From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-18.7 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_RED, USER_AGENT_GIT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id A6AB6C433E9 for ; Mon, 28 Dec 2020 13:36:55 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 7961722B4B for ; Mon, 28 Dec 2020 13:36:55 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2390723AbgL1Ngi (ORCPT ); Mon, 28 Dec 2020 08:36:38 -0500 Received: from mail.kernel.org ([198.145.29.99]:36930 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2390523AbgL1Ngd (ORCPT ); Mon, 28 Dec 2020 08:36:33 -0500 Received: by mail.kernel.org (Postfix) with ESMTPSA id 935E1205CB; Mon, 28 Dec 2020 13:35:51 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1609162552; bh=cYKIWtitTmOCqJ67n06KAUnkiW4C0HOfRQEAM2qKt70=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=vCK3ZYXlXhq9HqTz5+/53/cXbtXAl51s5iW1Mho3m5qDDRGV/eqeqrnD7uxCr+Atf 7N1R59E4uQAv7Q8AFcEOhu3e6Q42KpRRGKRXG7kEc1P/BmE0+JG/a+RJP9jQNmhF33 Of4vxsMYgajBe0Ibne8wFuBGEuRyPamSGOVovHnE= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Olivier Benjamin , Pawel Wieczorkiewicz , Julien Grall , Juergen Gross Subject: [PATCH 4.19 338/346] xen-blkback: set ring->xenblkd to NULL after kthread_stop() Date: Mon, 28 Dec 2020 13:50:57 +0100 Message-Id: <20201228124936.096961407@linuxfoundation.org> X-Mailer: git-send-email 2.29.2 In-Reply-To: <20201228124919.745526410@linuxfoundation.org> References: <20201228124919.745526410@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Pawel Wieczorkiewicz commit 1c728719a4da6e654afb9cc047164755072ed7c9 upstream. When xen_blkif_disconnect() is called, the kernel thread behind the block interface is stopped by calling kthread_stop(ring->xenblkd). The ring->xenblkd thread pointer being non-NULL determines if the thread has been already stopped. Normally, the thread's function xen_blkif_schedule() sets the ring->xenblkd to NULL, when the thread's main loop ends. However, when the thread has not been started yet (i.e. wake_up_process() has not been called on it), the xen_blkif_schedule() function would not be called yet. In such case the kthread_stop() call returns -EINTR and the ring->xenblkd remains dangling. When this happens, any consecutive call to xen_blkif_disconnect (for example in frontend_changed() callback) leads to a kernel crash in kthread_stop() (e.g. NULL pointer dereference in exit_creds()). This is XSA-350. Cc: # 4.12 Fixes: a24fa22ce22a ("xen/blkback: don't use xen_blkif_get() in xen-blkback kthread") Reported-by: Olivier Benjamin Reported-by: Pawel Wieczorkiewicz Signed-off-by: Pawel Wieczorkiewicz Reviewed-by: Julien Grall Reviewed-by: Juergen Gross Signed-off-by: Juergen Gross Signed-off-by: Greg Kroah-Hartman --- drivers/block/xen-blkback/xenbus.c | 1 + 1 file changed, 1 insertion(+) --- a/drivers/block/xen-blkback/xenbus.c +++ b/drivers/block/xen-blkback/xenbus.c @@ -264,6 +264,7 @@ static int xen_blkif_disconnect(struct x if (ring->xenblkd) { kthread_stop(ring->xenblkd); + ring->xenblkd = NULL; wake_up(&ring->shutdown_wq); }