3 files changed, 339 insertions, 0 deletions

diff --git a/security/yama/Kconfig b/security/yama/Kconfig
new file mode 100644
index 000000000000..51d6709d8bbd
--- /dev/null
+++ b/security/yama/Kconfig
@@ -0,0 +1,13 @@
+config SECURITY_YAMA
+        bool "Yama support"
+        depends on SECURITY
+        select SECURITYFS
+        select SECURITY_PATH
+        default n
+        help
+          This selects Yama, which extends DAC support with additional
+          system-wide security settings beyond regular Linux discretionary
+          access controls. Currently available is ptrace scope restriction.
+          Further information can be found in Documentation/security/Yama.txt.
+
+          If you are unsure how to answer this question, answer N.
diff --git a/security/yama/Makefile b/security/yama/Makefile
new file mode 100644
index 000000000000..8b5e06588456
--- /dev/null
+++ b/security/yama/Makefile
@@ -0,0 +1,3 @@
+obj-$(CONFIG_SECURITY_YAMA) := yama.o
+
+yama-y := yama_lsm.o
diff --git a/security/yama/yama_lsm.c b/security/yama/yama_lsm.c
new file mode 100644
index 000000000000..573723843a04
--- /dev/null
+++ b/security/yama/yama_lsm.c
@@ -0,0 +1,323 @@
+/*
+ * Yama Linux Security Module
+ *
+ * Author: Kees Cook <keescook@chromium.org>
+ *
+ * Copyright (C) 2010 Canonical, Ltd.
+ * Copyright (C) 2011 The Chromium OS Authors.
+ *
+ * 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 <linux/security.h>
+#include <linux/sysctl.h>
+#include <linux/ptrace.h>
+#include <linux/prctl.h>
+#include <linux/ratelimit.h>
+
+static int ptrace_scope = 1;
+
+/* describe a ptrace relationship for potential exception */
+struct ptrace_relation {
+        struct task_struct *tracer;
+        struct task_struct *tracee;
+        struct list_head node;
+};
+
+static LIST_HEAD(ptracer_relations);
+static DEFINE_SPINLOCK(ptracer_relations_lock);
+
+/**
+ * yama_ptracer_add - add/replace an exception for this tracer/tracee pair
+ * @tracer: the task_struct of the process doing the ptrace
+ * @tracee: the task_struct of the process to be ptraced
+ *
+ * Each tracee can have, at most, one tracer registered. Each time this
+ * is called, the prior registered tracer will be replaced for the tracee.
+ *
+ * Returns 0 if relationship was added, -ve on error.
+ */
+static int yama_ptracer_add(struct task_struct *tracer,
+                            struct task_struct *tracee)
+{
+        int rc = 0;
+        struct ptrace_relation *added;
+        struct ptrace_relation *entry, *relation = NULL;
+
+        added = kmalloc(sizeof(*added), GFP_KERNEL);
+        if (!added)
+                return -ENOMEM;
+
+        spin_lock_bh(&ptracer_relations_lock);
+        list_for_each_entry(entry, &ptracer_relations, node)
+                if (entry->tracee == tracee) {
+                        relation = entry;
+                        break;
+                }
+        if (!relation) {
+                relation = added;
+                relation->tracee = tracee;
+                list_add(&relation->node, &ptracer_relations);
+        }
+        relation->tracer = tracer;
+
+        spin_unlock_bh(&ptracer_relations_lock);
+        if (added != relation)
+                kfree(added);
+
+        return rc;
+}
+
+/**
+ * yama_ptracer_del - remove exceptions related to the given tasks
+ * @tracer: remove any relation where tracer task matches
+ * @tracee: remove any relation where tracee task matches
+ */
+static void yama_ptracer_del(struct task_struct *tracer,
+                             struct task_struct *tracee)
+{
+        struct ptrace_relation *relation, *safe;
+
+        spin_lock_bh(&ptracer_relations_lock);
+        list_for_each_entry_safe(relation, safe, &ptracer_relations, node)
+                if (relation->tracee == tracee ||
+                    (tracer && relation->tracer == tracer)) {
+                        list_del(&relation->node);
+                        kfree(relation);
+                }
+        spin_unlock_bh(&ptracer_relations_lock);
+}
+
+/**
+ * yama_task_free - check for task_pid to remove from exception list
+ * @task: task being removed
+ */
+static void yama_task_free(struct task_struct *task)
+{
+        yama_ptracer_del(task, task);
+}
+
+/**
+ * yama_task_prctl - check for Yama-specific prctl operations
+ * @option: operation
+ * @arg2: argument
+ * @arg3: argument
+ * @arg4: argument
+ * @arg5: argument
+ *
+ * Return 0 on success, -ve on error.  -ENOSYS is returned when Yama
+ * does not handle the given option.
+ */
+static int yama_task_prctl(int option, unsigned long arg2, unsigned long arg3,
+                           unsigned long arg4, unsigned long arg5)
+{
+        int rc;
+        struct task_struct *myself = current;
+
+        rc = cap_task_prctl(option, arg2, arg3, arg4, arg5);
+        if (rc != -ENOSYS)
+                return rc;
+
+        switch (option) {
+        case PR_SET_PTRACER:
+                /* Since a thread can call prctl(), find the group leader
+                 * before calling _add() or _del() on it, since we want
+                 * process-level granularity of control. The tracer group
+                 * leader checking is handled later when walking the ancestry
+                 * at the time of PTRACE_ATTACH check.
