From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out30-133.freemail.mail.aliyun.com (out30-133.freemail.mail.aliyun.com [115.124.30.133]) (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 53FA439DBDB for ; Fri, 21 Aug 2026 09:43:48 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=115.124.30.133 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1787305434; cv=none; b=oRamIhr6xInlc6SvaQ7EQl2O/zZ5PLvciYN2ZE7xzMT1eONLbwUbJfeRAUsTkqSi7G/ejhZVq+5lRzp4D8WlV1ytJq4Btwpt3dYRvSQQKgrskqJVMRk2jSFEeZ2ujZPBVWJSBmJrVHP+w8WO14hVXiuNKHpLHQYguE3cNwehRk4= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1787305434; c=relaxed/simple; bh=aDkfHaQnUx+u6tOWJkwto0jjaDrFKtIIxAA4ZunJrfI=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: Content-Type:MIME-Version; b=qw/INHNCeLxkAaD1lzSBCyO5m+TI2m3xtNODieaaTOGgc/CUsB5afzR5xdoK0eL48HLnPzePSKN/uKrYvviCJsxOcrNR9jTMnK81YMAdeu4yQ0HoM+prVbspA5Y2BtaW5N+E0EpZcSktF5BgLGPhwDsHOCbsJ7fEKJ5iWliZnSk= 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=GqdVUjaS; arc=none smtp.client-ip=115.124.30.133 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="GqdVUjaS" DKIM-Signature:v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.alibaba.com; s=default; t=1787305423; h=From:To:Subject:Date:Message-ID:Content-Type:MIME-Version; bh=aDkfHaQnUx+u6tOWJkwto0jjaDrFKtIIxAA4ZunJrfI=; b=GqdVUjaSji9237z2MBALfcNmsokFF2N/u2hvkLN0jxMapOpdqcabCpUzBtYP73rCyDQoRrCmYYXgUVZ+aVzLwy7hYYmN/+8sGpewvG9PA1tJNcEzt9xwzJy1zPAj0SwdovvgEDy8UYxETyANr2di4altdPDoB9dsGAFuwUuadf8= X-Alimail-AntiSpam:AC=PASS;BC=-1|-1;BR=01201311R191e4;CH=green;DM=||false|;DS=||;FP=0|-1|-1|-1|0|-1|-1|-1;HT=maildocker-contentspam033037026112;MF=chuyf26@linux.alibaba.com;NM=1;PH=DS;RN=3;SR=0;TI=SMTPD_---0X9Lvg8P_1787305422; Received: from x31j07255.sqa.na131(mailfrom:Chuyf26@linux.alibaba.com fp:SMTPD_---0X9Lvg8P_1787305422 cluster:ay36) by smtp.aliyun-inc.com; Fri, 21 Aug 2026 17:43:43 +0800 From: Chuyf26 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: Fri, 21 Aug 2026 17:42:08 +0800 Message-ID: <178730532802.474692.15922523828621281026@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. Chuyf26