From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-dl1-f52.google.com (mail-dl1-f52.google.com [74.125.82.52]) (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 1366F3A6B99 for ; Sat, 28 Mar 2026 18:27:11 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=74.125.82.52 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1774722434; cv=none; b=X65wAr4Cf43JLfwx22S2Svh08sw53M3fxGnuAuMYIT50Ql0gbjG7lnBVj5z4Tfm6LcoLz0PC3WquDg6+qigQDBnrssuU8TcibfwMA0QeV9yZ/5Ltd60Tt1Fp/wNPiV4pm+tsMmrW6jGa5pO5eFzhBOdW6MedvZ/SXCny6Cli6l0= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1774722434; c=relaxed/simple; bh=SWg8L6uuWco3cS12n7DkcRHrGPFWu23NRGVl6A+OY40=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=P/2z90ahdk3HxsH675vi3hTqeUt8pL+NsdbXEgS0/6e1VtKflUqhRmU+kin4EW9xL4avo6OlMeLJPOQpfHWHLYQC9aFYvMXDQe3fP0iW2iFKBjNsVe//qYPQiycXbGJU2+aMwdQHeExnFh0wXLfAC0WpbJgtYkOIzVoTtE+CCrw= 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.20230601.gappssmtp.com header.i=@networkplumber-org.20230601.gappssmtp.com header.b=jKv0NNEc; arc=none smtp.client-ip=74.125.82.52 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.20230601.gappssmtp.com header.i=@networkplumber-org.20230601.gappssmtp.com header.b="jKv0NNEc" Received: by mail-dl1-f52.google.com with SMTP id a92af1059eb24-127380532eeso3243660c88.1 for ; Sat, 28 Mar 2026 11:27:11 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=networkplumber-org.20230601.gappssmtp.com; s=20230601; t=1774722431; x=1775327231; 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=j2ZbLPQZvohPDkPozjnrqd1E31roY/uNx4kiTZpqtWE=; b=jKv0NNEcT2F56byzs6xrNI4UxD6OhDh3v6bmW6qj9Kd3FAVD33QPk8Tb/ZuSqNDlLY URC6KBRL/4nr9HP0QIl3JdA0U35eos+y1kM9gpYevuuKQAVLDwYnETggMn+vSqdNd3Rc RgPn9C1lo70ZGGQi0ZdzImKHekYhtpER8imOh1i3Ac91QD4Hxg2jSckr6ylfMqpp+LZo 7LuAtW1Rg/GNWFek0x5z0sRJmc0Wk6dJRkzUvrkDmSZy3Dr/yEmCJhWm49SC0T2/bA/t b0YAWbF5W8MNVhMhJ7PjrfHZfsPRLB41TP5tFXdjSQC2CPVXegtKuEuYWA57X+zX39Ae pu6A== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20251104; t=1774722431; x=1775327231; 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=j2ZbLPQZvohPDkPozjnrqd1E31roY/uNx4kiTZpqtWE=; b=T+HIkMPMFxLPV9RH3XUaccHEoDPIHdHhRtQon6p7r0Xk/LReEyZhwu1ksIRtKpLLqw jaFBGbn/8tODyovF5lQdL8bDQ2og9OqhBgXJfQFiS4ybTAGpqm0lJ+V8M2bwIOYEdbY7 oWIKCFP4bJG21L/9xwb8qgNQMaxxtscQAwa78bS0kzqy8f1HYuYYG5rXoirYrxwGf9I2 4BZx2VpKVqVRSsEUtbjTBEGgev6a/mCoLNkxFpQJI9x42FEqIcDKDgomm1nS5/2KfjPE steMj+wjDzU6i20e0kfZn624c60Ch2wORltjNlU/UYZpHoTey2QapiX6WzBasylbu/Cr 7mmA== X-Forwarded-Encrypted: i=1; AJvYcCVHIqivQXIPWRCOw8LF5S3DsQ9pvR4aawU+4gT2xJRpYlWq4FAj1TVBI8G8Sd01q/WyuM69H5m53ycbekQ=@vger.kernel.org X-Gm-Message-State: AOJu0YyDTKBd2pClEGSExXzYiJj5spqLCu6cnILCdmMr50DG74/AqQhN l0pLTn/x8PUHTMpE4FpjE7AXxXiD0U7ZkesTry5cmiHcrzMf8/13mZW+MtXNYRKk6C0= X-Gm-Gg: ATEYQzyVCzhVIMHFNAkM7Zjj/0UIyXbTZsfAzMFlqzEnJpyF3plCgflU84x0TY6qj3M e5bC82HS2Eqi0XVxNLzCPgCB7vd2zX8TTbn2+Yu0JD2aNfG6DmTj1P+5rdJNuXQTf4FQ1Ms7fOm mhY7wEw4RkUVWwTYUGY/t59ewXG6QTQpiYNX2Cykh1187znz+kYXgDoPzzWZDLXUHwkwJNyglq0 DNUyuFW8QIJl6P53nX5iNj0r/xitKIt6vfM4MTJjBbKLJ9P0pPCSVVpXPpi5ejSlF+aNRxVCv8f LvEQc8ml5tGogXV8a3yH85XsW/smRb+3T7UxyjKo3+5KoePom74AN3d1Kd/slPx4AOlvSRNeDjS yD/qi6pJhY2beJJfYEnXYyAlcw4BDZpNb443COOAk5onGNIOeyTWWB6I7sDGYq7S2sVtH3FqdbH uxEMT4H0YvcwuXSUtk04w9NayldJsefRLPwDqaeB1f6gE= X-Received: by 2002:a05:7022:eacd:b0:12a:713b:8964 with SMTP id a92af1059eb24-12ab2866749mr4684581c88.11.1774722431162; Sat, 28 Mar 2026 11:27:11 -0700 (PDT) Received: from phoenix.lan ([104.202.29.139]) by smtp.gmail.com with ESMTPSA id a92af1059eb24-12ab97cb08csm3909263c88.3.2026.03.28.11.27.10 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sat, 28 Mar 2026 11:27:10 -0700 (PDT) From: Stephen Hemminger To: netdev@vger.kernel.org Cc: Stephen Hemminger , Jamal Hadi Salim , Jiri Pirko , "David S. Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Simon Horman , Yousuk Seung , Neal Cardwell , linux-kernel@vger.kernel.org (open list) Subject: [PATCH net-next 3/6] net/sched: netem: fix slot delay calculation overflow Date: Sat, 28 Mar 2026 11:26:04 -0700 Message-ID: <20260328182704.456993-4-stephen@networkplumber.org> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20260328182704.456993-1-stephen@networkplumber.org> References: <20260328182704.456993-1-stephen@networkplumber.org> Precedence: bulk X-Mailing-List: linux-kernel@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 --- 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 de22d754cb79..69c93f7ade62 100644 --- a/net/sched/sch_netem.c +++ b/net/sched/sch_netem.c @@ -658,9 +658,8 @@ 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