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 <keescook@chromium.org> Acked-by: John Johansen <john.johansen@canonical.com> Signed-off-by: James Morris <jmorris@namei.org>

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 <keescook@chromium.org> Acked-by: John Johansen <john.johansen@canonical.com> Signed-off-by: James Morris <jmorris@namei.org>
Kees Cook · James Morris
1 parent 1a2a4d06e1
Showing 8 changed files with 411 additions and 0 deletions Side-by-side Diff
Documentation/security/00-INDEX
Documentation/security/Yama.txt
include/linux/prctl.h
security/Kconfig
security/Makefile
security/yama/Kconfig
security/yama/Makefile
security/yama/yama_lsm.c
@@ -6,6 +6,8 @@
 	- 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
+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.
+
+==============================================================
@@ -114,5 +114,11 @@
 # 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 */
@@ -187,6 +187,7 @@
 source security/smack/Kconfig
 source security/tomoyo/Kconfig
 source security/apparmor/Kconfig
+source security/yama/Kconfig
  
 source security/integrity/Kconfig
  
@@ -196,6 +197,7 @@
 	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 @@
 	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 @@
 	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
@@ -7,6 +7,7 @@
 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-$(CONFIG_AUDIT)			+= lsm_audit.o
 obj-$(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
+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.
+obj-$(CONFIG_SECURITY_YAMA) := yama.o
+
+yama-y := yama_lsm.o
+/*
+ * 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);
...	...	@@ -6,6 +6,8 @@
6	6	- how to get started with the SELinux security enhancement.
7	7	Smack.txt
8	8	- documentation on the Smack Linux Security Module.
	9	+Yama.txt
	10	+ - documentation on the Yama Linux Security Module.
9	11	apparmor.txt
10	12	- documentation on the AppArmor security extension.
11	13	credentials.txt
	1	+Yama is a Linux Security Module that collects a number of system-wide DAC
	2	+security protections that are not handled by the core kernel itself. To
	3	+select it at boot time, specify "security=yama" (though this will disable
	4	+any other LSM).
	5	+
	6	+Yama is controlled through sysctl in /proc/sys/kernel/yama:
	7	+
	8	+- ptrace_scope
	9	+
	10	+==============================================================
	11	+
	12	+ptrace_scope:
	13	+
	14	+As Linux grows in popularity, it will become a larger target for
	15	+malware. One particularly troubling weakness of the Linux process
	16	+interfaces is that a single user is able to examine the memory and
	17	+running state of any of their processes. For example, if one application
	18	+(e.g. Pidgin) was compromised, it would be possible for an attacker to
	19	+attach to other running processes (e.g. Firefox, SSH sessions, GPG agent,
	20	+etc) to extract additional credentials and continue to expand the scope
	21	+of their attack without resorting to user-assisted phishing.
	22	+
	23	+This is not a theoretical problem. SSH session hijacking
	24	+(http://www.storm.net.nz/projects/7) and arbitrary code injection
	25	+(http://c-skills.blogspot.com/2007/05/injectso.html) attacks already
	26	+exist and remain possible if ptrace is allowed to operate as before.
	27	+Since ptrace is not commonly used by non-developers and non-admins, system
	28	+builders should be allowed the option to disable this debugging system.
	29	+
	30	+For a solution, some applications use prctl(PR_SET_DUMPABLE, ...) to
	31	+specifically disallow such ptrace attachment (e.g. ssh-agent), but many
	32	+do not. A more general solution is to only allow ptrace directly from a
	33	+parent to a child process (i.e. direct "gdb EXE" and "strace EXE" still
	34	+work), or with CAP_SYS_PTRACE (i.e. "gdb --pid=PID", and "strace -p PID"
	35	+still work as root).
	36	+
	37	+For software that has defined application-specific relationships
	38	+between a debugging process and its inferior (crash handlers, etc),
	39	+prctl(PR_SET_PTRACER, pid, ...) can be used. An inferior can declare which
	40	+other process (and its descendents) are allowed to call PTRACE_ATTACH
	41	+against it. Only one such declared debugging process can exists for
	42	+each inferior at a time. For example, this is used by KDE, Chromium, and
	43	+Firefox's crash handlers, and by Wine for allowing only Wine processes
	44	+to ptrace each other.
