Commit 782e4179 authored by Waiman Long's avatar Waiman Long Committed by Andrew Morton
Browse files

mm/kmemleak: fix UAF bug in kmemleak_scan() 

Commit 6edda04c ("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.

Link: https://lkml.kernel.org/r/20230119040111.350923-3-longman@redhat.com


Fixes: 6edda04c ("mm/kmemleak: prevent soft lockup in first object iteration loop of kmemleak_scan()")
Signed-off-by: default avatarWaiman Long <longman@redhat.com>
Reviewed-by: default avatarCatalin Marinas <catalin.marinas@arm.com>
Cc: Muchun Song <songmuchun@bytedance.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
parent 6061e740

mm/kmemleak.c

+29 −6
Original line number Diff line number Diff line
@@ -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)
@@ -148,6 +149,7 @@ 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
@@ -571,7 +578,9 @@ static void __remove_object(struct kmemleak_object *object) 
	rb_erase(&object->rb_node, object->flags & OBJECT_PHYS ?

				   &object_phys_tree_root :

				   &object_tree_root);

	if (!(object->del_state & DELSTATE_NO_DELETE))

		list_del_rcu(&object->object_list);

	object->del_state |= DELSTATE_REMOVED;

}



/*
@@ -643,6 +652,7 @@ 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()) {
@@ -1479,9 +1489,22 @@ 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);

}