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=-2.4 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS,UNPARSEABLE_RELAY,USER_AGENT_SANE_1 autolearn=no 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 ABEE2C35248 for ; Sat, 1 Feb 2020 05:57:11 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 38989206A2 for ; Sat, 1 Feb 2020 05:57:11 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=oracle.com header.i=@oracle.com header.b="aVAm7YmX" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726335AbgBAF5H (ORCPT ); Sat, 1 Feb 2020 00:57:07 -0500 Received: from userp2120.oracle.com ([156.151.31.85]:50950 "EHLO userp2120.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726014AbgBAF5H (ORCPT ); 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Sat, 1 Feb 2020 05:56:36 GMT Received: from aserv0121.oracle.com (aserv0121.oracle.com [141.146.126.235]) by aserp3020.oracle.com with ESMTP id 2xw15wm6kt-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Sat, 01 Feb 2020 05:56:36 +0000 Received: from abhmp0019.oracle.com (abhmp0019.oracle.com [141.146.116.25]) by aserv0121.oracle.com (8.14.4/8.13.8) with ESMTP id 0115uR75028315; Sat, 1 Feb 2020 05:56:27 GMT Received: from kadam (/129.205.23.165) by default (Oracle Beehive Gateway v4.0) with ESMTP ; Fri, 31 Jan 2020 21:56:26 -0800 Date: Sat, 1 Feb 2020 08:56:12 +0300 From: Dan Carpenter To: syzbot Cc: airlied@linux.ie, alexander.deucher@amd.com, amd-gfx@lists.freedesktop.org, chris@chris-wilson.co.uk, christian.koenig@amd.com, daniel@ffwll.ch, davem@davemloft.net, dri-devel@lists.freedesktop.org, emil.velikov@collabora.com, eric@anholt.net, linaro-mm-sig@lists.linaro.org, linux-kernel@vger.kernel.org, linux-media@vger.kernel.org, netdev@vger.kernel.org, robdclark@chromium.org, seanpaul@chromium.org, sumit.semwal@linaro.org, syzkaller-bugs@googlegroups.com Subject: Re: KASAN: use-after-free Read in vgem_gem_dumb_create Message-ID: <20200201055612.GF1778@kadam> References: <000000000000ae2f81059d7716b8@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <000000000000ae2f81059d7716b8@google.com> User-Agent: Mutt/1.9.4 (2018-02-28) X-Proofpoint-Virus-Version: vendor=nai engine=6000 definitions=9517 signatures=668685 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 suspectscore=2 malwarescore=0 phishscore=0 bulkscore=0 spamscore=0 mlxscore=0 mlxlogscore=999 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1911140001 definitions=main-2002010040 X-Proofpoint-Virus-Version: vendor=nai engine=6000 definitions=9517 signatures=668685 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 priorityscore=1501 malwarescore=0 suspectscore=2 phishscore=0 bulkscore=0 spamscore=0 clxscore=1011 lowpriorityscore=0 mlxscore=0 impostorscore=0 mlxlogscore=999 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1911140001 definitions=main-2002010041 Sender: netdev-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org I don't totally understand the stack trace but I do see a double free bug. drivers/gpu/drm/vgem/vgem_drv.c 186 static struct drm_gem_object *vgem_gem_create(struct drm_device *dev, 187 struct drm_file *file, 188 unsigned int *handle, 189 unsigned long size) 190 { 191 struct drm_vgem_gem_object *obj; 192 int ret; 193 194 obj = __vgem_gem_create(dev, size); obj->base.handle_count is zero. 195 if (IS_ERR(obj)) 196 return ERR_CAST(obj); 197 198 ret = drm_gem_handle_create(file, &obj->base, handle); We bump it +1 and then the error handling calls drm_gem_object_handle_put_unlocked(obj); which calls drm_gem_object_put_unlocked(); which frees obj. 199 drm_gem_object_put_unlocked(&obj->base); So this is a double free. Could someone check my thinking and send a patch? It's just a one liner. Otherwise I can send it on Monday. 200 if (ret) 201 return ERR_PTR(ret); 202 203 return &obj->base; 204 } regards, dan carpenter