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From: "Mickaël Salaün" <mic@digikod.net>
To: linux-kernel@vger.kernel.org
Cc: "Mickaël Salaün" <mic@digikod.net>,
	"Alexander Viro" <viro@zeniv.linux.org.uk>,
	"Alexei Starovoitov" <ast@kernel.org>,
	"Andrew Morton" <akpm@linux-foundation.org>,
	"Andy Lutomirski" <luto@amacapital.net>,
	"Arnaldo Carvalho de Melo" <acme@kernel.org>,
	"Casey Schaufler" <casey@schaufler-ca.com>,
	"Daniel Borkmann" <daniel@iogearbox.net>,
	"David Drysdale" <drysdale@google.com>,
	"David S . Miller" <davem@davemloft.net>,
	"Eric W . Biederman" <ebiederm@xmission.com>,
	"James Morris" <jmorris@namei.org>, "Jann Horn" <jann@thejh.net>,
	"John Johansen" <john.johansen@canonical.com>,
	"Jonathan Corbet" <corbet@lwn.net>,
	"Kees Cook" <keescook@chromium.org>,
	"Michael Kerrisk" <mtk.manpages@gmail.com>,
	"Mickaël Salaün" <mickael.salaun@ssi.gouv.fr>,
	"Paul Moore" <paul@paul-moore.com>,
	"Sargun Dhillon" <sargun@sargun.me>,
	"Serge E . Hallyn" <serge@hallyn.com>,
	"Shuah Khan" <shuah@kernel.org>,
	"Stephen Smalley" <sds@tycho.nsa.gov>,
	"Tejun Heo" <tj@kernel.org>,
	"Tetsuo Handa" <penguin-kernel@I-love.SAKURA.ne.jp>,
	"Thomas Graf" <tgraf@suug.ch>, "Tycho Andersen" <tycho@tycho.ws>,
	"Will Drewry" <wad@chromium.org>,
	kernel-hardening@lists.openwall.com, linux-api@vger.kernel.org,
	linux-fsdevel@vger.kernel.org,
	linux-security-module@vger.kernel.org, netdev@vger.kernel.org
Subject: [PATCH bpf-next v10 07/10] landlock: Add ptrace restrictions
Date: Sun, 21 Jul 2019 23:31:13 +0200
Message-ID: <20190721213116.23476-8-mic@digikod.net> (raw)
In-Reply-To: <20190721213116.23476-1-mic@digikod.net>

A landlocked process has less privileges than a non-landlocked process
and must then be subject to additional restrictions when manipulating
processes. To be allowed to use ptrace(2) and related syscalls on a
target process, a landlocked process must have a subset of the target
process' rules.

Signed-off-by: Mickaël Salaün <mic@digikod.net>
Cc: Alexei Starovoitov <ast@kernel.org>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Daniel Borkmann <daniel@iogearbox.net>
Cc: David S. Miller <davem@davemloft.net>
Cc: James Morris <jmorris@namei.org>
Cc: Kees Cook <keescook@chromium.org>
Cc: Serge E. Hallyn <serge@hallyn.com>
---

Changes since v6:
* factor out ptrace check
* constify pointers
* cleanup headers
* use the new security_add_hooks()
---
 security/landlock/Makefile       |   2 +-
 security/landlock/hooks_ptrace.c | 121 +++++++++++++++++++++++++++++++
 security/landlock/hooks_ptrace.h |   8 ++
 security/landlock/init.c         |   2 +
 4 files changed, 132 insertions(+), 1 deletion(-)
 create mode 100644 security/landlock/hooks_ptrace.c
 create mode 100644 security/landlock/hooks_ptrace.h

diff --git a/security/landlock/Makefile b/security/landlock/Makefile
index 270ece5d93de..4500ddb0767e 100644
--- a/security/landlock/Makefile
+++ b/security/landlock/Makefile
@@ -2,4 +2,4 @@ obj-$(CONFIG_SECURITY_LANDLOCK) := landlock.o
 
