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linux-sg2042/security/device_cgroup.c

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/*
* device_cgroup.c - device cgroup subsystem
*
* Copyright 2007 IBM Corp
*/
#include <linux/device_cgroup.h>
#include <linux/cgroup.h>
#include <linux/ctype.h>
#include <linux/list.h>
#include <linux/uaccess.h>
#include <linux/seq_file.h>
#include <linux/slab.h>
#include <linux/rcupdate.h>
#include <linux/mutex.h>
#define ACC_MKNOD 1
#define ACC_READ 2
#define ACC_WRITE 4
#define ACC_MASK (ACC_MKNOD | ACC_READ | ACC_WRITE)
#define DEV_BLOCK 1
#define DEV_CHAR 2
#define DEV_ALL 4 /* this represents all devices */
static DEFINE_MUTEX(devcgroup_mutex);
enum devcg_behavior {
DEVCG_DEFAULT_NONE,
DEVCG_DEFAULT_ALLOW,
DEVCG_DEFAULT_DENY,
};
/*
* exception list locking rules:
* hold devcgroup_mutex for update/read.
* hold rcu_read_lock() for read.
*/
struct dev_exception_item {
u32 major, minor;
short type;
short access;
struct list_head list;
struct rcu_head rcu;
};
struct dev_cgroup {
struct cgroup_subsys_state css;
struct list_head exceptions;
enum devcg_behavior behavior;
};
static inline struct dev_cgroup *css_to_devcgroup(struct cgroup_subsys_state *s)
{
return s ? container_of(s, struct dev_cgroup, css) : NULL;
}
static inline struct dev_cgroup *task_devcgroup(struct task_struct *task)
{
return css_to_devcgroup(task_css(task, devices_cgrp_id));
}
/*
* called under devcgroup_mutex
*/
static int dev_exceptions_copy(struct list_head *dest, struct list_head *orig)
{
struct dev_exception_item *ex, *tmp, *new;
lockdep_assert_held(&devcgroup_mutex);
list_for_each_entry(ex, orig, list) {
new = kmemdup(ex, sizeof(*ex), GFP_KERNEL);
if (!new)
goto free_and_exit;
list_add_tail(&new->list, dest);
}
return 0;
free_and_exit:
list_for_each_entry_safe(ex, tmp, dest, list) {
list_del(&ex->list);
kfree(ex);
}
return -ENOMEM;
}
/*
* called under devcgroup_mutex
*/
static int dev_exception_add(struct dev_cgroup *dev_cgroup,
struct dev_exception_item *ex)
{
struct dev_exception_item *excopy, *walk;
lockdep_assert_held(&devcgroup_mutex);
excopy = kmemdup(ex, sizeof(*ex), GFP_KERNEL);
if (!excopy)
return -ENOMEM;
list_for_each_entry(walk, &dev_cgroup->exceptions, list) {
if (walk->type != ex->type)
continue;
if (walk->major != ex->major)
continue;
if (walk->minor != ex->minor)
continue;
walk->access |= ex->access;
kfree(excopy);
excopy = NULL;
}
if (excopy != NULL)
list_add_tail_rcu(&excopy->list, &dev_cgroup->exceptions);
return 0;
}
/*
* called under devcgroup_mutex
*/
static void dev_exception_rm(struct dev_cgroup *dev_cgroup,
struct dev_exception_item *ex)
{
struct dev_exception_item *walk, *tmp;
lockdep_assert_held(&devcgroup_mutex);
list_for_each_entry_safe(walk, tmp, &dev_cgroup->exceptions, list) {
if (walk->type != ex->type)
continue;
if (walk->major != ex->major)
continue;
if (walk->minor != ex->minor)
continue;
walk->access &= ~ex->access;
if (!walk->access) {
list_del_rcu(&walk->list);
kfree_rcu(walk, rcu);
}
}
}
static void __dev_exception_clean(struct dev_cgroup *dev_cgroup)
{
struct dev_exception_item *ex, *tmp;
list_for_each_entry_safe(ex, tmp, &dev_cgroup->exceptions, list) {
list_del_rcu(&ex->list);
kfree_rcu(ex, rcu);
}
}
/**
* dev_exception_clean - frees all entries of the exception list
* @dev_cgroup: dev_cgroup with the exception list to be cleaned
*
* called under devcgroup_mutex
*/
static void dev_exception_clean(struct dev_cgroup *dev_cgroup)
{
lockdep_assert_held(&devcgroup_mutex);
__dev_exception_clean(dev_cgroup);
}
