[PATCH v6 08/11] evm: Allow setxattr() and setattr() for unmodified metadata
roberto.sassu at huawei.com
Tue May 11 14:21:28 UTC 2021
> From: Mimi Zohar [mailto:zohar at linux.ibm.com]
> Sent: Tuesday, May 11, 2021 4:12 PM
> 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
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.
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