On Thu, Apr 6, 2023 at 11:23 PM Stefan Berger <stefanb@xxxxxxxxxxxxx> 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 > > > The new proposed i_version increase occurs on the inode that IMA sees later on for > the file that's being executed and on which it must do a re-evaluation. > > Upon file changes ima_inode_free() seems to see two ima_file_free() calls, > one for what seems to be the upper layer (used for vfs_* functions below) > and once for the lower one. > The important thing is that IMA will see the lower one when the file gets > executed later on and this is the one that I instrumented now to have its > i_version increased, which in turn triggers the re-evaluation of the file post > modification. > > static ssize_t ovl_write_iter(struct kiocb *iocb, struct iov_iter *iter) > [...] > struct fd real; > [...] > ret = ovl_real_fdget(file, &real); > if (ret) > goto out_unlock; > > [...] > if (is_sync_kiocb(iocb)) { > file_start_write(real.file); > --> ret = vfs_iter_write(real.file, iter, &iocb->ki_pos, > ovl_iocb_to_rwf(ifl)); > file_end_write(real.file); > /* Update size */ > ovl_copyattr(inode); > } else { > struct ovl_aio_req *aio_req; > > ret = -ENOMEM; > aio_req = kmem_cache_zalloc(ovl_aio_request_cachep, GFP_KERNEL); > if (!aio_req) > goto out; > > file_start_write(real.file); > /* Pacify lockdep, same trick as done in aio_write() */ > __sb_writers_release(file_inode(real.file)->i_sb, > SB_FREEZE_WRITE); > aio_req->fd = real; > real.flags = 0; > aio_req->orig_iocb = iocb; > kiocb_clone(&aio_req->iocb, iocb, real.file); > aio_req->iocb.ki_flags = ifl; > aio_req->iocb.ki_complete = ovl_aio_rw_complete; > refcount_set(&aio_req->ref, 2); > --> ret = vfs_iocb_iter_write(real.file, &aio_req->iocb, iter); > ovl_aio_put(aio_req); > if (ret != -EIOCBQUEUED) > ovl_aio_cleanup_handler(aio_req); > } > if (ret > 0) <--- this get it to work > inode_maybe_inc_iversion(inode, false); <--- since this inode is known to IMA If the aio is queued, then I think increasing i_version here may be premature. Note that in this code flow, the ovl ctime is updated in ovl_aio_cleanup_handler() => ovl_copyattr() after file_end_write(), similar to the is_sync_kiocb() code patch. It probably makes most sense to include i_version in ovl_copyattr(). Note that this could cause ovl i_version to go backwards on copy up (i.e. after first open for write) when switching from the lower inode i_version to the upper inode i_version. Jeff's proposal to use vfs_getattr_nosec() in IMA code is fine too. It will result in the same i_version jump. IMO it wouldn't hurt to have a valid i_version value in the ovl inode as well. If the ovl inode values would not matter, we would not have needed ovl_copyattr() at all, but it's not good to keep vfs in the dark... Thanks, Amir.