	45	+
	46	+0 - classic ptrace permissions: a process can PTRACE_ATTACH to any other
	47	+ process running under the same uid, as long as it is dumpable (i.e.
	48	+ did not transition uids, start privileged, or have called
	49	+ prctl(PR_SET_DUMPABLE...) already).
	50	+
	51	+1 - restricted ptrace: a process must have a predefined relationship
	52	+ with the inferior it wants to call PTRACE_ATTACH on. By default,
	53	+ this relationship is that of only its descendants when the above
	54	+ classic criteria is also met. To change the relationship, an
	55	+ inferior can call prctl(PR_SET_PTRACER, debugger, ...) to declare
	56	+ an allowed debugger PID to call PTRACE_ATTACH on the inferior.
	57	+
	58	+The original children-only logic was based on the restrictions in grsecurity.
	59	+
	60	+==============================================================
...	...	@@ -114,5 +114,11 @@
114	114	# define PR_SET_MM_START_BRK 6
115	115	# define PR_SET_MM_BRK 7
116	116
	117	+/*
	118	+ * Set specific pid that is allowed to ptrace the current task.
	119	+ * A value of 0 mean "no process".
	120	+ */
	121	+#define PR_SET_PTRACER 0x59616d61
	122	+
117	123	#endif /* _LINUX_PRCTL_H */
...	...	@@ -187,6 +187,7 @@
187	187	source security/smack/Kconfig
188	188	source security/tomoyo/Kconfig
189	189	source security/apparmor/Kconfig
	190	+source security/yama/Kconfig
190	191
191	192	source security/integrity/Kconfig
192	193
...	...	@@ -196,6 +197,7 @@
196	197	default DEFAULT_SECURITY_SMACK if SECURITY_SMACK
197	198	default DEFAULT_SECURITY_TOMOYO if SECURITY_TOMOYO
198	199	default DEFAULT_SECURITY_APPARMOR if SECURITY_APPARMOR
	200	+ default DEFAULT_SECURITY_YAMA if SECURITY_YAMA
199	201	default DEFAULT_SECURITY_DAC
200	202
201	203	help
...	...	@@ -214,6 +216,9 @@
214	216	config DEFAULT_SECURITY_APPARMOR
215	217	bool "AppArmor" if SECURITY_APPARMOR=y
216	218
	219	+ config DEFAULT_SECURITY_YAMA
	220	+ bool "Yama" if SECURITY_YAMA=y
	221	+
217	222	config DEFAULT_SECURITY_DAC
218	223	bool "Unix Discretionary Access Controls"
219	224
...	...	@@ -225,6 +230,7 @@
225	230	default "smack" if DEFAULT_SECURITY_SMACK
226	231	default "tomoyo" if DEFAULT_SECURITY_TOMOYO
227	232	default "apparmor" if DEFAULT_SECURITY_APPARMOR
	233	+ default "yama" if DEFAULT_SECURITY_YAMA
228	234	default "" if DEFAULT_SECURITY_DAC
229	235
230	236	endmenu
...	...	@@ -7,6 +7,7 @@
7	7	subdir-$(CONFIG_SECURITY_SMACK) += smack
8	8	subdir-$(CONFIG_SECURITY_TOMOYO) += tomoyo
9	9	subdir-$(CONFIG_SECURITY_APPARMOR) += apparmor
	10	+subdir-$(CONFIG_SECURITY_YAMA) += yama
10	11
11	12	# always enable default capabilities
12	13	obj-y += commoncap.o
...	...	@@ -21,6 +22,7 @@
21	22	obj-$(CONFIG_AUDIT) += lsm_audit.o
22	23	obj-$(CONFIG_SECURITY_TOMOYO) += tomoyo/built-in.o
23	24	obj-$(CONFIG_SECURITY_APPARMOR) += apparmor/built-in.o
	25	+obj-$(CONFIG_SECURITY_YAMA) += yama/built-in.o
24	26	obj-$(CONFIG_CGROUP_DEVICE) += device_cgroup.o
25	27
26	28	# Object integrity file lists
	1	+config SECURITY_YAMA
	2	+ bool "Yama support"
	3	+ depends on SECURITY
	4	+ select SECURITYFS
	5	+ select SECURITY_PATH
	6	+ default n
	7	+ help
	8	+ This selects Yama, which extends DAC support with additional
	9	+ system-wide security settings beyond regular Linux discretionary
	10	+ access controls. Currently available is ptrace scope restriction.
