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authorMickaël Salaün <mic@linux.microsoft.com>2021-04-22 17:41:14 +0200
committerJames Morris <jamorris@linux.microsoft.com>2021-04-22 12:22:10 -0700
commitafe81f754117dd96853677c5cb815f49abef0ba0 (patch)
tree9c89ace4b459dece96d08922e6ae9be04bf22091 /security/landlock/ptrace.c
parent385975dca53eb41031d0cbd1de318eb1bc5d6bb9 (diff)
landlock: Add ptrace restrictions
Using ptrace(2) and related debug features on a target process can lead to a privilege escalation. Indeed, ptrace(2) can be used by an attacker to impersonate another task and to remain undetected while performing malicious activities. Thanks to ptrace_may_access(), various part of the kernel can check if a tracer is more privileged than a tracee. A landlocked process has fewer 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's rules (i.e. the tracee must be in a sub-domain of the tracer). Cc: James Morris <jmorris@namei.org> Signed-off-by: Mickaël Salaün <mic@linux.microsoft.com> Reviewed-by: Jann Horn <jannh@google.com> Acked-by: Serge Hallyn <serge@hallyn.com> Reviewed-by: Kees Cook <keescook@chromium.org> Link: https://lore.kernel.org/r/20210422154123.13086-5-mic@digikod.net Signed-off-by: James Morris <jamorris@linux.microsoft.com>
Diffstat (limited to 'security/landlock/ptrace.c')
-rw-r--r--security/landlock/ptrace.c120
1 files changed, 120 insertions, 0 deletions
diff --git a/security/landlock/ptrace.c b/security/landlock/ptrace.c
new file mode 100644
index 000000000000..f55b82446de2
--- /dev/null
+++ b/security/landlock/ptrace.c
@@ -0,0 +1,120 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Landlock LSM - Ptrace hooks
+ *
+ * Copyright © 2017-2020 Mickaël Salaün <mic@digikod.net>
+ * Copyright © 2019-2020 ANSSI
+ */
+
+#include <asm/current.h>
+#include <linux/cred.h>
+#include <linux/errno.h>
+#include <linux/kernel.h>
+#include <linux/lsm_hooks.h>
+#include <linux/rcupdate.h>
+#include <linux/sched.h>
+
+#include "common.h"
+#include "cred.h"
+#include "ptrace.h"
+#include "ruleset.h"
+#include "setup.h"
+
+/**
+ * domain_scope_le - Checks domain ordering for scoped ptrace
+ *
+ * @parent: Parent domain.
+ * @child: Potential child of @parent.
+ *
+ * Checks if the @parent domain is less or equal to (i.e. an ancestor, which
+ * means a subset of) the @child domain.
+ */
+static bool domain_scope_le(const struct landlock_ruleset *const parent,
+ const struct landlock_ruleset *const child)
+{
+ const struct landlock_hierarchy *walker;
+
+ if (!parent)
+ return true;
+ if (!child)
+ return false;
+ for (walker = child->hierarchy; walker; walker = walker->parent) {
+ if (walker == parent->hierarchy)
+ /* @parent is in the scoped hierarchy of @child. */
+ return true;
+ }
+ /* There is no relationship between @parent and @child. */
+ return false;
+}
+
+static bool task_is_scoped(const struct task_struct *const parent,
+ const struct task_struct *const child)
+{
+ bool is_scoped;
+ const struct landlock_ruleset *dom_parent, *dom_child;
+
+ rcu_read_lock();
+ dom_parent = landlock_get_task_domain(parent);
+ dom_child = landlock_get_task_domain(child);
+ is_scoped = domain_scope_le(dom_parent, dom_child);
+ rcu_read_unlock();
+ return is_scoped;
+}
+
+static int task_ptrace(const struct task_struct *const parent,
+ const struct task_struct *const child)
+{
+ /* Quick return for non-landlocked tasks. */
+ if (!landlocked(parent))
+ return 0;
+ if (task_is_scoped(parent, child))
+ return 0;
+ return -EPERM;
+}
+
+/**
+ * hook_ptrace_access_check - Determines whether the current process may access
+ * another
+ *
+ * @child: Process to be accessed.
+ * @mode: Mode of attachment.
+ *
+ * If the current task has Landlock rules, then the child must have at least
+ * the same rules. Else denied.
+ *
+ * Determines whether a process may access another, returning 0 if permission
+ * granted, -errno if denied.
+ */
+static int hook_ptrace_access_check(struct task_struct *const child,
+ const unsigned int mode)
+{
+ return task_ptrace(current, child);
+}
+
+/**
+ * hook_ptrace_traceme - Determines whether another process may trace the
+ * current one
+ *
+ * @parent: 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.
+ *
+ * Determines 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 *const parent)
+{
+ return task_ptrace(parent, current);
+}
+
+static struct security_hook_list landlock_hooks[] __lsm_ro_after_init = {
+ LSM_HOOK_INIT(ptrace_access_check, hook_ptrace_access_check),
+ LSM_HOOK_INIT(ptrace_traceme, hook_ptrace_traceme),
+};
+
+__init void landlock_add_ptrace_hooks(void)
+{
+ security_add_hooks(landlock_hooks, ARRAY_SIZE(landlock_hooks),
+ LANDLOCK_NAME);
+}