> From: Mimi Zohar [mailto:zohar@xxxxxxxxxxxxx] > Sent: Tuesday, May 11, 2021 4:41 PM > On Tue, 2021-05-11 at 14:21 +0000, Roberto Sassu wrote: > > > > > > 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. > > > > yes, given that the IMA and EVM flags are reset, it should not be > > a problem to allow changes. However, I think it is useful to keep > > the current behavior. For example, it would prevent an accidental > > change of the SELinux label during the relabeling process. > > I understand we might want to prevent accidental or malicious changes, > but that isn't the purpose of this patch set. The patch description > would also need to be updated to reflect the real purpose. We would be changing the expectation that metadata changes are denied, which was defined with the original patches. I would prefer to keep the current behavior, but if your suggestion is to allow metadata changes, I will modify the patch set. Roberto HUAWEI TECHNOLOGIES Duesseldorf GmbH, HRB 56063 Managing Director: Li Peng, Li Jian, Shi Yanli > thanks, > > Mimi