	11	+ Further information can be found in Documentation/security/Yama.txt.
	12	+
	13	+ If you are unsure how to answer this question, answer N.
	1	+obj-$(CONFIG_SECURITY_YAMA) := yama.o
	2	+
	3	+yama-y := yama_lsm.o
	1	+/*
	2	+ * Yama Linux Security Module
	3	+ *
	4	+ * Author: Kees Cook <keescook@chromium.org>
	5	+ *
	6	+ * Copyright (C) 2010 Canonical, Ltd.
	7	+ * Copyright (C) 2011 The Chromium OS Authors.
	8	+ *
	9	+ * This program is free software; you can redistribute it and/or modify
	10	+ * it under the terms of the GNU General Public License version 2, as
	11	+ * published by the Free Software Foundation.
	12	+ *
	13	+ */
	14	+
	15	+#include <linux/security.h>
	16	+#include <linux/sysctl.h>
	17	+#include <linux/ptrace.h>
	18	+#include <linux/prctl.h>
	19	+#include <linux/ratelimit.h>
	20	+
	21	+static int ptrace_scope = 1;
	22	+
	23	+/* describe a ptrace relationship for potential exception */
	24	+struct ptrace_relation {
	25	+ struct task_struct *tracer;
	26	+ struct task_struct *tracee;
	27	+ struct list_head node;
	28	+};
	29	+
	30	+static LIST_HEAD(ptracer_relations);
	31	+static DEFINE_SPINLOCK(ptracer_relations_lock);
	32	+
	33	+/**
	34	+ * yama_ptracer_add - add/replace an exception for this tracer/tracee pair
	35	+ * @tracer: the task_struct of the process doing the ptrace
	36	+ * @tracee: the task_struct of the process to be ptraced
	37	+ *
	38	+ * Each tracee can have, at most, one tracer registered. Each time this
	39	+ * is called, the prior registered tracer will be replaced for the tracee.
	40	+ *
	41	+ * Returns 0 if relationship was added, -ve on error.
	42	+ */
	43	+static int yama_ptracer_add(struct task_struct *tracer,
	44	+ struct task_struct *tracee)
	45	+{
	46	+ int rc = 0;
	47	+ struct ptrace_relation *added;
	48	+ struct ptrace_relation entry, relation = NULL;
	49	+
	50	+ added = kmalloc(sizeof(*added), GFP_KERNEL);
	51	+ if (!added)
	52	+ return -ENOMEM;
	53	+
	54	+ spin_lock_bh(&ptracer_relations_lock);
	55	+ list_for_each_entry(entry, &ptracer_relations, node)
	56	+ if (entry->tracee == tracee) {
	57	+ relation = entry;
	58	+ break;
	59	+ }
	60	+ if (!relation) {
	61	+ relation = added;
	62	+ relation->tracee = tracee;
	63	+ list_add(&relation->node, &ptracer_relations);
	64	+ }
	65	+ relation->tracer = tracer;
	66	+
	67	+ spin_unlock_bh(&ptracer_relations_lock);
	68	+ if (added != relation)
	69	+ kfree(added);
	70	+
	71	+ return rc;
	72	+}
	73	+
	74	+/**
	75	+ * yama_ptracer_del - remove exceptions related to the given tasks
	76	+ * @tracer: remove any relation where tracer task matches
	77	+ * @tracee: remove any relation where tracee task matches
	78	+ */
	79	+static void yama_ptracer_del(struct task_struct *tracer,
	80	+ struct task_struct *tracee)
	81	+{
	82	+ struct ptrace_relation relation, safe;
	83	+
	84	+ spin_lock_bh(&ptracer_relations_lock);
	85	+ list_for_each_entry_safe(relation, safe, &ptracer_relations, node)
	86	+ if (relation->tracee == tracee \|\|
	87	+ relation->tracer == tracer) {
	88	+ list_del(&relation->node);
	89	+ kfree(relation);
	90	+ }
	91	+ spin_unlock_bh(&ptracer_relations_lock);
	92	+}
	93	+
	94	+/**
	95	+ * yama_task_free - check for task_pid to remove from exception list
	96	+ * @task: task being removed
	97	+ */
	98	+static void yama_task_free(struct task_struct *task)
	99	+{
	100	+ yama_ptracer_del(task, task);
	101	+}
	102	+
	103	+/**
	104	+ * yama_task_prctl - check for Yama-specific prctl operations
	105	+ * @option: operation
	106	+ * @arg2: argument
	107	+ * @arg3: argument
	108	+ * @arg4: argument
	109	+ * @arg5: argument
	110	+ *
	111	+ * Return 0 on success, -ve on error. -ENOSYS is returned when Yama
	112	+ * does not handle the given option.
