From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 58D312264AB; Sat, 12 Sep 2026 19:16:07 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789240568; cv=none; b=SMNDnarkza+MAKRNRRsvPJFJaunLn0+gVQxa/5g0OfCBykNkiRq35EMFvmYGb4WBXCo+cl000mXl0/h53XtfqurA/9/g7TkejfFeEjC9REWlxHzroNeZ+LEp8LPMNX8zHh+/l/e2/3IOFFgWPo+gr17FdYP677MNfF7sh9cgPZE= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789240568; c=relaxed/simple; bh=oT5K1Tf72QRGGJTLGHvrhFXma8dnSQsk5orocBd29+c=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=d3vG4Aqdz5Ay9lw5Ud1awnRtg6xgfmx4lQtYwvuTUyXlrNgno+qctjtGCJ17fkolCit6H9Ye7SdrkOR9+vRdGisRp6vFML/rDDWxnArTB+YlAYyxYQqIFaO6VbnUT4n6w86yNxRLBJQ2fJT1zC02Ptv/z3kvu/uMct2TM4T19do= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=H7aFjh7q; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="H7aFjh7q" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 2D78D1F000FF; Sat, 12 Sep 2026 19:16:05 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1789240567; bh=5OJuzilk4szryXCAHPEYlHYbNqSsrZ0GTEXiRp3MexA=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=H7aFjh7qrfek4YffYgW5/L44YihXBm91FwywTxrA9Vs9hMMcyVjeI+D7/vU5K7J+9 tCJ9lcNWw7yQLotqBAKAqa/T5PLR4HYwFWMyKo9b/2KpAMwnF580DZ6RFERu8PLdBy svT9/TSPTHAhyTZe44IDJLLfPdzeB0u2dnFGHwXg= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, vega@nebusec.ai, Victor Nogueira , Jamal Hadi Salim , Paolo Abeni , Sasha Levin Subject: [PATCH 5.15 894/935] net/sched: fq_codel: clamp default quantum and mtu Date: Sat, 12 Sep 2026 09:05:24 +0200 Message-ID: <20260912065547.317645865@linuxfoundation.org> X-Mailer: git-send-email 2.55.0 In-Reply-To: <20260912065526.833703348@linuxfoundation.org> References: <20260912065526.833703348@linuxfoundation.org> User-Agent: quilt/0.69 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: patches@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 5.15-stable review patch. If anyone has any objections, please let me know. ------------------ From: Jamal Hadi Salim [ Upstream commit d9ebd8f9aa8b2773235889cb903fafd61f2d8585 ] fq_codel_init() sets q->quantum = psched_mtu(qdisc_dev(sch)) without clamping. A device with a huge MTU (e.g. dummy with max_mtu == 0 accepting MTU 2147483634) makes psched_mtu() return 0x80000000, which overflows the signed flow->deficit to INT_MIN in fq_codel_dequeue(), causing an infinite loop and soft lockup. Emulate fq_codel_change() and constrain to [256, FQ_CODEL_QUANTUM_MAX]. The same unclamped psched_mtu() is assigned to q->cparams.mtu a bit below, and fq_codel_change() never updates it. codel_should_drop() tests "*backlog <= params->mtu"; with mtu == 0x80000000 (~2 GiB) and the default 32 MiB memory_limit, the test is always true, so CoDel is silently and completely disabled (no drops, no ECN). Declare a single clamped mtu and assign both q->quantum and q->cparams.mtu from it, which also removes the double psched_mtu() call. Conditions to recreate the bug: a device whose MTU (plus hard_header_len) wraps psched_mtu() into the sign bit (e.g. a dummy device with max_mtu == 0 accepting MTU 2147483634). Requires CAP_NET_ADMIN in a user namespace. Fixes: 4b549a2ef4be ("fq_codel: Fair Queue Codel AQM") Reported-by: vega@nebusec.ai Tested-by: Victor Nogueira Signed-off-by: Jamal Hadi Salim Link: https://patch.msgid.link/20260822195509.112717-3-jhs@mojatatu.com Signed-off-by: Paolo Abeni Signed-off-by: Sasha Levin --- net/sched/sch_fq_codel.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-) diff --git a/net/sched/sch_fq_codel.c b/net/sched/sch_fq_codel.c index d2fe36b454d07..f801b6af33c0d 100644 --- a/net/sched/sch_fq_codel.c +++ b/net/sched/sch_fq_codel.c @@ -491,6 +491,7 @@ static int fq_codel_init(struct Qdisc *sch, struct nlattr *opt, struct netlink_ext_ack *extack) { struct fq_codel_sched_data *q = qdisc_priv(sch); + u32 mtu; int i; int err; @@ -498,13 +499,14 @@ static int fq_codel_init(struct Qdisc *sch, struct nlattr *opt, q->flows_cnt = 1024; q->memory_limit = 32 << 20; /* 32 MBytes */ q->drop_batch_size = 64; - q->quantum = psched_mtu(qdisc_dev(sch)); + mtu = clamp_t(u32, psched_mtu(qdisc_dev(sch)), 256, FQ_CODEL_QUANTUM_MAX); + q->quantum = mtu; INIT_LIST_HEAD(&q->new_flows); INIT_LIST_HEAD(&q->old_flows); codel_params_init(&q->cparams); codel_stats_init(&q->cstats); q->cparams.ecn = true; - q->cparams.mtu = psched_mtu(qdisc_dev(sch)); + q->cparams.mtu = mtu; if (opt) { err = fq_codel_change(sch, opt, extack); -- 2.53.0