diff options
Diffstat (limited to 'security/yama/yama_lsm.c')
| -rw-r--r-- | security/yama/yama_lsm.c | 440 |
1 files changed, 440 insertions, 0 deletions
diff --git a/security/yama/yama_lsm.c b/security/yama/yama_lsm.c new file mode 100644 index 000000000..24aae2ae2 --- /dev/null +++ b/security/yama/yama_lsm.c @@ -0,0 +1,440 @@ +/* + * 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> +#include <linux/workqueue.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); + +/** + * 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 + */ +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. + */ +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 || (int)arg2 == -1) { + 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; + + rcu_read_lock(); + 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; + 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. + */ +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) { + switch (ptrace_scope) { + case YAMA_SCOPE_DISABLED: + /* No additional restrictions. */ + break; + case YAMA_SCOPE_RELATIONAL: + rcu_read_lock(); + if (!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) { + printk_ratelimited(KERN_NOTICE + "ptrace of pid %d was attempted by: %s (pid %d)\n", + child->pid, current->comm, current->pid); + } + + 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. + */ +int yama_ptrace_traceme(struct task_struct *parent) +{ + int rc; + + /* If standard caps disallows it, so does Yama. We should + * only tighten restrictions further. + */ + rc = cap_ptrace_traceme(parent); + if (rc) + return rc; + + /* 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) { + printk_ratelimited(KERN_NOTICE + "ptraceme of pid %d was attempted by: %s (pid %d)\n", + current->pid, parent->comm, parent->pid); + } + + return rc; +} + +#ifndef CONFIG_SECURITY_YAMA_STACKED +static struct security_operations yama_ops = { + .name = "yama", + + .ptrace_access_check = yama_ptrace_access_check, + .ptrace_traceme = yama_ptrace_traceme, + .task_prctl = yama_task_prctl, + .task_free = yama_task_free, +}; +#endif + +#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; + +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, + }, + { } +}; +#endif /* CONFIG_SYSCTL */ + +static __init int yama_init(void) +{ +#ifndef CONFIG_SECURITY_YAMA_STACKED + if (!security_module_enable(&yama_ops)) + return 0; +#endif + + printk(KERN_INFO "Yama: becoming mindful.\n"); + +#ifndef CONFIG_SECURITY_YAMA_STACKED + if (register_security(&yama_ops)) + panic("Yama: kernel registration failed.\n"); +#endif + +#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); |