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Subject[PATCH 2/2] net: sched: avoid duplicates in qdisc dump
From: Jiri Kosina <jkosina@suse.cz>

tc_dump_qdisc() performs dumping of the per-device qdiscs in two phases;
first, the "standard" dev->qdisc is being dumped. Second, if there is/are
ingress queue(s), they are being dumped as well.

After conversion of netdevice's qdisc linked-list into hashtable, these
two sets are not in two disjunctive sets/lists any more, but are both
"reachable" directly from netdevice's hashtable. As a consequence, the
"full-depth" dump of the ingress qdiscs results in immediately hitting the
netdevice hashtable again, and duplicating the dump that has already been
performed for dev->qdisc.
What in fact needs to be dumped in case of ingress queue is "just" the
top-level ingress qdisc, as everything else has been dumped already.

Fix this by extending tc_dump_qdisc_root() in a way that it can be instructed
whether it should (while performing the "full" per-netdev qdisc dump) perform
the whole recursion, or just dump "additional" top-level (ingress) qdiscs
without performing any kind of recursion.

This fixes duplicate dumps such as

qdisc mq 0: root
qdisc pfifo_fast 0: parent :4 bands 3 priomap 1 2 2 2 1 2 0 0 1 1 1 1 1 1 1 1
qdisc pfifo_fast 0: parent :3 bands 3 priomap 1 2 2 2 1 2 0 0 1 1 1 1 1 1 1 1
qdisc pfifo_fast 0: parent :2 bands 3 priomap 1 2 2 2 1 2 0 0 1 1 1 1 1 1 1 1
qdisc pfifo_fast 0: parent :1 bands 3 priomap 1 2 2 2 1 2 0 0 1 1 1 1 1 1 1 1
qdisc clsact ffff: parent ffff:fff1
qdisc pfifo_fast 0: parent :4 bands 3 priomap 1 2 2 2 1 2 0 0 1 1 1 1 1 1 1 1
qdisc pfifo_fast 0: parent :3 bands 3 priomap 1 2 2 2 1 2 0 0 1 1 1 1 1 1 1 1
qdisc pfifo_fast 0: parent :2 bands 3 priomap 1 2 2 2 1 2 0 0 1 1 1 1 1 1 1 1
qdisc pfifo_fast 0: parent :1 bands 3 priomap 1 2 2 2 1 2 0 0 1 1 1 1 1 1 1 1

Fixes: 59cc1f61f ("net: sched: convert qdisc linked list to hashtable")
Reported-by: Daniel Borkmann <daniel@iogearbox.net>
Tested-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>
---
net/sched/sch_api.c | 14 ++++++++++----
1 file changed, 10 insertions(+), 4 deletions(-)

diff --git a/net/sched/sch_api.c b/net/sched/sch_api.c
index 2b75d68..749811f 100644
--- a/net/sched/sch_api.c
+++ b/net/sched/sch_api.c
@@ -1440,7 +1440,7 @@ err_out:

static int tc_dump_qdisc_root(struct Qdisc *root, struct sk_buff *skb,
struct netlink_callback *cb,
- int *q_idx_p, int s_q_idx)
+ int *q_idx_p, int s_q_idx, bool recur)
{
int ret = 0, q_idx = *q_idx_p;
struct Qdisc *q;
@@ -1460,7 +1460,13 @@ static int tc_dump_qdisc_root(struct Qdisc *root, struct sk_buff *skb,
q_idx++;
}

- if (!qdisc_dev(root))
+ /* If dumping singletons, there is no qdisc_dev(root) and the singleton
+ * itself has already been dumped.
+ *
+ * If we've already dumped the top-level (ingress) qdisc above and the global
+ * qdisc hashtable, we don't want to hit it again
+ */
+ if (!qdisc_dev(root) || !recur)
goto out;

hash_for_each(qdisc_dev(root)->qdisc_hash, b, q, hash) {
@@ -1504,13 +1510,13 @@ static int tc_dump_qdisc(struct sk_buff *skb, struct netlink_callback *cb)
s_q_idx = 0;
q_idx = 0;

- if (tc_dump_qdisc_root(dev->qdisc, skb, cb, &q_idx, s_q_idx) < 0)
+ if (tc_dump_qdisc_root(dev->qdisc, skb, cb, &q_idx, s_q_idx, true) < 0)
goto done;

dev_queue = dev_ingress_queue(dev);
if (dev_queue &&
tc_dump_qdisc_root(dev_queue->qdisc_sleeping, skb, cb,
- &q_idx, s_q_idx) < 0)
+ &q_idx, s_q_idx, false) < 0)
goto done;

cont:
--
1.9.2
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