Quoting Rob Landley (2019-05-22 12:26:43) > > > On 5/22/19 11:17 AM, hpa@xxxxxxxxx wrote: > > On May 20, 2019 2:39:46 AM PDT, Roberto Sassu <roberto.sassu@xxxxxxxxxx> wrote: > >> On 5/18/2019 12:17 AM, Arvind Sankar wrote: > >>> On Fri, May 17, 2019 at 02:47:31PM -0700, H. Peter Anvin wrote: > >>>> On 5/17/19 2:02 PM, Arvind Sankar wrote: > >>>>> On Fri, May 17, 2019 at 01:18:11PM -0700, hpa@xxxxxxxxx wrote: > >>>>>> > >>>>>> Ok... I just realized this does not work for a modular initramfs, > >> composed at load time from multiple files, which is a very real > >> problem. Should be easy enough to deal with: instead of one large file, > >> use one companion file per source file, perhaps something like > >> filename..xattrs (suggesting double dots to make it less likely to > >> conflict with a "real" file.) No leading dot, as it makes it more > >> likely that archivers will sort them before the file proper. > >>>>> This version of the patch was changed from the previous one exactly > >> to deal with this case -- > >>>>> it allows for the bootloader to load multiple initramfs archives, > >> each > >>>>> with its own .xattr-list file, and to have that work properly. > >>>>> Could you elaborate on the issue that you see? > >>>>> > >>>> > >>>> Well, for one thing, how do you define "cpio archive", each with its > >> own > >>>> .xattr-list file? Second, that would seem to depend on the ordering, > >> no, > >>>> in which case you depend critically on .xattr-list file following > >> the > >>>> files, which most archivers won't do. > >>>> > >>>> Either way it seems cleaner to have this per file; especially if/as > >> it > >>>> can be done without actually mucking up the format. > >>>> > >>>> I need to run, but I'll post a more detailed explanation of what I > >> did > >>>> in a little bit. > >>>> > >>>> -hpa > >>>> > >>> Not sure what you mean by how do I define it? Each cpio archive will > >>> contain its own .xattr-list file with signatures for the files within > >>> it, that was the idea. > >>> > >>> You need to review the code more closely I think -- it does not > >> depend > >>> on the .xattr-list file following the files to which it applies. > >>> > >>> The code first extracts .xattr-list as though it was a regular file. > >> If > >>> a later dupe shows up (presumably from a second archive, although the > >>> patch will actually allow a second one in the same archive), it will > >>> then process the existing .xattr-list file and apply the attributes > >>> listed within it. It then will proceed to read the second one and > >>> overwrite the first one with it (this is the normal behaviour in the > >>> kernel cpio parser). At the end once all the archives have been > >>> extracted, if there is an .xattr-list file in the rootfs it will be > >>> parsed (it would've been the last one encountered, which hasn't been > >>> parsed yet, just extracted). > >>> > >>> Regarding the idea to use the high 16 bits of the mode field in > >>> the header that's another possibility. It would just require > >> additional > >>> support in the program that actually creates the archive though, > >> which > >>> the current patch doesn't. > >> > >> Yes, for adding signatures for a subset of files, no changes to the ram > >> disk generator are necessary. Everything is done by a custom module. To > >> support a generic use case, it would be necessary to modify the > >> generator to execute getfattr and the awk script after files have been > >> placed in the temporary directory. > >> > >> If I understood the new proposal correctly, it would be task for cpio > >> to > >> read file metadata after the content and create a new record for each > >> file with mode 0x18000, type of metadata encoded in the file name and > >> metadata as file content. I don't know how easy it would be to modify > >> cpio. Probably the amount of changes would be reasonable. > > I could make toybox cpio do it in a weekend, and could probably throw a patch at > usr/gen_init_cpio.c while I'm at it. I prototyped something like that a couple > years ago, it's not hard. > > The real question is scripts/gen_initramfs_list.sh and the text format it > produces. We can currently generate cpio files with different ownership and > permissions than the host system can represent (when not building as root, on a > filesystem that may not support xattrs or would get unhappy about conflicting > selinux annotations). We work around it by having the metadata represented > textually in the initramfs_list file gen_initramfs_list.sh produces and > gen_init_cpio.c consumes. > > xattrs are a terrible idea the Macintosh invented so Finder could remember where > you moved a file's icon in its folder without having to modify the file, and > then things like OS/2 copied it and Windows picked it up from there and went "Of > course, this is a security mechanism!" and... sigh. > > This is "data that is not data", it's metadata of unbounded size. It seems like > it should go in gen_initramfs_list.sh but as what, keyword=value pairs that > might have embedded newlines in them? A base64 encoding? Something else? I the previous try to add xattrs to cpio I've used hex encoding in gen_initramfs_list.sh: https://lkml.org/lkml/2018/1/24/851 - gen_init_cpio: set extended attributes for newcx format https://lkml.org/lkml/2018/1/24/852 - gen_initramfs_list.sh: add -x option to enable newcx format
