netdev - [PATCH net] net_sched: sch_fq: fix incorrect behavior for small weights

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [thread-next>] [day] [month] [year] [list]

Message-ID: <20240824181901.953776-1-edumazet@google.com>
Date: Sat, 24 Aug 2024 18:19:01 +0000
From: Eric Dumazet <edumazet@...gle.com>
To: "David S . Miller" <davem@...emloft.net>, Jakub Kicinski <kuba@...nel.org>, 
	Paolo Abeni <pabeni@...hat.com>
Cc: netdev@...r.kernel.org, eric.dumazet@...il.com, 
	Eric Dumazet <edumazet@...gle.com>, John Sperbeck <jsperbeck@...gle.com>, 
	Neal Cardwell <ncardwell@...gle.com>
Subject: [PATCH net] net_sched: sch_fq: fix incorrect behavior for small weights

fq_dequeue() has a complex logic to find packets in one of the 3 bands.

As Neal found out, it is possible that one band has a deficit smaller
than its weight. fq_dequeue() can return NULL while some packets are
elligible for immediate transmit.

In this case, more than one iteration is needed to refill pband->credit.

With default parameters (weights 589824 196608 65536) bug can trigger
if large BIG TCP packets are sent to the lowest priority band.

Bisected-by: John Sperbeck <jsperbeck@...gle.com>
Diagnosed-by: Neal Cardwell <ncardwell@...gle.com>
Fixes: 29f834aa326e ("net_sched: sch_fq: add 3 bands and WRR scheduling")
Signed-off-by: Eric Dumazet <edumazet@...gle.com>
Reviewed-by: Neal Cardwell <ncardwell@...gle.com>
---
 net/sched/sch_fq.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/net/sched/sch_fq.c b/net/sched/sch_fq.c
index 238974725679327b0a0d483c011e15fc94ab0878..19a49af5a9e527ed0371a3bb96e0113755375eac 100644
--- a/net/sched/sch_fq.c
+++ b/net/sched/sch_fq.c
@@ -663,7 +663,9 @@ static struct sk_buff *fq_dequeue(struct Qdisc *sch)
 			pband = &q->band_flows[q->band_nr];
 			pband->credit = min(pband->credit + pband->quantum,
 					    pband->quantum);
-			goto begin;
+			if (pband->credit > 0)
+				goto begin;
+			retry = 0;
 		}
 		if (q->time_next_delayed_flow != ~0ULL)
 			qdisc_watchdog_schedule_range_ns(&q->watchdog,
-- 
2.46.0.295.g3b9ea8a38a-goog