static inline bool is_devcg_online(const struct dev_cgroup *devcg)
{
return (devcg->behavior != DEVCG_DEFAULT_NONE);
}
/**
* devcgroup_online - initializes devcgroup's behavior and exceptions based on
* parent's
* @css: css getting online
* returns 0 in case of success, error code otherwise
*/
static int devcgroup_online(struct cgroup_subsys_state *css)
{
struct dev_cgroup *dev_cgroup = css_to_devcgroup(css);
struct dev_cgroup *parent_dev_cgroup = css_to_devcgroup(css->parent);
int ret = 0;
mutex_lock(&devcgroup_mutex);
if (parent_dev_cgroup == NULL)
dev_cgroup->behavior = DEVCG_DEFAULT_ALLOW;
else {
ret = dev_exceptions_copy(&dev_cgroup->exceptions,
&parent_dev_cgroup->exceptions);
if (!ret)
dev_cgroup->behavior = parent_dev_cgroup->behavior;
}
mutex_unlock(&devcgroup_mutex);
return ret;
}
static void devcgroup_offline(struct cgroup_subsys_state *css)
{
struct dev_cgroup *dev_cgroup = css_to_devcgroup(css);
mutex_lock(&devcgroup_mutex);
dev_cgroup->behavior = DEVCG_DEFAULT_NONE;
mutex_unlock(&devcgroup_mutex);
}
/*
* called from kernel/cgroup.c with cgroup_lock() held.
*/
static struct cgroup_subsys_state *
devcgroup_css_alloc(struct cgroup_subsys_state *parent_css)
{
struct dev_cgroup *dev_cgroup;
dev_cgroup = kzalloc(sizeof(*dev_cgroup), GFP_KERNEL);
if (!dev_cgroup)
return ERR_PTR(-ENOMEM);
INIT_LIST_HEAD(&dev_cgroup->exceptions);
dev_cgroup->behavior = DEVCG_DEFAULT_NONE;
return &dev_cgroup->css;
}
static void devcgroup_css_free(struct cgroup_subsys_state *css)
{
struct dev_cgroup *dev_cgroup = css_to_devcgroup(css);
__dev_exception_clean(dev_cgroup);
kfree(dev_cgroup);
}
#define DEVCG_ALLOW 1
#define DEVCG_DENY 2
#define DEVCG_LIST 3
#define MAJMINLEN 13
#define ACCLEN 4
static void set_access(char *acc, short access)
{
int idx = 0;
memset(acc, 0, ACCLEN);
if (access & ACC_READ)
acc[idx++] = 'r';
if (access & ACC_WRITE)
acc[idx++] = 'w';
if (access & ACC_MKNOD)
acc[idx++] = 'm';
}
static char type_to_char(short type)
{
if (type == DEV_ALL)
return 'a';
if (type == DEV_CHAR)
return 'c';
if (type == DEV_BLOCK)
return 'b';
return 'X';
}
static void set_majmin(char *str, unsigned m)
{
if (m == ~0)
strcpy(str, "*");
else
sprintf(str, "%u", m);
}
static int devcgroup_seq_show(struct seq_file *m, void *v)
{
struct dev_cgroup *devcgroup = css_to_devcgroup(seq_css(m));
struct dev_exception_item *ex;
char maj[MAJMINLEN], min[MAJMINLEN], acc[ACCLEN];
rcu_read_lock();
/*
* To preserve the compatibility:
* - Only show the "all devices" when the default policy is to allow
* - List the exceptions in case the default policy is to deny
* This way, the file remains as a "whitelist of devices"
*/
if (devcgroup->behavior == DEVCG_DEFAULT_ALLOW) {
set_access(acc, ACC_MASK);
set_majmin(maj, ~0);
set_majmin(min, ~0);
seq_printf(m, "%c %s:%s %s\n", type_to_char(DEV_ALL),
maj, min, acc);
} else {
list_for_each_entry_rcu(ex, &devcgroup->exceptions, list) {
set_access(acc, ex->access);
set_majmin(maj, ex->major);
set_majmin(min, ex->minor);
seq_printf(m, "%c %s:%s %s\n", type_to_char(ex->type),
maj, min, acc);
}
}
rcu_read_unlock();
return 0;
}
/**
* match_exception - iterates the exception list trying to find a complete match
* @exceptions: list of exceptions
* @type: device type (DEV_BLOCK or DEV_CHAR)
* @major: device file major number, ~0 to match all
* @minor: device file minor number, ~0 to match all
* @access: permission mask (ACC_READ, ACC_WRITE, ACC_MKNOD)
*
* It is considered a complete match if an exception is found that will
* contain the entire range of provided parameters.
