[PATCH net v3 1/1] net/sched: cls_flower: avoid stale mask references after delete

[Ren Wei <n05ec@lzu.edu.cn>]

From: Yuhang Zheng <z1652074432@gmail.com>

Flower releases a mask reference when a filter is removed from the
classifier. The filter object can remain alive while dump, walk, or
hardware reoffload paths hold a reference to it. Those paths can then
dereference f->mask after the mask has already been released.

Keep the mask reference until the filter reference count reaches zero.
Release the mask synchronously from the final __fl_put() while the caller
still holds the tcf_proto reference, and leave the existing RCU work to
free the mask. This keeps the mask available to every reader that still
holds the filter.

The filter is still removed from the classifier indexes immediately.
Therefore, a deleted filter can temporarily retain an otherwise empty
mask; fl_delete() uses the handle IDR, rather than the mask list, to
determine whether the classifier has become empty.

Failed mask assignment can leave fnew->mask as an error or borrowed
pointer without an owned mask reference. Clear it before the common
failure path so the final put cannot release an unowned reference.

This fix does not add fields, snapshots, or per-filter memory.

Fixes: 92149190067d ("net: sched: flower: set unlocked flag for flower proto ops")
Cc: stable@vger.kernel.org
Reported-by: Xin Liu <bird@lzu.edu.cn>
Tested-by: Yucheng Lu <kanolyc@gmail.com>
Signed-off-by: Yuhang Zheng <z1652074432@gmail.com>
Signed-off-by: Ren Wei <n05ec@lzu.edu.cn>
---
 net/sched/cls_flower.c | 50 +++++++++++++++++++++++-------------------
 1 file changed, 28 insertions(+), 22 deletions(-)

diff --git a/net/sched/cls_flower.c b/net/sched/cls_flower.c
index 1cefea571efd..92a7f2d6efc0 100644
--- a/net/sched/cls_flower.c
+++ b/net/sched/cls_flower.c
@@ -518,15 +518,22 @@ static void fl_hw_update_stats(struct tcf_proto *tp, struct cls_fl_filter *f,
 	tcf_exts_hw_stats_update(&f->exts, &cls_flower.stats, cls_flower.use_act_stats);
 }
 
-static void __fl_put(struct cls_fl_filter *f)
+static bool __fl_put(struct tcf_proto *tp, struct cls_fl_filter *f)
 {
+	bool last = false;
+
 	if (!refcount_dec_and_test(&f->refcnt))
-		return;
+		return false;
+
+	if (f->mask)
+		last = fl_mask_put(fl_head_dereference(tp), f->mask);
 
 	if (tcf_exts_get_net(&f->exts))
 		tcf_queue_work(&f->rwork, fl_destroy_filter_work);
 	else
 		__fl_destroy_filter(f);
+
+	return last;
 }
 
 static struct cls_fl_filter *__fl_get(struct cls_fl_head *head, u32 handle)
@@ -572,11 +579,10 @@ static int __fl_delete(struct tcf_proto *tp, struct cls_fl_filter *f,
 	list_del_rcu(&f->list);
 	spin_unlock(&tp->lock);
 
-	*last = fl_mask_put(head, f->mask);
 	if (!tc_skip_hw(f->flags))
 		fl_hw_destroy_filter(tp, f, rtnl_held, extack);
 	tcf_unbind_filter(tp, &f->res);
-	__fl_put(f);
+	*last = __fl_put(tp, f);
 
 	return 0;
 }
@@ -617,7 +623,7 @@ static void fl_put(struct tcf_proto *tp, void *arg)
 {
 	struct cls_fl_filter *f = arg;
 
-	__fl_put(f);
+	__fl_put(tp, f);
 }
 
 static void *fl_get(struct tcf_proto *tp, u32 handle)
@@ -2488,12 +2494,14 @@ static int fl_change(struct net *net, struct sk_buff *in_skb,
 	}
 
 	err = fl_check_assign_mask(head, fnew, fold, mask);
-	if (err)
+	if (err) {
+		fnew->mask = NULL;
 		goto unbind_filter;
+	}
 
 	err = fl_ht_insert_unique(fnew, fold, &in_ht);
 	if (err)
-		goto errout_mask;
+		goto unbind_filter;
 
 	if (!tc_skip_hw(fnew->flags)) {
 		err = fl_hw_replace_filter(tp, fnew, rtnl_held, extack);
@@ -2547,7 +2555,6 @@ static int fl_change(struct net *net, struct sk_buff *in_skb,
 
 		spin_unlock(&tp->lock);
 
