Commit 6edda04ccc7c ("mm/kmemleak: prevent soft lockup in first
object iteration loop of kmemleak_scan()") fixes soft lockup problem
in kmemleak_scan() by periodically doing a cond_resched(). It does
take a reference of the current object before doing it. Unfortunately,
if the object has been deleted from the object_list, the next object
pointed to by its next pointer may no longer be valid after coming
back from cond_resched(). This can result in use-after-free and other
nasty problem.
Fix this problem by adding a del_state flag into kmemleak_object
structure to synchronize the object deletion process between
kmemleak_cond_resched() and __remove_object() to make sure that the
object remained in the object_list in the duration of the cond_resched()
call.
Fixes: 6edda04ccc7c ("mm/kmemleak: prevent soft lockup in first object iteration loop of kmemleak_scan()")
Signed-off-by: Waiman Long <longman@xxxxxxxxxx>
---
mm/kmemleak.c | 35 +++++++++++++++++++++++++++++------
1 file changed, 29 insertions(+), 6 deletions(-)
diff --git a/mm/kmemleak.c b/mm/kmemleak.c
index e7cb521236bf..0ece170fc9ef 100644
--- a/mm/kmemleak.c
+++ b/mm/kmemleak.c
@@ -13,11 +13,12 @@
*
* The following locks and mutexes are used by kmemleak:
*
- * - kmemleak_lock (raw_spinlock_t): protects the object_list modifications and
- * accesses to the object_tree_root (or object_phys_tree_root). The
- * object_list is the main list holding the metadata (struct kmemleak_object)
- * for the allocated memory blocks. The object_tree_root and object_phys_tree_root
- * are red black trees used to look-up metadata based on a pointer to the
+ * - kmemleak_lock (raw_spinlock_t): protects the object_list as well as
+ * del_state modifications and accesses to the object_tree_root (or
+ * object_phys_tree_root). The object_list is the main list holding the
+ * metadata (struct kmemleak_object) for the allocated memory blocks.
+ * The object_tree_root and object_phys_tree_root are red
+ * black trees used to look-up metadata based on a pointer to the
* corresponding memory block. The object_phys_tree_root is for objects
* allocated with physical address. The kmemleak_object structures are
* added to the object_list and object_tree_root (or object_phys_tree_root)
@@ -147,6 +148,7 @@ struct kmemleak_object {
struct rcu_head rcu; /* object_list lockless traversal */
/* object usage count; object freed when use_count == 0 */
atomic_t use_count;
+ unsigned int del_state; /* deletion state */
unsigned long pointer;
size_t size;
/* pass surplus references to this pointer */
@@ -177,6 +179,11 @@ struct kmemleak_object {
/* flag set for object allocated with physical address */
#define OBJECT_PHYS (1 << 4)
+/* set when __remove_object() called */
+#define DELSTATE_REMOVED (1 << 0)
+/* set to temporarily prevent deletion from object_list */
+#define DELSTATE_NO_DELETE (1 << 1)
+
#define HEX_PREFIX " "
/* number of bytes to print per line; must be 16 or 32 */
#define HEX_ROW_SIZE 16
@@ -567,7 +574,9 @@ static void __remove_object(struct kmemleak_object *object)
rb_erase(&object->rb_node, object->flags & OBJECT_PHYS ?
&object_phys_tree_root :
&object_tree_root);
- list_del_rcu(&object->object_list);
+ if (!(object->del_state & DELSTATE_NO_DELETE))
+ list_del_rcu(&object->object_list);
+ object->del_state |= DELSTATE_REMOVED;
}
/*
@@ -633,6 +642,7 @@ static void __create_object(unsigned long ptr, size_t size,
object->count = 0; /* white color initially */
object->jiffies = jiffies;
object->checksum = 0;
+ object->del_state = 0;
/* task information */
if (in_hardirq()) {
@@ -1470,9 +1480,22 @@ static void kmemleak_cond_resched(struct kmemleak_object *object)
if (!get_object(object))
return; /* Try next object */
+ raw_spin_lock_irq(&kmemleak_lock);
+ if (object->del_state & DELSTATE_REMOVED)
+ goto unlock_put; /* Object removed */
+ object->del_state |= DELSTATE_NO_DELETE;
+ raw_spin_unlock_irq(&kmemleak_lock);
+
rcu_read_unlock();
cond_resched();
rcu_read_lock();
+
+ raw_spin_lock_irq(&kmemleak_lock);
+ if (object->del_state & DELSTATE_REMOVED)
+ list_del_rcu(&object->object_list);
+ object->del_state &= ~DELSTATE_NO_DELETE;
+unlock_put:
+ raw_spin_unlock_irq(&kmemleak_lock);
put_object(object);
}
--
2.31.1