	113	+ */
	114	+static int yama_task_prctl(int option, unsigned long arg2, unsigned long arg3,
	115	+ unsigned long arg4, unsigned long arg5)
	116	+{
	117	+ int rc;
	118	+ struct task_struct *myself = current;
	119	+
	120	+ rc = cap_task_prctl(option, arg2, arg3, arg4, arg5);
	121	+ if (rc != -ENOSYS)
	122	+ return rc;
	123	+
	124	+ switch (option) {
	125	+ case PR_SET_PTRACER:
	126	+ /* Since a thread can call prctl(), find the group leader
	127	+ * before calling _add() or _del() on it, since we want
	128	+ * process-level granularity of control. The tracer group
	129	+ * leader checking is handled later when walking the ancestry
	130	+ * at the time of PTRACE_ATTACH check.
	131	+ */
	132	+ rcu_read_lock();
	133	+ if (!thread_group_leader(myself))
	134	+ myself = rcu_dereference(myself->group_leader);
	135	+ get_task_struct(myself);
	136	+ rcu_read_unlock();
	137	+
	138	+ if (arg2 == 0) {
	139	+ yama_ptracer_del(NULL, myself);
	140	+ rc = 0;
	141	+ } else {
	142	+ struct task_struct *tracer;
	143	+
	144	+ rcu_read_lock();
	145	+ tracer = find_task_by_vpid(arg2);
	146	+ if (tracer)
	147	+ get_task_struct(tracer);
	148	+ else
	149	+ rc = -EINVAL;
	150	+ rcu_read_unlock();
	151	+
	152	+ if (tracer) {
	153	+ rc = yama_ptracer_add(tracer, myself);
	154	+ put_task_struct(tracer);
	155	+ }
	156	+ }
	157	+
	158	+ put_task_struct(myself);
	159	+ break;
	160	+ }
	161	+
	162	+ return rc;
	163	+}
	164	+
	165	+/**
	166	+ * task_is_descendant - walk up a process family tree looking for a match
	167	+ * @parent: the process to compare against while walking up from child
	168	+ * @child: the process to start from while looking upwards for parent
	169	+ *
	170	+ * Returns 1 if child is a descendant of parent, 0 if not.
	171	+ */
	172	+static int task_is_descendant(struct task_struct *parent,
	173	+ struct task_struct *child)
	174	+{
	175	+ int rc = 0;
	176	+ struct task_struct *walker = child;
	177	+
	178	+ if (!parent \|\| !child)
	179	+ return 0;
	180	+
	181	+ rcu_read_lock();
	182	+ if (!thread_group_leader(parent))
	183	+ parent = rcu_dereference(parent->group_leader);
	184	+ while (walker->pid > 0) {
	185	+ if (!thread_group_leader(walker))
	186	+ walker = rcu_dereference(walker->group_leader);
	187	+ if (walker == parent) {
	188	+ rc = 1;
	189	+ break;
	190	+ }
	191	+ walker = rcu_dereference(walker->real_parent);
	192	+ }
	193	+ rcu_read_unlock();
	194	+
	195	+ return rc;
	196	+}
	197	+
	198	+/**
	199	+ * ptracer_exception_found - tracer registered as exception for this tracee
	200	+ * @tracer: the task_struct of the process attempting ptrace
	201	+ * @tracee: the task_struct of the process to be ptraced
	202	+ *
	203	+ * Returns 1 if tracer has is ptracer exception ancestor for tracee.
