Whenever codel drops packets during peek, it calls qdisc_tree_reduce_backlog. An issue arises because it calls qdisc_tree_reduce_backlog before it reincrements the qlen. If qlen drops to zero, but peek returns an skb, the parent's qlen_notify callback will be executed even though codel still has 1 packet on the queue and, thus, will mistakenly deactivate the parent's class causing issues like a wild memory access when qfq has codel as a child: [ 36.339843][ T370] Oops: general protection fault, probably for non-canonical address 0xfbd59c0000000024: 0000 [#1] SMP KASAN NOPTI [ 36.340408][ T370] KASAN: maybe wild-memory-access in range [0xdead000000000120-0xdead000000000127] [ 36.340737][ T370] CPU: 2 UID: 0 PID: 370 Comm: tc Not tainted 7.1.0-rc5-00287-g66e13b626592 #87 PREEMPT(full) [ 36.341113][ T370] Hardware name: Bochs Bochs, BIOS Bochs 01/01/2011 [ 36.341357][ T370] RIP: 0010:qfq_deactivate_agg (include/linux/list.h:1029 (discriminator 2) include/linux/list.h:1043 (discriminator 2) net/sched/sch_qfq.c:1369 (discriminator 2) net/sched/sch_qfq.c:1395 (discriminator 2)) sch_qfq [ 36.342221][ T370] RSP: 0018:ffff8881100ef370 EFLAGS: 00010216 [ 36.342422][ T370] RAX: 0000000000000000 RBX: ffff8881058a9568 RCX: dffffc0000000000 [ 36.342664][ T370] RDX: 1ffff11021064dc3 RSI: ffff888108326e00 RDI: dffffc0000000000 [ 36.342905][ T370] RBP: ffff8881058a8280 R08: dead000000000122 R09: 1bd5a00000000024 [ 36.343140][ T370] R10: fffffbfff2940329 R11: fffffbfff2940329 R12: 0000000000000000 [ 36.343383][ T370] R13: dead000000000100 R14: ffff8881058a9580 R15: ffff8881058a9578 [ 36.343631][ T370] FS: 00007fc04b0ca780(0000) GS:ffff888184fef000(0000) knlGS:0000000000000000 [ 36.343911][ T370] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [ 36.344116][ T370] CR2: 0000557c02c02000 CR3: 000000010e0ba000 CR4: 0000000000750ef0 [ 36.344359][ T370] PKRU: 55555554 [ 36.344481][ T370] Call Trace: ... [ 36.345054][ T370] qfq_reset_qdisc (net/sched/sch_qfq.c:357 net/sched/sch_qfq.c:1487) sch_qfq [ 36.345222][ T370] qdisc_reset (net/sched/sch_generic.c:1057) [ 36.345503][ T370] __qdisc_destroy (net/sched/sch_generic.c:1096) [ 36.345677][ T370] qdisc_graft (net/sched/sch_api.c:1062 net/sched/sch_api.c:1053 net/sched/sch_api.c:1159) [ 36.346335][ T370] tc_get_qdisc (net/sched/sch_api.c:1528 net/sched/sch_api.c:1556) Fix this by only calling qdisc_tree_reduce_backlog in peek after the qlen is restored. Fixes: 342debc12183 ("codel: remove sch->q.qlen check before qdisc_tree_reduce_backlog()") Acked-by: Jamal Hadi Salim Signed-off-by: Victor Nogueira --- net/sched/sch_codel.c | 48 ++++++++++++++++++++++++++++++++++++++----- 1 file changed, 43 insertions(+), 5 deletions(-) diff --git a/net/sched/sch_codel.c b/net/sched/sch_codel.c index 317aae0ec7bd..7d5076196aff 100644 --- a/net/sched/sch_codel.c +++ b/net/sched/sch_codel.c @@ -56,7 +56,7 @@ static void drop_func(struct sk_buff *skb, void *ctx) qdisc_qstats_drop(sch); } -static struct sk_buff *codel_qdisc_dequeue(struct Qdisc *sch) +static struct sk_buff *__codel_qdisc_dequeue(struct Qdisc *sch) { struct codel_sched_data *q = qdisc_priv(sch); struct sk_buff *skb; @@ -65,13 +65,51 @@ static struct sk_buff *codel_qdisc_dequeue(struct Qdisc *sch) &q->stats, qdisc_pkt_len, codel_get_enqueue_time, drop_func, dequeue_func); + if (skb) + qdisc_bstats_update(sch, skb); + return skb; +} + +static void codel_dequeue_drop(struct Qdisc *sch) +{ + struct codel_sched_data *q = qdisc_priv(sch); + if (q->stats.drop_count) { - qdisc_tree_reduce_backlog(sch, q->stats.drop_count, q->stats.drop_len); + qdisc_tree_reduce_backlog(sch, q->stats.drop_count, + q->stats.drop_len); q->stats.drop_count = 0; q->stats.drop_len = 0; } - if (skb) - qdisc_bstats_update(sch, skb); +} + +static struct sk_buff *codel_qdisc_dequeue(struct Qdisc *sch) +{ + struct sk_buff *skb; + + skb = __codel_qdisc_dequeue(sch); + + codel_dequeue_drop(sch); + + return skb; +} + +static struct sk_buff *codel_peek(struct Qdisc *sch) +{ + struct sk_buff *skb = skb_peek(&sch->gso_skb); + + if (!skb) { + skb = __codel_qdisc_dequeue(sch); + + if (skb) { + __skb_queue_head(&sch->gso_skb, skb); + /* it's still part of the queue */ + qdisc_qstats_backlog_inc(sch, skb); + sch->q.qlen++; + } + + codel_dequeue_drop(sch); + } + return skb; } @@ -257,7 +295,7 @@ static struct Qdisc_ops codel_qdisc_ops __read_mostly = { .enqueue = codel_qdisc_enqueue, .dequeue = codel_qdisc_dequeue, - .peek = qdisc_peek_dequeued, + .peek = codel_peek, .init = codel_init, .reset = codel_reset, .change = codel_change, -- 2.54.0