-		fl_mask_put(head, fold->mask);
 		if (!tc_skip_hw(fold->flags))
 			fl_hw_destroy_filter(tp, fold, rtnl_held, NULL);
 		tcf_unbind_filter(tp, &fold->res);
@@ -2555,7 +2562,7 @@ static int fl_change(struct net *net, struct sk_buff *in_skb,
 		 * after this.
 		 */
 		refcount_dec(&fold->refcnt);
-		__fl_put(fold);
+		__fl_put(tp, fold);
 	} else {
 		idr_replace(&head->handle_idr, fnew, fnew->handle);
 
@@ -2580,9 +2587,6 @@ static int fl_change(struct net *net, struct sk_buff *in_skb,
 	if (in_ht)
 		rhashtable_remove_fast(&fnew->mask->ht, &fnew->ht_node,
 				       fnew->mask->filter_ht_params);
-errout_mask:
-	fl_mask_put(head, fnew->mask);
-
 unbind_filter:
 	if (bound_to_filter) {
 		if (flags & TCA_ACT_FLAGS_NO_RTNL)
@@ -2598,14 +2602,14 @@ static int fl_change(struct net *net, struct sk_buff *in_skb,
 		idr_remove(&head->handle_idr, fnew->handle);
 		spin_unlock(&tp->lock);
 	}
-	__fl_put(fnew);
+	__fl_put(tp, fnew);
 errout_tb:
 	kfree(tb);
 errout_mask_alloc:
 	tcf_queue_work(&mask->rwork, fl_uninit_mask_free_work);
 errout_fold:
 	if (fold)
-		__fl_put(fold);
+		__fl_put(tp, fold);
 	return err;
 }
 
@@ -2618,8 +2622,10 @@ static int fl_delete(struct tcf_proto *tp, void *arg, bool *last,
 	int err = 0;
 
 	err = __fl_delete(tp, f, &last_on_mask, rtnl_held, extack);
-	*last = list_empty(&head->masks);
-	__fl_put(f);
+	spin_lock(&tp->lock);
+	*last = idr_is_empty(&head->handle_idr);
+	spin_unlock(&tp->lock);
+	__fl_put(tp, f);
 
 	return err;
 }
@@ -2641,12 +2647,12 @@ static void fl_walk(struct tcf_proto *tp, struct tcf_walker *arg,
 		rcu_read_unlock();
 
 		if (arg->fn(tp, f, arg) < 0) {
-			__fl_put(f);
+			__fl_put(tp, f);
 			arg->stop = 1;
 			rcu_read_lock();
 			break;
 		}
-		__fl_put(f);
+		__fl_put(tp, f);
 		arg->count++;
 		rcu_read_lock();
 	}
@@ -2697,7 +2703,7 @@ static int fl_reoffload(struct tcf_proto *tp, bool add, flow_setup_cb_t *cb,
 		cls_flower.rule =
 			flow_rule_alloc(tcf_exts_num_actions(&f->exts));
 		if (!cls_flower.rule) {
-			__fl_put(f);
+			__fl_put(tp, f);
 			return -ENOMEM;
 		}
 
@@ -2715,7 +2721,7 @@ static int fl_reoffload(struct tcf_proto *tp, bool add, flow_setup_cb_t *cb,
 		if (err) {
 			kfree(cls_flower.rule);
 			if (tc_skip_sw(f->flags)) {
-				__fl_put(f);
+				__fl_put(tp, f);
 				return err;
 			}
 			goto next_flow;
@@ -2731,11 +2737,11 @@ static int fl_reoffload(struct tcf_proto *tp, bool add, flow_setup_cb_t *cb,
 		kfree(cls_flower.rule);
 
 		if (err) {
-			__fl_put(f);
+			__fl_put(tp, f);
 			return err;
 		}
 next_flow:
-		__fl_put(f);
+		__fl_put(tp, f);
 	}
 
 	return 0;
-- 
2.52.0