*
* Return: true in case it matches an exception completely
*/
static bool match_exception(struct list_head *exceptions, short type,
u32 major, u32 minor, short access)
{
struct dev_exception_item *ex;
list_for_each_entry_rcu(ex, exceptions, list) {
if ((type & DEV_BLOCK) && !(ex->type & DEV_BLOCK))
continue;
if ((type & DEV_CHAR) && !(ex->type & DEV_CHAR))
continue;
if (ex->major != ~0 && ex->major != major)
continue;
if (ex->minor != ~0 && ex->minor != minor)
continue;
/* provided access cannot have more than the exception rule */
if (access & (~ex->access))
continue;
return true;
}
return false;
}
/**
* match_exception_partial - iterates the exception list trying to find a partial match
* @exceptions: list of exceptions
* @type: device type (DEV_BLOCK or DEV_CHAR)
* @major: device file major number, ~0 to match all
* @minor: device file minor number, ~0 to match all
* @access: permission mask (ACC_READ, ACC_WRITE, ACC_MKNOD)
*
* It is considered a partial match if an exception's range is found to
* contain *any* of the devices specified by provided parameters. This is
* used to make sure no extra access is being granted that is forbidden by
* any of the exception list.
*
* Return: true in case the provided range mat matches an exception completely
*/
static bool match_exception_partial(struct list_head *exceptions, short type,
u32 major, u32 minor, short access)
{
struct dev_exception_item *ex;
list_for_each_entry_rcu(ex, exceptions, list) {
if ((type & DEV_BLOCK) && !(ex->type & DEV_BLOCK))
continue;
if ((type & DEV_CHAR) && !(ex->type & DEV_CHAR))
continue;
/*
* We must be sure that both the exception and the provided
* range aren't masking all devices
*/
if (ex->major != ~0 && major != ~0 && ex->major != major)
continue;
if (ex->minor != ~0 && minor != ~0 && ex->minor != minor)
continue;
/*
* In order to make sure the provided range isn't matching
* an exception, all its access bits shouldn't match the
* exception's access bits
*/
if (!(access & ex->access))
continue;
return true;
}
return false;
}
/**
* verify_new_ex - verifies if a new exception is allowed by parent cgroup's permissions
* @dev_cgroup: dev cgroup to be tested against
* @refex: new exception
* @behavior: behavior of the exception's dev_cgroup
*
* This is used to make sure a child cgroup won't have more privileges
* than its parent
*/
static bool verify_new_ex(struct dev_cgroup *dev_cgroup,
struct dev_exception_item *refex,
enum devcg_behavior behavior)
{
bool match = false;
rcu_lockdep_assert(rcu_read_lock_held() ||
lockdep_is_held(&devcgroup_mutex),
"device_cgroup:verify_new_ex called without proper synchronization");
if (dev_cgroup->behavior == DEVCG_DEFAULT_ALLOW) {
if (behavior == DEVCG_DEFAULT_ALLOW) {
/*
* new exception in the child doesn't matter, only
* adding extra restrictions
*/
return true;
} else {
/*
* new exception in the child will add more devices
* that can be acessed, so it can't match any of
* parent's exceptions, even slightly
*/
match = match_exception_partial(&dev_cgroup->exceptions,
refex->type,
refex->major,
refex->minor,
refex->access);
if (match)
return false;
return true;
}
} else {
/*
* Only behavior == DEVCG_DEFAULT_DENY allowed here, therefore
* the new exception will add access to more devices and must
* be contained completely in an parent's exception to be
* allowed
*/
