Messages in this thread | | | Subject | Re: [PATCH v4 0/3] initramfs: add support for xattrs in the initial ram disk | From | Roberto Sassu <> | Date | Mon, 1 Jul 2019 16:42:13 +0300 |
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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.
Roberto
-- HUAWEI TECHNOLOGIES Duesseldorf GmbH, HRB 56063 Managing Director: Bo PENG, Jian LI, Yanli SHI
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