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 95817334695; Sat, 30 May 2026 17:24:22 +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=1780161863; cv=none; b=HHVjj5lpGAQCZx3/bZuTzrxvvgaNNGdqhL9Lok5CbYWbvx9jkD7gGKxq4boEF0Z0k9yj4Kx9Bew8OMUttdatQ1cUOb5CZzHs6g7a6e9QTUTykDtBTocjXbLdwSBegvYoOsgopyaAOJhYNd9Z7kcxYI3Dl8ofvR+iSl5NCfy+D28= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1780161863; c=relaxed/simple; bh=81RrSrxcVfxzgnIwjWtSdPXmCoy6EvXbtAh6ffNEmBA=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=n1zmgKvti8AD6af1g09CHGVD2ImB5O8PEqCKOkoarUdhSRleUwTsFR90qkBC36vyuVtzCMwH8UXkwNK5bjVygsYDXgw5mTCMQVo0+l5BifO/+a+CKvRXCeBGyobWSmZF3+9F8OSdYldXB+WEoupkEdGohxNRFzKulpGxg+hMGyE= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=WrC3iUkW; 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="WrC3iUkW" Received: by smtp.kernel.org (Postfix) with ESMTPSA id D88EB1F00893; Sat, 30 May 2026 17:24:21 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1780161862; bh=WWBn0cMIvhMtqhM8gEX9cjOAnVEGY6LUOTIYz76cuTA=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=WrC3iUkWBJy6aMb3+4yQY4MqjBBQixibaMtXSGh4yGKazX8+AsGhSNRw5NxvXT52l 5rMQcG7JK9kL0UsAVeZxL8CGOeg6FpCNVeXsm4BzLHLVNuTRtYD1U5ieNaimc34uIQ DoIYyk+aiUdqtmHbl2Unpt+Hvw8kQWs6NJbbOEUs= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Stephen Hemminger , Simon Horman , Jakub Kicinski , Sasha Levin Subject: [PATCH 6.1 749/969] net/sched: netem: fix slot delay calculation overflow Date: Sat, 30 May 2026 18:04:33 +0200 Message-ID: <20260530160321.242762995@linuxfoundation.org> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20260530160300.485627683@linuxfoundation.org> References: <20260530160300.485627683@linuxfoundation.org> User-Agent: quilt/0.69 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 6.1-stable review patch. If anyone has any objections, please let me know. ------------------ From: Stephen Hemminger [ Upstream commit 51e94e1e2fef351c74d69eb53666df808d26af95 ] 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 Link: https://patch.msgid.link/20260418032027.900913-6-stephen@networkplumber.org Signed-off-by: Jakub Kicinski Signed-off-by: Sasha Levin --- 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 adb2bab79c87c..2c47bd8dba647 100644 --- a/net/sched/sch_netem.c +++ b/net/sched/sch_netem.c @@ -647,9 +647,8 @@ 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