diff options
| -rw-r--r-- | Documentation/security/00-INDEX | 2 | ||||
| -rw-r--r-- | Documentation/security/Yama.txt | 60 | ||||
| -rw-r--r-- | include/linux/prctl.h | 6 | ||||
| -rw-r--r-- | security/Kconfig | 6 | ||||
| -rw-r--r-- | security/Makefile | 2 | ||||
| -rw-r--r-- | security/yama/Kconfig | 13 | ||||
| -rw-r--r-- | security/yama/Makefile | 3 | ||||
| -rw-r--r-- | security/yama/yama_lsm.c | 319 |
8 files changed, 411 insertions, 0 deletions
diff --git a/Documentation/security/00-INDEX b/Documentation/security/00-INDEX index 99b85d3..eeed1de 100644 --- a/Documentation/security/00-INDEX +++ b/Documentation/security/00-INDEX @@ -6,6 +6,8 @@ SELinux.txt - how to get started with the SELinux security enhancement. Smack.txt - documentation on the Smack Linux Security Module. +Yama.txt + - documentation on the Yama Linux Security Module. apparmor.txt - documentation on the AppArmor security extension. credentials.txt diff --git a/Documentation/security/Yama.txt b/Documentation/security/Yama.txt new file mode 100644 index 0000000..4f0b789 --- /dev/null +++ b/Documentation/security/Yama.txt @@ -0,0 +1,60 @@ +Yama is a Linux Security Module that collects a number of system-wide DAC +security protections that are not handled by the core kernel itself. To +select it at boot time, specify "security=yama" (though this will disable +any other LSM). + +Yama is controlled through sysctl in /proc/sys/kernel/yama: + +- ptrace_scope + +============================================================== + +ptrace_scope: + +As Linux grows in popularity, it will become a larger target for +malware. One particularly troubling weakness of the Linux process +interfaces is that a single user is able to examine the memory and +running state of any of their processes. For example, if one application +(e.g. Pidgin) was compromised, it would be possible for an attacker to +attach to other running processes (e.g. Firefox, SSH sessions, GPG agent, +etc) to extract additional credentials and continue to expand the scope +of their attack without resorting to user-assisted phishing. + +This is not a theoretical problem. SSH session hijacking +(http://www.storm.net.nz/projects/7) and arbitrary code injection +(http://c-skills.blogspot.com/2007/05/injectso.html) attacks already +exist and remain possible if ptrace is allowed to operate as before. +Since ptrace is not commonly used by non-developers and non-admins, system +builders should be allowed the option to disable this debugging system. + +For a solution, some applications use prctl(PR_SET_DUMPABLE, ...) to +specifically disallow such ptrace attachment (e.g. ssh-agent), but many +do not. A more general solution is to only allow ptrace directly from a +parent to a child process (i.e. direct "gdb EXE" and "strace EXE" still +work), or with CAP_SYS_PTRACE (i.e. "gdb --pid=PID", and "strace -p PID" +still work as root). + +For software that has defined application-specific relationships +between a debugging process and its inferior (crash handlers, etc), +prctl(PR_SET_PTRACER, pid, ...) can be used. An inferior can declare which +other process (and its descendents) are allowed to call PTRACE_ATTACH +against it. Only one such declared debugging process can exists for +each inferior at a time. For example, this is used by KDE, Chromium, and +Firefox's crash handlers, and by Wine for allowing only Wine processes +to ptrace each other. + +0 - classic ptrace permissions: a process can PTRACE_ATTACH to any other + process running under the same uid, as long as it is dumpable (i.e. + did not transition uids, start privileged, or have called + prctl(PR_SET_DUMPABLE...) already). + +1 - restricted ptrace: a process must have a predefined relationship + with the inferior it wants to call PTRACE_ATTACH on. By default, + this relationship is that of only its descendants