From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out30-101.freemail.mail.aliyun.com (out30-101.freemail.mail.aliyun.com [115.124.30.101]) (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 A285B3E929C for ; Thu, 3 Sep 2026 09:26:34 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=115.124.30.101 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788427599; cv=none; b=DwHiORNA2CjZSf7e7TIYfz9tAuzvKJGtZMiYTQMaBOxKEiyGFsjzKpQKiFdfiU2YkjmocE91em1+cyTqRvBp3MU5OQHuToLS7HKUFmHLMEG0KIWaeVVRC+drWbIEDLNoSZyzTzczPNJKequp+22ong6j3FzQGAnNjeXnek5V/bg= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788427599; c=relaxed/simple; bh=5W4ArnJ86wA+s53i49IW1Ss6cZ7Vs8PEMrypqQMgHeI=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: Content-Type:MIME-Version; b=Sr+iyluWOB5nefgMMeaD+p3FHLualOw54K3t+1Pd+V+m/w0+R8dX3ZcZDf0xG8fEpY3z8hf7zY7t89ZJmkk/Ctkzf3dnT+EuKLtH8ULO/SmM1CSPAbyG1h1LCFHvJIkRjFl5UyuUl+MzxvgvUQ6o1u60srf/gKSoxG+Is/2JFWU= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.alibaba.com; spf=pass smtp.mailfrom=linux.alibaba.com; dkim=pass (1024-bit key) header.d=linux.alibaba.com header.i=@linux.alibaba.com header.b=sOcqjool; arc=none smtp.client-ip=115.124.30.101 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.alibaba.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.alibaba.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.alibaba.com header.i=@linux.alibaba.com header.b="sOcqjool" DKIM-Signature:v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.alibaba.com; s=default; t=1788427590; h=From:To:Subject:Date:Message-ID:Content-Type:MIME-Version; bh=5W4ArnJ86wA+s53i49IW1Ss6cZ7Vs8PEMrypqQMgHeI=; b=sOcqjoolXhtNRqP4ADWAAqMIVOzmFD6bHN+tIqpWt0FBsYUw/08m7G351ppgUsqD5cSWXXfpcDRAZ58jNEtOI5fhAmmA/5oveFVuKAEphd4qyB/H3BRqokXBUr2Lf/za8cnkRXTNLK8zTfFvZD8Ag15v3TXciuWeEGs0z6uGst8= X-Alimail-AntiSpam:AC=PASS;BC=-1|-1;BR=01201311R161e4;CH=green;DM=||false|;DS=||;FP=0|-1|-1|-1|0|-1|-1|-1;HT=maildocker-contentspam033032089153;MF=chuyf26@linux.alibaba.com;NM=1;PH=DS;RN=3;SR=0;TI=SMTPD_---0XAFZIge_1788427589; Received: from x31j07255.sqa.na131(mailfrom:Chuyf26@linux.alibaba.com fp:SMTPD_---0XAFZIge_1788427589 cluster:ay36) by smtp.aliyun-inc.com; Thu, 03 Sep 2026 17:26:29 +0800 From: Yifei Chu To: horms@kernel.org Cc: xeb@mail.ru, netdev@vger.kernel.org Subject: Re: [PATCH] pptp: reject payloads shorter than the PPP protocol field Date: Thu, 03 Sep 2026 17:24:30 +0800 Message-ID: <178842747087.1044540.6008885003196112246@linux.alibaba.com> In-Reply-To: <20260821092618.GF265046@horms.kernel.org> References: <20260818162143.gn-j15t2twSq3EK4tluniorb9JMdD9cS6_NWtWioiRc@z> <20260821092618.GF265046@horms.kernel.org> Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Simon, you are right. I double-checked the arithmetic: when len == 1, pskb_may_pull(skb, 1 + len) only guarantees 2 bytes, so p[1] is read one byte past the validated area, but the pre-existing len < p[1] + 2 check rejects the frame for every possible value of that byte, and the len < 2 clause only hides the read behind short-circuit evaluation. There is no control-flow change, so this is hardening at best rather than a fix, and given the read stays inside the skb allocation I am withdrawing this patch instead of resubmitting it for net-next without a Fixes tag. The point in finding 2 about the p[1] / p[2] mismatch is valid, but as there is no memory-safety consequence I do not plan to pursue it here either. The pptp patch from the same series is addressed in a separate reply. Yifei Chu