From patchwork Mon May 16 19:36:39 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Patchwork-Submitter: Greg Kroah-Hartman X-Patchwork-Id: 573809 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 2212BC433EF for ; Mon, 16 May 2022 19:54:02 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1343521AbiEPTyA (ORCPT ); Mon, 16 May 2022 15:54:00 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:56674 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1347749AbiEPTwR (ORCPT ); Mon, 16 May 2022 15:52:17 -0400 Received: from ams.source.kernel.org (ams.source.kernel.org [145.40.68.75]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 95EAF427D5; Mon, 16 May 2022 12:47:54 -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 0FA89B81613; Mon, 16 May 2022 19:47:42 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 4A42BC385AA; Mon, 16 May 2022 19:47:40 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1652730460; bh=Uj3lyYJac3hTdmS1S+asSpqVLL6qsv9Cd4vdF79qDb0=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=GtKgbxAO+AUDHiYyoakvllKHXdC1wkFhdQ20YujpP4QEKtAICxs6I8IvRkGB72w7L XP6GX4A5u5se8ahhq57z1Hl8HbAKftnMoHwk09OcBDBGCE57a2PyOjG/EKf+RYBuUU mFbfZBJJaVD77pzmKSg7LnOZuykvKdaT7ByywecE= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, =?utf-8?q?Thi=C3=A9baud_Weksteen?= , Paul Moore , Luis Chamberlain Subject: [PATCH 5.10 39/66] firmware_loader: use kernel credentials when reading firmware Date: Mon, 16 May 2022 21:36:39 +0200 Message-Id: <20220516193620.544847305@linuxfoundation.org> X-Mailer: git-send-email 2.36.1 In-Reply-To: <20220516193619.400083785@linuxfoundation.org> References: <20220516193619.400083785@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org From: Thiébaud Weksteen commit 581dd69830341d299b0c097fc366097ab497d679 upstream. Device drivers may decide to not load firmware when probed to avoid slowing down the boot process should the firmware filesystem not be available yet. In this case, the firmware loading request may be done when a device file associated with the driver is first accessed. The credentials of the userspace process accessing the device file may be used to validate access to the firmware files requested by the driver. Ensure that the kernel assumes the responsibility of reading the firmware. This was observed on Android for a graphic driver loading their firmware when the device file (e.g. /dev/mali0) was first opened by userspace (i.e. surfaceflinger). The security context of surfaceflinger was used to validate the access to the firmware file (e.g. /vendor/firmware/mali.bin). Previously, Android configurations were not setting up the firmware_class.path command line argument and were relying on the userspace fallback mechanism. In this case, the security context of the userspace daemon (i.e. ueventd) was consistently used to read firmware files. More Android devices are now found to set firmware_class.path which gives the kernel the opportunity to read the firmware directly (via kernel_read_file_from_path_initns). In this scenario, the current process credentials were used, even if unrelated to the loading of the firmware file. Signed-off-by: Thiébaud Weksteen Cc: # 5.10 Reviewed-by: Paul Moore Acked-by: Luis Chamberlain Link: https://lore.kernel.org/r/20220502004952.3970800-1-tweek@google.com Signed-off-by: Greg Kroah-Hartman --- drivers/base/firmware_loader/main.c | 17 +++++++++++++++++ 1 file changed, 17 insertions(+) --- a/drivers/base/firmware_loader/main.c +++ b/drivers/base/firmware_loader/main.c @@ -793,6 +793,8 @@ _request_firmware(const struct firmware size_t offset, u32 opt_flags) { struct firmware *fw = NULL; + struct cred *kern_cred = NULL; + const struct cred *old_cred; bool nondirect = false; int ret; @@ -809,6 +811,18 @@ _request_firmware(const struct firmware if (ret <= 0) /* error or already assigned */ goto out; + /* + * We are about to try to access the firmware file. Because we may have been + * called by a driver when serving an unrelated request from userland, we use + * the kernel credentials to read the file. + */ + kern_cred = prepare_kernel_cred(NULL); + if (!kern_cred) { + ret = -ENOMEM; + goto out; + } + old_cred = override_creds(kern_cred); + ret = fw_get_filesystem_firmware(device, fw->priv, "", NULL); /* Only full reads can support decompression, platform, and sysfs. */ @@ -834,6 +848,9 @@ _request_firmware(const struct firmware } else ret = assign_fw(fw, device); + revert_creds(old_cred); + put_cred(kern_cred); + out: if (ret < 0) { fw_abort_batch_reqs(fw);