Re: [PATCH v3] debugobjects: stop accessing objects after releasing spinlock

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On 25.10.2023 23:39, Andrzej Hajda wrote:

After spinlock release object can be modified/freed by concurrent thread.
Using it in such case is error prone, even for printing object state.
To avoid such situation local copy of the object is created if necessary.

Sample buggy scenario:
1. Thread tries to deactivate destroyed object, debugobjects detects it,
    spin lock is released, thread is preempted.
2. Other thread frees debugobject, then allocates new one on the same memory
    location, ie 'obj' variable from 1st thread point to it - it is possible
    because there is no locking.
3. Then preemption occurs, and 1st thread reports error for wrong object.

Signed-off-by: Andrzej Hajda <andrzej.hajda@xxxxxxxxx>
---
v2: add missing switch breaks
v3: abandon single-point-of-unlock approach


Gently ping.

Regards
Andrzej



---
  lib/debugobjects.c | 196 +++++++++++++++++++++--------------------------------
  1 file changed, 77 insertions(+), 119 deletions(-)

diff --git a/lib/debugobjects.c b/lib/debugobjects.c
index a517256a270b71..c074dbbec084a6 100644
--- a/lib/debugobjects.c
+++ b/lib/debugobjects.c
@@ -620,9 +620,8 @@ static void debug_objects_fill_pool(void)
  static void
  __debug_object_init(void *addr, const struct debug_obj_descr *descr, int onstack)
  {
-	enum debug_obj_state state;
  	struct debug_bucket *db;
-	struct debug_obj *obj;
+	struct debug_obj *obj, o;
  	unsigned long flags;
debug_objects_fill_pool(); 
@@ -643,24 +642,18 @@ __debug_object_init(void *addr, const struct debug_obj_descr *descr, int onstack
  	case ODEBUG_STATE_INIT:
  	case ODEBUG_STATE_INACTIVE:
  		obj->state = ODEBUG_STATE_INIT;
-		break;
-
-	case ODEBUG_STATE_ACTIVE:
-		state = obj->state;
  		raw_spin_unlock_irqrestore(&db->lock, flags);
-		debug_print_object(obj, "init");
-		debug_object_fixup(descr->fixup_init, addr, state);
-		return;
-
-	case ODEBUG_STATE_DESTROYED:
-		raw_spin_unlock_irqrestore(&db->lock, flags);
-		debug_print_object(obj, "init");
  		return;
  	default:
  		break;
  	}
+ o = *obj; 
  	raw_spin_unlock_irqrestore(&db->lock, flags);
+	debug_print_object(&o, "init");
+
+	if (o.state == ODEBUG_STATE_ACTIVE)
+		debug_object_fixup(descr->fixup_init, addr, o.state);
  }
/** 
@@ -701,11 +694,9 @@ EXPORT_SYMBOL_GPL(debug_object_init_on_stack);
  int debug_object_activate(void *addr, const struct debug_obj_descr *descr)
  {
  	struct debug_obj o = { .object = addr, .state = ODEBUG_STATE_NOTAVAILABLE, .descr = descr };
-	enum debug_obj_state state;
  	struct debug_bucket *db;
  	struct debug_obj *obj;
  	unsigned long flags;
-	int ret;
if (!debug_objects_enabled) 
  		return 0;
@@ -717,49 +708,38 @@ int debug_object_activate(void *addr, const struct debug_obj_descr *descr)
  	raw_spin_lock_irqsave(&db->lock, flags);
obj = lookup_object_or_alloc(addr, db, descr, false, true); 
-	if (likely(!IS_ERR_OR_NULL(obj))) {
-		bool print_object = false;
-
+	if (unlikely(!obj)) {
+		raw_spin_unlock_irqrestore(&db->lock, flags);
+		debug_objects_oom();
+		return 0;
+	} else if (likely(!IS_ERR(obj))) {
  		switch (obj->state) {
-		case ODEBUG_STATE_INIT:
-		case ODEBUG_STATE_INACTIVE:
-			obj->state = ODEBUG_STATE_ACTIVE;
-			ret = 0;
-			break;
-
  		case ODEBUG_STATE_ACTIVE:
-			state = obj->state;
-			raw_spin_unlock_irqrestore(&db->lock, flags);
-			debug_print_object(obj, "activate");
-			ret = debug_object_fixup(descr->fixup_activate, addr, state);
-			return ret ? 0 : -EINVAL;
-
  		case ODEBUG_STATE_DESTROYED:
-			print_object = true;
-			ret = -EINVAL;
  			break;
+		case ODEBUG_STATE_INIT:
+		case ODEBUG_STATE_INACTIVE:
+			obj->state = ODEBUG_STATE_ACTIVE;
+			fallthrough;