 landlock-y := init.o \
 	enforce.o enforce_seccomp.o \
-	hooks.o hooks_fs.o
+	hooks.o hooks_fs.o hooks_ptrace.o
diff --git a/security/landlock/hooks_ptrace.c b/security/landlock/hooks_ptrace.c
new file mode 100644
index 000000000000..7f5e8b994e93
--- /dev/null
+++ b/security/landlock/hooks_ptrace.c
@@ -0,0 +1,121 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Landlock LSM - ptrace hooks
+ *
+ * Copyright © 2017 Mickaël Salaün <mic@digikod.net>
+ */
+
+#include <asm/current.h>
+#include <linux/errno.h>
+#include <linux/kernel.h> /* ARRAY_SIZE */
+#include <linux/lsm_hooks.h>
+#include <linux/sched.h> /* struct task_struct */
+#include <linux/seccomp.h>
+
+#include "common.h" /* struct landlock_prog_set */
+#include "hooks.h" /* landlocked() */
+#include "hooks_ptrace.h"
+
+static bool progs_are_subset(const struct landlock_prog_set *parent,
+		const struct landlock_prog_set *child)
+{
+	size_t i;
+
+	if (!parent || !child)
+		return false;
+	if (parent == child)
+		return true;
+
+	for (i = 0; i < ARRAY_SIZE(child->programs); i++) {
+		struct landlock_prog_list *walker;
+		bool found_parent = false;
+
+		if (!parent->programs[i])
+			continue;
+		for (walker = child->programs[i]; walker;
+				walker = walker->prev) {
+			if (walker == parent->programs[i]) {
+				found_parent = true;
+				break;
+			}
+		}
+		if (!found_parent)
+			return false;
+	}
+	return true;
+}
+
+static bool task_has_subset_progs(const struct task_struct *parent,
+		const struct task_struct *child)
+{
+#ifdef CONFIG_SECCOMP_FILTER
+	if (progs_are_subset(parent->seccomp.landlock_prog_set,
+				child->seccomp.landlock_prog_set))
+		/* must be ANDed with other providers (i.e. cgroup) */
+		return true;
+#endif /* CONFIG_SECCOMP_FILTER */
+	return false;
+}
+
+static int task_ptrace(const struct task_struct *parent,
+		const struct task_struct *child)
+{
+	if (!landlocked(parent))
+		return 0;
+
+	if (!landlocked(child))
+		return -EPERM;
+
+	if (task_has_subset_progs(parent, child))
+		return 0;
+
+	return -EPERM;
+}
+
+/**
+ * hook_ptrace_access_check - determine whether the current process may access
+ *			      another
+ *
+ * @child: the process to be accessed
+ * @mode: the mode of attachment
+ *
+ * If the current task has Landlock programs, then the child must have at least
+ * the same programs.  Else denied.
+ *
+ * Determine whether a process may access another, returning 0 if permission
+ * granted, -errno if denied.
+ */
+static int hook_ptrace_access_check(struct task_struct *child,
+		unsigned int mode)
+{
+	return task_ptrace(current, child);
+}
+
+/**
+ * hook_ptrace_traceme - determine whether another process may trace the
+ *			 current one
+ *
+ * @parent: the task proposed to be the tracer
+ *
+ * If the parent has Landlock programs, then the current task must have the
+ * same or more programs.
+ * Else denied.
+ *
+ * Determine whether the nominated task is permitted to trace the current
+ * process, returning 0 if permission is granted, -errno if denied.
+ */
+static int hook_ptrace_traceme(struct task_struct *parent)
+{
+	return task_ptrace(parent, current);
+}
+
+static struct security_hook_list landlock_hooks[] = {
+	LSM_HOOK_INIT(ptrace_access_check, hook_ptrace_access_check),
+	LSM_HOOK_INIT(ptrace_traceme, hook_ptrace_traceme),
+};
+
+__init void landlock_add_hooks_ptrace(void)
+{
+	security_add_hooks(landlock_hooks, ARRAY_SIZE(landlock_hooks),
+			LANDLOCK_NAME);
+}
diff --git a/security/landlock/hooks_ptrace.h b/security/landlock/hooks_ptrace.h
new file mode 100644
index 000000000000..2c2b8a13037f
--- /dev/null
+++ b/security/landlock/hooks_ptrace.h
@@ -0,0 +1,8 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * Landlock LSM - ptrace hooks
+ *
+ * Copyright © 2017 Mickaël Salaün <mic@digikod.net>
+ */
+
+__init void landlock_add_hooks_ptrace(void);
diff --git a/security/landlock/init.c b/security/landlock/init.c
index eec4467cb5ee..35165fc8a595 100644
--- a/security/landlock/init.c
+++ b/security/landlock/init.c
@@ -13,6 +13,7 @@
 
