/* * 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/lsm_hooks.h> #include <linux/sysctl.h> #include <linux/ptrace.h> #include <linux/prctl.h> #include <linux/ratelimit.h> #include <linux/workqueue.h> #include <linux/string_helpers.h> #include <linux/task_work.h> #include <linux/sched.h> #include <linux/spinlock.h> #define YAMA_SCOPE_DISABLED 0 #define YAMA_SCOPE_RELATIONAL 1 #define YAMA_SCOPE_CAPABILITY 2 #define YAMA_SCOPE_NO_ATTACH 3 static int ptrace_scope = YAMA_SCOPE_RELATIONAL; /* describe a ptrace relationship for potential exception */ struct ptrace_relation { struct task_struct *tracer; struct task_struct *tracee; bool invalid; struct list_head node; struct rcu_head rcu; }; static LIST_HEAD(ptracer_relations); static DEFINE_SPINLOCK(ptracer_relations_lock); static void yama_relation_cleanup(struct work_struct *work); static DECLARE_WORK(yama_relation_work, yama_relation_cleanup); struct access_report_info { struct callback_head work; const char *access; struct task_struct *target; struct task_struct *agent; }; static void __report_access(struct callback_head *work) { struct access_report_info *info = container_of(work, struct access_report_info, work); char *target_cmd, *agent_cmd; target_cmd = kstrdup_quotable_cmdline(info->target, GFP_KERNEL); agent_cmd = kstrdup_quotable_cmdline(info->agent, GFP_KERNEL); pr_notice_ratelimited( "ptrace %s of \"%s\"[%d] was attempted by \"%s\"[%d]\n", info->access, target_cmd, info->target->pid, agent_cmd, info->agent->pid); kfree(agent_cmd); kfree(target_cmd); put_task_struct(info->agent); put_task_struct(info->target); kfree(info); } /* defers execution because cmdline access can sleep */ static void report_access(const char *access, struct task_struct *target, struct task_struct *agent) { struct access_report_info *info; char agent_comm[sizeof(agent->comm)]; assert_spin_locked(&target->alloc_lock); /* for target->comm */ if (current->flags & PF_KTHREAD) { /* I don't think kthreads call task_work_run() before exiting. * Imagine angry ranting about procfs here. */ pr_notice_ratelimited( "ptrace %s of \"%s\"[%d] was attempted by \"%s\"[%d]\n", access, target->comm, target->pid, get_task_comm(agent_comm, agent), agent->pid); return; } info = kmalloc(sizeof(*info), GFP_ATOMIC); if (!info) return; init_task_work(&info->work, __report_access); get_task_struct(target); get_task_struct(agent); info->access = access; info->target = target; info->agent = agent; if (task_work_add(current, &info->work, true) == 0) return; /* success */ WARN(1, "report_access called from exiting task"); put_task_struct(target); put_task_struct(agent); kfree(info); } /** * yama_relation_cleanup - remove invalid entries from the relation list * */ static void yama_relation_cleanup(struct work_struct *work) { struct ptrace_relation *relation; spin_lock(&ptracer_relations_lock); rcu_read_lock(); list_for_each_entry_rcu(relation, &ptracer_relations, node) { if (relation->invalid) { list_del_rcu(&relation->node); kfree_rcu(relation, rcu); } } rcu_read_unlock(); spin_unlock(&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) { struct ptrace_relation *relation, *added; added = kmalloc(sizeof(*added), GFP_KERNEL); if (!added) return -ENOMEM; added->tracee = tracee; added->tracer = tracer; added->invalid = false; spin_lock(&ptracer_relations_lock); rcu_read_lock(); list_for_each_entry_rcu(relation, &ptracer_relations, node) { if (relation->invalid) continue; if (relation->tracee == tracee) { list_replace_rcu(&relation->node, &added->node); kfree_rcu(relation, rcu); goto out; } } list_add_rcu(&added->node, &ptracer_relations); out: rcu_read_unlock(); spin_unlock(&ptracer_relations_lock); return 0; } /** * 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; bool marked = false; rcu_read_lock(); list_for_each_entry_rcu(relation, &ptracer_relations, node) { if (relation->invalid) continue; if (relation->tracee == tracee || (tracer && relation->tracer == tracer)) { relation->invalid = true; marked = true; } } rcu_read_unlock(); if (marked) schedule_work(&yama_relation_work); } /** * 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 = -ENOSYS; struct task_struct *myself = current; 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 || (int)arg2 == -1) { rc = yama_ptracer_add(NULL, myself); } else { struct task_struct *tracer; tracer = find_get_task_by_vpid(arg2); if (!tracer) { rc = -EINVAL; } else { 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 a 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; rcu_read_lock(); /* * If there's already an active tracing relationship, then make an * exception for the sake of other accesses, like process_vm_rw(). */ parent = ptrace_parent(tracee); if (parent != NULL && same_thread_group(parent, tracer)) { rc = 1; goto unlock; } /* Look for a PR_SET_PTRACER relationship. */ if (!thread_group_leader(tracee)) tracee = rcu_dereference(tracee->group_leader); list_for_each_entry_rcu(relation, &ptracer_relations, node) { if (relation->invalid) continue; if (relation->tracee == tracee) { parent = relation->tracer; found = true; break; } } if (found && (parent == NULL || task_is_descendant(parent, tracer))) rc = 1; unlock: rcu_read_unlock(); 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 = 0; /* require ptrace target be a child of ptracer on attach */ if (mode & PTRACE_MODE_ATTACH) { switch (ptrace_scope) { case YAMA_SCOPE_DISABLED: /* No additional restrictions. */ break; case YAMA_SCOPE_RELATIONAL: rcu_read_lock(); if (!pid_alive(child)) rc = -EPERM; if (!rc && !task_is_descendant(current, child) && !ptracer_exception_found(current, child) && !ns_capable(__task_cred(child)->user_ns, CAP_SYS_PTRACE)) rc = -EPERM; rcu_read_unlock(); break; case YAMA_SCOPE_CAPABILITY: rcu_read_lock(); if (!ns_capable(__task_cred(child)->user_ns, CAP_SYS_PTRACE)) rc = -EPERM; rcu_read_unlock(); break; case YAMA_SCOPE_NO_ATTACH: default: rc = -EPERM; break; } } if (rc && (mode & PTRACE_MODE_NOAUDIT) == 0) report_access("attach", child, current); return rc; } /** * yama_ptrace_traceme - validate PTRACE_TRACEME calls * @parent: task that will become the ptracer of the current task * * Returns 0 if following the ptrace is allowed, -ve on error. */ static int yama_ptrace_traceme(struct task_struct *parent) { int rc = 0; /* Only disallow PTRACE_TRACEME on more aggressive settings. */ switch (ptrace_scope) { case YAMA_SCOPE_CAPABILITY: if (!has_ns_capability(parent, current_user_ns(), CAP_SYS_PTRACE)) rc = -EPERM; break; case YAMA_SCOPE_NO_ATTACH: rc = -EPERM; break; } if (rc) { task_lock(current); report_access("traceme", current, parent); task_unlock(current); } return rc; } static struct security_hook_list yama_hooks[] __lsm_ro_after_init = { LSM_HOOK_INIT(ptrace_access_check, yama_ptrace_access_check), LSM_HOOK_INIT(ptrace_traceme, yama_ptrace_traceme), LSM_HOOK_INIT(task_prctl, yama_task_prctl), LSM_HOOK_INIT(task_free, yama_task_free), }; #ifdef CONFIG_SYSCTL static int yama_dointvec_minmax(struct ctl_table *table, int write, void __user *buffer, size_t *lenp, loff_t *ppos) { struct ctl_table table_copy; if (write && !capable(CAP_SYS_PTRACE)) return -EPERM; /* Lock the max value if it ever gets set. */ table_copy = *table; if (*(int *)table_copy.data == *(int *)table_copy.extra2) table_copy.extra1 = table_copy.extra2; return proc_dointvec_minmax(&table_copy, write, buffer, lenp, ppos); } static int zero; static int max_scope = YAMA_SCOPE_NO_ATTACH; static 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 = yama_dointvec_minmax, .extra1 = &zero, .extra2 = &max_scope, }, { } }; static void __init yama_init_sysctl(void) { if (!register_sysctl_paths(yama_sysctl_path, yama_sysctl_table)) panic("Yama: sysctl registration failed.\n"); } #else static inline void yama_init_sysctl(void) { } #endif /* CONFIG_SYSCTL */ static int __init yama_init(void) { pr_info("Yama: becoming mindful.\n"); security_add_hooks(yama_hooks, ARRAY_SIZE(yama_hooks), "yama"); yama_init_sysctl(); return 0; } DEFINE_LSM(yama) = { .name = "yama", .init = yama_init, };