  		default:
-			ret = 0;
-			break;
+			raw_spin_unlock_irqrestore(&db->lock, flags);
+			return 0;
  		}
-		raw_spin_unlock_irqrestore(&db->lock, flags);
-		if (print_object)
-			debug_print_object(obj, "activate");
-		return ret;
  	}
+ o = *obj; 
  	raw_spin_unlock_irqrestore(&db->lock, flags);
+	debug_print_object(&o, "activate");
- /* If NULL the allocation has hit OOM */ 
-	if (!obj) {
-		debug_objects_oom();
-		return 0;
+	switch (o.state) {
+	case ODEBUG_STATE_ACTIVE:
+	case ODEBUG_STATE_NOTAVAILABLE:
+		if (debug_object_fixup(descr->fixup_activate, addr, o.state))
+			return 0;
+		fallthrough;
+	default:
+		return -EINVAL;
  	}
-
-	/* Object is neither static nor tracked. It's not initialized */
-	debug_print_object(&o, "activate");
-	ret = debug_object_fixup(descr->fixup_activate, addr, ODEBUG_STATE_NOTAVAILABLE);
-	return ret ? 0 : -EINVAL;
  }
  EXPORT_SYMBOL_GPL(debug_object_activate);
@@ -770,10 +750,10 @@ EXPORT_SYMBOL_GPL(debug_object_activate); 
   */
  void debug_object_deactivate(void *addr, const struct debug_obj_descr *descr)
  {
+	struct debug_obj o = { .object = addr, .state = ODEBUG_STATE_NOTAVAILABLE, .descr = descr };
  	struct debug_bucket *db;
  	struct debug_obj *obj;
  	unsigned long flags;
-	bool print_object = false;
if (!debug_objects_enabled) 
  		return;
@@ -785,33 +765,24 @@ void debug_object_deactivate(void *addr, const struct debug_obj_descr *descr)
  	obj = lookup_object(addr, db);
  	if (obj) {
  		switch (obj->state) {
+		case ODEBUG_STATE_DESTROYED:
+			break;
  		case ODEBUG_STATE_INIT:
  		case ODEBUG_STATE_INACTIVE:
  		case ODEBUG_STATE_ACTIVE:
-			if (!obj->astate)
-				obj->state = ODEBUG_STATE_INACTIVE;
-			else
-				print_object = true;
-			break;
-
-		case ODEBUG_STATE_DESTROYED:
-			print_object = true;
-			break;
+			if (obj->astate)
+				break;
+			obj->state = ODEBUG_STATE_INACTIVE;
+			fallthrough;
  		default:
-			break;
+			raw_spin_unlock_irqrestore(&db->lock, flags);
+			return;
  		}
+		o = *obj;
  	}
raw_spin_unlock_irqrestore(&db->lock, flags); 
-	if (!obj) {
-		struct debug_obj o = { .object = addr,
-				       .state = ODEBUG_STATE_NOTAVAILABLE,
-				       .descr = descr };
-
-		debug_print_object(&o, "deactivate");
-	} else if (print_object) {
-		debug_print_object(obj, "deactivate");
-	}
+	debug_print_object(&o, "deactivate");
  }
  EXPORT_SYMBOL_GPL(debug_object_deactivate);
@@ -822,11 +793,9 @@ EXPORT_SYMBOL_GPL(debug_object_deactivate); 
   */
  void debug_object_destroy(void *addr, const struct debug_obj_descr *descr)
  {
-	enum debug_obj_state state;
  	struct debug_bucket *db;
-	struct debug_obj *obj;
+	struct debug_obj *obj, o;
  	unsigned long flags;
-	bool print_object = false;
if (!debug_objects_enabled) 
  		return;
@@ -836,32 +805,31 @@ void debug_object_destroy(void *addr, const struct debug_obj_descr *descr)
  	raw_spin_lock_irqsave(&db->lock, flags);
obj = lookup_object(addr, db); 
-	if (!obj)
-		goto out_unlock;
+	if (!obj) {
+		raw_spin_unlock_irqrestore(&db->lock, flags);
+		return;
+	}
switch (obj->state) { 
+	case ODEBUG_STATE_ACTIVE:
+	case ODEBUG_STATE_DESTROYED:
+		break;
  	case ODEBUG_STATE_NONE:
  	case ODEBUG_STATE_INIT:
  	case ODEBUG_STATE_INACTIVE:
  		obj->state = ODEBUG_STATE_DESTROYED;
-		break;
-	case ODEBUG_STATE_ACTIVE:
-		state = obj->state;
+		fallthrough;
+	default:
  		raw_spin_unlock_irqrestore(&db->lock, flags);
-		debug_print_object(obj, "destroy");
-		debug_object_fixup(descr->fixup_destroy, addr, state);
  		return;
-
-	case ODEBUG_STATE_DESTROYED:
-		print_object = true;
-		break;
-	default:
-		break;
  	}
-out_unlock:
+
+	o = *obj;
  	raw_spin_unlock_irqrestore(&db->lock, flags);
-	if (print_object)
-		debug_print_object(obj, "destroy");
+	debug_print_object(&o, "destroy");