match = match_exception(&dev_cgroup->exceptions, refex->type,
refex->major, refex->minor,
refex->access);
if (match)
/* parent has an exception that matches the proposed */
return true;
else
return false;
}
return false;
}
/*
* parent_has_perm:
* when adding a new allow rule to a device exception list, the rule
* must be allowed in the parent device
*/
static int parent_has_perm(struct dev_cgroup *childcg,
struct dev_exception_item *ex)
{
struct dev_cgroup *parent = css_to_devcgroup(childcg->css.parent);
if (!parent)
return 1;
return verify_new_ex(parent, ex, childcg->behavior);
}
/**
* parent_allows_removal - verify if it's ok to remove an exception
* @childcg: child cgroup from where the exception will be removed
* @ex: exception being removed
*
* When removing an exception in cgroups with default ALLOW policy, it must
* be checked if removing it will give the child cgroup more access than the
* parent.
*
* Return: true if it's ok to remove exception, false otherwise
*/
static bool parent_allows_removal(struct dev_cgroup *childcg,
struct dev_exception_item *ex)
{
struct dev_cgroup *parent = css_to_devcgroup(childcg->css.parent);
if (!parent)
return true;
/* It's always allowed to remove access to devices */
if (childcg->behavior == DEVCG_DEFAULT_DENY)
return true;
/*
* Make sure you're not removing part or a whole exception existing in
* the parent cgroup
*/
return !match_exception_partial(&parent->exceptions, ex->type,
ex->major, ex->minor, ex->access);
}
/**
* may_allow_all - checks if it's possible to change the behavior to
* allow based on parent's rules.
* @parent: device cgroup's parent
* returns: != 0 in case it's allowed, 0 otherwise
*/
static inline int may_allow_all(struct dev_cgroup *parent)
{
if (!parent)
return 1;
return parent->behavior == DEVCG_DEFAULT_ALLOW;
}
/**
* revalidate_active_exceptions - walks through the active exception list and
* revalidates the exceptions based on parent's
* behavior and exceptions. The exceptions that
* are no longer valid will be removed.
* Called with devcgroup_mutex held.
* @devcg: cgroup which exceptions will be checked
*
* This is one of the three key functions for hierarchy implementation.
* This function is responsible for re-evaluating all the cgroup's active
* exceptions due to a parent's exception change.
* Refer to Documentation/cgroups/devices.txt for more details.
*/
static void revalidate_active_exceptions(struct dev_cgroup *devcg)
{
struct dev_exception_item *ex;
struct list_head *this, *tmp;
list_for_each_safe(this, tmp, &devcg->exceptions) {
ex = container_of(this, struct dev_exception_item, list);
if (!parent_has_perm(devcg, ex))
dev_exception_rm(devcg, ex);
}
}
/**
* propagate_exception - propagates a new exception to the children
* @devcg_root: device cgroup that added a new exception
* @ex: new exception to be propagated
*
* returns: 0 in case of success, != 0 in case of error
*/
static int propagate_exception(struct dev_cgroup *devcg_root,
struct dev_exception_item *ex)
{
struct cgroup_subsys_state *pos;
int rc = 0;
rcu_read_lock();
css_for_each_descendant_pre(pos, &devcg_root->css) {
struct dev_cgroup *devcg = css_to_devcgroup(pos);
/*
* Because devcgroup_mutex is held, no devcg will become
* online or offline during the tree walk (see on/offline
* methods), and online ones are safe to access outside RCU
* read lock without bumping refcnt.