	204	+ */
	205	+static int ptracer_exception_found(struct task_struct *tracer,
	206	+ struct task_struct *tracee)
	207	+{
	208	+ int rc = 0;
	209	+ struct ptrace_relation *relation;
	210	+ struct task_struct *parent = NULL;
	211	+
	212	+ spin_lock_bh(&ptracer_relations_lock);
	213	+ rcu_read_lock();
	214	+ if (!thread_group_leader(tracee))
	215	+ tracee = rcu_dereference(tracee->group_leader);
	216	+ list_for_each_entry(relation, &ptracer_relations, node)
	217	+ if (relation->tracee == tracee) {
	218	+ parent = relation->tracer;
	219	+ break;
	220	+ }
	221	+
	222	+ if (task_is_descendant(parent, tracer))
	223	+ rc = 1;
	224	+ rcu_read_unlock();
	225	+ spin_unlock_bh(&ptracer_relations_lock);
	226	+
	227	+ return rc;
	228	+}
	229	+
	230	+/**
	231	+ * yama_ptrace_access_check - validate PTRACE_ATTACH calls
	232	+ * @child: task that current task is attempting to ptrace
	233	+ * @mode: ptrace attach mode
	234	+ *
	235	+ * Returns 0 if following the ptrace is allowed, -ve on error.
	236	+ */
	237	+static int yama_ptrace_access_check(struct task_struct *child,
	238	+ unsigned int mode)
	239	+{
	240	+ int rc;
	241	+
	242	+ /* If standard caps disallows it, so does Yama. We should
	243	+ * only tighten restrictions further.
	244	+ */
	245	+ rc = cap_ptrace_access_check(child, mode);
	246	+ if (rc)
	247	+ return rc;
	248	+
	249	+ /* require ptrace target be a child of ptracer on attach */
	250	+ if (mode == PTRACE_MODE_ATTACH &&
	251	+ ptrace_scope &&
	252	+ !task_is_descendant(current, child) &&
	253	+ !ptracer_exception_found(current, child) &&
	254	+ !capable(CAP_SYS_PTRACE))
	255	+ rc = -EPERM;
	256	+
	257	+ if (rc) {
	258	+ char name[sizeof(current->comm)];
	259	+ printk_ratelimited(KERN_NOTICE "ptrace of non-child"
	260	+ " pid %d was attempted by: %s (pid %d)\n",
	261	+ child->pid,
	262	+ get_task_comm(name, current),
	263	+ current->pid);
	264	+ }
	265	+
	266	+ return rc;
	267	+}
	268	+
	269	+static struct security_operations yama_ops = {
	270	+ .name = "yama",
	271	+
	272	+ .ptrace_access_check = yama_ptrace_access_check,
	273	+ .task_prctl = yama_task_prctl,
	274	+ .task_free = yama_task_free,
	275	+};
	276	+
	277	+#ifdef CONFIG_SYSCTL
	278	+static int zero;
	279	+static int one = 1;
	280	+
	281	+struct ctl_path yama_sysctl_path[] = {
	282	+ { .procname = "kernel", },
	283	+ { .procname = "yama", },
	284	+ { }
	285	+};
	286	+
	287	+static struct ctl_table yama_sysctl_table[] = {
	288	+ {
	289	+ .procname = "ptrace_scope",
	290	+ .data = &ptrace_scope,
	291	+ .maxlen = sizeof(int),
	292	+ .mode = 0644,
	293	+ .proc_handler = proc_dointvec_minmax,
	294	+ .extra1 = &zero,
	295	+ .extra2 = &one,
	296	+ },
	297	+ { }
	298	+};
	299	+#endif /* CONFIG_SYSCTL */
	300	+
	301	+static __init int yama_init(void)
	302	+{
	303	+ if (!security_module_enable(&yama_ops))
	304	+ return 0;
	305	+
	306	+ printk(KERN_INFO "Yama: becoming mindful.\n");
	307	+
	308	+ if (register_security(&yama_ops))
	309	+ panic("Yama: kernel registration failed.\n");
	310	+
	311	+#ifdef CONFIG_SYSCTL
	312	+ if (!register_sysctl_paths(yama_sysctl_path, yama_sysctl_table))
	313	+ panic("Yama: sysctl registration failed.\n");
	314	+#endif
	315	+
	316	+ return 0;
	317	+}
	318	+
	319	+security_initcall(yama_init);