On Thu, 2023-04-06 at 17:58 -0400, Stefan Berger wrote: > > On 4/6/23 17:24, Jeff Layton wrote: > > On Thu, 2023-04-06 at 16:22 -0400, Stefan Berger wrote: > > > > > > On 4/6/23 15:37, Jeff Layton wrote: > > > > On Thu, 2023-04-06 at 15:11 -0400, Stefan Berger wrote: > > > > > > > > > > On 4/6/23 14:46, Jeff Layton wrote: > > > > > > On Thu, 2023-04-06 at 17:01 +0200, Christian Brauner wrote: > > > > > > > On Thu, Apr 06, 2023 at 10:36:41AM -0400, Paul Moore wrote: > > > > > > > > > > > > > > > > > Correct. As long as IMA is also measuring the upper inode then it seems > > > > > > like you shouldn't need to do anything special here. > > > > > > > > > > Unfortunately IMA does not notice the changes. With the patch provided in the other email IMA works as expected. > > > > > > > > > > > > > > > > > It looks like remeasurement is usually done in ima_check_last_writer. > > > > That gets called from __fput which is called when we're releasing the > > > > last reference to the struct file. > > > > > > > > You've hooked into the ->release op, which gets called whenever > > > > filp_close is called, which happens when we're disassociating the file > > > > from the file descriptor table. > > > > > > > > So...I don't get it. Is ima_file_free not getting called on your file > > > > for some reason when you go to close it? It seems like that should be > > > > handling this. > > > > > > I would ditch the original proposal in favor of this 2-line patch shown here: > > > > > > https://lore.kernel.org/linux-integrity/a95f62ed-8b8a-38e5-e468-ecbde3b221af@xxxxxxxxxxxxx/T/#m3bd047c6e5c8200df1d273c0ad551c645dd43232 > > > > > > > > > > Ok, I think I get it. IMA is trying to use the i_version from the > > overlayfs inode. > > > > I suspect that the real problem here is that IMA is just doing a bare > > inode_query_iversion. Really, we ought to make IMA call > > vfs_getattr_nosec (or something like it) to query the getattr routine in > > the upper layer. Then overlayfs could just propagate the results from > > the upper layer in its response. > > You mean compare known stat against current ? It seems more expensive to stat the file > rather than using the simple i_version-has-changed indicator. > getattr is fairly cheap on a local filesystem. It's more expensive with something networked, but that's the price of correctness. > > That sort of design may also eventually help IMA work properly with more > > exotic filesystems, like NFS or Ceph. > > And these don't support i_version at all? They absolutely do. Their change attributes are mediated by the server, so they can't use the kernel's mechanism for IS_I_VERSION inodes. They can report that field in their ->getattr routines however. -- Jeff Layton <jlayton@xxxxxxxxxx>
