From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-pl1-f182.google.com (mail-pl1-f182.google.com [209.85.214.182]) (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 315F62609E9 for ; Wed, 30 Apr 2025 15:19:07 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.214.182 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1746026350; cv=none; b=b3sRdBwcjHQJaS6GjOOx3QW35fjUQhLz02+jFAKsl8PaKjejc+0cz1h8KeF6K6WmGBokr62SCJp7GgoDfzyHIxvkqZpqM63MkLAY9frG0YQ6WqrYr3mcGVAqe9bmhVE9LQzZpMhDS3yWfQP32WIHAx8hIpDBxbXEOQo5MhmJqNU= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1746026350; c=relaxed/simple; bh=k0FOJLh/nrH5atHCLTum0f+gEit7p1b+V6IEj8adq2Q=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=QJcvOu0MqYswkfFrD8Fh1Nl8j8qHh0lMtDVehs/Ydlg8ny3CDbRmTvFpnASmJJCVeRl2u9FxxyKIOgVRvLKsTYeGhfzYZ4HGuGZyZ5lyMDt91ualrFU2tNfp3/w8rtS+Z8KrA4mMuIloSjYRSNvMFrnfu/4V0yeNZGV7k1HwNv8= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=mojatatu.com; spf=none smtp.mailfrom=mojatatu.com; dkim=pass (2048-bit key) header.d=mojatatu-com.20230601.gappssmtp.com header.i=@mojatatu-com.20230601.gappssmtp.com header.b=B7rbG7wz; arc=none smtp.client-ip=209.85.214.182 Authentication-Results: smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=mojatatu.com Authentication-Results: smtp.subspace.kernel.org; spf=none smtp.mailfrom=mojatatu.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=mojatatu-com.20230601.gappssmtp.com header.i=@mojatatu-com.20230601.gappssmtp.com header.b="B7rbG7wz" Received: by mail-pl1-f182.google.com with SMTP id d9443c01a7336-227cf12df27so117075ad.0 for ; Wed, 30 Apr 2025 08:19:07 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=mojatatu-com.20230601.gappssmtp.com; s=20230601; t=1746026347; x=1746631147; darn=vger.kernel.org; h=content-transfer-encoding:in-reply-to:from:content-language :references:cc:to:subject:user-agent:mime-version:date:message-id :from:to:cc:subject:date:message-id:reply-to; bh=JdUWR5k2M5czEHSSqbFFrj3vpW9VIK+bhKoz8pO6nFY=; b=B7rbG7wztrA92mO/8AHaDHII6hdY+8j6X4w2QQvz4y+jNAXtVB1HhZwjqxnbiPlmMD c//Wx9esiezuUb2PXwfJzahD4fp1tTgw/VTbDn7ukEVGQSJqbta8cJfWg8XeKMqkLl0j zkXtoTQWYX+fsfMdqtcqRZdGSpaNik5up/v/X8P2uFOqnzRbkNxGGZNzgw/tOn/+Dq5d g7zQ7oQiNznFoxRky9k75gW2LJlaNEopG2vzjeQu2NAqMjEyuOQ+LDMt8qPWG8ilDsdd rCnHL11bTOou365Ew+WugYRc8rqQ6zwONoVkXNg7ln1K6uiZcbOK59CYtkambsSTq2hk 0F9Q== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1746026347; x=1746631147; h=content-transfer-encoding:in-reply-to:from:content-language :references:cc:to:subject:user-agent:mime-version:date:message-id :x-gm-message-state:from:to:cc:subject:date:message-id:reply-to; bh=JdUWR5k2M5czEHSSqbFFrj3vpW9VIK+bhKoz8pO6nFY=; b=UelyCbScbOCgihOtO+o1mLRqN78QzYw5hvVX9W9UJgqv4x/U5mlssR/G+EZ0e3lJzG /HwNHqiMcydT0aQHzeaQzQatP/3Zp8G2KhF1AjHnH6UXdNY5Dxn1WMOa8UK7AvLoluVC bMfMyV7cqFB4x71fFG3Eept1+pb/YJN59T3qR1Mla57AiMGIaD7aYIwBGFk57pWxrjrG KusUwvtGV0mQucZ61rf+rpTaMXP1EQguMphPC7HfzKTMSxOmFXObUNkB6Hb8TEgUoNtR R6NrY59Qv1qtOwlG2lzc0zpUaCsiKO1T1qVd6m+LsZFnVYJ6ACZt+StAKNL6LFK6W9cJ KsKg== X-Forwarded-Encrypted: i=1; AJvYcCUyUcLrykSfnm3hsPICBvZsE/5xJyHGimyPTn7oll2fiobLYH2D3GqZ5QUL9TV6X2Hr0mS0sSU=@vger.kernel.org X-Gm-Message-State: AOJu0YzABfWSG3arbLTvSWVei85SVnfV/XePd4HGRztHqnW72N3E54MD ZCwHvikDG/+h7MNN+lMDt/2mLQvGcaqJaduGcVDFOTZ0GaScN5j1cMOZVPrsSQ== X-Gm-Gg: ASbGncs5HBWKwYO5pd6EdtQxJ3Cf7Ny+6OHJWh37rmdwNo3TOXgboVwThjxMGrVcVv6 