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@xxxxxxxxxxx>
Cc: Alexei Starovoitov <ast@xxxxxxxxxx>
Cc: Andy Lutomirski <luto@xxxxxxxxxxxxxx>
Cc: Daniel Borkmann <daniel@xxxxxxxxxxxxx>
Cc: David S. Miller <davem@xxxxxxxxxxxxx>
Cc: James Morris <james.l.morris@xxxxxxxxxx>
Cc: Kees Cook <keescook@xxxxxxxxxxxx>
Cc: Serge E. Hallyn <serge@xxxxxxxxxx>
---
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 | 124 +++++++++++++++++++++++++++++++++++++++
security/landlock/hooks_ptrace.h | 11 ++++
security/landlock/init.c | 2 +
4 files changed, 138 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 d0f532a93b4e..605504d852d3 100644
--- a/security/landlock/Makefile
+++ b/security/landlock/Makefile
@@ -3,4 +3,4 @@ obj-$(CONFIG_SECURITY_LANDLOCK) := landlock.o
landlock-y := init.o chain.o task.o \
tag.o tag_fs.o \
enforce.o enforce_seccomp.o \
- hooks.o hooks_cred.o hooks_fs.o
+ hooks.o hooks_cred.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..f1b977b9c808
--- /dev/null
+++ b/security/landlock/hooks_ptrace.c
@@ -0,0 +1,124 @@
+/*
+ * Landlock LSM - ptrace hooks
+ *
+ * Copyright © 2017 Mickaël Salaün <mic@xxxxxxxxxxx>
+ *
+ * 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_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..15b1f3479e0e
--- /dev/null
+++ b/security/landlock/hooks_ptrace.h
@@ -0,0 +1,11 @@
+/*
+ * Landlock LSM - ptrace hooks
+ *
+ * Copyright © 2017 Mickaël Salaün <mic@xxxxxxxxxxx>
+ *
+ * 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 3486272d17b2..0f16848f5ad1 100644
--- a/security/landlock/init.c
+++ b/security/landlock/init.c
@@ -17,6 +17,7 @@
#include "common.h" /* LANDLOCK_* */
#include "hooks_fs.h"
#include "hooks_cred.h"
+#include "hooks_ptrace.h"
static bool bpf_landlock_is_valid_access(int off, int size,
enum bpf_access_type type, struct bpf_insn_access_aux *info,
@@ -232,5 +233,6 @@ void __init landlock_add_hooks(void)
{
pr_info(LANDLOCK_NAME ": Ready to sandbox with seccomp\n");
landlock_add_hooks_cred();
+ landlock_add_hooks_ptrace();
landlock_add_hooks_fs();
}
--
2.16.2
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