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Subject[PATCH net-next v6 07/11] landlock: Add ptrace restrictions
Date
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.

New in v6

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 <james.l.morris@oracle.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Serge E. Hallyn <serge@hallyn.com>
---
security/landlock/Makefile | 2 +-
security/landlock/hooks_ptrace.c | 126 +++++++++++++++++++++++++++++++++++++++
security/landlock/hooks_ptrace.h | 11 ++++
security/landlock/init.c | 2 +
4 files changed, 140 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 da8ba8b5183e..099a56ca4842 100644
--- a/security/landlock/Makefile
+++ b/security/landlock/Makefile
@@ -2,4 +2,4 @@ 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_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..8ab53baba9ad
--- /dev/null
+++ b/security/landlock/hooks_ptrace.c
@@ -0,0 +1,126 @@
+/*
+ * Landlock LSM - ptrace hooks
+ *
+ * Copyright © 2017 Mickaël Salaün <mic@digikod.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/kernel.h> /* ARRAY_SIZE */
+#include <linux/landlock.h> /* struct landlock_events */
+#include <linux/lsm_hooks.h>
+#include <linux/sched.h> /* struct task_struct */
+#include <linux/seccomp.h>
+
+#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;
+}
+
+/**
+ * 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)
+{
+ if (!landlocked(current))
+ return 0;
+
+ if (!landlocked(child))
+ return -EPERM;
+
+ if (landlock_task_has_subset_events(current, child))
+ return 0;
+
+ return -EPERM;
+}
+
+/**
+ * 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)
+{
+ if (!landlocked(parent))
+ return 0;
+
+ if (!landlocked(current))
+ return -EPERM;
+
+ if (landlock_task_has_subset_events(parent, current))
+ return 0;
+
+ return -EPERM;
+}
+
+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)
+{
+ landlock_register_hooks(landlock_hooks, ARRAY_SIZE(landlock_hooks));
+}
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@digikod.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 ef8a3da69860..c8bce3142a32 100644
--- a/security/landlock/init.c
+++ b/security/landlock/init.c
@@ -14,6 +14,7 @@
#include <linux/lsm_hooks.h>

#include "hooks_fs.h"
+#include "hooks_ptrace.h"


static inline bool bpf_landlock_is_valid_access(int off, int size,
@@ -137,6 +138,7 @@ void __init landlock_add_hooks(void)
{
pr_info("landlock: Version %u, ready to sandbox with %s\n",
LANDLOCK_VERSION, "seccomp");
+ landlock_add_hooks_ptrace();
landlock_add_hooks_fs();
security_add_hooks(NULL, 0, "landlock");
bpf_register_prog_type(&bpf_landlock_type);
--
2.11.0
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