On 12/07/2018 05:21 AM, Peter Zijlstra wrote: > On Thu, Dec 06, 2018 at 05:11:40PM -0800, Bart Van Assche wrote: >> The next patch in this series uses the class name in code that >> detects calls to lock_acquire() while a class key is being freed. Hence >> retain the class name for lock classes that are being freed. > From readin the discussion with v2; you meant to say: 'uses the class > name pointer', right? You're not actually ever going to dereference it, > since that would be a UaF. > >> Cc: Peter Zijlstra <pet...@infradead.org> >> Cc: Waiman Long <long...@redhat.com> >> Cc: Johannes Berg <johan...@sipsolutions.net> >> Signed-off-by: Bart Van Assche <bvanass...@acm.org> >> --- >> 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); >> - >> - RCU_INIT_POINTER(class->key, NULL); >> - RCU_INIT_POINTER(class->name, NULL); >> } >> >> static inline int within(const void *addr, void *start, unsigned long size) >> -- >> 2.20.0.rc2.403.gdbc3b29805-goog >> I still prefer keeping the clearing statements. Leaving key behind should be OK as it is just a long value to be compared against. The variable name is a different story as it is a pointer that will reference bytes that it points to unless you save the name in a safe storage area and change the pointer to point there.
Cheers, Longman
