From patchwork Sun Jun 9 10:43:37 2024 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Jonathan Calmels X-Patchwork-Id: 13691210 X-Patchwork-Delegate: bpf@iogearbox.net Received: from flow3-smtp.messagingengine.com (flow3-smtp.messagingengine.com [103.168.172.138]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id A86EA2C181; Sun, 9 Jun 2024 10:40:56 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=103.168.172.138 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1717929658; cv=none; b=B88DVSSn6NFfVZKO+yOqq4igTnY/LQeok3eZWGnqrXEjX9BZsSsiYKe3sjgfsMuYu9JsFxJdddGnwp8FdxG+5Wzm+/6veE6fXsVLCFourju/b6ccc8hkp8Qr+zp56jh7eSKha8gPaETmqC2EllrJkc9yS2BYTtABuCV8TW1mSDs= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1717929658; c=relaxed/simple; bh=Te9b2tTgFLIjn+G+t41oNEnaKLeIvcknA3SYrFEQ1WA=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=UaAlVMZHGXpCRt6hmqsJ26uAjVL1cSedgRv6Eqxhegn0e+PHigmudChHUsaXynCzqdVzb+Og4a8SAy/iQJI1uhHYgugRww8LrwjRerzSOJfQXN0ub8hmSx5Zh4xXt+7J1nADeYx9ukx5+GpMJEG/Tamu8VAD0sp0C1654ep2Kcw= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=3xx0.net; spf=pass smtp.mailfrom=3xx0.net; dkim=pass (2048-bit key) header.d=3xx0.net header.i=@3xx0.net header.b=UqNy3PyQ; dkim=pass (2048-bit key) header.d=messagingengine.com header.i=@messagingengine.com header.b=mGpmevGf; arc=none smtp.client-ip=103.168.172.138 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=3xx0.net Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=3xx0.net Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=3xx0.net header.i=@3xx0.net header.b="UqNy3PyQ"; dkim=pass (2048-bit key) header.d=messagingengine.com header.i=@messagingengine.com header.b="mGpmevGf" Received: from compute5.internal (compute5.nyi.internal [10.202.2.45]) by mailflow.nyi.internal (Postfix) with ESMTP id D663B200230; Sun, 9 Jun 2024 06:40:55 -0400 (EDT) Received: from mailfrontend2 ([10.202.2.163]) by compute5.internal (MEProxy); Sun, 09 Jun 2024 06:40:55 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=3xx0.net; h=cc :cc:content-transfer-encoding:content-type:date:date:from:from :in-reply-to:in-reply-to:message-id:mime-version:references :reply-to:subject:subject:to:to; s=fm1; t=1717929655; x= 1717933255; bh=XpZy3c6xoasiD2Syf1e7KNVl4niFLU+xqznRa2cRaQY=; b=U qNy3PyQhOH732E7pX54uA3DCObeosJ+3w1bM4h6PkM2TyOXtPe/X0C7NeDBarAuo bscAip/ZjGHinjSrMO965JZL9l3X+NmdjU8lc4p0JMQ1kCBtPfZzesdnYahUht/Y SmpLd4vgq1rB96M7R1mpl0jYE8AeKKwqc5DVGUObjxfkeNdWEvf1P9G9MFmlOXih WsmRaPVhEutfR5aL4ufVoG7BY3sxlZNu7WEaiifcC+9RTuazDpTIfhDwbyRQdU76 8BB1Epbsh7d5SYG4MbMELRbmH6s79Znf3/qb8BC50Bgvu74JM4HoZd8BXgz0DePe BTd+aBrY9kbdKRaP4bUuw== DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d= messagingengine.com; h=cc:cc:content-transfer-encoding :content-type:date:date:feedback-id:feedback-id:from:from :in-reply-to:in-reply-to:message-id:mime-version:references :reply-to:subject:subject:to:to:x-me-proxy:x-me-proxy :x-me-sender:x-me-sender:x-sasl-enc; s=fm1; t=1717929655; x= 1717933255; bh=XpZy3c6xoasiD2Syf1e7KNVl4niFLU+xqznRa2cRaQY=; b=m GpmevGfJ6mIMqMWXF3GfuRbVuOA2qHUusWXetaTnZatmccDgLfYt9+gS8WJKZ7Vt sVvca/vuyK2rJxBkV+rov0Rv9vhlzkbXlOZeQ3W7UD5V3xUr9bHqYbXdrD90kW8T mfIcvLN9T/J4zqKyxGkMok8jg2c0FsbVkpZoIbqXOmOpRQOnjybVqC8UkVKGPmNB mM/wMt3j1YfbluAoPiUhWXFbadxAJSCEXovKZtA+IhaBy83V4Yz/GJNv6uzAznAR