On Tue, Oct 18, 2022 at 09:12:08PM +0800, Yu Kuai wrote: > > > 在 2022/10/18 21:00, Greg KH 写道: > > On Tue, Oct 18, 2022 at 09:14:31PM +0800, Yu Kuai wrote: > > > The return value will be used in later patch to fix uaf for slave_dir > > > and bd_holder_dir in block layer. > > > > Then the user will be incorrect, this is not ok, you should never care > > if you are the last "put" on an object at all. Hint, what happens right > > after you call this and get the result? > > > > I tried to reset the pointer to NULL in patch 2 to prevent uaf. That is not ok, sorry. > And the > whole kobject_put() and pointer reset is protected by a mutex, the mutex > will be used on the reader side before kobject_get as well. So, in fact, > I'm protecting them by the mutex... Still not ok. You never know who else has a reference on a kobject, that's the point of reference counted objects. > I can bypass it by using another reference anyway. But let's see if > anyone has suggestions on the other patch. > > > sorry, but NAK. > > I know the best way is too refactor the lifecycle of the problematic > bd_holder_dir/slave_dir, however, I gave that up because this seems > quite complicated and influence is very huge... Please fix it up properly, core changes like this should not be needed. thanks, greg k-h
