From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-oi1-f182.google.com (mail-oi1-f182.google.com [209.85.167.182]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id DA9F9382F2F for ; Sun, 12 Apr 2026 15:24:43 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.167.182 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1776007485; cv=none; b=kaUqdavA4NF8ge/txIUBkFzlQbScNuDlc5HpeCKUwLLZlF/jBC1Dblh5oJ/45wWcEBsostKffVpmk7DtTEg+NigaEfv60opfDTTufsBudUqcYOM9jQzkjtz0D0n4ZMY4L4lqEeqIXXBy5CgRrksyOLRInw3UtjDJFSmjCTgCWQI= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1776007485; c=relaxed/simple; bh=V2tJ/vwxtv1JaoqQpiwU5wG5dp1eaZ/b5hMOD+aRAco=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=W2boAgAX6wWYeXNc/MTjc1WqxyEfyQ/7bVHr2+xWW+PhYVJx0Klk5RTINjQimlwWGXlfdjd5AIqecfsw4QH8jhm6A5ibAqbzd92CorIggMGprSlunm3gtmZZpsx9mB2xsmN8huy/rx+Cu/DOa+VZQk4I+YpOHOj+wuomCm+0wOI= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=networkplumber.org; spf=pass smtp.mailfrom=networkplumber.org; dkim=pass (2048-bit key) header.d=networkplumber-org.20251104.gappssmtp.com header.i=@networkplumber-org.20251104.gappssmtp.com header.b=HMDQabcM; arc=none smtp.client-ip=209.85.167.182 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=networkplumber.org Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=networkplumber.org Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=networkplumber-org.20251104.gappssmtp.com header.i=@networkplumber-org.20251104.gappssmtp.com header.b="HMDQabcM" Received: by mail-oi1-f182.google.com with SMTP id 5614622812f47-4704fb0d5b8so2337455b6e.0 for ; Sun, 12 Apr 2026 08:24:43 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=networkplumber-org.20251104.gappssmtp.com; s=20251104; t=1776007483; x=1776612283; darn=vger.kernel.org; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:date:subject:cc:to:from:from:to:cc:subject:date :message-id:reply-to; bh=T7qXhqZv5DD8Qd3CVsBEDZPd4YmYSOSggm0tUgn0D6c=; b=HMDQabcMBu/0742knKA9uTg4AniBsR4K22gotHxjEsImqXM9Gx1xFtRvNwLmJv67ay jQXRlFVOSj02qgsehuKdeC4K0axUIObmgPd8aWaNYAdSbfCFampDXsOPN/Zp7j42P+D8 xOzklt4LrZWjUwqKiPtLPmmAX44UcpXu1dR2a7jX/5hlb+TipDdUy7SWW8StdIIJWgO6 AQcxMB6iRWLNsN41zdpvLTsaHyJUdunmXAPyBljaPJcrw1+66lg60DQR1e5mFYXnG240 DGa8BvX6JUCcaqX+PlhUGd+fqpFMfb3ChTJhRoT4xXsS8CY1CZrSyGJejszXGNgtuGw9 WvxA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20251104; t=1776007483; x=1776612283; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:date:subject:cc:to:from:x-gm-gg:x-gm-message-state:from :to:cc:subject:date:message-id:reply-to; bh=T7qXhqZv5DD8Qd3CVsBEDZPd4YmYSOSggm0tUgn0D6c=; b=nDfUa1upn+SGbu9Y2Anaa8Ltll1I4Q4/bQ1gDc+ZXuKR4FZv8QjLP8l/ilBB5E5I6U x3y6TwF6CO5TUczN/sUQPakVc8+bN5wq1EyK0IEvVs744eIKGHkKvw4b00Y7fHO5S/cg m1GNuvntSIGKe8KcZhOkhoPzgG3F88i2HWbBDh7ucspn+jX36sykRsOJyOBfJujGvLbo AqHLgCJRiLlEa8n2wW0lmJh5bRrs9AeMORloRo83tucBEYZ0yIpcUjyU/Ofyib1wpSlV YulmWEPRmuHRp9QeVxx3XwMaGSrIsTOy97rwoqEmP2MQeq/xmqE8NcsyYyCjXN3KCkpy MCEg== X-Gm-Message-State: AOJu0YwNlcs4y6Msp/9J7ewrVLqFCxBQ916WNdc+48m3+Kw6b/i/mu/q AKP5os7KpuwyYD3ekjHv9aSzKU6lm5jbFJE84vBHfBn6b651/ezkYhUUJS0+P9Vp60pCim90a5j c6B69 X-Gm-Gg: AeBDietHJLijFEXinTr971yOaeQ41OcB94faGfW29gUwDLkJj4Uyed785Kt0+3GnUhE wQKz61yU9OGUE5avWqrNXlBtIsGuhohsi2euiFNgtl8aYZY3gWnzxQ2lKU3o2jFh0GtNb22TRR5 gonkmkdShaVidzkABR5GQWK1bB1Vzms/1XwZVBN5Xin1Xa32rSIoI+FOcRjNMQ/z+qbQ56aKNsx A0GTVphqxlnVR4JGnpqNmmnpZ1ZsRqehw/YL5BZZWEZLRCLDYiLH0lnKNofcgaKu1KLzMC/rGVb JHEtwRVL4HWat8c5RrhE9fVNOwDuLWA5kVII1FsnEk32vpGnP7Pk037i1SW1EuJpfhJqriFJide bjgeZP7nSHRs4RQLiGLzvOAaKLF3LaIdA02n0/AHij5KeOC+3GI2w/iv2zd6L18drDK/O7L0OCL wdbDh+Fv6ogX5zOWYkCee7TK4Gtl+9SJPc X-Received: by 2002:a05:6808:1807:b0:462:a91b:b080 with SMTP id 5614622812f47-478b64a385bmr4834819b6e.1.1776007482976; Sun, 12 Apr 2026 08:24:42 -0700 (PDT) Received: from phoenix.lan ([104.202.41.210]) by smtp.gmail.com with ESMTPSA id 5614622812f47-478a2f557b5sm4911726b6e.11.2026.04.12.08.24.41 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sun, 12 Apr 2026 08:24:42 -0700 (PDT) From: Stephen Hemminger To: netdev@vger.kernel.org Cc: Stephen Hemminger , Simon Horman , Jamal Hadi Salim , Jiri Pirko , "David S. Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Yousuk Seung , Neal Cardwell , linux-kernel@vger.kernel.org (open list) Subject: [PATTCH net v6 5/5] net/sched: netem: fix slot delay calculation overflow Date: Sun, 12 Apr 2026 08:23:55 -0700 Message-ID: <20260412152429.143474-6-stephen@networkplumber.org> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20260412152429.143474-1-stephen@networkplumber.org> References: <20260412152429.143474-1-stephen@networkplumber.org> Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit get_slot_next() computes a random delay between min_delay and max_delay using: get_random_u32() * (max_delay - min_delay) >> 32 This overflows signed 64-bit arithmetic when the delay range exceeds approximately 2.1 seconds (2^31 nanoseconds), producing a negative result that effectively disables slot-based pacing. This is a realistic configuration for WAN emulation (e.g., slot 1s 5s). Use mul_u64_u32_shr() which handles the widening multiply without overflow. Fixes: 0a9fe5c375b5 ("netem: slotting with non-uniform distribution") Signed-off-by: Stephen Hemminger Reviewed-by: Simon Horman --- net/sched/sch_netem.c | 5 ++--- 1 file changed, 2 insertions(+), 3 deletions(-) diff --git a/net/sched/sch_netem.c b/net/sched/sch_netem.c index 16368948bde9..452ad2b483a5 100644 --- a/net/sched/sch_netem.c +++ b/net/sched/sch_netem.c @@ -659,9 +659,8 @@ static void get_slot_next(struct netem_sched_data *q, u64 now) if (!q->slot_dist) next_delay = q->slot_config.min_delay + - (get_random_u32() * - (q->slot_config.max_delay - - q->slot_config.min_delay) >> 32); + mul_u64_u32_shr(q->slot_config.max_delay - q->slot_config.min_delay, + get_random_u32(), 32); else next_delay = tabledist(q->slot_config.dist_delay, (s32)(q->slot_config.dist_jitter), -- 2.53.0