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