Re: [PATCH v4 2/4] initramfs: print helpful cpio error on "crc" magic

[David Disseldorp <ddiss@suse.de>]

On Wed, 10 Nov 2021 17:30:54 +0000, Matthew Wilcox wrote:

> On Wed, Nov 10, 2021 at 01:38:48PM +0100, David Disseldorp wrote:
> > Contrary to the buffer-format.rst documentation, initramfs cpio
> > extraction does not support "crc" archives, which carry "070702"
> > header magic. Make it a little clearer that "newc" (magic="070701") is
> > the only supported cpio format, by extending the POSIX.1 ASCII
> > (magic="070707") specific error message to also cover "crc" magic.  
> 
> Wouldn't it be easier to just add support?

Well, no, this patch already exists. :-)

> As far as I can tell from
> looking at documentation, the "crc" format is the same as newc, except
> that it uses some reserved bits to store the crc.  Since we ignore those
> bits, we could just check for either 070701 or 070702.

Sure, it'd be pretty straightforward to implement "crc" format support,
but I'm not sure how useful a 32-bit checksum would be... If we're going
down this route, wouldn't proper IMA/EVM support make sense via some new
cpio variant with space for the attributes (or as header/trailer like
bootconfig)?
cc'ing Jeff, as I seem to recall him mentioning some work in this area.

Cheers, David