+
+	if (o.state == ODEBUG_STATE_ACTIVE)
+		debug_object_fixup(descr->fixup_destroy, addr, o.state);
  }
  EXPORT_SYMBOL_GPL(debug_object_destroy);
@@ -872,9 +840,8 @@ EXPORT_SYMBOL_GPL(debug_object_destroy); 
   */
  void debug_object_free(void *addr, const struct debug_obj_descr *descr)
  {
-	enum debug_obj_state state;
  	struct debug_bucket *db;
-	struct debug_obj *obj;
+	struct debug_obj *obj, o;
  	unsigned long flags;
if (!debug_objects_enabled) 
@@ -885,24 +852,26 @@ void debug_object_free(void *addr, const struct debug_obj_descr *descr)
  	raw_spin_lock_irqsave(&db->lock, flags);
obj = lookup_object(addr, db); 
-	if (!obj)
-		goto out_unlock;
+	if (!obj) {
+		raw_spin_unlock_irqrestore(&db->lock, flags);
+		return;
+	}
switch (obj->state) { 
  	case ODEBUG_STATE_ACTIVE:
-		state = obj->state;
-		raw_spin_unlock_irqrestore(&db->lock, flags);
-		debug_print_object(obj, "free");
-		debug_object_fixup(descr->fixup_free, addr, state);
-		return;
+		break;
  	default:
  		hlist_del(&obj->node);
  		raw_spin_unlock_irqrestore(&db->lock, flags);
  		free_object(obj);
  		return;
  	}
-out_unlock:
+
+	o = *obj;
  	raw_spin_unlock_irqrestore(&db->lock, flags);
+	debug_print_object(&o, "free");
+
+	debug_object_fixup(descr->fixup_free, addr, o.state);
  }
  EXPORT_SYMBOL_GPL(debug_object_free);
@@ -954,10 +923,10 @@ void 
  debug_object_active_state(void *addr, const struct debug_obj_descr *descr,
  			  unsigned int expect, unsigned int next)
  {
+	struct debug_obj o = { .object = addr, .state = ODEBUG_STATE_NOTAVAILABLE, .descr = descr };
  	struct debug_bucket *db;
  	struct debug_obj *obj;
  	unsigned long flags;
-	bool print_object = false;
if (!debug_objects_enabled) 
  		return;
@@ -970,28 +939,20 @@ debug_object_active_state(void *addr, const struct debug_obj_descr *descr,
  	if (obj) {
  		switch (obj->state) {
  		case ODEBUG_STATE_ACTIVE:
-			if (obj->astate == expect)
+			if (obj->astate == expect) {
  				obj->astate = next;
-			else
-				print_object = true;
+				raw_spin_unlock_irqrestore(&db->lock, flags);
+				return;
+			}
  			break;
-
  		default:
-			print_object = true;
  			break;
  		}
+		o = *obj;
  	}
raw_spin_unlock_irqrestore(&db->lock, flags); 
-	if (!obj) {
-		struct debug_obj o = { .object = addr,
-				       .state = ODEBUG_STATE_NOTAVAILABLE,
-				       .descr = descr };
-
-		debug_print_object(&o, "active_state");
-	} else if (print_object) {
-		debug_print_object(obj, "active_state");
-	}
+	debug_print_object(&o, "active_state");
  }
  EXPORT_SYMBOL_GPL(debug_object_active_state);
@@ -999,11 +960,9 @@ EXPORT_SYMBOL_GPL(debug_object_active_state); 
  static void __debug_check_no_obj_freed(const void *address, unsigned long size)
  {
  	unsigned long flags, oaddr, saddr, eaddr, paddr, chunks;
-	const struct debug_obj_descr *descr;
-	enum debug_obj_state state;
  	struct debug_bucket *db;
  	struct hlist_node *tmp;
-	struct debug_obj *obj;
+	struct debug_obj *obj, o;
  	int cnt, objs_checked = 0;
saddr = (unsigned long) address; 
@@ -1026,12 +985,11 @@ static void __debug_check_no_obj_freed(const void *address, unsigned long size)
switch (obj->state) { 
  			case ODEBUG_STATE_ACTIVE:
-				descr = obj->descr;
-				state = obj->state;
+				o = *obj;
  				raw_spin_unlock_irqrestore(&db->lock, flags);
-				debug_print_object(obj, "free");
-				debug_object_fixup(descr->fixup_free,
-						   (void *) oaddr, state);
+				debug_print_object(&o, "free");
+				debug_object_fixup(o.descr->fixup_free,
+						   (void *) oaddr, o.state);
  				goto repeat;
  			default:
  				hlist_del(&obj->node);

---
base-commit: 201c8a7bd1f3f415920a2df4b8a8817e973f42fe
change-id: 20231025-debugobjects_fix-66e5292557c4

Best regards,
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