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Message-Id: <20170821000933.13024-8-mic@digikod.net>
Date: Mon, 21 Aug 2017 02:09:30 +0200
From: Mickaël Salaün <mic@...ikod.net>
To: linux-kernel@...r.kernel.org
Cc: Mickaël Salaün <mic@...ikod.net>,
Alexei Starovoitov <ast@...nel.org>,
Andy Lutomirski <luto@...capital.net>,
Arnaldo Carvalho de Melo <acme@...nel.org>,
Casey Schaufler <casey@...aufler-ca.com>,
Daniel Borkmann <daniel@...earbox.net>,
David Drysdale <drysdale@...gle.com>,
"David S . Miller" <davem@...emloft.net>,
"Eric W . Biederman" <ebiederm@...ssion.com>,
James Morris <james.l.morris@...cle.com>, Jann Horn <jann@...jh.net>,
Jonathan Corbet <corbet@....net>,
Matthew Garrett <mjg59@...f.ucam.org>,
Michael Kerrisk <mtk.manpages@...il.com>,
Kees Cook <keescook@...omium.org>, Paul Moore <paul@...l-moore.com>,
Sargun Dhillon <sargun@...gun.me>,
"Serge E . Hallyn" <serge@...lyn.com>, Shuah Khan <shuah@...nel.org>,
Tejun Heo <tj@...nel.org>, Thomas Graf <tgraf@...g.ch>,
Will Drewry <wad@...omium.org>, kernel-hardening@...ts.openwall.com,
linux-api@...r.kernel.org, linux-security-module@...r.kernel.org,
netdev@...r.kernel.org
Subject: [PATCH net-next v7 07/10] landlock: Add ptrace restrictions
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@...ikod.net>
Cc: Alexei Starovoitov <ast@...nel.org>
Cc: Andy Lutomirski <luto@...capital.net>
Cc: Daniel Borkmann <daniel@...earbox.net>
Cc: David S. Miller <davem@...emloft.net>
Cc: James Morris <james.l.morris@...cle.com>
Cc: Kees Cook <keescook@...omium.org>
Cc: Serge E. Hallyn <serge@...lyn.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 | 123 +++++++++++++++++++++++++++++++++++++++
security/landlock/hooks_ptrace.h | 11 ++++
security/landlock/init.c | 2 +
4 files changed, 137 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 8153b024ffd7..7ff911328e74 100644
--- a/security/landlock/Makefile
+++ b/security/landlock/Makefile
@@ -5,4 +5,4 @@ ccflags-$(CONFIG_SECURITY_LANDLOCK) += -Werror=unused-function
obj-$(CONFIG_SECURITY_LANDLOCK) := landlock.o
-landlock-y := init.o providers.o hooks.o hooks_fs.o
+landlock-y := init.o providers.o hooks.o hooks_ptrace.o hooks_fs.o
diff --git a/security/landlock/hooks_ptrace.c b/security/landlock/hooks_ptrace.c
new file mode 100644
index 000000000000..0f1c13172f54
--- /dev/null
+++ b/security/landlock/hooks_ptrace.c
@@ -0,0 +1,123 @@
+/*
+ * Landlock LSM - ptrace hooks
+ *
+ * Copyright © 2017 Mickaël Salaün <mic@...ikod.net>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2, as
+ * published by the Free Software Foundation.
+ */
+
+#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_events */
+#include "hooks.h" /* landlocked() */
+#include "hooks_ptrace.h"
+
+
+static bool landlock_events_are_subset(const struct landlock_events *parent,
+ const struct landlock_events *child)
+{
+ size_t i;
+
+ if (!parent || !child)
+ return false;
+ if (parent == child)
+ return true;
+
+ for (i = 0; i < ARRAY_SIZE(child->rules); i++) {
+ struct landlock_rule *walker;
+ bool found_parent = false;
+
+ if (!parent->rules[i])
+ continue;
+ for (walker = child->rules[i]; walker; walker = walker->prev) {
+ if (walker == parent->rules[i]) {
+ found_parent = true;
+ break;
+ }
+ }
+ if (!found_parent)
+ return false;
+ }
+ return true;
+}
+
+static bool landlock_task_has_subset_events(const struct task_struct *parent,
+ const struct task_struct *child)
+{
+#ifdef CONFIG_SECCOMP_FILTER
+ if (landlock_events_are_subset(parent->seccomp.landlock_events,
+ child->seccomp.landlock_events))
+ /* must be ANDed with other providers (i.e. cgroup) */
+ return true;
+#endif /* CONFIG_SECCOMP_FILTER */
+ return false;
+}
+
+static int landlock_task_ptrace(const struct task_struct *parent,
+ const struct task_struct *child)
+{
+ if (!landlocked(parent))
+ return 0;
+
+ if (!landlocked(child))
+ return -EPERM;
+
+ if (landlock_task_has_subset_events(parent, child))
+ return 0;
+
+ return -EPERM;
+}
+
+/**
+ * landlock_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 rules, then the child must have at least
+ * the same rules. Else denied.
+ *
+ * Determine whether a process may access another, returning 0 if permission
+ * granted, -errno if denied.
+ */
+static int landlock_ptrace_access_check(struct task_struct *child,
+ unsigned int mode)
+{
+ return landlock_task_ptrace(current, child);
+}
+
+/**
+ * landlock_ptrace_traceme - determine whether another process may trace the
+ * current one
+ *
+ * @parent: the task proposed to be the tracer
+ *
+ * If the parent has Landlock rules, then the current task must have the same
+ * or more rules.
+ * 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 landlock_ptrace_traceme(struct task_struct *parent)
+{
+ return landlock_task_ptrace(parent, current);
+}
+
+static struct security_hook_list landlock_hooks[] = {
+ LSM_HOOK_INIT(ptrace_access_check, landlock_ptrace_access_check),
+ LSM_HOOK_INIT(ptrace_traceme, landlock_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..15b1f3479e0e
--- /dev/null
+++ b/security/landlock/hooks_ptrace.h
@@ -0,0 +1,11 @@
+/*
+ * Landlock LSM - ptrace hooks
+ *
+ * Copyright © 2017 Mickaël Salaün <mic@...ikod.net>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2, as
+ * published by the Free Software Foundation.
+ */
+
+__init void landlock_add_hooks_ptrace(void);
diff --git a/security/landlock/init.c b/security/landlock/init.c
index 81f373f7cc52..424f457b1832 100644
--- a/security/landlock/init.c
+++ b/security/landlock/init.c
@@ -14,6 +14,7 @@
#include "common.h" /* LANDLOCK_* */
#include "hooks_fs.h"
+#include "hooks_ptrace.h"
static inline bool bpf_landlock_is_valid_access(int off, int size,
@@ -122,5 +123,6 @@ void __init landlock_add_hooks(void)
{
pr_info("%s: ABI %u, ready to sandbox with %s\n",
LANDLOCK_NAME, LANDLOCK_ABI, "seccomp");
+ landlock_add_hooks_ptrace();
landlock_add_hooks_fs();
}
--
2.14.1
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