Re: [PATCH v3 12/25] security: Introduce inode_post_setattr hook

[Roberto Sassu <roberto.sassu@huaweicloud.com>]

On Thu, 2023-10-12 at 07:43 -0400, Mimi Zohar wrote:
> On Thu, 2023-10-12 at 09:42 +0200, Roberto Sassu wrote:
> > On Wed, 2023-10-11 at 20:08 -0400, Mimi Zohar wrote:
> > > gOn Mon, 2023-09-04 at 15:34 +0200, Roberto Sassu wrote:
> > > > From: Roberto Sassu <roberto.sassu@huawei.com>
> > > > 
> > > > In preparation for moving IMA and EVM to the LSM infrastructure, introduce
> > > > the inode_post_setattr hook.
> > > > 
> > > > It is useful for EVM to recalculate the HMAC on modified file attributes
> > > > and other file metadata, after it verified the HMAC of current file
> > > > metadata with the inode_setattr hook.
> > > 
> > > "useful"?  
> > > 
> > > At inode_setattr hook, EVM verifies the file's existing HMAC value.  At
> > > inode_post_setattr, EVM re-calculates the file's HMAC based on the
> > > modified file attributes and other file metadata.
> > > 
> > > > 
> > > > LSMs should use the new hook instead of inode_setattr, when they need to
> > > > know that the operation was done successfully (not known in inode_setattr).
> > > > The new hook cannot return an error and cannot cause the operation to be
> > > > reverted.
> > > 
> > > Other LSMs could similarly update security xattrs or ...
> > 
> > I added your sentence. The one above is to satisfy Casey's request to
> > justify the addition of the new hook, and to explain why inode_setattr
> > is not sufficient.
> 
> I was suggesting simplifying the wording.  Perhaps something like:
> 
> Other LSMs could similarly take some action after successful file attri
> bute change.

Ok, will use that.

Thanks

Roberto