GtMUY8iA4BCQ4q/N5lJBJatWC1i5ZzTY3h7TTst73bBd7ByOa64jt0h88sSMfRu7Uh3ekunfoRK QRhkh0CYFju85A3biTgdgQPbKgbxpsKAiOIVXLvBODHS2k6kk3jh5KUzOc9cM9dDrrGCkDGhdX7 xsE01+xHrjMyDEiy16GOdGciOsYNxV7npXCmwpGc5LNNueXyabYXsr8JVggFyxDzaWLlN4HMWb8 I7wRC7UMRovB/K/PE1l6DOJ2UMdhI2UMo5YM7JsPafapPBcVD8kkdntAHQ1cIYXNDzF0H8TyOff NUqp3Ri9aiAE= X-Google-Smtp-Source: AGHT+IE7/XS6Y6OX84+IPYbBAixOrFvMqopCI+5yqm1fZqocjNURnwxmE71XeoS1GvDmb1jzk5OozA== X-Received: by 2002:a17:903:1a44:b0:223:5187:a886 with SMTP id d9443c01a7336-22df4815a10mr47742635ad.22.1746026347315; Wed, 30 Apr 2025 08:19:07 -0700 (PDT) Received: from ?IPV6:2804:7f1:e2c0:32dc:1373:7adc:1124:6935? ([2804:7f1:e2c0:32dc:1373:7adc:1124:6935]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-22db50e772bsm123821265ad.132.2025.04.30.08.19.05 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 30 Apr 2025 08:19:06 -0700 (PDT) Message-ID: Date: Wed, 30 Apr 2025 12:19:03 -0300 Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [Patch net 1/2] sch_htb: make htb_deactivate() idempotent To: Cong Wang , netdev@vger.kernel.org Cc: jhs@mojatatu.com, jiri@resnulli.us, alan@wylie.me.uk References: <20250428232955.1740419-1-xiyou.wangcong@gmail.com> <20250428232955.1740419-2-xiyou.wangcong@gmail.com> Content-Language: en-US From: Victor Nogueira In-Reply-To: <20250428232955.1740419-2-xiyou.wangcong@gmail.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 4/28/25 20:29, Cong Wang wrote: > Alan reported a NULL pointer dereference in htb_next_rb_node() > after we made htb_qlen_notify() idempotent. > > It turns out in the following case it introduced some regression: > > htb_dequeue_tree(): > |-> fq_codel_dequeue() > |-> qdisc_tree_reduce_backlog() > |-> htb_qlen_notify() > |-> htb_deactivate() > |-> htb_next_rb_node() > |-> htb_deactivate() > > For htb_next_rb_node(), after calling the 1st htb_deactivate(), the > clprio[prio]->ptr could be already set to NULL, which means > htb_next_rb_node() is vulnerable here. If I'm not missing something, the issue seems to be that fq_codel_dequeue or codel_qdisc_dequeue may call qdisc_tree_reduce_backlog with sch->q.qlen == 0 after commit 342debc12183. This will cause htb_qlen_notify to be called which will deactivate before we call htb_next_rb_node further down in htb_dequeue_tree (as you said above). If that's so, couldn't we instead of doing: > @@ -348,7 +348,8 @@ static void htb_add_to_wait_tree(struct htb_sched *q, > */ > static inline void htb_next_rb_node(struct rb_node **n) > { > - *n = rb_next(*n); > + if (*n) > + *n = rb_next(*n); > } do something like: @@ -921,7 +921,9 @@ static struct sk_buff *htb_dequeue_tree(struct htb_sched *q, const int prio, cl->leaf.deficit[level] -= qdisc_pkt_len(skb); if (cl->leaf.deficit[level] < 0) { cl->leaf.deficit[level] += cl->quantum; - htb_next_rb_node(level ? &cl->parent->inner.clprio[prio].ptr : + /* Account for (fq_)codel child deactivating after dequeue */ + if (likely(cl->prio_activity)) + htb_next_rb_node(level ? &cl->parent->inner.clprio[prio].ptr : &q->hlevel[0].hprio[prio].ptr); } /* this used to be after charge_class but this constelation That way it's clear that the issue is a corner case where the child qdisc deactivates the parent. Otherwise it seems like we need to check for (*n) being NULL for every call to htb_next_rb_node. cheers, Victor