when the above + classic criteria is also met. To change the relationship, an + inferior can call prctl(PR_SET_PTRACER, debugger, ...) to declare + an allowed debugger PID to call PTRACE_ATTACH on the inferior. + +The original children-only logic was based on the restrictions in grsecurity. + +============================================================== diff --git a/include/linux/prctl.h b/include/linux/prctl.h index 7ddc7f1..4d0e5bc 100644 --- a/include/linux/prctl.h +++ b/include/linux/prctl.h @@ -114,4 +114,10 @@ # define PR_SET_MM_START_BRK 6 # define PR_SET_MM_BRK 7 +/* + * Set specific pid that is allowed to ptrace the current task. + * A value of 0 mean "no process". + */ +#define PR_SET_PTRACER 0x59616d61 + #endif /* _LINUX_PRCTL_H */ diff --git a/security/Kconfig b/security/Kconfig index 51bd5a0..ccc61f8 100644 --- a/security/Kconfig +++ b/security/Kconfig @@ -187,6 +187,7 @@ source security/selinux/Kconfig source security/smack/Kconfig source security/tomoyo/Kconfig source security/apparmor/Kconfig +source security/yama/Kconfig source security/integrity/Kconfig @@ -196,6 +197,7 @@ choice default DEFAULT_SECURITY_SMACK if SECURITY_SMACK default DEFAULT_SECURITY_TOMOYO if SECURITY_TOMOYO default DEFAULT_SECURITY_APPARMOR if SECURITY_APPARMOR + default DEFAULT_SECURITY_YAMA if SECURITY_YAMA default DEFAULT_SECURITY_DAC help @@ -214,6 +216,9 @@ choice config DEFAULT_SECURITY_APPARMOR bool "AppArmor" if SECURITY_APPARMOR=y + config DEFAULT_SECURITY_YAMA + bool "Yama" if SECURITY_YAMA=y + config DEFAULT_SECURITY_DAC bool "Unix Discretionary Access Controls" @@ -225,6 +230,7 @@ config DEFAULT_SECURITY default "smack" if DEFAULT_SECURITY_SMACK default "tomoyo" if DEFAULT_SECURITY_TOMOYO default "apparmor" if DEFAULT_SECURITY_APPARMOR + default "yama" if DEFAULT_SECURITY_YAMA default "" if DEFAULT_SECURITY_DAC endmenu diff --git a/security/Makefile b/security/Makefile index a5e502f..c26c81e 100644 --- a/security/Makefile +++ b/security/Makefile @@ -7,6 +7,7 @@ subdir-$(CONFIG_SECURITY_SELINUX) += selinux subdir-$(CONFIG_SECURITY_SMACK) += smack subdir-$(CONFIG_SECURITY_TOMOYO) += tomoyo subdir-$(CONFIG_SECURITY_APPARMOR) += apparmor +subdir-$(CONFIG_SECURITY_YAMA) += yama # always enable default capabilities obj-y += commoncap.o @@ -21,6 +22,7 @@ obj-$(CONFIG_SECURITY_SMACK) += smack/built-in.o obj-$(CONFIG_AUDIT) += lsm_audit.o obj-$(CONFIG_SECURITY_TOMOYO) += tomoyo/built-in.o obj-$(CONFIG_SECURITY_APPARMOR) += apparmor/built-in.o +obj-$(CONFIG_SECURITY_YAMA) += yama/built-in.o obj-$(CONFIG_CGROUP_DEVICE) += device_cgroup.o # Object integrity file lists diff --git a/security/yama/Kconfig b/security/yama/Kconfig new file mode 100644 index 0000000..51d6709 --- /dev/null +++ b/security/yama/Kconfig @@ -0,0 +1,13 @@ +config SECURITY_YAMA + bool "Yama support" + depends on SECURITY + select SECURITYFS + select SECURITY_PATH + default n + help + This selects Yama, which extends DAC support with additional + system-wide security settings beyond regular Linux discretionary + access controls. Currently available is ptrace scope restriction. + Further information can be found in Documentation/security/Yama.txt. + + If you are unsure how to answer this question, answer N. diff --git a/security/yama/Makefile b/security/yama/Makefile new file mode 100644 index 0000000..8b5e065 --- /dev/null +++ b/security/yama/Makefile @@ -0,0 +1,3 @@ +obj-$(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 0000000..dd4d360 --- /dev/null +++ b/security/yama/yama_lsm.c @@ -0,0 +1,319 @@ +/* + * 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 || + 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 { + 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; + + 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; + break; + } + + if (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); |