*/
if (pos == &devcg_root->css || !is_devcg_online(devcg))
continue;
rcu_read_unlock();
/*
* in case both root's behavior and devcg is allow, a new
* restriction means adding to the exception list
*/
if (devcg_root->behavior == DEVCG_DEFAULT_ALLOW &&
devcg->behavior == DEVCG_DEFAULT_ALLOW) {
rc = dev_exception_add(devcg, ex);
if (rc)
break;
} else {
/*
* in the other possible cases:
* root's behavior: allow, devcg's: deny
* root's behavior: deny, devcg's: deny
* the exception will be removed
*/
dev_exception_rm(devcg, ex);
}
revalidate_active_exceptions(devcg);
rcu_read_lock();
}
rcu_read_unlock();
return rc;
}
/*
* Modify the exception list using allow/deny rules.
* CAP_SYS_ADMIN is needed for this. It's at least separate from CAP_MKNOD
* so we can give a container CAP_MKNOD to let it create devices but not
* modify the exception list.
* It seems likely we'll want to add a CAP_CONTAINER capability to allow
* us to also grant CAP_SYS_ADMIN to containers without giving away the
* device exception list controls, but for now we'll stick with CAP_SYS_ADMIN
*
* Taking rules away is always allowed (given CAP_SYS_ADMIN). Granting
* new access is only allowed if you're in the top-level cgroup, or your
* parent cgroup has the access you're asking for.
*/
static int devcgroup_update_access(struct dev_cgroup *devcgroup,
int filetype, char *buffer)
{
const char *b;
char temp[12]; /* 11 + 1 characters needed for a u32 */
int count, rc = 0;
struct dev_exception_item ex;
struct dev_cgroup *parent = css_to_devcgroup(devcgroup->css.parent);
if (!capable(CAP_SYS_ADMIN))
return -EPERM;
memset(&ex, 0, sizeof(ex));
b = buffer;
switch (*b) {
case 'a':
switch (filetype) {
case DEVCG_ALLOW:
if (css_has_online_children(&devcgroup->css))
return -EINVAL;
if (!may_allow_all(parent))
return -EPERM;
dev_exception_clean(devcgroup);
devcgroup->behavior = DEVCG_DEFAULT_ALLOW;
if (!parent)
break;
rc = dev_exceptions_copy(&devcgroup->exceptions,
&parent->exceptions);
if (rc)
return rc;
break;
case DEVCG_DENY:
if (css_has_online_children(&devcgroup->css))
return -EINVAL;
dev_exception_clean(devcgroup);
devcgroup->behavior = DEVCG_DEFAULT_DENY;
break;
default:
return -EINVAL;
}
return 0;
case 'b':
ex.type = DEV_BLOCK;
break;
case 'c':
ex.type = DEV_CHAR;
break;
default:
return -EINVAL;
}
b++;
if (!isspace(*b))
return -EINVAL;
b++;
if (*b == '*') {
ex.major = ~0;
b++;
} else if (isdigit(*b)) {
memset(temp, 0, sizeof(temp));
for (count = 0; count < sizeof(temp) - 1; count++) {
temp[count] = *b;
b++;
if (!isdigit(*b))
break;
}
rc = kstrtou32(temp, 10, &ex.major);
if (rc)
return -EINVAL;
} else {
return -EINVAL;
}
if (*b != ':')
return -EINVAL;
b++;
/* read minor */
if (*b == '*') {
ex.minor = ~0;
b++;
} else if (isdigit(*b)) {
memset(temp, 0, sizeof(temp));
for (count = 0; count < sizeof(temp) - 1; count++) {
temp[count] = *b;
b++;
if (!isdigit(*b))
break;
}
rc = kstrtou32(temp, 10, &ex.minor);
if (rc)
return -EINVAL;
} else {
return -EINVAL;
}
if (!isspace(*b))
return -EINVAL;
for (b++, count = 0; count < 3; count++, b++) {
switch (*b) {
case 'r':
ex.access |= ACC_READ;
break;
case 'w':
ex.access |= ACC_WRITE;
break;
case 'm':
ex.access |= ACC_MKNOD;
break;
case '\n':
case '\0':
count = 3;
break;
default:
return -EINVAL;
}
}
switch (filetype) {
case DEVCG_ALLOW:
/*
