kmemleak: Protect the seq start/next/stop sequence by rcu_read_lock()

Objects passed to kmemleak_seq_next() have an incremented reference
count (hence not freed) but they may point via object_list.next to
other freed objects. To avoid this, the whole start/next/stop sequence
must be protected by rcu_read_lock().

Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 1 insertions, 3 deletions

diff --git a/mm/kmemleak.c b/mm/kmemleak.c
index 5aabd41ffb8f..487267310a84 100644
--- a/mm/kmemleak.c
+++ b/mm/kmemleak.c
@@ -1217,7 +1217,6 @@ static void *kmemleak_seq_start(struct seq_file *seq, loff_t *pos)
         }
         object = NULL;
 out:
-        rcu_read_unlock();
         return object;
 }
 
@@ -1233,13 +1232,11 @@ static void *kmemleak_seq_next(struct seq_file *seq, void *v, loff_t *pos)
 
         ++(*pos);
 
-        rcu_read_lock();
         list_for_each_continue_rcu(n, &object_list) {
                 next_obj = list_entry(n, struct kmemleak_object, object_list);
                 if (get_object(next_obj))
                         break;
         }
-        rcu_read_unlock();
 
         put_object(prev_obj);
         return next_obj;
@@ -1255,6 +1252,7 @@ static void kmemleak_seq_stop(struct seq_file *seq, void *v)
                  * kmemleak_seq_start may return ERR_PTR if the scan_mutex
                  * waiting was interrupted, so only release it if !IS_ERR.
                  */
+                rcu_read_unlock();
                 mutex_unlock(&scan_mutex);
                 if (v)
                         put_object(v);