+                 */
+                rcu_read_lock();
+                if (!thread_group_leader(myself))
+                        myself = rcu_dereference(myself->group_leader);
+                get_task_struct(myself);
+                rcu_read_unlock();
+
+                if (arg2 == 0) {
+                        yama_ptracer_del(NULL, myself);
+                        rc = 0;
+                } else if (arg2 == PR_SET_PTRACER_ANY) {
+                        rc = yama_ptracer_add(NULL, myself);
+                } else {
+                        struct task_struct *tracer;
+
+                        rcu_read_lock();
+                        tracer = find_task_by_vpid(arg2);
+                        if (tracer)
+                                get_task_struct(tracer);
+                        else
+                                rc = -EINVAL;
+                        rcu_read_unlock();
+
+                        if (tracer) {
+                                rc = yama_ptracer_add(tracer, myself);
+                                put_task_struct(tracer);
+                        }
+                }
+
+                put_task_struct(myself);
+                break;
+        }
+
+        return rc;
+}
+
+/**
+ * task_is_descendant - walk up a process family tree looking for a match
+ * @parent: the process to compare against while walking up from child
+ * @child: the process to start from while looking upwards for parent
+ *
+ * Returns 1 if child is a descendant of parent, 0 if not.
+ */
+static int task_is_descendant(struct task_struct *parent,
+                              struct task_struct *child)
+{
+        int rc = 0;
+        struct task_struct *walker = child;
+
+        if (!parent || !child)
+                return 0;
+
+        rcu_read_lock();
+        if (!thread_group_leader(parent))
+                parent = rcu_dereference(parent->group_leader);
+        while (walker->pid > 0) {
+                if (!thread_group_leader(walker))
+                        walker = rcu_dereference(walker->group_leader);
+                if (walker == parent) {
+                        rc = 1;
+                        break;
+                }
+                walker = rcu_dereference(walker->real_parent);
+        }
+        rcu_read_unlock();
+
+        return rc;
+}
+
+/**
+ * ptracer_exception_found - tracer registered as exception for this tracee
+ * @tracer: the task_struct of the process attempting ptrace
+ * @tracee: the task_struct of the process to be ptraced
+ *
+ * Returns 1 if tracer has is ptracer exception ancestor for tracee.
+ */
+static int ptracer_exception_found(struct task_struct *tracer,
+                                   struct task_struct *tracee)
+{
+        int rc = 0;
+        struct ptrace_relation *relation;
+        struct task_struct *parent = NULL;
+        bool found = false;
+
+        spin_lock_bh(&ptracer_relations_lock);
+        rcu_read_lock();
+        if (!thread_group_leader(tracee))
+                tracee = rcu_dereference(tracee->group_leader);
+        list_for_each_entry(relation, &ptracer_relations, node)
+                if (relation->tracee == tracee) {
+                        parent = relation->tracer;
+                        found = true;
+                        break;
+                }
+
+        if (found && (parent == NULL || task_is_descendant(parent, tracer)))
+                rc = 1;
+        rcu_read_unlock();
+        spin_unlock_bh(&ptracer_relations_lock);
+
+        return rc;
+}
+
+/**
+ * yama_ptrace_access_check - validate PTRACE_ATTACH calls
+ * @child: task that current task is attempting to ptrace
+ * @mode: ptrace attach mode
+ *
+ * Returns 0 if following the ptrace is allowed, -ve on error.
+ */
+static int yama_ptrace_access_check(struct task_struct *child,
+                                    unsigned int mode)
+{
+        int rc;
+
+        /* If standard caps disallows it, so does Yama.  We should
+         * only tighten restrictions further.
+         */
+        rc = cap_ptrace_access_check(child, mode);
+        if (rc)
+                return rc;
+
+        /* require ptrace target be a child of ptracer on attach */
+        if (mode == PTRACE_MODE_ATTACH &&
+            ptrace_scope &&
+            !task_is_descendant(current, child) &&
+            !ptracer_exception_found(current, child) &&
+            !capable(CAP_SYS_PTRACE))
+                rc = -EPERM;
+
+        if (rc) {
+                char name[sizeof(current->comm)];
+                printk_ratelimited(KERN_NOTICE "ptrace of non-child"
+                        " pid %d was attempted by: %s (pid %d)\n",
+                        child->pid,
+                        get_task_comm(name, current),
+                        current->pid);
+        }
+
+        return rc;
+}
+
+static struct security_operations yama_ops = {
+        .name =                 "yama",
+
+        .ptrace_access_check =  yama_ptrace_access_check,
+        .task_prctl =           yama_task_prctl,
+        .task_free =            yama_task_free,
+};
+
+#ifdef CONFIG_SYSCTL
+static int zero;
+static int one = 1;
+
+struct ctl_path yama_sysctl_path[] = {
+        { .procname = "kernel", },
+        { .procname = "yama", },
+        { }
+};
+
+static struct ctl_table yama_sysctl_table[] = {
+        {
+                .procname       = "ptrace_scope",
+                .data           = &ptrace_scope,
+                .maxlen         = sizeof(int),
+                .mode           = 0644,
+                .proc_handler   = proc_dointvec_minmax,
+                .extra1         = &zero,
+                .extra2         = &one,
+        },
+        { }
+};
+#endif /* CONFIG_SYSCTL */
+
+static __init int yama_init(void)
+{
+        if (!security_module_enable(&yama_ops))
+                return 0;
+
+        printk(KERN_INFO "Yama: becoming mindful.\n");
+
+        if (register_security(&yama_ops))
+                panic("Yama: kernel registration failed.\n");
+
+#ifdef CONFIG_SYSCTL
+        if (!register_sysctl_paths(yama_sysctl_path, yama_sysctl_table))
+                panic("Yama: sysctl registration failed.\n");
+#endif
+
+        return 0;
+}
+
+security_initcall(yama_init);