From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) (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 E0F8F3D413F for ; Fri, 17 Jul 2026 15:16:36 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=170.10.133.124 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784301398; cv=none; b=jWRj2S8/Tex5sAO4eRW4whOJzFrB8a47/H96godPovT9lvnJoaTHi4gQcGxhHc63YlJsIDbjdz4rXwzys4dSlLDdFTheWgwFvvXqnodxOaeeyeiVxzMttG6+Ssux0OEOMSrnT7IhI8cDWzLlGyMyaJrjWjH63biCxq1I93Fl6rY= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784301398; c=relaxed/simple; bh=NNibbsMBzcBhzHKyyVyWoEjs9JNqg5eZd/fl/Nu8GEg=; h=From:To:Cc:Subject:Date:Message-ID:MIME-Version; b=ujHCTMGCZKrb2sJlLYMnK1jSP0HFJaXmJScLuwuLQ6q6HV8lNk6YrOmNW8sJXqgMAba+LazwMOAz+vtaNtWmoLiceFaON++LLfdjgV1VdVQRv8TivfRhS5PgxEnfOXp4IHbxJ/kluPXOvgfphCSs47MwhTKIp3vrF1ayNQgJel0= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=redhat.com; spf=pass smtp.mailfrom=redhat.com; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b=DFmc4Pkw; arc=none smtp.client-ip=170.10.133.124 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=redhat.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=redhat.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="DFmc4Pkw" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1784301396; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding; bh=TRhb9mvNrRYyHgkhEJwct4IUo2+m3ly9XG+UwgjaINA=; b=DFmc4Pkwz+/lTEM2cIbn9uQpxabB0OHplxAzml/OtByR6iHeCcgj/0EeeyPmhuDbAVSZxB V+LqC+w0VRCU56HdKdIUfPzCaD3hKoQARrigUSuk2kKoqG3tgU5Ao8lYiveEyd+xbj+hif ICE8FdDdpQrp1MadIcgeb7oUUQBmB2o= Received: from mx-prod-mc-05.mail-002.prod.us-west-2.aws.redhat.com (ec2-54-186-198-63.us-west-2.compute.amazonaws.com [54.186.198.63]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-302-dNHHZgzCNfWqsyxdkLZFtg-1; Fri, 17 Jul 2026 11:16:30 -0400 X-MC-Unique: dNHHZgzCNfWqsyxdkLZFtg-1 X-Mimecast-MFC-AGG-ID: dNHHZgzCNfWqsyxdkLZFtg_1784301389 Received: from mx-prod-int-01.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-01.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.4]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mx-prod-mc-05.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 5CFF11955D8D; Fri, 17 Jul 2026 15:16:29 +0000 (UTC) Received: from lenovo-t14s.redhat.corp (headnet05.pony-001.prod.iad2.dc.redhat.com [10.2.32.117]) by mx-prod-int-01.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTP id 726A33004182; Fri, 17 Jul 2026 15:16:27 +0000 (UTC) From: Laurent Vivier To: linux-kernel@vger.kernel.org Cc: netdev@vger.kernel.org, Jakub Kicinski , linux-usb@vger.kernel.org, Stefano Brivio , Oliver Neukum , Laurent Vivier , stable@vger.kernel.org Subject: [PATCH net] usbnet: cap max_mtu for drivers without bind callback Date: Fri, 17 Jul 2026 17:16:26 +0200 Message-ID: <20260717151626.2913171-1-lvivier@redhat.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Scanned-By: MIMEDefang 3.4.1 on 10.30.177.4 Commit c7159e960f14 ("usbnet: limit max_mtu based on device's hard_mtu") caps max_mtu inside the if (info->bind) block in usbnet_probe(). Drivers without a bind callback never enter this block, so max_mtu stays at ETH_MAX_MTU. QEMU's usb-net device (0x0525/0xa4a2) is claimed by the cdc_subset driver which has no bind callback. The guest accepts any MTU from DHCP (e.g. 65520 from passt), leading to TCP segments that exceed the device's 2048-byte receive buffer and are silently dropped. Move the max_mtu capping after the if/else block so it applies to all usbnet drivers. Fixes: c7159e960f14 ("usbnet: limit max_mtu based on device's hard_mtu") Cc: stable@vger.kernel.org Link: https://gitlab.com/qemu-project/qemu/-/issues/3268 Link: https://bugs.passt.top/show_bug.cgi?id=189 Signed-off-by: Laurent Vivier --- drivers/net/usb/usbnet.c | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-) diff --git a/drivers/net/usb/usbnet.c b/drivers/net/usb/usbnet.c index 25518635b7b7..d87299025552 100644 --- a/drivers/net/usb/usbnet.c +++ b/drivers/net/usb/usbnet.c @@ -1825,10 +1825,6 @@ usbnet_probe(struct usb_interface *udev, const struct usb_device_id *prod) if ((dev->driver_info->flags & FLAG_NOARP) != 0) net->flags |= IFF_NOARP; - if ((dev->driver_info->flags & FLAG_NOMAXMTU) == 0 && - net->max_mtu > (dev->hard_mtu - net->hard_header_len)) - net->max_mtu = dev->hard_mtu - net->hard_header_len; - if (net->mtu > (dev->hard_mtu - net->hard_header_len)) net->mtu = dev->hard_mtu - net->hard_header_len; @@ -1851,6 +1847,10 @@ usbnet_probe(struct usb_interface *udev, const struct usb_device_id *prod) if (status == 0 && !usb_check_bulk_endpoints(udev, ep_addrs)) status = -EINVAL; } + if ((dev->driver_info->flags & FLAG_NOMAXMTU) == 0 && + net->max_mtu > (dev->hard_mtu - net->hard_header_len)) + net->max_mtu = dev->hard_mtu - net->hard_header_len; + if (status >= 0 && dev->status) status = init_status(dev, udev); if (status < 0) -- 2.54.0