AFcbxiXoutSy5hAYpQ+RtGJH5UywxdNvOTOxhQssELcFsrOOyJbK2WXfuPZGUK4U 3mxF0P6YInPFOZp55XBhQ== X-ME-Sender: X-ME-Received: X-ME-Proxy-Cause: gggruggvucftvghtrhhoucdtuddrgedvledrfedtjedgfeduucetufdoteggodetrfdotf fvucfrrhhofhhilhgvmecuhfgrshhtofgrihhlpdfqfgfvpdfurfetoffkrfgpnffqhgen uceurghilhhouhhtmecufedttdenucesvcftvggtihhpihgvnhhtshculddquddttddmne cujfgurhephffvvefufffkofgjfhgggfestdekredtredttdenucfhrhhomheplfhonhgr thhhrghnucevrghlmhgvlhhsuceojhgtrghlmhgvlhhsseefgiigtddrnhgvtheqnecugg ftrfgrthhtvghrnheptdejhfelheejfeeutdekgeevueetkedtgfelkeejgfffhefgveet teffueegvdeknecuvehluhhsthgvrhfuihiivgeptdenucfrrghrrghmpehmrghilhhfrh homhepjhgtrghlmhgvlhhsseefgiigtddrnhgvth X-ME-Proxy: Feedback-ID: i76614979:Fastmail Received: by mail.messagingengine.com (Postfix) with ESMTPA; Sun, 9 Jun 2024 06:40:51 -0400 (EDT) From: Jonathan Calmels To: brauner@kernel.org, ebiederm@xmission.com, Jonathan Corbet , Paul Moore , James Morris , "Serge E. Hallyn" , KP Singh , Matt Bobrowski , Alexei Starovoitov , Daniel Borkmann , Andrii Nakryiko , Martin KaFai Lau , Eduard Zingerman , Song Liu , Yonghong Song , John Fastabend , Stanislav Fomichev , Hao Luo , Jiri Olsa , Luis Chamberlain , Kees Cook , Joel Granados , John Johansen , David Howells , Jarkko Sakkinen , Stephen Smalley , Ondrej Mosnacek , Mykola Lysenko , Shuah Khan Cc: containers@lists.linux.dev, Jonathan Calmels , linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-doc@vger.kernel.org, linux-security-module@vger.kernel.org, bpf@vger.kernel.org, apparmor@lists.ubuntu.com, keyrings@vger.kernel.org, selinux@vger.kernel.org, linux-kselftest@vger.kernel.org Subject: [PATCH v2 4/4] bpf,lsm: Allow editing capabilities in BPF-LSM hooks Date: Sun, 9 Jun 2024 03:43:37 -0700 Message-ID: <20240609104355.442002-5-jcalmels@3xx0.net> X-Mailer: git-send-email 2.45.2 In-Reply-To: <20240609104355.442002-1-jcalmels@3xx0.net> References: <20240609104355.442002-1-jcalmels@3xx0.net> Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-Patchwork-Delegate: bpf@iogearbox.net This patch allows modifying the various capabilities of the struct cred in BPF-LSM hooks. More specifically, the userns_create hook called prior to creating a new user namespace. With the introduction of userns capabilities, this effectively provides a simple way for LSMs to control the capabilities granted to a user namespace and all its descendants. Update the selftests accordingly by dropping CAP_SYS_ADMIN in namespaces and checking the resulting task's bounding set. Signed-off-by: Jonathan Calmels --- include/linux/lsm_hook_defs.h | 2 +- include/linux/security.h | 4 +- kernel/bpf/bpf_lsm.c | 55 +++++++++++++++++++ security/apparmor/lsm.c | 2 +- security/security.c | 6 +- security/selinux/hooks.c | 2 +- .../selftests/bpf/prog_tests/deny_namespace.c | 12 ++-- .../selftests/bpf/progs/test_deny_namespace.c | 7 ++- 8 files changed, 76 insertions(+), 14 deletions(-) diff --git a/include/linux/lsm_hook_defs.h b/include/linux/lsm_hook_defs.h index f804b76cde44..58d6d8f2511f 100644 --- a/include/linux/lsm_hook_defs.h +++ b/include/linux/lsm_hook_defs.h @@ -250,7 +250,7 @@ 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, userns_create, 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/security.h