From patchwork Thu Apr 9 03:39:07 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: "tianjia.zhang" X-Patchwork-Id: 11481187 Return-Path: Received: from mail.kernel.org (pdx-korg-mail-1.web.codeaurora.org [172.30.200.123]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id D58781871 for ; Thu, 9 Apr 2020 03:39:26 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id BE6B4206F5 for ; Thu, 9 Apr 2020 03:39:26 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726670AbgDIDjN (ORCPT ); Wed, 8 Apr 2020 23:39:13 -0400 Received: from out30-57.freemail.mail.aliyun.com ([115.124.30.57]:59673 "EHLO out30-57.freemail.mail.aliyun.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726552AbgDIDjN (ORCPT ); Wed, 8 Apr 2020 23:39:13 -0400 X-Alimail-AntiSpam: AC=PASS;BC=-1|-1;BR=01201311R171e4;CH=green;DM=||false|;DS=||;FP=0|-1|-1|-1|0|-1|-1|-1;HT=e01e01419;MF=tianjia.zhang@linux.alibaba.com;NM=1;PH=DS;RN=8;SR=0;TI=SMTPD_---0Tv0dk.x_1586403549; Received: from localhost(mailfrom:tianjia.zhang@linux.alibaba.com fp:SMTPD_---0Tv0dk.x_1586403549) by smtp.aliyun-inc.com(127.0.0.1); Thu, 09 Apr 2020 11:39:10 +0800 From: Tianjia Zhang To: zohar@linux.ibm.com, dmitry.kasatkin@gmail.com, jmorris@namei.org, serge@hallyn.com, zhangliguang@linux.alibaba.com Cc: linux-integrity@vger.kernel.org, linux-security-module@vger.kernel.org, linux-kernel@vger.kernel.org Subject: [PATCH 2/2] ima: support to tune appraise mode in runtime Date: Thu, 9 Apr 2020 11:39:07 +0800 Message-Id: <20200409033907.102833-3-tianjia.zhang@linux.alibaba.com> X-Mailer: git-send-email 2.17.1 In-Reply-To: <20200409033907.102833-1-tianjia.zhang@linux.alibaba.com> References: <20200409033907.102833-1-tianjia.zhang@linux.alibaba.com> Sender: owner-linux-security-module@vger.kernel.org Precedence: bulk List-ID: In order to tune appraise mode in runtime, writing a PKCS#7 signature corresponding the signed content is required. The content should be off, enforce, log or fix. Given a simple way to archive this: $ echo -n off > mode $ openssl smime -sign -nocerts -noattr -binary \ -in mode -inkey \ -signer -outform der -out mode.p7s $ sudo cat mode.p7s \ > /sys/kernel/security/ima/appraise_mode Note that the signing key must be a trust key located in system trusted keyring. So even the root privilege cannot simply disable the enforcement. Signed-off-by: luanshi Signed-off-by: Tianjia Zhang Reported-by: kbuild test robot --- security/integrity/ima/ima_fs.c | 102 ++++++++++++++++++++++++++++++++ 1 file changed, 102 insertions(+) diff --git a/security/integrity/ima/ima_fs.c b/security/integrity/ima/ima_fs.c index 65384f6ac0d9..c21ca145de0f 100644 --- a/security/integrity/ima/ima_fs.c +++ b/security/integrity/ima/ima_fs.c @@ -20,11 +20,15 @@ #include #include #include +#include #include "ima.h" static DEFINE_MUTEX(ima_write_mutex); +/* maximum length of token allowed for signed appraise mode */ +#define APPRAISE_MAX_TOKEN_SIZE (512 * 1024) + bool ima_canonical_fmt; static int __init default_canonical_fmt_setup(char *str) { @@ -466,8 +470,106 @@ static ssize_t ima_appraise_mode_read(struct file *filp, return simple_read_from_buffer(buf, count, ppos, mode, strlen(mode)); } +static int check_signature_info(char *buf, size_t count) +{ + u8 *p; + + /* + * In order to tune the appraise mode, a PKCS#7 signature is + * supplied. + * + * Assuming ASN.1 encoding supplied, the minimal length would be + * 4-byte header plus at least 256-byte payload. + */ + if (count < 260) + return -EINVAL; + + p = (u8 *)buf; + + /* The primitive type must be a sequence */ + if (p[0] != 0x30 || p[1] != 0x82) + return -EINVAL; + + /* Match up the length of the supplied buffer */ + if (be16_to_cpup((__be16 *)(p + 2)) != count - 4) + return -EINVAL; + + return 0; +} + +/* Verify the supplied PKCS#7 signature. The signed content may be off, + * enforce, log, fix. + */ +static int repopulate_ima_appraise_mode(void *pkcs7, size_t pkcs7_len) +{ + static char *appraise_mode_strings[] = { "off", "enforce", "fix", "log" }; + static int appraise_modes[] = { + 0, + IMA_APPRAISE_ENFORCE, + IMA_APPRAISE_FIX, + IMA_APPRAISE_LOG, + }; + int index, ret = -1; + const char *s; + int size = ARRAY_SIZE(appraise_mode_strings); + + for (index = 0; index < size; index++) { + s = appraise_mode_strings[index]; + ret = verify_pkcs7_signature(s, strlen(s), pkcs7, pkcs7_len, + NULL, VERIFYING_UNSPECIFIED_SIGNATURE, + NULL, NULL); + if (!ret) + break; + } + + if (index == size) + goto out; + + ima_appraise = appraise_modes[index]; + +out: + return ret; +} + +static ssize_t ima_appraise_mode_write(struct file *filp, + const char __user *ubuf, + size_t count, loff_t *ppos) +{ + char *buf; + ssize_t ret; + + if (*ppos > 1) + return -EFBIG; + + if (count > APPRAISE_MAX_TOKEN_SIZE) + return -EFBIG; + + buf = kmalloc(count, GFP_KERNEL); + if (!buf) + return -ENOMEM; + + ret = simple_write_to_buffer(buf, count, ppos, ubuf, count); + if (ret <= 0) + goto out; + + ret = check_signature_info(buf, count); + if (ret) + goto out; + + ret = repopulate_ima_appraise_mode(buf, count); + if (ret) + goto out; + + ret = count; + +out: + kfree(buf); + return ret; +} + static const struct file_operations ima_appraise_mode_ops = { .read = ima_appraise_mode_read, + .write = ima_appraise_mode_write, .llseek = generic_file_llseek, };