From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-pf1-f174.google.com (mail-pf1-f174.google.com [209.85.210.174]) (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 4AEB5CA6B for ; Tue, 6 May 2025 20:40:18 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.210.174 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1746564019; cv=none; b=Ia59VgEqSZEU7KDkj+M+qMwpczMG1bj8SuUzo4jsnuEnh62QltR7p+Di+FyOzVNG69XSKroWBdd/C8F7uCn0JpnV31WXFHExfyJAdmo+55h1rRHJeO/8kxJdwMlC2/tPotXffX4G7xZUtNWlahKsNp1logWKTWUKro973B3pHwg= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1746564019; c=relaxed/simple; bh=fHPMFFzOMABPaX3VDb1UExZue0kUfOn449yA23fqF0Y=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=IUXGdaVOB6r+t0sS1oxONQvN/ofzHbZukiIaK5678swG8N2hBhxzF34PiEZWCeRe49SVWeKDMCps55Bw/plFvMp6hF2uX3o+SbLPhIxMtZb2RPCxKG3QsGzeLYGBfNbDak+HGHBUtH4BdaHPO0obSQReDClH79fs2BY6EKSMq7o= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=gmail.com; spf=pass smtp.mailfrom=gmail.com; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b=aMjCBo89; arc=none smtp.client-ip=209.85.210.174 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=gmail.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=gmail.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="aMjCBo89" Received: by mail-pf1-f174.google.com with SMTP id d2e1a72fcca58-74068f95d9fso3219844b3a.0 for ; Tue, 06 May 2025 13:40:18 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20230601; t=1746564017; x=1747168817; darn=vger.kernel.org; h=in-reply-to:content-disposition:mime-version:references:message-id :subject:cc:to:from:date:from:to:cc:subject:date:message-id:reply-to; bh=Pprqtj6nNwJ7kvGMAS6wH9Xjmd67CzDbSMXZu91bNsE=; b=aMjCBo89YY9HY0W9ZojqLkHgFOqAeVsAK9631X2j7gkcONwIcuHvmkhWTQd1XElk33 QXj/a20FkDeoQJzZrD4ltSJqnev4KP9cS+I0D+jVf3YFARi5bUUvkJK6KbN5/1BR+/OH Ejb8SfRam2gbxSryLsKKiPmZbbRpG0XxACn9DR/yczkxY9Jg203bLw59UuSubLcy7qhZ 96mtv2RcBibbul8qeEsmePoE2xYF6wwsl99NryXXpiKhOgSprqnW/mYzTCo2n81v0zeh faznZ6E+mr77jINx3JOhVTYrde/Eh+K9wVK5cl+DNcttu1E9zJzHnHtXHJCbqP7CJlHS mMLg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1746564017; x=1747168817; h=in-reply-to:content-disposition:mime-version:references:message-id :subject:cc:to:from:date:x-gm-message-state:from:to:cc:subject:date :message-id:reply-to; bh=Pprqtj6nNwJ7kvGMAS6wH9Xjmd67CzDbSMXZu91bNsE=; b=tnF4S5LLWUNKzBauUnw8APRVkQ8LtgPDKDMQY95sWQcIUbQS+zK9sPYOmY0xR8/coi C27UrL0nVx+OLYIrkNrQQjnKRn/G1xrkJ2xKLppLWFSsS7U+gA4pI9Zckvxq/lOLAiJp K5zzNhxfclmhzp2Re+R+KZFxjfARxyQhTfL2ha7fp6wFGINVYvJbyC85xbqp4Q12ftKy 0Altt2lyJUsoj366ytwpKFvIQDuEDsOFaAbg15RTP9+aDoWPX/ioDtBGHZZLfBGD6eUr oc3lr61wXS2hvMVSlWOkqi0s+73HqBpHE7g08mUm7Z24Fg58nby/7q2DKgfplGXFAygO 7Hog== X-Gm-Message-State: AOJu0YwAffWMDGOhhOLMTNpZ6Cw1zTGbW8s1hNrdQ1X53YUX9bel6/UL j+w1fidsvGaTZMFkzJn57BupVcmO1q0oV6wUt+zZpZr+1Y255rH0 X-Gm-Gg: ASbGncvHUrSZIoWmMnYlLijL2sCX+tu2EMfkudafwnLq5BIZIJ2cLULOdPn+Cc+aBBJ CFAkb3b7aHNvfSakTkWzFe//SlLQnpEt0rrwKBOfoEaJSbvqlP8JbgLAk4H3GnNf+tzZHtyuVMS xuJ1lW2TYgmR8BDLTfFLNwM7Vn7p+d0F4lw2+qGcIQm9j9udhCAvGZSr2T774JGs61evMkGQye4 QgdCk+QRlMXefVSmhyhcCb4L6uQ87hcxo7NEkfBR2VwvNfL/gFhuAt9B3TIOn9Rx0OoUgVzKmoN 9TuYnjmWdZ2cinDeDKzsqIdJxpmyr6VKLL6zTuXYddWH X-Google-Smtp-Source: AGHT+IEF1s7O9vut6ixzO5bv4GCT3R+Po0/p4+ioZsXM8d+LagD0fdM3d1tsS0fQb9+wxwn/G0iXSg== X-Received: by 2002:a05:6a21:1193:b0:1f5:8e33:c417 with SMTP id adf61e73a8af0-2148b526afdmr1023524637.2.1746564017439; Tue, 06 May 2025 13:40:17 -0700 (PDT) Received: from localhost ([129.210.115.104]) by smtp.gmail.com with ESMTPSA id 41be03b00d2f7-b1fb3b5ace3sm6670464a12.21.2025.05.06.13.40.16 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 06 May 2025 13:40:16 -0700 (PDT) Date: Tue, 6 May 2025 13:40:15 -0700 From: Cong Wang To: Savy Cc: netdev@vger.kernel.org, jiri@resnulli.us, jhs@mojatatu.com, willsroot@protonmail.com Subject: Re: [Patch net 1/2] net_sched: Flush gso_skb list too during ->change() Message-ID: References: <20250506001549.65391-1-xiyou.wangcong@gmail.com> <20250506001549.65391-2-xiyou.wangcong@gmail.com> Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: On Tue, May 06, 2025 at 02:00:36PM +0000, Savy wrote: > On Tuesday, May 6th, 2025 at 12:15 AM, Cong Wang wrote: > > > > > the main skb queue was trimmed, potentially leaving packets in the gso_skb > > list. This could result in NULL pointer dereference when we only check > > sch->q.qlen against sch->limit. > > > > > > Hi Cong, > > With this version of the patch, the null-ptr-deref can still be triggered. > We also need to decrement sch->q.qlen if __skb_dequeue() returns a valid skb. > > We will take Codel as an example. > > while (sch->q.qlen > sch->limit) { > struct sk_buff *skb = qdisc_dequeue_internal(sch, true); > ... > } > > If sch->q.qlen is 1 and there is a single packet in the gso_skb list, > if sch->limit is dropped to 0 in codel_change, then qdisc_dequeue_internal() -> __skb_dequeue() > will remove the skb from the gso_skb list, leaving sch->q.qlen unaltered. > At this point, the while loop continues, as sch->q.qlen is still 1, but now both the main queue and gso_skb are empty, > so when qdisc_dequeue_internal() is called again, it returns NULL, and the null-ptr-deref occurs. Excellent catch! You are right, I missed qlen--. Also, actually I accidentally messed up the 2nd boolean parameter for some Qdisc's. I will update the patch and send out V2 shortly today. Thanks!