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); From patchwork Thu Jul 21 17:28:06 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Frederick Lawler X-Patchwork-Id: 12925643 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 1BBBCC43334 for ; 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Thu, 21 Jul 2022 10:28:17 -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 2/4] bpf-lsm: Make bpf_lsm_userns_create() sleepable Date: Thu, 21 Jul 2022 12:28:06 -0500 Message-Id: <20220721172808.585539-3-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 Users may want to audit calls to security_create_user_ns() and access user space memory. Also create_user_ns() runs without pagefault_disabled(). Therefore, make bpf_lsm_userns_create() sleepable for mandatory access control policies. Signed-off-by: Frederick Lawler Acked-by: Christian Brauner (Microsoft) --- Changes since v2: - Rename create_user_ns hook to userns_create Changes since v1: - None --- kernel/bpf/bpf_lsm.c | 1 + 1 file changed, 1 insertion(+) diff --git a/kernel/bpf/bpf_lsm.c b/kernel/bpf/bpf_lsm.c index c1351df9f7ee..4593437809cc 100644 --- a/kernel/bpf/bpf_lsm.c +++ b/kernel/bpf/bpf_lsm.c @@ -250,6 +250,7 @@ BTF_ID(func, bpf_lsm_task_getsecid_obj) BTF_ID(func, bpf_lsm_task_prctl) BTF_ID(func, bpf_lsm_task_setscheduler) BTF_ID(func, bpf_lsm_task_to_inode) +BTF_ID(func, bpf_lsm_userns_create) BTF_SET_END(sleepable_lsm_hooks) bool bpf_lsm_is_sleepable_hook(u32 btf_id) From patchwork Thu Jul 21 17:28:07 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Frederick Lawler X-Patchwork-Id: 12925644 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 241A1C433EF for ; Thu, 21 Jul 2022 17:28:45 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231940AbiGUR2o (ORCPT ); Thu, 21 Jul 2022 13:28:44 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:54812 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229975AbiGUR2c (ORCPT ); Thu, 21 Jul 2022 13:28:32 -0400 Received: from mail-oa1-x36.google.com (mail-oa1-x36.google.com [IPv6:2001:4860:4864:20::36]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 6E5078B481 for ; Thu, 21 Jul 2022 10:28:20 -0700 (PDT) Received: by mail-oa1-x36.google.com with SMTP id 586e51a60fabf-10d6ddda695so3369815fac.0 for ; Thu, 21 Jul 2022 10:28:20 -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=DDUrciOiWPS12pMfDzHR0QWKvrVADVqrg238UND6/6k=; b=PVCt8IkXNmzVX/uc6ya8bkYX0e9fl24bayGiIk1x14nKbBagTPU3Ptt2JJXdPMlO85 12cNDzBYSZCw8OtBNQqKKCEU4r2rcBnVENIXy4RF9NnywMQX5OvKHOols3UKsNfMscdm CaxupZgwvLbU5eQrXzoQ+7vBNCWXwhKr3KSVU= 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=DDUrciOiWPS12pMfDzHR0QWKvrVADVqrg238UND6/6k=; b=ohowg0ruasvkETNMYWUqSOGPnxYyf9M9bmH4y7DqKCZr/k/zqqs4CcUPd4rCZc3X5i PMTkW3f5jELATSJDZ8syCRZk+tAU47Jni9eON8/Qj4Wy0TAZqK+Oyzpi4mZ1UeUpwsi/ vyGGjcyYDegQa1Z+JnyWi4LmiFNN8WuaXSs/CIWMbK/VLNLhIzXgZVY2eoDSUVwquDG1 9apowL2PAZf92wE9qNiMoJk7JIPZTXzjfZIvywxx0aN0H7TVGT0AMXNUmngI3EO36goG DikXBongJ/iS8dAnA9CQGSNTs4nRxp9tlPxfnrgFaGhfbVAGYdh8DtT9y4ds3t5N6ib2 8ctA== X-Gm-Message-State: AJIora+XZdrjoJFfhFldVWNQCiYf9jYMP6MSetsUWNxUHaF8+72Wg2Gw jlVHLNYgrJ/eXU+cn06qe4wWVg== X-Google-Smtp-Source: AGRyM1vxESDsPtIrONW7Ys2w4N7FenuuR8XS0fA2zPxLvr9jts48tPFbchJ6aya0gahguJLwVoCt9Q== X-Received: by 2002:a05:6870:c889:b0:10c:7f1:c6b8 with SMTP id er9-20020a056870c88900b0010c07f1c6b8mr5644044oab.280.1658424500003; Thu, 21 Jul 2022 10:28:20 -0700 (PDT) Received: from localhost.localdomain ([184.4.90.121]) by smtp.gmail.com with ESMTPSA id du24-20020a0568703a1800b00101c83352c6sm1106207oab.34.2022.07.21.10.28.18 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 21 Jul 2022 10:28:19 -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 3/4] selftests/bpf: Add tests verifying bpf lsm userns_create hook Date: Thu, 21 Jul 2022 12:28:07 -0500 Message-Id: <20220721172808.585539-4-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 The LSM hook userns_create was introduced to provide LSM's an opportunity to block or allow unprivileged user namespace creation. This test serves two purposes: it provides a test eBPF implementation, and tests the hook successfully blocks or allows user namespace creation. This tests 4 cases: 1. Unattached bpf program does not block unpriv user namespace creation. 