b/include/linux/security.h index 21cf70346b33..ffb1b0dd2aef 100644 --- a/include/linux/security.h +++ b/include/linux/security.h @@ -465,7 +465,7 @@ 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_create_user_ns(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); @@ -1294,7 +1294,7 @@ 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) +static inline int security_create_user_ns(struct cred *cred) { return 0; } diff --git a/kernel/bpf/bpf_lsm.c b/kernel/bpf/bpf_lsm.c index 68240c3c6e7d..6edba93ff883 100644 --- a/kernel/bpf/bpf_lsm.c +++ b/kernel/bpf/bpf_lsm.c @@ -382,10 +382,65 @@ bool bpf_lsm_is_trusted(const struct bpf_prog *prog) return !btf_id_set_contains(&untrusted_lsm_hooks, prog->aux->attach_btf_id); } +static int bpf_lsm_btf_struct_access(struct bpf_verifier_log *log, + const struct bpf_reg_state *reg, + int off, int size) +{ + const struct btf_type *cred; + const struct btf_type *t; + s32 type_id; + size_t end; + + type_id = btf_find_by_name_kind(reg->btf, "cred", BTF_KIND_STRUCT); + if (type_id < 0) + return -EINVAL; + + t = btf_type_by_id(reg->btf, reg->btf_id); + cred = btf_type_by_id(reg->btf, type_id); + if (t != cred) { + bpf_log(log, "only read is supported\n"); + return -EACCES; + } + + switch (off) { + case offsetof(struct cred, cap_inheritable): + end = offsetofend(struct cred, cap_inheritable); + break; + case offsetof(struct cred, cap_permitted): + end = offsetofend(struct cred, cap_permitted); + break; + case offsetof(struct cred, cap_effective): + end = offsetofend(struct cred, cap_effective); + break; + case offsetof(struct cred, cap_bset): + end = offsetofend(struct cred, cap_bset); + break; + case offsetof(struct cred, cap_ambient): + end = offsetofend(struct cred, cap_ambient); + break; + case offsetof(struct cred, cap_userns): + end = offsetofend(struct cred, cap_userns); + break; + default: + bpf_log(log, "no write support to cred at off %d\n", off); + return -EACCES; + } + + if (off + size > end) { + bpf_log(log, + "write access at off %d with size %d beyond the member of cred ended at %zu\n", + off, size, end); + return -EACCES; + } + + return 0; +} + const struct bpf_prog_ops lsm_prog_ops = { }; const struct bpf_verifier_ops lsm_verifier_ops = { .get_func_proto = bpf_lsm_func_proto, .is_valid_access = btf_ctx_access, + .btf_struct_access = bpf_lsm_btf_struct_access, }; diff --git a/security/apparmor/lsm.c b/security/apparmor/lsm.c index 6239777090c4..310c9fa3d4b4 100644 --- a/security/apparmor/lsm.c +++ b/security/apparmor/lsm.c @@ -1036,7 +1036,7 @@ static int apparmor_task_kill(struct task_struct *target, struct kernel_siginfo return error; } -static int apparmor_userns_create(const struct cred *cred) +static int apparmor_userns_create(struct cred *cred) { struct aa_label *label; struct aa_profile *profile; diff --git a/security/security.c b/security/security.c index e5da848c50b9..83cf2025c58e 100644 --- a/security/security.c +++ b/security/security.c @@ -3558,14 +3558,14 @@ void security_task_to_inode(struct task_struct *p, struct inode *inode) } /** - * security_create_user_ns() - Check if creating a new userns is allowed + * security_create_user_ns() - Review permissions prior to userns creation * @cred: prepared creds * - * Check permission prior to creating a new user