* If the default policy is to allow by default, try to remove
* an matching exception instead. And be silent about it: we
* don't want to break compatibility
*/
if (devcgroup->behavior == DEVCG_DEFAULT_ALLOW) {
/* Check if the parent allows removing it first */
if (!parent_allows_removal(devcgroup, &ex))
return -EPERM;
dev_exception_rm(devcgroup, &ex);
break;
}
if (!parent_has_perm(devcgroup, &ex))
return -EPERM;
rc = dev_exception_add(devcgroup, &ex);
break;
case DEVCG_DENY:
/*
* If the default policy is to deny by default, try to remove
* an matching exception instead. And be silent about it: we
* don't want to break compatibility
*/
if (devcgroup->behavior == DEVCG_DEFAULT_DENY)
dev_exception_rm(devcgroup, &ex);
else
rc = dev_exception_add(devcgroup, &ex);
if (rc)
break;
/* we only propagate new restrictions */
rc = propagate_exception(devcgroup, &ex);
break;
default:
rc = -EINVAL;
}
return rc;
}
static ssize_t devcgroup_access_write(struct kernfs_open_file *of,
char *buf, size_t nbytes, loff_t off)
{
int retval;
mutex_lock(&devcgroup_mutex);
retval = devcgroup_update_access(css_to_devcgroup(of_css(of)),
of_cft(of)->private, strstrip(buf));
mutex_unlock(&devcgroup_mutex);
return retval ?: nbytes;
}
static struct cftype dev_cgroup_files[] = {
{
.name = "allow",
.write = devcgroup_access_write,
.private = DEVCG_ALLOW,
},
{
.name = "deny",
.write = devcgroup_access_write,
.private = DEVCG_DENY,
},
{
.name = "list",
.seq_show = devcgroup_seq_show,
.private = DEVCG_LIST,
},
{ } /* terminate */
};
struct cgroup_subsys devices_cgrp_subsys = {
.css_alloc = devcgroup_css_alloc,
.css_free = devcgroup_css_free,
.css_online = devcgroup_online,
.css_offline = devcgroup_offline,
.base_cftypes = dev_cgroup_files,
};
/**
* __devcgroup_check_permission - checks if an inode operation is permitted
* @dev_cgroup: the dev cgroup to be tested against
* @type: device type
* @major: device major number
* @minor: device minor number
* @access: combination of ACC_WRITE, ACC_READ and ACC_MKNOD
*
* returns 0 on success, -EPERM case the operation is not permitted
*/
static int __devcgroup_check_permission(short type, u32 major, u32 minor,
short access)
{
struct dev_cgroup *dev_cgroup;
bool rc;
rcu_read_lock();
dev_cgroup = task_devcgroup(current);
if (dev_cgroup->behavior == DEVCG_DEFAULT_ALLOW)
/* Can't match any of the exceptions, even partially */
rc = !match_exception_partial(&dev_cgroup->exceptions,
type, major, minor, access);
else
/* Need to match completely one exception to be allowed */
rc = match_exception(&dev_cgroup->exceptions, type, major,
minor, access);
rcu_read_unlock();
if (!rc)
return -EPERM;
return 0;
}
int __devcgroup_inode_permission(struct inode *inode, int mask)
{
short type, access = 0;
if (S_ISBLK(inode->i_mode))
type = DEV_BLOCK;
if (S_ISCHR(inode->i_mode))
type = DEV_CHAR;
if (mask & MAY_WRITE)
access |= ACC_WRITE;
if (mask & MAY_READ)
access |= ACC_READ;
return __devcgroup_check_permission(type, imajor(inode), iminor(inode),
access);
}
int devcgroup_inode_mknod(int mode, dev_t dev)
{
short type;
if (!S_ISBLK(mode) && !S_ISCHR(mode))
return 0;
if (S_ISBLK(mode))
type = DEV_BLOCK;
else
type = DEV_CHAR;
return __devcgroup_check_permission(type, MAJOR(dev), MINOR(dev),
ACC_MKNOD);
}
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