 #include "common.h" /* LANDLOCK_* */
 #include "hooks_fs.h"
+#include "hooks_ptrace.h"
 
 static bool bpf_landlock_is_valid_access(int off, int size,
 		enum bpf_access_type type, const struct bpf_prog *prog,
@@ -130,6 +131,7 @@ const struct bpf_prog_ops landlock_prog_ops = {};
 static int __init landlock_init(void)
 {
 	pr_info(LANDLOCK_NAME ": Initializing (sandbox with seccomp)\n");
+	landlock_add_hooks_ptrace();
 	landlock_add_hooks_fs();
 	return 0;
 }
-- 
2.22.0


  parent reply index

Thread overview: 22+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-07-21 21:31 [PATCH bpf-next v10 00/10] Landlock LSM: Toward unprivileged sandboxing Mickaël Salaün
2019-07-21 21:31 ` [PATCH bpf-next v10 01/10] fs,security: Add a new file access type: MAY_CHROOT Mickaël Salaün
2019-07-21 21:31 ` [PATCH bpf-next v10 02/10] bpf: Add expected_attach_triggers and a is_valid_triggers() verifier Mickaël Salaün
2019-07-21 21:31 ` [PATCH bpf-next v10 03/10] bpf,landlock: Define an eBPF program type for Landlock hooks Mickaël Salaün
2019-07-21 21:31 ` [PATCH bpf-next v10 04/10] seccomp,landlock: Enforce Landlock programs per process hierarchy Mickaël Salaün
2019-07-21 21:31 ` [PATCH bpf-next v10 05/10] landlock: Handle filesystem access control Mickaël Salaün
2019-07-21 21:31 ` [PATCH bpf-next v10 06/10] bpf,landlock: Add a new map type: inode Mickaël Salaün
2019-07-27  1:40   ` Alexei Starovoitov
2019-07-31 18:46     ` Mickaël Salaün
2019-07-31 18:58       ` Alexei Starovoitov
2019-07-31 19:11         ` Mickaël Salaün
2019-08-01 17:35           ` Alexei Starovoitov
2019-08-06 16:24             ` Mickaël Salaün
2019-09-08 22:09       ` Mickaël Salaün
2019-09-08 22:19         ` Al Viro
2019-07-21 21:31 ` Mickaël Salaün [this message]
2019-07-21 21:31 ` [PATCH bpf-next v10 08/10] bpf: Add a Landlock sandbox example Mickaël Salaün
2019-07-21 21:31 ` [PATCH bpf-next v10 09/10] bpf,landlock: Add tests for Landlock Mickaël Salaün
2019-07-21 21:31 ` [PATCH bpf-next v10 10/10] landlock: Add user and kernel documentation " Mickaël Salaün
2019-07-31  1:53   ` Randy Dunlap
2019-08-01 17:03     ` Mickaël Salaün
2019-08-01 17:49       ` Randy Dunlap

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