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DEFINITIONS
This source file includes following definitions.
- css_to_devcgroup
- cgroup_to_devcgroup
- task_devcgroup
- devcgroup_can_attach
- dev_whitelist_copy
- dev_whitelist_add
- whitelist_item_free
- dev_whitelist_rm
- devcgroup_create
- devcgroup_destroy
- set_access
- type_to_char
- set_majmin
- devcgroup_seq_read
- may_access_whitelist
- parent_has_perm
- devcgroup_update_access
- devcgroup_access_write
- devcgroup_populate
- devcgroup_inode_permission
- devcgroup_inode_mknod
/*
* dev_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>
#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 */
/*
* whitelist locking rules:
* cgroup_lock() cannot be taken under dev_cgroup->lock.
* dev_cgroup->lock can be taken with or without cgroup_lock().
*
* modifications always require cgroup_lock
* modifications to a list which is visible require the
* dev_cgroup->lock *and* cgroup_lock()
* walking the list requires dev_cgroup->lock or cgroup_lock().
*
* reasoning: dev_whitelist_copy() needs to kmalloc, so needs
* a mutex, which the cgroup_lock() is. Since modifying
* a visible list requires both locks, either lock can be
* taken for walking the list.
*/
struct dev_whitelist_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 whitelist;
spinlock_t lock;
};
static inline struct dev_cgroup *css_to_devcgroup(struct cgroup_subsys_state *s)
{
return container_of(s, struct dev_cgroup, css);
}
static inline struct dev_cgroup *cgroup_to_devcgroup(struct cgroup *cgroup)
{
return css_to_devcgroup(cgroup_subsys_state(cgroup, devices_subsys_id));
}
static inline struct dev_cgroup *task_devcgroup(struct task_struct *task)
{
return css_to_devcgroup(task_subsys_state(task, devices_subsys_id));
}
struct cgroup_subsys devices_subsys;
static int devcgroup_can_attach(struct cgroup_subsys *ss,
struct cgroup *new_cgroup, struct task_struct *task)
{
if (current != task && !capable(CAP_SYS_ADMIN))
return -EPERM;
return 0;
}
/*
* called under cgroup_lock()
*/
static int dev_whitelist_copy(struct list_head *dest, struct list_head *orig)
{
struct dev_whitelist_item *wh, *tmp, *new;
list_for_each_entry(wh, orig, list) {
new = kmalloc(sizeof(*wh), GFP_KERNEL);
if (!new)
goto free_and_exit;
new->major = wh->major;
new->minor = wh->minor;
new->type = wh->type;
new->access = wh->access;
list_add_tail(&new->list, dest);
}
return 0;
free_and_exit:
list_for_each_entry_safe(wh, tmp, dest, list) {
list_del(&wh->list);
kfree(wh);
}
return -ENOMEM;
}
/* Stupid prototype - don't bother combining existing entries */
/*
* called under cgroup_lock()
* since the list is visible to other tasks, we need the spinlock also
*/
static int dev_whitelist_add(struct dev_cgroup *dev_cgroup,
struct dev_whitelist_item *wh)
{
struct dev_whitelist_item *whcopy, *walk;
whcopy = kmalloc(sizeof(*whcopy), GFP_KERNEL);
if (!whcopy)
return -ENOMEM;
memcpy(whcopy, wh, sizeof(*whcopy));
spin_lock(&dev_cgroup->lock);
list_for_each_entry(walk, &dev_cgroup->whitelist, list) {
if (walk->type != wh->type)
continue;
if (walk->major != wh->major)
continue;
if (walk->minor != wh->minor)
continue;
walk->access |= wh->access;
kfree(whcopy);
whcopy = NULL;
}
if (whcopy != NULL)
list_add_tail_rcu(&whcopy->list, &dev_cgroup->whitelist);
spin_unlock(&dev_cgroup->lock);
return 0;
}
static void whitelist_item_free(struct rcu_head *rcu)
{
struct dev_whitelist_item *item;
item = container_of(rcu, struct dev_whitelist_item, rcu);
kfree(item);
}
/*
* called under cgroup_lock()
* since the list is visible to other tasks, we need the spinlock also
*/
static void dev_whitelist_rm(struct dev_cgroup *dev_cgroup,
struct dev_whitelist_item *wh)
{
struct dev_whitelist_item *walk, *tmp;
spin_lock(&dev_cgroup->lock);
list_for_each_entry_safe(walk, tmp, &dev_cgroup->whitelist, list) {
if (walk->type == DEV_ALL)
goto remove;
if (walk->type != wh->type)
continue;
if (walk->major != ~0 && walk->major != wh->major)
continue;
if (walk->minor != ~0 && walk->minor != wh->minor)
continue;
remove:
walk->access &= ~wh->access;
if (!walk->access) {
list_del_rcu(&walk->list);
call_rcu(&walk->rcu, whitelist_item_free);
}
}
spin_unlock(&dev_cgroup->lock);
}
/*
* called from kernel/cgroup.c with cgroup_lock() held.
