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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id DE3CAC433F5 for ; Tue, 10 May 2022 13:36:50 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S241599AbiEJNkn (ORCPT ); Tue, 10 May 2022 09:40:43 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:56730 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S243768AbiEJN1X (ORCPT ); Tue, 10 May 2022 09:27:23 -0400 Received: from ams.source.kernel.org (ams.source.kernel.org [145.40.68.75]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 497D92BD217; Tue, 10 May 2022 06:20:28 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ams.source.kernel.org (Postfix) with ESMTPS id 78A21B81CF8; Tue, 10 May 2022 13:20:26 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id B4504C385C2; Tue, 10 May 2022 13:20:24 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1652188825; bh=dnjGH4X54RaK+1LVipStRQRfJJyRB8ZUDUbQ9R3Sj8s=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=v0cP42nx9jKGt3J4IraM3AlwY+QuQ73heQZnHVckZz7UZqq8gArcGE8iF3DoLpg5H e43wm3GMyTVrkq6l4QsiYjPPu+BSjCCMTyXIhUTsfJbpEG14x4ULTVkMyVGVd2n3hj 7fLICB44fEiKggrACBU9muuWLKze9TutSfZFeQk0= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Dan Carpenter , Hillf Danton , syzbot+0dc4444774d419e916c8@syzkaller.appspotmail.com, Emil Velikov , Daniel Vetter , Sean Paul , Chris Wilson , Eric Anholt , Sam Ravnborg , Rob Clark , Daniel Vetter , Ovidiu Panait Subject: [PATCH 4.19 57/88] drm/vgem: Close use-after-free race in vgem_gem_create Date: Tue, 10 May 2022 15:07:42 +0200 Message-Id: <20220510130735.399310423@linuxfoundation.org> X-Mailer: git-send-email 2.36.1 In-Reply-To: <20220510130733.735278074@linuxfoundation.org> References: <20220510130733.735278074@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: Daniel Vetter commit 4b848f20eda5974020f043ca14bacf7a7e634fc8 upstream. There's two references floating around here (for the object reference, not the handle_count reference, that's a different thing): - The temporary reference held by vgem_gem_create, acquired by creating the object and released by calling drm_gem_object_put_unlocked. - The reference held by the object handle, created by drm_gem_handle_create. This one generally outlives the function, except if a 2nd thread races with a GEM_CLOSE ioctl call. So usually everything is correct, except in that race case, where the access to gem_object->size could be looking at freed data already. Which again isn't a real problem (userspace shot its feet off already with the race, we could return garbage), but maybe someone can exploit this as an information leak. Cc: Dan Carpenter Cc: Hillf Danton Reported-by: syzbot+0dc4444774d419e916c8@syzkaller.appspotmail.com Cc: stable@vger.kernel.org Cc: Emil Velikov Cc: Daniel Vetter Cc: Sean Paul Cc: Chris Wilson Cc: Eric Anholt Cc: Sam Ravnborg Cc: Rob Clark Reviewed-by: Chris Wilson Signed-off-by: Daniel Vetter Link: https://patchwork.freedesktop.org/patch/msgid/20200202132133.1891846-1-daniel.vetter@ffwll.ch [OP: backport to 4.19: adjusted DRM_DEBUG() -> DRM_DEBUG_DRIVER()] Signed-off-by: Ovidiu Panait Signed-off-by: Greg Kroah-Hartman --- drivers/gpu/drm/vgem/vgem_drv.c | 9 ++++++--- 1 file changed, 6 insertions(+), 3 deletions(-) --- a/drivers/gpu/drm/vgem/vgem_drv.c +++ b/drivers/gpu/drm/vgem/vgem_drv.c @@ -189,9 +189,10 @@ static struct drm_gem_object *vgem_gem_c return ERR_CAST(obj); ret = drm_gem_handle_create(file, &obj->base, handle); - drm_gem_object_put_unlocked(&obj->base); - if (ret) + if (ret) { + drm_gem_object_put_unlocked(&obj->base); return ERR_PTR(ret); + } return &obj->base; } @@ -214,7 +215,9 @@ static int vgem_gem_dumb_create(struct d args->size = gem_object->size; args->pitch = pitch; - DRM_DEBUG_DRIVER("Created object of size %lld\n", size); + drm_gem_object_put_unlocked(gem_object); + + DRM_DEBUG_DRIVER("Created object of size %llu\n", args->size); return 0; }