net/sched: Fixes for sch_ingress and sch_clsact

Link to v5: https://lore.kernel.org/r/[email protected]/
Link to v4: https://lore.kernel.org/r/[email protected]/
Link to v3 (incomplete): https://lore.kernel.org/r/[email protected]/
Link to v2: https://lore.kernel.org/r/[email protected]/
Link to v1: https://lore.kernel.org/r/[email protected]/

Hi all,

These are v6 fixes for ingress and clsact Qdiscs, including only first 4 patches (already tested and reviewed) from v5. Patch 5 and 6 from previous versions are still under discussion and will be sent separately. Per-patch changelog omitted.

Change in v6:
- only include first 4 patches from previous versions

Changes in v5:
- for [6/6], reinitialize @q, @p (suggested by Vlad) and @tcm after the "replay:" tag
- for [1,2/6], do nothing in ->destroy() if ->parent isn't ffff:fff1, as reported by Pedro

Change in v3, v4:
- add in-body From: tags

Changes in v2:
- for [1-5/6], include tags from Jamal and Pedro
- for [6/6], as suggested by Vlad, replay the request if the current Qdisc has any ongoing (RTNL-unlocked) filter requests, instead of returning -EBUSY to the user
- use Closes: tag as warned by checkpatch

[1,2/6]: ingress and clsact Qdiscs should only be created under ffff:fff1
[3/6]: Under ffff:fff1, only create ingress and clsact Qdiscs (for now,
at least)
[4/6]: After creating ingress and clsact Qdiscs under ffff:fff1, do not
graft them again to anywhere else (e.g. as the inner Qdisc of a TBF Qdisc)
[5/6]: Prepare for [6/6], do not reuse that for-loop in qdisc_graft()
for ingress and clsact Qdiscs
[6/6]: Fix use-after-free [a] in mini_qdisc_pair_swap()

[a] https://syzkaller.appspot.com/bug?extid=b53a9c0d1ea4ad62da8b

Thanks,
Peilin Ye (4):
net/sched: sch_ingress: Only create under TC_H_INGRESS net/sched: sch_clsact: Only create under TC_H_CLSACT net/sched: Reserve TC_H_INGRESS (TC_H_CLSACT) for ingress (clsact)
Qdiscs
net/sched: Prohibit regrafting ingress or clsact Qdiscs

 net/sched/sch_api.c     | 12 +++++++++++-
 net/sched/sch_ingress.c | 16 ++++++++++++++--
 2 files changed, 25 insertions(+), 3 deletions(-)

2.20.1

From: Peilin Ye <[email protected]>

ingress Qdiscs are only supposed to be created under TC_H_INGRESS. Return -EOPNOTSUPP if 'parent' is not TC_H_INGRESS, similar to mq_init().

---
 net/sched/sch_ingress.c | 6 ++++++
 1 file changed, 6 insertions(+)

index 84838128b9c5..f9ef6deb2770 100644
@@ -80,6 +80,9 @@ static int ingress_init(struct Qdisc *sch, struct nlattr *opt,
 	struct net_device *dev = qdisc_dev(sch);
 	int err;
 
+	if (sch->parent != TC_H_INGRESS)
+		return -EOPNOTSUPP;
+
 	net_inc_ingress_queue();
 
 	mini_qdisc_pair_init(&q->miniqp, sch, &dev->miniq_ingress);

@@ -101,6 +104,9 @@ static void ingress_destroy(struct Qdisc *sch)
 {
 	struct ingress_sched_data *q = qdisc_priv(sch);
 
+	if (sch->parent != TC_H_INGRESS)
+		return;
+
 	tcf_block_put_ext(q->block, sch, &q->block_info);
 	net_dec_ingress_queue();
 }

2.20.1

From: Peilin Ye <[email protected]>

clsact Qdiscs are only supposed to be created under TC_H_CLSACT (which equals TC_H_INGRESS). Return -EOPNOTSUPP if 'parent' is not TC_H_CLSACT.

---
 net/sched/sch_ingress.c | 6 ++++++
 1 file changed, 6 insertions(+)

index f9ef6deb2770..35963929e117 100644
@@ -225,6 +225,9 @@ static int clsact_init(struct Qdisc *sch, struct nlattr *opt,
 	struct net_device *dev = qdisc_dev(sch);
 	int err;
 
+	if (sch->parent != TC_H_CLSACT)
+		return -EOPNOTSUPP;
+
 	net_inc_ingress_queue();
 	net_inc_egress_queue();
 

@@ -254,6 +257,9 @@ static void clsact_destroy(struct Qdisc *sch)
 {
 	struct clsact_sched_data *q = qdisc_priv(sch);
 