*/
static struct cgroup_subsys_state *devcgroup_create(struct cgroup_subsys *ss,
struct cgroup *cgroup)
{
struct dev_cgroup *dev_cgroup, *parent_dev_cgroup;
struct cgroup *parent_cgroup;
int ret;
dev_cgroup = kzalloc(sizeof(*dev_cgroup), GFP_KERNEL);
if (!dev_cgroup)
return ERR_PTR(-ENOMEM);
INIT_LIST_HEAD(&dev_cgroup->whitelist);
parent_cgroup = cgroup->parent;
if (parent_cgroup == NULL) {
struct dev_whitelist_item *wh;
wh = kmalloc(sizeof(*wh), GFP_KERNEL);
if (!wh) {
kfree(dev_cgroup);
return ERR_PTR(-ENOMEM);
}
wh->minor = wh->major = ~0;
wh->type = DEV_ALL;
wh->access = ACC_MASK;
list_add(&wh->list, &dev_cgroup->whitelist);
} else {
parent_dev_cgroup = cgroup_to_devcgroup(parent_cgroup);
ret = dev_whitelist_copy(&dev_cgroup->whitelist,
&parent_dev_cgroup->whitelist);
if (ret) {
kfree(dev_cgroup);
return ERR_PTR(ret);
}
}
spin_lock_init(&dev_cgroup->lock);
return &dev_cgroup->css;
}
static void devcgroup_destroy(struct cgroup_subsys *ss,
struct cgroup *cgroup)
{
struct dev_cgroup *dev_cgroup;
struct dev_whitelist_item *wh, *tmp;
dev_cgroup = cgroup_to_devcgroup(cgroup);
list_for_each_entry_safe(wh, tmp, &dev_cgroup->whitelist, list) {
list_del(&wh->list);
kfree(wh);
}
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_read(struct cgroup *cgroup, struct cftype *cft,
struct seq_file *m)
{
struct dev_cgroup *devcgroup = cgroup_to_devcgroup(cgroup);
struct dev_whitelist_item *wh;
char maj[MAJMINLEN], min[MAJMINLEN], acc[ACCLEN];
rcu_read_lock();
list_for_each_entry_rcu(wh, &devcgroup->whitelist, list) {
set_access(acc, wh->access);
set_majmin(maj, wh->major);
set_majmin(min, wh->minor);
seq_printf(m, "%c %s:%s %s\n", type_to_char(wh->type),
maj, min, acc);
}
rcu_read_unlock();
return 0;
}
/*
* may_access_whitelist:
* does the access granted to dev_cgroup c contain the access
* requested in whitelist item refwh.
* return 1 if yes, 0 if no.
* call with c->lock held
*/
static int may_access_whitelist(struct dev_cgroup *c,
struct dev_whitelist_item *refwh)
{
struct dev_whitelist_item *whitem;
list_for_each_entry(whitem, &c->whitelist, list) {
if (whitem->type & DEV_ALL)
return 1;
if ((refwh->type & DEV_BLOCK) && !(whitem->type & DEV_BLOCK))
continue;
if ((refwh->type & DEV_CHAR) && !(whitem->type & DEV_CHAR))
continue;
if (whitem->major != ~0 && whitem->major != refwh->major)
continue;
if (whitem->minor != ~0 && whitem->minor != refwh->minor)
continue;
if (refwh->access & (~whitem->access))
continue;
return 1;
}
return 0;
}
/*
* parent_has_perm:
* when adding a new allow rule to a device whitelist, the rule
* must be allowed in the parent device
*/
static int parent_has_perm(struct dev_cgroup *childcg,
struct dev_whitelist_item *wh)
{
struct cgroup *pcg = childcg->css.cgroup->parent;
struct dev_cgroup *parent;
int ret;
if (!pcg)
return 1;
parent = cgroup_to_devcgroup(pcg);
spin_lock(&parent->lock);
ret = may_access_whitelist(parent, wh);
spin_unlock(&parent->lock);
return ret;
}
/*
* Modify the whitelist 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 whitelist.
