From nobody Mon Jun 8 13:32:05 2026 Received: from azure-sdnproxy.icoremail.net (azure-sdnproxy.icoremail.net [207.46.229.174]) by smtp.subspace.kernel.org (Postfix) with ESMTP id 0A29E346FAD; Fri, 29 May 2026 06:21:57 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=207.46.229.174 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1780035723; cv=none; b=LbVoMzIp4cuKnLdVKV6bogUDIyvcAJ1PEvdBEr1+PjuJUHvBIfRbljLglSPtZjY4rA6JSP1BPSi0pgzv+rAoDyksTvjIVpadIjoO0ypF8TCq/X0XlLgXmuuj5ua+zzJQW3b4Y7a6Pr92ebmipbI/zimPknuF+suZ5zqKsPTPf9I= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1780035723; c=relaxed/simple; bh=CHF6QtmzT6Tk5OH9nu3VaO5GO8oOAbuQK7nlBFs8uhU=; h=From:To:Cc:Subject:Date:Message-ID:MIME-Version; b=HB3dioBxOEPB5M6cuBaKw7C5ki2KFSaI++p5NyDJexRm15j+Wwmuq6g3Jqdk2RKmosQSafqyB/N9fqFkkHtxKf8wsw2d/4q7YyxuZw1NkIvANxXie2imu4/AOS8RbZ2YdFeGeDaXzUMZJZ/hHSRVBHleNWUGTTRHAY3eX+QstN8= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=mails.tsinghua.edu.cn; spf=pass smtp.mailfrom=mails.tsinghua.edu.cn; dkim=pass (1024-bit key) header.d=mails.tsinghua.edu.cn header.i=@mails.tsinghua.edu.cn header.b=h3hRAA4i; arc=none smtp.client-ip=207.46.229.174 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=mails.tsinghua.edu.cn Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=mails.tsinghua.edu.cn Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=mails.tsinghua.edu.cn header.i=@mails.tsinghua.edu.cn header.b="h3hRAA4i" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=mails.tsinghua.edu.cn; s=dkim; h=Received:From:To:Cc:Subject: Date:Message-ID:MIME-Version:Content-Transfer-Encoding; bh=ix23Q yk0YdItmhR/wIfPOtWcJ6bXqWw3b9V10mrkzUI=; b=h3hRAA4i60pJRgHAuFeEK SLe71kjRprpVnMe3rNncHhUIVhsC2vXZh+GXuU+TA/uHIq480TiMyxd/36oLvxTi PMm5YUBD0s6IpzqDVXF0puqXDRJz/sZDSuLeTdKjlbd0UtMsrm+MnJboxfDbh+rP inx2qQFpr6mq6ScYkDpbdg= Received: from localhost.localdomain (unknown [211.102.241.99]) by web5 (Coremail) with SMTP id zAQGZQC3bb1xMBlqAzb3AQ--.36352S2; Fri, 29 May 2026 14:21:38 +0800 (CST) From: Yizhou Zhao To: netdev@vger.kernel.org Cc: Yizhou Zhao , "David S . Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Simon Horman , Kees Cook , linux-kernel@vger.kernel.org, Yuxiang Yang , Ao Wang , Xuewei Feng , Qi Li , Ke Xu Subject: [PATCH net] vlan: prevent unsigned underflow in VLAN MTU calculation over MACsec Date: Fri, 29 May 2026 14:21:33 +0800 Message-ID: <20260529062135.70490-1-zhaoyz24@mails.tsinghua.edu.cn> X-Mailer: git-send-email 2.46.2 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-CM-TRANSID: zAQGZQC3bb1xMBlqAzb3AQ--.36352S2 X-Coremail-Antispam: 1UD129KBjvJXoWxAr1UtF45Zr1rGr4xAF1xuFg_yoW5Gry3pF WjkFy7JrWUtryqqrWvqa1kZr4UJa1qv397Ar98C3WxAw45GFySqr48KFZxGrW8Za97CF18 Jr47Ar4jkws0gFDanT9S1TB71UUUUU7qnTZGkaVYY2UrUUUUjbIjqfuFe4nvWSU5nxnvy2 9KBjDU0xBIdaVrnRJUUUP014x267AKxVW8JVW5JwAFc2x0x2IEx4CE42xK8VAvwI8IcIk0 rVWrJVCq3wAFIxvE14AKwVWUJVWUGwA2ocxC64kIII0Yj41l84x0c7CEw4AK67xGY2AK02 1l84ACjcxK6xIIjxv20xvE14v26w1j6s0DM28EF7xvwVC0I7IYx2IY6xkF7I0E14v26r4U JVWxJr1l84ACjcxK6I8E87Iv67AKxVW0oVCq3wA2z4x0Y4vEx4A2jsIEc7CjxVAFwI0_Gc