Merge branch 'net-sched-improve-class-lifetime-handling'

Pedro Tammela says:

====================
net/sched: improve class lifetime handling

Valis says[0]:
============
Three classifiers (cls_fw, cls_u32 and cls_route) always copy
tcf_result struct into the new instance of the filter on update.

This causes a problem when updating a filter bound to a class,
as tcf_unbind_filter() is always called on the old instance in the
success path, decreasing filter_cnt of the still referenced class
and allowing it to be deleted, leading to a use-after-free.
============

Turns out these could have been spotted easily with proper warnings.
Improve the current class lifetime with wrappers that check for
overflow/underflow.

While at it add an extack for when a class in use is deleted.

[0] https://lore.kernel.org/all/20230721174856.3045-1-sec@valis.email/
====================

Link: https://lore.kernel.org/r/20230728153537.1865379-1-pctammela@mojatatu.comSigned-off-by: Paolo Abeni <pabeni@redhat.com>

include/net/sch_generic.h

@@ -599,6 +599,7 @@ get_default_qdisc_ops(const struct net_device *dev, int ntx)
 
 struct Qdisc_class_common {
 	u32			classid;
+	unsigned int		filter_cnt;
 	struct hlist_node	hnode;
 };
 
@@ -633,6 +634,31 @@ qdisc_class_find(const struct Qdisc_class_hash *hash, u32 id)
 	return NULL;
 }
 
+static inline bool qdisc_class_in_use(const struct Qdisc_class_common *cl)
+{
+	return cl->filter_cnt > 0;
+}
+
+static inline void qdisc_class_get(struct Qdisc_class_common *cl)
+{
+	unsigned int res;
+
+	if (check_add_overflow(cl->filter_cnt, 1, &res))
+		WARN(1, "Qdisc class overflow");
+
+	cl->filter_cnt = res;
+}
+
+static inline void qdisc_class_put(struct Qdisc_class_common *cl)
+{
+	unsigned int res;
+
+	if (check_sub_overflow(cl->filter_cnt, 1, &res))
+		WARN(1, "Qdisc class underflow");
+
+	cl->filter_cnt = res;
+}
+
 static inline int tc_classid_to_hwtc(struct net_device *dev, u32 classid)
 {
 	u32 hwtc = TC_H_MIN(classid) - TC_H_MIN_PRIORITY;

net/sched/sch_drr.c

@@ -17,7 +17,6 @@
 
 struct drr_class {
 	struct Qdisc_class_common	common;
-	unsigned int			filter_cnt;
 
 	struct gnet_stats_basic_sync		bstats;
 	struct gnet_stats_queue		qstats;
@@ -150,8 +149,10 @@ static int drr_delete_class(struct Qdisc *sch, unsigned long arg,
 	struct drr_sched *q = qdisc_priv(sch);
 	struct drr_class *cl = (struct drr_class *)arg;
 
-	if (cl->filter_cnt > 0)
+	if (qdisc_class_in_use(&cl->common)) {
+		NL_SET_ERR_MSG(extack, "DRR class is in use");
 		return -EBUSY;
+	}
 
 	sch_tree_lock(sch);
 
@@ -187,8 +188,8 @@ static unsigned long drr_bind_tcf(struct Qdisc *sch, unsigned long parent,
 {
 	struct drr_class *cl = drr_find_class(sch, classid);
 
-	if (cl != NULL)
-		cl->filter_cnt++;
+	if (cl)
+		qdisc_class_get(&cl->common);
 
 	return (unsigned long)cl;
 }
@@ -197,7 +198,7 @@ static void drr_unbind_tcf(struct Qdisc *sch, unsigned long arg)
 {
 	struct drr_class *cl = (struct drr_class *)arg;
 
-	cl->filter_cnt--;
+	qdisc_class_put(&cl->common);
 }
 
 static int drr_graft_class(struct Qdisc *sch, unsigned long arg,

net/sched/sch_hfsc.c

@@ -116,7 +116,6 @@ struct hfsc_class {
 	struct net_rate_estimator __rcu *rate_est;
 	struct tcf_proto __rcu *filter_list; /* filter list */
 	struct tcf_block *block;
-	unsigned int	filter_cnt;	/* filter count */
 	unsigned int	level;		/* class level in hierarchy */
 
 	struct hfsc_sched *sched;	/* scheduler data */
@@ -1094,8 +1093,11 @@ hfsc_delete_class(struct Qdisc *sch, unsigned long arg,
 	struct hfsc_sched *q = qdisc_priv(sch);
 	struct hfsc_class *cl = (struct hfsc_class *)arg;
 