2. Attached bpf program allows user namespace creation given CAP_SYS_ADMIN privileges. 3. Attached bpf program denies user namespace creation for a user without CAP_SYS_ADMIN. 4. The sleepable implementation loads Signed-off-by: Frederick Lawler Acked-by: Christian Brauner (Microsoft) --- The generic deny_namespace file name is used for future namespace expansion. I didn't want to limit these files to just the create_user_ns hook. Changes since v2: - Rename create_user_ns hook to userns_create Changes since v1: - Introduce this patch --- .../selftests/bpf/prog_tests/deny_namespace.c | 88 +++++++++++++++++++ .../selftests/bpf/progs/test_deny_namespace.c | 39 ++++++++ 2 files changed, 127 insertions(+) create mode 100644 tools/testing/selftests/bpf/prog_tests/deny_namespace.c create mode 100644 tools/testing/selftests/bpf/progs/test_deny_namespace.c diff --git a/tools/testing/selftests/bpf/prog_tests/deny_namespace.c b/tools/testing/selftests/bpf/prog_tests/deny_namespace.c new file mode 100644 index 000000000000..9e4714295008 --- /dev/null +++ b/tools/testing/selftests/bpf/prog_tests/deny_namespace.c @@ -0,0 +1,88 @@ +// SPDX-License-Identifier: GPL-2.0 +#define _GNU_SOURCE +#include +#include "test_deny_namespace.skel.h" +#include +#include "cap_helpers.h" + +#define STACK_SIZE (1024 * 1024) +static char child_stack[STACK_SIZE]; + +int clone_callback(void *arg) +{ + return 0; +} + +static int create_new_user_ns(void) +{ + int status; + pid_t cpid; + + cpid = clone(clone_callback, child_stack + STACK_SIZE, + CLONE_NEWUSER | SIGCHLD, NULL); + + if (cpid == -1) + return errno; + + if (cpid == 0) + return 0; + + waitpid(cpid, &status, 0); + if (WIFEXITED(status)) + return WEXITSTATUS(status); + + return -1; +} + +static void test_userns_create_bpf(void) +{ + __u32 cap_mask = 1ULL << CAP_SYS_ADMIN; + __u64 old_caps = 0; + + ASSERT_OK(create_new_user_ns(), "priv new user ns"); + + cap_disable_effective(cap_mask, &old_caps); + + ASSERT_EQ(create_new_user_ns(), EPERM, "unpriv new user ns"); + + if (cap_mask & old_caps) + cap_enable_effective(cap_mask, NULL); +} + +static void test_unpriv_userns_create_no_bpf(void) +{ + __u32 cap_mask = 1ULL << CAP_SYS_ADMIN; + __u64 old_caps = 0; + + cap_disable_effective(cap_mask, &old_caps); + + ASSERT_OK(create_new_user_ns(), "no-bpf unpriv new user ns"); + + if (cap_mask & old_caps) + cap_enable_effective(cap_mask, NULL); +} + +void test_deny_namespace(void) +{ + struct test_deny_namespace *skel = NULL; + int err; + + if (test__start_subtest("unpriv_userns_create_no_bpf")) + test_unpriv_userns_create_no_bpf(); + + skel = test_deny_namespace__open_and_load(); + if (!ASSERT_OK_PTR(skel, "skel load")) + goto close_prog; + + err = test_deny_namespace__attach(skel); + if (!ASSERT_OK(err, "attach")) + goto close_prog; + + if (test__start_subtest("userns_create_bpf")) + test_userns_create_bpf(); + + test_deny_namespace__detach(skel); + +close_prog: + test_deny_namespace__destroy(skel); +} diff --git a/tools/testing/selftests/bpf/progs/test_deny_namespace.c b/tools/testing/selftests/bpf/progs/test_deny_namespace.c new file mode 100644 index 000000000000..9ec9dabc8372 --- /dev/null +++ b/tools/testing/selftests/bpf/progs/test_deny_namespace.c @@ -0,0 +1,39 @@ +// SPDX-License-Identifier: GPL-2.0 +#include +#include +#include +#include +#include + +struct kernel_cap_struct { + __u32 cap[_LINUX_CAPABILITY_U32S_3]; +} __attribute__((preserve_access_index)); + +struct cred { + struct kernel_cap_struct cap_effective; +} __attribute__((preserve_access_index)); + +char _license[] SEC("license") = "GPL"; + +SEC("lsm/userns_create") +int BPF_PROG(test_userns_create, const struct cred *cred, int ret) +{ + struct kernel_cap_struct caps = cred->cap_effective; + int cap_index = CAP_TO_INDEX(CAP_SYS_ADMIN); + __u32 cap_mask = CAP_TO_MASK(CAP_SYS_ADMIN); + + if (ret) + return 0; + + ret = -EPERM; + if (caps.cap[cap_index] & cap_mask) + return 0; + + return -EPERM; +} + +SEC("lsm.s/userns_create") +int BPF_PROG(test_sleepable_userns_create, const struct cred *cred, int ret) +{ + return 0; +} From patchwork Thu Jul 21 17:28:08 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Frederick Lawler X-Patchwork-Id: 12925645 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 EEE17C43334 for ; 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Thu, 21 Jul 2022 10:28:21 -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 4/4] selinux: Implement userns_create hook Date: Thu, 21 Jul 2022 12:28:08 -0500 Message-Id: <20220721172808.585539-5-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 Unprivileged user namespace creation is an intended feature to enable sandboxing, however this feature is often used to as an initial step to perform a privilege escalation attack. This patch implements a new user_namespace { create } access control permission to restrict which domains allow or deny user namespace creation. This is necessary for system administrators to quickly protect their systems while waiting for vulnerability patches to be applied. This permission can be used in the following way: allow domA_t domA_t : user_namespace { create }; Signed-off-by: Frederick Lawler --- Changes since v2: - Rename create_user_ns hook to userns_create - Use user_namespace as an object opposed to a generic namespace object - s/domB_t/domA_t in commit message Changes since v1: - Introduce this patch --- security/selinux/hooks.c | 9 +++++++++ security/selinux/include/classmap.h | 2 ++ 2 files changed, 11 insertions(+) diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c index beceb89f68d9..afc9da0249e7 100644 --- a/security/selinux/hooks.c +++ b/security/selinux/hooks.c @@ -4227,6 +4227,14 @@ static void selinux_task_to_inode(struct task_struct *p, spin_unlock(&isec->lock); } +static int selinux_userns_create(const struct cred *cred) +{ + u32 sid = current_sid(); + + return avc_has_perm(&selinux_state, sid, sid, SECCLASS_USER_NAMESPACE, + USER_NAMESPACE__CREATE, NULL); +} + /* Returns error only if unable to parse addresses */ static int selinux_parse_skb_ipv4(struct sk_buff *skb, struct common_audit_data *ad, u8 *proto) @@ -7117,6 +7125,7 @@ static struct security_hook_list selinux_hooks[] __lsm_ro_after_init = { LSM_HOOK_INIT(task_movememory, selinux_task_movememory), LSM_HOOK_INIT(task_kill, selinux_task_kill), LSM_HOOK_INIT(task_to_inode, selinux_task_to_inode), + LSM_HOOK_INIT(userns_create, selinux_userns_create), LSM_HOOK_INIT(ipc_permission, selinux_ipc_permission), LSM_HOOK_INIT(ipc_getsecid, selinux_ipc_getsecid), diff --git a/security/selinux/include/classmap.h b/security/selinux/include/classmap.h index ff757ae5f253..0bff55bb9cde 100644 --- a/security/selinux/include/classmap.h +++ b/security/selinux/include/classmap.h @@ -254,6 +254,8 @@ const struct security_class_mapping secclass_map[] = { { COMMON_FILE_PERMS, NULL } }, { "io_uring", { "override_creds", "sqpoll", NULL } }, + { "user_namespace", + { "create", NULL } }, { NULL } };