From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (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 C51DA225791 for ; Thu, 13 Aug 2026 00:53:32 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1786582414; cv=none; b=c3f7r96KwB50UOV6ylengp6tKED6hRO3CJ/4h9WC9kiUq91U2j65oQqJuQyNQAaxB6jVtMG2kKJvBC9WPp3RnAVOFyn4G6ToXXcApENjND2JbFwfhsLs76eGyJS9/ZfX+/fdBOZXAzt+nK5X96QSjackRQIL5es5Jw0K7FULITA= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1786582414; c=relaxed/simple; bh=M7qskYTbbAgzAqdu71dDlyg/YhFZ8+ppSMdpssEaUno=; h=Subject:To:Cc:From:Date:Message-ID:MIME-Version:Content-Type; b=AvhOxjDQ1smCg+VpjOFA5nxzb57DQGiUJk9AiP+GNmEV+1ctoJQIK8cahjuAb1BlhLswgtV9LOjZY6/lKeWrDQ6+CC2x7JRtdeKLKIO31NwmTUipWLxJtZBkpboM020zbJZYl6hke4+gsWsmQQo2RZqVpY2shtdxlx7YDh6phAM= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=sbJ3v3DE; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="sbJ3v3DE" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 0CC471F000E9; Thu, 13 Aug 2026 00:53:31 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1786582412; bh=ZSM/qOftY1qYX+pcCq0lvZNQaK4f1rklGQkJevpCXAM=; h=Subject:To:Cc:From:Date; b=sbJ3v3DEzHlnVV55Hg71L1jQUnM+wad7g+1pGlMXyIxDoz9V/rv2JunQlFwSkyz0X V1aVfsUOrUbJclrchlnuWystQxeICHu6Rr3wEuktBXXpYFBrPSlYghlkn9jTIpDpMG hwO/1Z8ZfZlVMzODgq0Q5pwS27moafdkyXmeqGbk= Subject: FAILED: patch "[PATCH] usbnet: cap max_mtu for drivers without bind callback" failed to apply to 6.12-stable tree To: lvivier@redhat.com,kuba@kernel.org Cc: From: Date: Thu, 13 Aug 2026 09:51:52 +0900 Message-ID: <2026081352-septic-context-9d85@gregkh> Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=ANSI_X3.4-1968 Content-Transfer-Encoding: 8bit The patch below does not apply to the 6.12-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to . To reproduce the conflict and resubmit, you may use the following commands: git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-6.12.y git checkout FETCH_HEAD git cherry-pick -x 1505b2cb6ae1c7e8ac0c6e4590a204ffc3ab2b24 # git commit -s git send-email --to '' --in-reply-to '2026081352-septic-context-9d85@gregkh' --subject-prefix 'PATCH 6.12.y' 'HEAD^..' Possible dependencies: thanks, greg k-h ------------------ original commit in Linus's tree ------------------ >From 1505b2cb6ae1c7e8ac0c6e4590a204ffc3ab2b24 Mon Sep 17 00:00:00 2001 From: Laurent Vivier Date: Fri, 31 Jul 2026 11:27:11 +0200 Subject: [PATCH] usbnet: cap max_mtu for drivers without bind callback usbnet_probe() initializes max_mtu to ETH_MAX_MTU and only caps it inside the if (info->bind) block. 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. Initialize max_mtu to net->mtu at probe time and update it inside the bind block. Fixes: f77f0aee4da4 ("net: use core MTU range checking in USB NIC drivers") Cc: jarod@redhat.com 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 Link: https://patch.msgid.link/20260731092711.857684-1-lvivier@redhat.com Signed-off-by: Jakub Kicinski diff --git a/drivers/net/usb/usbnet.c b/drivers/net/usb/usbnet.c index 25518635b7b7..a19ecf718f36 100644 --- a/drivers/net/usb/usbnet.c +++ b/drivers/net/usb/usbnet.c @@ -1794,7 +1794,7 @@ usbnet_probe(struct usb_interface *udev, const struct usb_device_id *prod) */ dev->hard_mtu = net->mtu + net->hard_header_len; net->min_mtu = 0; - net->max_mtu = ETH_MAX_MTU; + net->max_mtu = net->mtu; net->netdev_ops = &usbnet_netdev_ops; net->watchdog_timeo = TX_TIMEOUT_JIFFIES; @@ -1804,6 +1804,7 @@ usbnet_probe(struct usb_interface *udev, const struct usb_device_id *prod) // allow device-specific bind/init procedures // NOTE net->name still not usable ... if (info->bind) { + net->max_mtu = ETH_MAX_MTU; status = info->bind(dev, udev); if (status < 0) goto out1;