed > >> to dracut.sh). > >> > >> Then, run: > >> > >> dracut -e xattr -I <file with xattr> (add -f to overwrite the ram disk) > >> > >> Xattrs can be seen by stopping the boot process for example by adding > >> rd.break to the kernel command line. > > > > A simple way of testing, without needing any changes other than the > > kernel patches, is to save the dracut temporary directory by supplying > > "--keep" on the dracut command line, calling > > usr/gen_initramfs_list.sh, followed by usr/gen_init_cpio with the "-e > > xattr" option. > > Alternatively, follow the instructions to create the embedded ram disk > with xattrs, and use the existing external ram disk created with dracut > to check if xattrs are created. True, but this alternative is for those who normally use dracut to create an initramfs, but don't want to update cpio or dracut. Mimi
