From 700920eb5ba4de5417b446c9a8bb008df2b973e0 Mon Sep 17 00:00:00 2001 From: David Howells Date: Wed, 18 Jan 2012 15:31:45 +0000 Subject: KEYS: Allow special keyrings to be cleared The kernel contains some special internal keyrings, for instance the DNS resolver keyring : 2a93faf1 I----- 1 perm 1f030000 0 0 keyring .dns_resolver: empty It would occasionally be useful to allow the contents of such keyrings to be flushed by root (cache invalidation). Allow a flag to be set on a keyring to mark that someone possessing the sysadmin capability can clear the keyring, even without normal write access to the keyring. Set this flag on the special keyrings created by the DNS resolver, the NFS identity mapper and the CIFS identity mapper. Signed-off-by: David Howells Acked-by: Jeff Layton Acked-by: Steve Dickson Signed-off-by: James Morris --- Documentation/networking/dns_resolver.txt | 4 ++++ Documentation/security/keys.txt | 4 ++++ 2 files changed, 8 insertions(+) (limited to 'Documentation') diff --git a/Documentation/networking/dns_resolver.txt b/Documentation/networking/dns_resolver.txt index 7f531ad8328..d86adcdae42 100644 --- a/Documentation/networking/dns_resolver.txt +++ b/Documentation/networking/dns_resolver.txt @@ -102,6 +102,10 @@ implemented in the module can be called after doing: If _expiry is non-NULL, the expiry time (TTL) of the result will be returned also. +The kernel maintains an internal keyring in which it caches looked up keys. +This can be cleared by any process that has the CAP_SYS_ADMIN capability by +the use of KEYCTL_KEYRING_CLEAR on the keyring ID. + =============================== READING DNS KEYS FROM USERSPACE diff --git a/Documentation/security/keys.txt b/Documentation/security/keys.txt index 4d75931d2d7..713ec232c56 100644 --- a/Documentation/security/keys.txt +++ b/Documentation/security/keys.txt @@ -554,6 +554,10 @@ The keyctl syscall functions are: process must have write permission on the keyring, and it must be a keyring (or else error ENOTDIR will result). + This function can also be used to clear special kernel keyrings if they + are appropriately marked if the user has CAP_SYS_ADMIN capability. The + DNS resolver cache keyring is an example of this. + (*) Link a key into a keyring: -- cgit v1.2.3-70-g09d2 From 2d514487faf188938a4ee4fb3464eeecfbdcf8eb Mon Sep 17 00:00:00 2001 From: Kees Cook Date: Wed, 21 Dec 2011 12:17:04 -0800 Subject: security: Yama LSM This adds the Yama Linux Security Module to collect DAC security improvements (specifically just ptrace restrictions for now) that have existed in various forms over the years and have been carried outside the mainline kernel by other Linux distributions like Openwall and grsecurity. Signed-off-by: Kees Cook Acked-by: John Johansen Signed-off-by: James Morris --- Documentation/security/00-INDEX | 2 + Documentation/security/Yama.txt | 60 ++++++++ include/linux/prctl.h | 6 + security/Kconfig | 6 + security/Makefile | 2 + security/yama/Kconfig | 13 ++ security/yama/Makefile | 3 + security/yama/yama_lsm.c | 319 ++++++++++++++++++++++++++++++++++++++++ 8 files changed, 411 insertions(+) create mode 100644 Documentation/security/Yama.txt create mode 100644 security/yama/Kconfig create mode 100644 security/yama/Makefile create mode 100644 security/yama/yama_lsm.c (limited to 'Documentation') diff --git a/Documentation/security/00-INDEX b/Documentation/security/00-INDEX index 99b85d39751..eeed1de546d 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 00000000000..4f0b7896a21 --- /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 7ddc7f1b480..4d0e5bc5458 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 51bd5a0b69a..ccc61f8006b 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 a5e502f8a05..c26c81e9257 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-$(CONFIG_CGROUP_DEVICE) += device_cgroup.o # Object integrity file lists diff --git a/security/yama/Kconfig b/security/yama/Kconfig new file mode 100644 index 00000000000..51d6709d8bb --- /dev/null +++ b/security/yama/Kconfig @@ -0,0 +1,13 @@ +config SECURITY_YAMA + bool "Yama support" + depends on SECURITY + select SECURITYFS + select SECURITY_PATH + default n + help + This selects Yama, which extends DAC support with additional + system-wide security settings beyond regular Linux discretionary + access controls. Currently available is ptrace scope restriction. + Further information can be found in Documentation/security/Yama.txt. + + If you are unsure how to answer this question, answer N. diff --git a/security/yama/Makefile b/security/yama/Makefile new file mode 100644 index 00000000000..8b5e0658845 --- /dev/null +++ b/security/yama/Makefile @@ -0,0 +1,3 @@ +obj-$(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 00000000000..dd4d36067c5 --- /dev/null +++ b/security/yama/yama_lsm.c @@ -0,0 +1,319 @@ +/* + * Yama Linux Security Module + * + * Author: Kees Cook + * + * 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 +#include +#include +#include +#include + +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); -- cgit v1.2.3-70-g09d2 From bf06189e4d14641c0148bea16e9dd24943862215 Mon Sep 17 00:00:00 2001 From: Kees Cook Date: Tue, 14 Feb 2012 16:48:09 -0800 Subject: Yama: add PR_SET_PTRACER_ANY For a process to entirely disable Yama ptrace restrictions, it can use the special PR_SET_PTRACER_ANY pid to indicate that any otherwise allowed process may ptrace it. This is stronger than calling PR_SET_PTRACER with pid "1" because it includes processes in external pid namespaces. This is currently needed by the Chrome renderer, since its crash handler (Breakpad) runs external to the renderer's pid namespace. Signed-off-by: Kees Cook Signed-off-by: James Morris --- Documentation/security/Yama.txt | 7 ++++++- include/linux/prctl.h | 1 + security/yama/yama_lsm.c | 8 ++++++-- 3 files changed, 13 insertions(+), 3 deletions(-) (limited to 'Documentation') diff --git a/Documentation/security/Yama.txt b/Documentation/security/Yama.txt index 4f0b7896a21..a9511f17906 100644 --- a/Documentation/security/Yama.txt +++ b/Documentation/security/Yama.txt @@ -41,7 +41,12 @@ 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. +to ptrace each other. If a process wishes to entirely disable these ptrace +restrictions, it can call prctl(PR_SET_PTRACER, PR_SET_PTRACER_ANY, ...) +so that any otherwise allowed process (even those in external pid namespaces) +may attach. + +The sysctl settings are: 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. diff --git a/include/linux/prctl.h b/include/linux/prctl.h index 4d0e5bc5458..a0413ac3abe 100644 --- a/include/linux/prctl.h +++ b/include/linux/prctl.h @@ -119,5 +119,6 @@ * A value of 0 mean "no process". */ #define PR_SET_PTRACER 0x59616d61 +# define PR_SET_PTRACER_ANY ((unsigned long)-1) #endif /* _LINUX_PRCTL_H */ diff --git a/security/yama/yama_lsm.c b/security/yama/yama_lsm.c index dd4d36067c5..573723843a0 100644 --- a/security/yama/yama_lsm.c +++ b/security/yama/yama_lsm.c @@ -84,7 +84,7 @@ static void yama_ptracer_del(struct task_struct *tracer, spin_lock_bh(&ptracer_relations_lock); list_for_each_entry_safe(relation, safe, &ptracer_relations, node) if (relation->tracee == tracee || - relation->tracer == tracer) { + (tracer && relation->tracer == tracer)) { list_del(&relation->node); kfree(relation); } @@ -138,6 +138,8 @@ static int yama_task_prctl(int option, unsigned long arg2, unsigned long arg3, 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; @@ -208,6 +210,7 @@ static int ptracer_exception_found(struct task_struct *tracer, int rc = 0; struct ptrace_relation *relation; struct task_struct *parent = NULL; + bool found = false; spin_lock_bh(&ptracer_relations_lock); rcu_read_lock(); @@ -216,10 +219,11 @@ static int ptracer_exception_found(struct task_struct *tracer, list_for_each_entry(relation, &ptracer_relations, node) if (relation->tracee == tracee) { parent = relation->tracer; + found = true; break; } - if (task_is_descendant(parent, tracer)) + if (found && (parent == NULL || task_is_descendant(parent, tracer))) rc = 1; rcu_read_unlock(); spin_unlock_bh(&ptracer_relations_lock); -- cgit v1.2.3-70-g09d2