-	if (cl->level > 0 || cl->filter_cnt > 0 || cl == &q->root)
+	if (cl->level > 0 || qdisc_class_in_use(&cl->cl_common) ||
+	    cl == &q->root) {
+		NL_SET_ERR_MSG(extack, "HFSC class in use");
 		return -EBUSY;
+	}
 
 	sch_tree_lock(sch);
 
@@ -1223,7 +1225,7 @@ hfsc_bind_tcf(struct Qdisc *sch, unsigned long parent, u32 classid)
 	if (cl != NULL) {
 		if (p != NULL && p->level <= cl->level)
 			return 0;
-		cl->filter_cnt++;
+		qdisc_class_get(&cl->cl_common);
 	}
 
 	return (unsigned long)cl;
@@ -1234,7 +1236,7 @@ hfsc_unbind_tcf(struct Qdisc *sch, unsigned long arg)
 {
 	struct hfsc_class *cl = (struct hfsc_class *)arg;
 
-	cl->filter_cnt--;
+	qdisc_class_put(&cl->cl_common);
 }
 
 static struct tcf_block *hfsc_tcf_block(struct Qdisc *sch, unsigned long arg,

net/sched/sch_htb.c

@@ -102,7 +102,6 @@ struct htb_class {
 
 	struct tcf_proto __rcu	*filter_list;	/* class attached filters */
 	struct tcf_block	*block;
-	int			filter_cnt;
 
 	int			level;		/* our level (see above) */
 	unsigned int		children;
@@ -1710,8 +1709,10 @@ static int htb_delete(struct Qdisc *sch, unsigned long arg,
 	 * tc subsys guarantee us that in htb_destroy it holds no class
 	 * refs so that we can remove children safely there ?
 	 */
-	if (cl->children || cl->filter_cnt)
+	if (cl->children || qdisc_class_in_use(&cl->common)) {
+		NL_SET_ERR_MSG(extack, "HTB class in use");
 		return -EBUSY;
+	}
 
 	if (!cl->level && htb_parent_last_child(cl))
 		last_child = 1;
@@ -2107,7 +2108,7 @@ static unsigned long htb_bind_filter(struct Qdisc *sch, unsigned long parent,
 	 * be broken by class during destroy IIUC.
 	 */
 	if (cl)
-		cl->filter_cnt++;
+		qdisc_class_get(&cl->common);
 	return (unsigned long)cl;
 }
 
@@ -2115,8 +2116,7 @@ static void htb_unbind_filter(struct Qdisc *sch, unsigned long arg)
 {
 	struct htb_class *cl = (struct htb_class *)arg;
 
-	if (cl)
-		cl->filter_cnt--;
+	qdisc_class_put(&cl->common);
 }
 
 static void htb_walk(struct Qdisc *sch, struct qdisc_walker *arg)

net/sched/sch_qfq.c

@@ -130,8 +130,6 @@ struct qfq_aggregate;
 struct qfq_class {
 	struct Qdisc_class_common common;
 
-	unsigned int filter_cnt;
-
 	struct gnet_stats_basic_sync bstats;
 	struct gnet_stats_queue qstats;
 	struct net_rate_estimator __rcu *rate_est;
@@ -545,8 +543,10 @@ static int qfq_delete_class(struct Qdisc *sch, unsigned long arg,
 	struct qfq_sched *q = qdisc_priv(sch);
 	struct qfq_class *cl = (struct qfq_class *)arg;
 
-	if (cl->filter_cnt > 0)
+	if (qdisc_class_in_use(&cl->common)) {
+		NL_SET_ERR_MSG_MOD(extack, "QFQ class in use");
 		return -EBUSY;
+	}
 
 	sch_tree_lock(sch);
 
@@ -580,8 +580,8 @@ static unsigned long qfq_bind_tcf(struct Qdisc *sch, unsigned long parent,
 {
 	struct qfq_class *cl = qfq_find_class(sch, classid);
 
-	if (cl != NULL)
-		cl->filter_cnt++;
+	if (cl)
+		qdisc_class_get(&cl->common);
 
 	return (unsigned long)cl;
 }
@@ -590,7 +590,7 @@ static void qfq_unbind_tcf(struct Qdisc *sch, unsigned long arg)
 {
 	struct qfq_class *cl = (struct qfq_class *)arg;
 
-	cl->filter_cnt--;
+	qdisc_class_put(&cl->common);
 }
 
 static int qfq_graft_class(struct Qdisc *sch, unsigned long arg,