From patchwork Thu Jul 21 17:28:05 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Frederick Lawler X-Patchwork-Id: 12925642 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 2E2C6C43334 for ; Thu, 21 Jul 2022 17:28:31 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231545AbiGUR23 (ORCPT ); Thu, 21 Jul 2022 13:28:29 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:54398 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229547AbiGUR2V (ORCPT ); Thu, 21 Jul 2022 13:28:21 -0400 Received: from mail-oa1-x31.google.com (mail-oa1-x31.google.com [IPv6:2001:4860:4864:20::31]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 281918AB12 for ; Thu, 21 Jul 2022 10:28:17 -0700 (PDT) Received: by mail-oa1-x31.google.com with SMTP id 586e51a60fabf-10bd4812c29so3261525fac.11 for ; Thu, 21 Jul 2022 10:28:17 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=cloudflare.com; s=google; h=from:to:cc:subject:date:message-id:in-reply-to:references :mime-version:content-transfer-encoding; bh=oSkp5XL8evSozcL3p6dp5pf7REvcEIJL7/dJNXUU/iU=; b=RTsFkn4w9Q+1HCvSArxhpw/M593UnODTkZBs5Hm875j+xZWAZK2wghDB3V5snivDg4 tzHaqxbKYm6pxwHgiND9geYCossCSEx8bRK0ORYhiwb1saYA/q0uDPWsU3k9njgcxZlw ScwEL0YCfwv6neSRlCeBxuwSJu1QYy7+NV1lc= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:from:to:cc:subject:date:message-id:in-reply-to :references:mime-version:content-transfer-encoding; bh=oSkp5XL8evSozcL3p6dp5pf7REvcEIJL7/dJNXUU/iU=; b=tA699IrTOBrjrxWrnooBGdHxIpooQowgbx2u3rD9YgpuCCrC1qhCeavhUcq2XGICpt gLHfnFadX5wjFqtOJarbY5X5hn7QY86E6uGiJV52bx7U/KwJlIRvWlFXNXGhZaIvTYza a89bXJAufKqQTPeb1CCfoP+Gmrz/x0YZ6jOpjcpEcDSiBWb5xQuW0g3dMjvDSDDAr6AC Pkn8ImEtykMxQ7xC08Gzs8LBH4Zju22eOsUksZ6+b7PjTY5k5/u5S2NbhbLff/k1fD0v zLwuuv4tfOMZODdQbSXRY6TDRVEQ4fyb5bGW6p8IBveugZgMlq1HP+dqS6jTjUeR6K8l M4Hw== X-Gm-Message-State: AJIora+R0Xf13nqmjCL7V0IpBzP4HQObJnDuapH5XpXP4ILhy8o9dLj2 T8mDP3IF4XjN25JHTkcTZ+smxA== X-Google-Smtp-Source: AGRyM1vn8iYdneqMQSfU5E7rKtCDDTFXE6gJ/E+orOgcQYDydQBDRlFTXDgzTF2YYM6Rsw5HvyJSJg== X-Received: by 2002:a05:6870:c353:b0:101:e7e4:9388 with SMTP id e19-20020a056870c35300b00101e7e49388mr5620686oak.45.1658424496479; Thu, 21 Jul 2022 10:28:16 -0700 (PDT) Received: from localhost.localdomain ([184.4.90.121]) by smtp.gmail.com with ESMTPSA id du24-20020a0568703a1800b00101c83352c6sm1106207oab.34.2022.07.21.10.28.14 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 21 Jul 2022 10:28:16 -0700 (PDT) From: Frederick Lawler To: kpsingh@kernel.org, revest@chromium.org, jackmanb@chromium.org, ast@kernel.org, daniel@iogearbox.net, andrii@kernel.org, kafai@fb.com, songliubraving@fb.com, yhs@fb.com, john.fastabend@gmail.com, jmorris@namei.org, serge@hallyn.com, paul@paul-moore.com, stephen.smalley.work@gmail.com, eparis@parisplace.org, shuah@kernel.org, brauner@kernel.org, casey@schaufler-ca.com, ebiederm@xmission.com, bpf@vger.kernel.org, linux-security-module@vger.kernel.org, selinux@vger.kernel.org, linux-kselftest@vger.kernel.org Cc: linux-kernel@vger.kernel.org, netdev@vger.kernel.org, kernel-team@cloudflare.com, cgzones@googlemail.com, karl@bigbadwolfsecurity.com, Frederick Lawler Subject: [PATCH v3 1/4] security, lsm: Introduce security_create_user_ns() Date: Thu, 21 Jul 2022 12:28:05 -0500 Message-Id: <20220721172808.585539-2-fred@cloudflare.com> X-Mailer: git-send-email 2.30.2 In-Reply-To: <20220721172808.585539-1-fred@cloudflare.com> References: <20220721172808.585539-1-fred@cloudflare.com> MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: linux-kselftest@vger.kernel.org Preventing user namespace (privileged or otherwise) creation comes in a few of forms in order of granularity: 1. /proc/sys/user/max_user_namespaces sysctl 2. OS specific patch(es) 3. CONFIG_USER_NS To block a task based on its attributes, the LSM hook cred_prepare is a good candidate for use because it provides more granular control, and it is called before create_user_ns(): cred = prepare_creds() security_prepare_creds() call_int_hook(cred_prepare, ... if (cred) create_user_ns(cred) Since security_prepare_creds() is meant for LSMs to copy and prepare