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

[Roberto Sassu]

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@xxxxxxxxxx>
> > 
> > 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.

Thanks

Roberto

> > 
> > Signed-off-by: Roberto Sassu <roberto.sassu@xxxxxxxxxx>
> 
> Reviewed-by: Mimi Zohar <zohar@xxxxxxxxxxxxx>