namespace. + * Check and/or modify permissions prior to creating a new user namespace. * * Return: Returns 0 if successful, otherwise < 0 error code. */ -int security_create_user_ns(const struct cred *cred) +int security_create_user_ns(struct cred *cred) { return call_int_hook(userns_create, cred); } diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c index 7eed331e90f0..28deb9510d8e 100644 --- a/security/selinux/hooks.c +++ b/security/selinux/hooks.c @@ -4263,7 +4263,7 @@ static void selinux_task_to_inode(struct task_struct *p, spin_unlock(&isec->lock); } -static int selinux_userns_create(const struct cred *cred) +static int selinux_userns_create(struct cred *cred) { u32 sid = current_sid(); diff --git a/tools/testing/selftests/bpf/prog_tests/deny_namespace.c b/tools/testing/selftests/bpf/prog_tests/deny_namespace.c index 1bc6241b755b..1500578f9a30 100644 --- a/tools/testing/selftests/bpf/prog_tests/deny_namespace.c +++ b/tools/testing/selftests/bpf/prog_tests/deny_namespace.c @@ -5,6 +5,8 @@ #include #include "cap_helpers.h" #include +#include +#include static int wait_for_pid(pid_t pid) { @@ -29,7 +31,7 @@ static int wait_for_pid(pid_t pid) * positive return value -> userns creation failed * 0 -> userns creation succeeded */ -static int create_user_ns(void) +static int create_user_ns(bool bpf) { pid_t pid; @@ -40,6 +42,8 @@ static int create_user_ns(void) if (pid == 0) { if (unshare(CLONE_NEWUSER)) _exit(EXIT_FAILURE); + if (bpf && prctl(PR_CAPBSET_READ, CAP_SYS_ADMIN)) + _exit(EXIT_FAILURE); _exit(EXIT_SUCCESS); } @@ -53,11 +57,11 @@ static void test_userns_create_bpf(void) cap_enable_effective(cap_mask, &old_caps); - ASSERT_OK(create_user_ns(), "priv new user ns"); + ASSERT_OK(create_user_ns(true), "priv new user ns"); cap_disable_effective(cap_mask, &old_caps); - ASSERT_EQ(create_user_ns(), EPERM, "unpriv new user ns"); + ASSERT_EQ(create_user_ns(true), EPERM, "unpriv new user ns"); if (cap_mask & old_caps) cap_enable_effective(cap_mask, NULL); @@ -70,7 +74,7 @@ static void test_unpriv_userns_create_no_bpf(void) cap_disable_effective(cap_mask, &old_caps); - ASSERT_OK(create_user_ns(), "no-bpf unpriv new user ns"); + ASSERT_OK(create_user_ns(false), "no-bpf unpriv new user ns"); if (cap_mask & old_caps) cap_enable_effective(cap_mask, NULL); diff --git a/tools/testing/selftests/bpf/progs/test_deny_namespace.c b/tools/testing/selftests/bpf/progs/test_deny_namespace.c index e96b901a733c..051906f80f4c 100644 --- a/tools/testing/selftests/bpf/progs/test_deny_namespace.c +++ b/tools/testing/selftests/bpf/progs/test_deny_namespace.c @@ -9,12 +9,13 @@ typedef struct { unsigned long long val; } kernel_cap_t; struct cred { kernel_cap_t cap_effective; + kernel_cap_t cap_userns; } __attribute__((preserve_access_index)); char _license[] SEC("license") = "GPL"; SEC("lsm.s/userns_create") -int BPF_PROG(test_userns_create, const struct cred *cred, int ret) +int BPF_PROG(test_userns_create, struct cred *cred, int ret) { kernel_cap_t caps = cred->cap_effective; __u64 cap_mask = 1ULL << CAP_SYS_ADMIN; @@ -23,8 +24,10 @@ int BPF_PROG(test_userns_create, const struct cred *cred, int ret) return 0; ret = -EPERM; - if (caps.val & cap_mask) + if (caps.val & cap_mask) { + cred->cap_userns.val &= ~cap_mask; return 0; + } return -EPERM; }