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 DE899C83F2C for ; Mon, 4 Sep 2023 08:01:48 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1346896AbjIDIBu (ORCPT ); Mon, 4 Sep 2023 04:01:50 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:56544 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230106AbjIDIBt (ORCPT ); Mon, 4 Sep 2023 04:01:49 -0400 Received: from madras.collabora.co.uk (madras.collabora.co.uk [46.235.227.172]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 8C44CB8 for ; Mon, 4 Sep 2023 01:01:45 -0700 (PDT) Received: from localhost (unknown [IPv6:2a01:e0a:2c:6930:5cf4:84a1:2763:fe0d]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits) server-digest SHA256) (No client certificate requested) (Authenticated sender: bbrezillon) by madras.collabora.co.uk (Postfix) with ESMTPSA id 4B1416607239; Mon, 4 Sep 2023 09:01:43 +0100 (BST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=collabora.com; s=mail; t=1693814504; bh=e788C098QfddEO6hbR3WKnWmYUt07fZ7PCwwrd1VwFI=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=EOqkLVtSqUOCgc8GPlpz2M4k/6FdauJ5pvx55T+jY+dq7Ot4IHIhnADdb4GXozeiH ndpbRAwKSPxos43fFKQUg+3BmY3ucNNfGNw5x19QqCbila88LyIU7j0wWq9q77/FMv qK9khOPykQCMpCGnjoyUmaXMdzBeSngN0ABciFV9Rg1LhIp3viYPbZFqZNG4xFtsED vgJv5Hp4u5XnY0JLuJvX2wcvp0dHadNCK5i7up4G1pyigyoGz9/b1qBSazHGNDpUiX KfgUeIuIS7OGuAMqg2kTT+ITINSyd08RoPgVYrCUdmEUPuFoe/gYlqqz+odKvv0Now 8Of5RikIDdL1Q== Date: Mon, 4 Sep 2023 10:01:40 +0200 From: Boris Brezillon To: Dmitry Osipenko Cc: David Airlie , Gerd Hoffmann , Gurchetan Singh , Chia-I Wu , Daniel Vetter , Maarten Lankhorst , Maxime Ripard , Thomas Zimmermann , Christian =?UTF-8?B?S8O2bmln?= , Qiang Yu , Steven Price , Emma Anholt , Melissa Wen , Will Deacon , Peter Zijlstra , Boqun Feng , Mark Rutland , dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org, kernel@collabora.com, virtualization@lists.linux-foundation.org, intel-gfx@lists.freedesktop.org Subject: Re: [PATCH v15 01/23] drm/shmem-helper: Fix UAF in error path when freeing SGT of imported GEM Message-ID: <20230904100140.6f4e3012@collabora.com> In-Reply-To: References: <20230827175449.1766701-1-dmitry.osipenko@collabora.com> <20230827175449.1766701-2-dmitry.osipenko@collabora.com> <20230828131647.18888896@collabora.com> Organization: Collabora X-Mailer: Claws Mail 4.1.1 (GTK 3.24.38; x86_64-redhat-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sat, 2 Sep 2023 21:15:39 +0300 Dmitry Osipenko wrote: > On 8/28/23 14:16, Boris Brezillon wrote: > > On Sun, 27 Aug 2023 20:54:27 +0300 > > Dmitry Osipenko wrote: > > > >> Freeing drm-shmem GEM right after creating it using > >> drm_gem_shmem_prime_import_sg_table() frees SGT of the imported dma-buf > >> and then dma-buf frees this SGT second time. > >> > >> The v3d_prime_import_sg_table() is example of a error code path where > >> dma-buf's SGT is freed by drm-shmem and then it's freed second time by > >> dma_buf_unmap_attachment() in drm_gem_prime_import_dev(). > >> > >> Add drm-shmem GEM flag telling that this is imported SGT shall not be > >> treated as own SGT, fixing the use-after-free bug. > >> > >> Cc: stable@vger.kernel.org > >> Fixes: 2194a63a818d ("drm: Add library for shmem backed GEM objects") > >> Signed-off-by: Dmitry Osipenko > >> --- > >> drivers/gpu/drm/drm_gem_shmem_helper.c | 3 ++- > >> include/drm/drm_gem_shmem_helper.h | 7 +++++++ > >> 2 files changed, 9 insertions(+), 1 deletion(-) > >> > >> diff --git a/drivers/gpu/drm/drm_gem_shmem_helper.c b/drivers/gpu/drm/drm_gem_shmem_helper.c > >> index a783d2245599..78d9cf2355a5 100644 > >> --- a/drivers/gpu/drm/drm_gem_shmem_helper.c > >> +++ b/drivers/gpu/drm/drm_gem_shmem_helper.c > >> @@ -141,7 +141,7 @@ void drm_gem_shmem_free(struct drm_gem_shmem_object *shmem) > >> > >> if (obj->import_attach) { > >> drm_prime_gem_destroy(obj, shmem->sgt); > >> - } else { > >> + } else if (!shmem->imported_sgt) { > >> dma_resv_lock(shmem->base.resv, NULL); > >> > >> drm_WARN_ON(obj->dev, shmem->vmap_use_count); > >> @@ -758,6 +758,7 @@ drm_gem_shmem_prime_import_sg_table(struct drm_device *dev, > >> return ERR_CAST(shmem); > >> > >> shmem->sgt = sgt; > >> + shmem->imported_sgt = true; > > > > > > I feel like adding more fields that can be used to do the is_imported() > > check is going to be even more confusing. Can we instead have > > > > /* drm_gem_shmem_prime_import_sg_table() can be called from a > > * driver specific ->import_sg_table() implementations that > > * have extra failable initialization steps. Assign > > * drm_gem_object::import_attach here (even though it's > > * assigned in drm_gem_prime_import_dev()), so we don't end up > > * with driver error paths calling drm_gem_shmem_free() with an > > * imported sg_table assigned to drm_gem_shmem_object::sgt and > > * drm_gem_object::import_attach left uninitialized. > > */ > > shmem->base.import_attach = attach; > > > > here? > > AFAICT, this is not going to work because obj->import_attach will be > released by drm_prime core by the time drm_gem_shmem_free() is invoked > and drm_gem_shmem_free() uses obj->import_attach as well. How can this happen? If something wrong happens in the driver-specific ->gem_prime_import_sg_table() implementation, drm_gem_shmem_free() will be called before ->gem_prime_import_sg_table() returns, and the attachment will only be released after that [1]. > I'll keep this > patch around unless there will be other suggestions. To me the flag is > good enough, I'll add a clarifying comment to the code in v16. I really think this is a bad idea, for the same reasons I gave in my reply to patch 2 (adding fields that need to be maintained when the state can be inferred from other fields is error prone). [1]https://elixir.bootlin.com/linux/latest/source/drivers/gpu/drm/drm_prime.c#L958