On Tue, 2018-12-04 at 15:31 -0500, Waiman Long wrote: > On 12/04/2018 02:08 PM, Bart Van Assche wrote: > > On Tue, 2018-12-04 at 13:57 -0500, Waiman Long wrote: > > > On 12/03/2018 07:28 PM, Bart Van Assche wrote: > > > > The next patch in this series uses the class name in code that > > > > detects lock class use-after-free. Hence retain the class name for > > > > lock classes that are being freed. > > > > > > > > Cc: Peter Zijlstra <[email protected]> > > > > Cc: Waiman Long <[email protected]> > > > > Cc: Johannes Berg <[email protected]> > > > > Signed-off-by: Bart Van Assche <[email protected]> > > > > --- > > > > kernel/locking/lockdep.c | 4 +--- > > > > 1 file changed, 1 insertion(+), 3 deletions(-) > > > > > > > > diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c > > > > index ecd92969674c..92bdb187987f 100644 > > > > --- a/kernel/locking/lockdep.c > > > > +++ b/kernel/locking/lockdep.c > > > > @@ -4147,10 +4147,8 @@ static void zap_class(struct lock_class *class) > > > > * Unhash the class and remove it from the all_lock_classes > > > > list: > > > > */ > > > > hlist_del_rcu(&class->hash_entry); > > > > + class->hash_entry.pprev = NULL; > > > > list_del(&class->lock_entry); > > > > -page > > > > - RCU_INIT_POINTER(class->key, NULL); > > > > - RCU_INIT_POINTER(class->name, NULL); > > > > } > > > > > > > > static inline int within(const void *addr, void *start, unsigned long > > > > size) > > > > > > Using the name after module unload can be problematic if it points to > > > memory space occupied by the unloaded kernel module. The memory page may > > > be invalid with the potential of crashing the kernel. You may have to > > > duplicate the name if it is really from the module address space. > > > > The class name shouldn't be used by any of the code I introduced in the > > lockdep infrastructure after unloading a kernel module finished unless if > > some of the kernel module code is still running after unloading the kernel > > module finished. I think if that happens that the kernel module author is > > to blame and not lockdep :-) > > > > Bart. > > You do use the name once in a WARN_ON check in check_prev_add(). You > commit log did say the class name will be used.
Hi Waiman, I will update the commit message and I will add a comment in check_prev_add() that explains that the newly added warning may trigger a use-after-free. Bart.
