Re: [PATCH v6 08/11] evm: Allow setxattr() and setattr() for unmodified metadata

Mimi Zohar
2021-05-11T14:12:11Z

Hi Roberto,

On Wed, 2021-05-05 at 13:33 +0200, Roberto Sassu wrote:
> With the patch to allow xattr/attr operations if a portable signature
> verification fails, cp and tar can copy all xattrs/attrs so that at the
> end of the process verification succeeds.
>
> However, it might happen that the xattrs/attrs are already set to the
> correct value (taken at signing time) and signature verification succeeds
> before the copy has completed. For example, an archive might contains files
> owned by root and the archive is extracted by root.
>
> Then, since portable signatures are immutable, all subsequent operations
> fail (e.g. fchown()), even if the operation is legitimate (does not alter
> the current value).
>
> This patch avoids this problem by reporting successful operation to user
> space when that operation does not alter the current value of xattrs/attrs.

I must be missing something. If both the IMA and EVM status flags are
reset after xattr or attr modification, do we really need to prevent
any metadata - same or different - changes? Both evm_protect_xattr()
and evm_inode_setattr() would need to be modified to allow
INTEGRITY_PASS_IMMUTABLE.

thanks,

Mimi