From patchwork Thu Apr 28 06:17:07 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Patchwork-Submitter: =?utf-8?q?Thi=C3=A9baud_Weksteen?= X-Patchwork-Id: 12830008 X-Patchwork-Delegate: paul@paul-moore.com 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 83A6EC433F5 for ; Thu, 28 Apr 2022 06:17:21 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S243442AbiD1GUd (ORCPT ); Thu, 28 Apr 2022 02:20:33 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:48030 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S236458AbiD1GUc (ORCPT ); Thu, 28 Apr 2022 02:20:32 -0400 Received: from mail-yb1-xb49.google.com (mail-yb1-xb49.google.com [IPv6:2607:f8b0:4864:20::b49]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 471B14ECC0 for ; Wed, 27 Apr 2022 23:17:19 -0700 (PDT) Received: by mail-yb1-xb49.google.com with SMTP id b12-20020a056902030c00b0061d720e274aso3680102ybs.20 for ; Wed, 27 Apr 2022 23:17:19 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20210112; h=date:message-id:mime-version:subject:from:to:cc :content-transfer-encoding; bh=u7wndHCcjBCq9MjMJkcDUIkWDGiU0w6bmfVGxnonv/M=; b=CU8+6WTyf1pgwQElEqOndsoRs3YaZpcUu6opi0AGd0maXtTGR66G7zc0icaWW+rvmI fNakozFmiEMeGyRPID/2ka15r4ZHFybMklZkkHG4zdTdW5QlEu9dHt4h0N5hWI0DLOA5 0wMkkmUpd8+K/ukZh5NY1svWbqmv8GvukIeuN6F/wOrc8NwfFMRUZZzANhQCk8bBQ+XP ByDw5XH4oOMoc91SwKVfBjZwuefrCyfzusxwI1Fhdm3xFHDbM/J6nwyDWtUwqUeBlKn1 R7DKon5BmObE9FeTpmkMGVfT9azOthpaUEb4/ZFCmnC/Ek5949LbpcLB9jzoqtzndJgt +IwQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:date:message-id:mime-version:subject:from:to:cc :content-transfer-encoding; bh=u7wndHCcjBCq9MjMJkcDUIkWDGiU0w6bmfVGxnonv/M=; b=U1Djesn52rYk5VN2QLWWCso+0aqErFyomVAlNzeUW4Zv/GvLy6PWnyoPpU7Ekk8Xlr 1H4XfeNgi9CEFJbElJ0A2RGbkvwntb5mdhPMYE4orAE5w9faTZk+1ScdG7ySqdmk1TR7 1NdyMWKpVcZ6EVEJBwkuiBuPuU6OYpyhop5ZMaOB3vOr1aFRWGAHJ6qMYuqeCO9ef3YL H5I6q8bmMKCFUlX6nUACY0kZKyfZugi+N2ZZTZMDTEvUqwHGxfYodl461PidNp406YXv Wl7fEJWFoJQ0uZ713y8+aICqYpo2lR5brFxafVSRVgIdWG2W0AD7JGUBW5TKMj2R1l08 eFdA== X-Gm-Message-State: AOAM530AeStL4n+JaTqLej6et15xc3wcv2JuAjKkrvchYlzaBWYZeXMG Fd2go1Mnzep+px1aPoLcpg7DsYklbg== X-Google-Smtp-Source: ABdhPJyFLVRpkOEbdtAoedpI4qeWJmLVRCV37Z9hNxVqgKTlw13xrBWkN+DFyXvA81TiAVYfpAcbjp+Bnw== X-Received: from tweek-sin.c.googlers.com ([fda3:e722:ac3:cc00:4f:4b78:c0a8:2bfd]) (user=tweek job=sendgmr) by 2002:a25:d55:0:b0:648:7008:61e0 with SMTP id 82-20020a250d55000000b00648700861e0mr16601052ybn.282.1651126638534; Wed, 27 Apr 2022 23:17:18 -0700 (PDT) Date: Thu, 28 Apr 2022 16:17:07 +1000 Message-Id: <20220428061707.768468-1-tweek@google.com> Mime-Version: 1.0 X-Mailer: git-send-email 2.36.0.464.gb9c8b46e94-goog Subject: [PATCH v3] firmware_loader: use kernel credentials when reading firmware From: " =?utf-8?q?Thi=C3=A9baud_Weksteen?= " To: Luis Chamberlain , Greg Kroah-Hartman , Qian Cai Cc: Jeffrey Vander Stoep , Saravana Kannan , Alistair Delva , Adam Shih , selinux@vger.kernel.org, linux-kernel@vger.kernel.org, " =?utf-8?q?Thi=C3=A9baud_Weksteen?= " Precedence: bulk List-ID: X-Mailing-List: selinux@vger.kernel.org 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 --- v3: - Add call to put_cred to avoid a memory leak. Confirmed that no new memory leak occurs on a Pixel 4a. - Update commit log. v2: Add comment drivers/base/firmware_loader/main.c | 17 +++++++++++++++++ 1 file changed, 17 insertions(+) diff --git a/drivers/base/firmware_loader/main.c b/drivers/base/firmware_loader/main.c index 94d1789a233e..406a907a4cae 100644 --- a/drivers/base/firmware_loader/main.c +++ b/drivers/base/firmware_loader/main.c @@ -735,6 +735,8 @@ _request_firmware(const struct firmware **firmware_p, const char *name, 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; @@ -751,6 +753,18 @@ _request_firmware(const struct firmware **firmware_p, const char *name, 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. */ @@ -776,6 +790,9 @@ _request_firmware(const struct firmware **firmware_p, const char *name, } else ret = assign_fw(fw, device); + revert_creds(old_cred); + put_cred(kern_cred); + out: if (ret < 0) { fw_abort_batch_reqs(fw);