+	if (sch->parent != TC_H_CLSACT)
+		return;
+
 	tcf_block_put_ext(q->egress_block, sch, &q->egress_block_info);
 	tcf_block_put_ext(q->ingress_block, sch, &q->ingress_block_info);
 

2.20.1

From: Peilin Ye <[email protected]>

Currently it is possible to add e.g. an HTB Qdisc under ffff:fff1 (TC_H_INGRESS, TC_H_CLSACT):

  $ ip link add name ifb0 type ifb
  $ tc qdisc add dev ifb0 parent ffff:fff1 htb
  $ tc qdisc add dev ifb0 clsact
  Error: Exclusivity flag on, cannot modify.
  $ drgn
  ...

htb

2

Only allow ingress and clsact Qdiscs under ffff:fff1. Return -EINVAL for everything else. Make TCQ_F_INGRESS a static flag of ingress and clsact Qdiscs.

---
 net/sched/sch_api.c     | 7 ++++++-
 net/sched/sch_ingress.c | 4 ++--
 2 files changed, 8 insertions(+), 3 deletions(-)

index fdb8f429333d..383195955b7d 100644
@@ -1252,7 +1252,12 @@ static struct Qdisc *qdisc_create(struct net_device *dev,
 	sch->parent = parent;
 
 	if (handle == TC_H_INGRESS) {
-		sch->flags |= TCQ_F_INGRESS;
+		if (!(sch->flags & TCQ_F_INGRESS)) {
+			NL_SET_ERR_MSG(extack,
+				       "Specified parent ID is reserved for ingress and clsact Qdiscs");
+			err = -EINVAL;
+			goto err_out3;
+		}
 		handle = TC_H_MAKE(TC_H_INGRESS, 0);
 	} else {
 		if (handle == 0) {

index 35963929e117..e43a45499372 100644
@@ -140,7 +140,7 @@ static struct Qdisc_ops ingress_qdisc_ops __read_mostly = {
 	.cl_ops			=	&ingress_class_ops,
 	.id			=	"ingress",
 	.priv_size		=	sizeof(struct ingress_sched_data),
-	.static_flags		=	TCQ_F_CPUSTATS,
+	.static_flags		=	TCQ_F_INGRESS | TCQ_F_CPUSTATS,
 	.init			=	ingress_init,
 	.destroy		=	ingress_destroy,
 	.dump			=	ingress_dump,

@@ -281,7 +281,7 @@ static struct Qdisc_ops clsact_qdisc_ops __read_mostly = {
 	.cl_ops			=	&clsact_class_ops,
 	.id			=	"clsact",
 	.priv_size		=	sizeof(struct clsact_sched_data),
-	.static_flags		=	TCQ_F_CPUSTATS,
+	.static_flags		=	TCQ_F_INGRESS | TCQ_F_CPUSTATS,
 	.init			=	clsact_init,
 	.destroy		=	clsact_destroy,
 	.dump			=	ingress_dump,

2.20.1

From: Peilin Ye <[email protected]>

Currently, after creating an ingress (or clsact) Qdisc and grafting it under TC_H_INGRESS (TC_H_CLSACT), it is possible to graft it again under e.g. a TBF Qdisc:

  $ ip link add ifb0 type ifb
  $ tc qdisc add dev ifb0 handle 1: root tbf rate 20kbit buffer 1600 limit 3000
  $ tc qdisc add dev ifb0 clsact
  $ tc qdisc link dev ifb0 handle ffff: parent 1:1
  $ tc qdisc show dev ifb0
  qdisc tbf 1: root refcnt 2 rate 20Kbit burst 1600b lat 560.0ms
  qdisc clsact ffff: parent ffff:fff1 refcnt 2
                                      ^^^^^^^^

clsact's refcount has increased: it is now grafted under both TC_H_CLSACT and 1:1.

ingress and clsact Qdiscs should only be used under TC_H_INGRESS (TC_H_CLSACT). Prohibit regrafting them.

---
 net/sched/sch_api.c | 5 +++++
 1 file changed, 5 insertions(+)

index 383195955b7d..49b9c1bbfdd9 100644
@@ -1596,6 +1596,11 @@ static int tc_modify_qdisc(struct sk_buff *skb, struct nlmsghdr *n,
 					NL_SET_ERR_MSG(extack, "Invalid qdisc name");
 					return -EINVAL;
 				}
+				if (q->flags & TCQ_F_INGRESS) {
+					NL_SET_ERR_MSG(extack,
+						       "Cannot regraft ingress or clsact Qdiscs");
+					return -EINVAL;
+				}
 				if (q == p ||
 				    (p && check_loop(q, p, 0))) {
 					NL_SET_ERR_MSG(extack, "Qdisc parent/child loop detected");

2.20.1