Quoting Arnd Bergmann (2018-01-25 01:29:12) > On Thu, Jan 25, 2018 at 4:27 AM, Taras Kondratiuk <takondra@xxxxxxxxx> wrote: > > Many of the Linux security/integrity features are dependent on file > > metadata, stored as extended attributes (xattrs), for making decisions. > > These features need to be initialized during initcall and enabled as > > early as possible for complete security coverage. > > > > Initramfs (tmpfs) supports xattrs, but newc CPIO archive format does not > > support including them into the archive. > > > > This patch describes "extended" newc format (newcx) that is based on > > newc and has following changes: > > - extended attributes support > > - increased size of filesize to support files >4GB. > > - increased mtime field size to have usec precision and more than > > 32-bit of seconds. > > - removed unused checksum field. > > > > Signed-off-by: Taras Kondratiuk <takondra@xxxxxxxxx> > > Signed-off-by: Mimi Zohar <zohar@xxxxxxxxxxxxxxxxxx> > > Signed-off-by: Victor Kamensky <kamensky@xxxxxxxxx> > > Ah nice, I like the extension of the time handling, that certainly > addresses one of the issues with y2038 that we have previously > hacked around in an ugly way (interpreting the 32-bit > number as unsigned). > > However, if this is to become a generally supported format > for cpio files, could we make it use nanosecond resolution > instead? The issue that I see with microseconds is that > storing a file in an archive and extracting it again would > otherwise keep the mtime stamp /almost/ identical on file > systems that have nanosecond resolution, but most of > the time a comparison would indicate that the files are > not the same. > > Unfortunately, the range of a 64-bit nanoseconds counter > is still a bit limited (584 years, or half of that if we make it > signed). While this is clearly enough for the uses in > initramfs, it still has a similar problem: someone creating > a fake timestamp a long time in the past or future on > a file system would lose information after going though > cpio. We can match statx(2) by having 64 bits for seconds plus 32 bits for nanoseconds. For initramfs nanoseconds field can be ignored during unpacking. -- To unsubscribe from this list: send the line "unsubscribe linux-doc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