CE3s1lnxkEFVAIw20F6cxK64vIFxWle2I262IYc4CY6c8Ij28IcVAaY2xG8wAqx4xG64xv F2IEw4CE5I8CrVC2j2WlYx0E2Ix0cI8IcVAFwI0_Jr0_Jr4lYx0Ex4A2jsIE14v26r1j6r 4UMcvjeVCFs4IE7xkEbVWUJVW8JwACjcxG0xvY0x0EwIxGrwACjI8F5VA0II8E6IAqYI8I 648v4I1lFIxGxcIEc7CjxVA2Y2ka0xkIwI1lc7CjxVAaw2AFwI0_Jw0_GFylc2xSY4AK67 AK6r47MxAIw28IcxkI7VAKI48JMxC20s026xCaFVCjc4AY6r1j6r4UMI8I3I0E5I8CrVAF wI0_Jr0_Jr4lx2IqxVCjr7xvwVAFwI0_JrI_JrWlx4CE17CEb7AF67AKxVWUtVW8ZwCIc4 0Y0x0EwIxGrwCI42IY6xIIjxv20xvE14v26r1j6r1xMIIF0xvE2Ix0cI8IcVCY1x0267AK xVW8JVWxJwCI42IY6xAIw20EY4v20xvaj40_Jr0_JF4lIxAIcVC2z280aVAFwI0_Jr0_Gr 1lIxAIcVC2z280aVCY1x0267AKxVW8JVW8JrUvcSsGvfC2KfnxnUUI43ZEXa7VUjgdbUUU UUU== X-CM-SenderInfo: 52kd05r2suqzpdlo2hxwvl0wxkxdhvlgxou0/1tbiAQQCAWoYwC6FfAABsi Content-Type: text/plain; charset="utf-8" When a VLAN device is created on top of a MACsec device (where `netif_reduces_vlan_mtu()` returns true) and the underlying device's MTU is smaller than `VLAN_HLEN` (4 bytes), subtracting `VLAN_HLEN` from the device MTU can underflow an unsigned integer. This wraps `max_mtu` to a value near `UINT_MAX`, bypassing MTU checks and allowing an invalidly large MTU on the VLAN device. The same underflow exists in `vlan_newlink()` where the ternary expression `real_dev->mtu - VLAN_HLEN` can wrap if the real device's MTU is smaller than `VLAN_HLEN`. Fix both locations by first verifying that `real_dev->mtu >=3D VLAN_HLEN` before performing the subtraction. If the underlying device's MTU is too small, return an appropriate error: - `vlan_dev_change_mtu()`: return `-ERANGE` - `vlan_newlink()`: return `-EINVAL` This ensures no invalid MTU values are set on VLAN devices when the underlying MACsec device is too small. Fixes: 18d3df3eab23 ("vlan: use a valid default mtu value for vlan over mac= sec") Reported-by: Yizhou Zhao Reported-by: Yuxiang Yang Reported-by: Ao Wang Reported-by: Xuewei Feng Reported-by: Qi Li Reported-by: Ke Xu Assisted-by: GLM:GLM-5.1 --- diff --git a/net/8021q/vlan_dev.c b/net/8021q/vlan_dev.c index c40f7d5..19c838c 100644 --- a/net/8021q/vlan_dev.c +++ b/net/8021q/vlan_dev.c @@ -145,8 +145,11 @@ static int vlan_dev_change_mtu(struct net_device *dev,= int new_mtu) struct net_device *real_dev =3D vlan_dev_priv(dev)->real_dev; unsigned int max_mtu =3D real_dev->mtu; =20 - if (netif_reduces_vlan_mtu(real_dev)) + if (netif_reduces_vlan_mtu(real_dev)) { + if (max_mtu < VLAN_HLEN) + return -ERANGE; + max_mtu -=3D VLAN_HLEN; + } if (max_mtu < new_mtu) return -ERANGE; =20 diff --git a/net/8021q/vlan_netlink.c b/net/8021q/vlan_netlink.c index a000b1e..52a47d2 100644 --- a/net/8021q/vlan_netlink.c +++ b/net/8021q/vlan_netlink.c @@ -178,8 +178,13 @@ static int vlan_newlink(struct net_device *dev, if (err < 0) return err; =20 - max_mtu =3D netif_reduces_vlan_mtu(real_dev) ? real_dev->mtu - VLAN_HLEN : - real_dev->mtu; + if (netif_reduces_vlan_mtu(real_dev)) { + if (real_dev->mtu < VLAN_HLEN) + return -EINVAL; + max_mtu =3D real_dev->mtu - VLAN_HLEN; + } else { + max_mtu =3D real_dev->mtu; + } if (!tb[IFLA_MTU]) dev->mtu =3D max_mtu; else if (dev->mtu > max_mtu) dev->mtu =3D max_mtu;