On February 17, 2018 4:15:12 PM PST, Mimi Zohar <zohar@xxxxxxxxxxxxxxxxxx> wrote: >On Fri, 2018-02-16 at 12:59 -0800, H. Peter Anvin wrote: >> On 02/16/18 12:33, Taras Kondratiuk 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 64 bits of seconds and added a >> > field for nanoseconds >> > - removed unused checksum field >> > >> >> If you are going to implement a new, non-backwards-compatible format, >> you shouldn't replicate the mistakes of the current format. >Specifically: >> >> 1. The use of ASCII-encoded fixed-length numbers is an idiotic legacy >> from an era before there were any portable way of dealing with >numbers >> with prespecified endianness. If you are going to use ASCII, make >them >> delimited so that they don't have fixed limits, or just use binary. >> >> The cpio header isn't fixed size, so that argument goes away, in fact >> the only way to determine the end of the header is to scan forward. >> >> 2. Alignment sensitivity! Because there is no header length >> information, the above scan tells you where the header ends, but >there >> is padding before the data, and the size of that padding is only >defined >> by alignment. >> >> 3. Inband encoding of EOF: if you actually have a filename >"TRAILER!!!" >> you have problems. >> >> But first, before you define a whole new format for which no tools >exist >> (you will have to work with the maintainers of the GNU tools to add >> support) you should see how complex it would be to support the POSIX >> tar/pax format, which already has all the features you are seeking, >and >> by now is well-supported. > >The discussion about including xattrs in the initramfs didn't start >yesterday. It's been on the list of measurement/appraisal gaps that >need to be closed for years. Initially I planned on using tar, but at >the 2014 Kernel Summit I spoke with Al at length. At the time, he was >very clear that tar is unnecessarily overly complicated and >recommended extending CPIO. > >I took his advice. Unfortunately, as soon as I posted an initial >patch set to include xattrs in CPIO, all of the problems with CPIO had >to be addressed before defining a new CPIO number. Unfortunately, >this wasn't the only measurement/appraisal gap that needed to be >addressed. I've been working on closing other gaps. > >I'm really happy that someone has taken the time to work on this. > Instead of derailing their attempt of extending CPIO to include >xattrs, I'd appreciate your making constructive suggestions. > >Mimi I'm not trying to derail anything, but I do want to see it done well if it is going to be done. I have several ideas already, but I may not have a chance to write them down properly until after the weekend due to family obligations. The assessment of pax/tar is useful; it should be added to the patch documentation in a future set. -- Sent from my Android device with K-9 Mail. Please excuse my brevity. -- 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