credentials, access control is an unintended use of the hook. Therefore introduce a new function security_create_user_ns() with an accompanying userns_create LSM hook. This hook takes the prepared creds for LSM authors to write policy against. On success, the new namespace is applied to credentials, otherwise an error is returned. Signed-off-by: Frederick Lawler Reviewed-by: Christian Brauner (Microsoft) --- Changes since v2: - Rename create_user_ns hook to userns_create Changes since v1: - Changed commit wording - Moved execution to be after id mapping check - Changed signature to only accept a const struct cred * --- include/linux/lsm_hook_defs.h | 1 + include/linux/lsm_hooks.h | 4 ++++ include/linux/security.h | 6 ++++++ kernel/user_namespace.c | 5 +++++ security/security.c | 5 +++++ 5 files changed, 21 insertions(+) diff --git a/include/linux/lsm_hook_defs.h b/include/linux/lsm_hook_defs.h index eafa1d2489fd..7ff93cb8ca8d 100644 --- a/include/linux/lsm_hook_defs.h +++ b/include/linux/lsm_hook_defs.h @@ -223,6 +223,7 @@ LSM_HOOK(int, -ENOSYS, task_prctl, int option, unsigned long arg2, unsigned long arg3, unsigned long arg4, unsigned long arg5) LSM_HOOK(void, LSM_RET_VOID, task_to_inode, struct task_struct *p, struct inode *inode) +LSM_HOOK(int, 0, userns_create, const struct cred *cred) LSM_HOOK(int, 0, ipc_permission, struct kern_ipc_perm *ipcp, short flag) LSM_HOOK(void, LSM_RET_VOID, ipc_getsecid, struct kern_ipc_perm *ipcp, u32 *secid) diff --git a/include/linux/lsm_hooks.h b/include/linux/lsm_hooks.h index 91c8146649f5..54fe534d0e01 100644 --- a/include/linux/lsm_hooks.h +++ b/include/linux/lsm_hooks.h @@ -799,6 +799,10 @@ * security attributes, e.g. for /proc/pid inodes. * @p contains the task_struct for the task. * @inode contains the inode structure for the inode. + * @userns_create: + * Check permission prior to creating a new user namespace. + * @cred points to prepared creds. + * Return 0 if successful, otherwise < 0 error code. * * Security hooks for Netlink messaging. * diff --git a/include/linux/security.h b/include/linux/security.h index 7fc4e9f49f54..a195bf33246a 100644 --- a/include/linux/security.h +++ b/include/linux/security.h @@ -435,6 +435,7 @@ int security_task_kill(struct task_struct *p, struct kernel_siginfo *info, int security_task_prctl(int option, unsigned long arg2, unsigned long arg3, unsigned long arg4, unsigned long arg5); void security_task_to_inode(struct task_struct *p, struct inode *inode); +int security_create_user_ns(const struct cred *cred); int security_ipc_permission(struct kern_ipc_perm *ipcp, short flag); void security_ipc_getsecid(struct kern_ipc_perm *ipcp, u32 *secid); int security_msg_msg_alloc(struct msg_msg *msg); @@ -1185,6 +1186,11 @@ static inline int security_task_prctl(int option, unsigned long arg2, static inline void security_task_to_inode(struct task_struct *p, struct inode *inode) { } +static inline int security_create_user_ns(const struct cred *cred) +{ + return 0; +} + static inline int security_ipc_permission(struct kern_ipc_perm *ipcp, short flag) { diff --git a/kernel/user_namespace.c b/kernel/user_namespace.c index 5481ba44a8d6..3f464bbda0e9 100644 --- a/kernel/user_namespace.c +++ b/kernel/user_namespace.c @@ -9,6 +9,7 @@ #include #include #include +#include #include #include #include @@ -113,6 +114,10 @@ int create_user_ns(struct cred *new) !kgid_has_mapping(parent_ns, group)) goto fail_dec; + ret = security_create_user_ns(new); + if (ret < 0) + goto fail_dec; + ret = -ENOMEM; ns = kmem_cache_zalloc(user_ns_cachep, GFP_KERNEL); if (!ns) diff --git a/security/security.c b/security/security.c index 188b8f782220..ec9b4696e86c 100644 --- a/security/security.c +++ b/security/security.c @@ -1903,6 +1903,11 @@ void security_task_to_inode(struct task_struct *p, struct inode *inode) call_void_hook(task_to_inode, p, inode); } +int security_create_user_ns(const struct cred *cred) +{ + return call_int_hook(userns_create, 0, cred); +} + int security_ipc_permission(struct kern_ipc_perm *ipcp, short flag) { return call_int_hook(ipc_permission, 0, ipcp, flag);