* 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 whitelist 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, const char *buffer)
{
struct dev_cgroup *cur_devcgroup;
const char *b;
char *endp;
int retval = 0, count;
struct dev_whitelist_item wh;
if (!capable(CAP_SYS_ADMIN))
return -EPERM;
cur_devcgroup = task_devcgroup(current);
memset(&wh, 0, sizeof(wh));
b = buffer;
switch (*b) {
case 'a':
wh.type = DEV_ALL;
wh.access = ACC_MASK;
wh.major = ~0;
wh.minor = ~0;
goto handle;
case 'b':
wh.type = DEV_BLOCK;
break;
case 'c':
wh.type = DEV_CHAR;
break;
default:
return -EINVAL;
}
b++;
if (!isspace(*b))
return -EINVAL;
b++;
if (*b == '*') {
wh.major = ~0;
b++;
} else if (isdigit(*b)) {
wh.major = simple_strtoul(b, &endp, 10);
b = endp;
} else {
return -EINVAL;
}
if (*b != ':')
return -EINVAL;
b++;
/* read minor */
if (*b == '*') {
wh.minor = ~0;
b++;
} else if (isdigit(*b)) {
wh.minor = simple_strtoul(b, &endp, 10);
b = endp;
} else {
return -EINVAL;
}
if (!isspace(*b))
return -EINVAL;
for (b++, count = 0; count < 3; count++, b++) {
switch (*b) {
case 'r':
wh.access |= ACC_READ;
break;
case 'w':
wh.access |= ACC_WRITE;
break;
case 'm':
wh.access |= ACC_MKNOD;
break;
case '\n':
case '\0':
count = 3;
break;
default:
return -EINVAL;
}
}
handle:
retval = 0;
switch (filetype) {
case DEVCG_ALLOW:
if (!parent_has_perm(devcgroup, &wh))
return -EPERM;
return dev_whitelist_add(devcgroup, &wh);
case DEVCG_DENY:
dev_whitelist_rm(devcgroup, &wh);
break;
default:
return -EINVAL;
}
return 0;
}
static int devcgroup_access_write(struct cgroup *cgrp, struct cftype *cft,
const char *buffer)
{
int retval;
if (!cgroup_lock_live_group(cgrp))
return -ENODEV;
retval = devcgroup_update_access(cgroup_to_devcgroup(cgrp),
cft->private, buffer);
cgroup_unlock();
return retval;
}
static struct cftype dev_cgroup_files[] = {
{
.name = "allow",
.write_string = devcgroup_access_write,
.private = DEVCG_ALLOW,
},
{
.name = "deny",
.write_string = devcgroup_access_write,
.private = DEVCG_DENY,
},
{
.name = "list",
.read_seq_string = devcgroup_seq_read,
.private = DEVCG_LIST,
},
};
static int devcgroup_populate(struct cgroup_subsys *ss,
struct cgroup *cgroup)
{
return cgroup_add_files(cgroup, ss, dev_cgroup_files,
ARRAY_SIZE(dev_cgroup_files));
}
struct cgroup_subsys devices_subsys = {
.name = "devices",
.can_attach = devcgroup_can_attach,
.create = devcgroup_create,
.destroy = devcgroup_destroy,
.populate = devcgroup_populate,
.subsys_id = devices_subsys_id,
};
int devcgroup_inode_permission(struct inode *inode, int mask)
{
struct dev_cgroup *dev_cgroup;
struct dev_whitelist_item *wh;
dev_t device = inode->i_rdev;
if (!device)
return 0;
if (!S_ISBLK(inode->i_mode) && !S_ISCHR(inode->i_mode))
return 0;
rcu_read_lock();
dev_cgroup = task_devcgroup(current);
list_for_each_entry_rcu(wh, &dev_cgroup->whitelist, list) {
if (wh->type & DEV_ALL)
goto acc_check;
if ((wh->type & DEV_BLOCK) && !S_ISBLK(inode->i_mode))
continue;
if ((wh->type & DEV_CHAR) && !S_ISCHR(inode->i_mode))
continue;
if (wh->major != ~0 && wh->major != imajor(inode))
continue;
if (wh->minor != ~0 && wh->minor != iminor(inode))
continue;
acc_check:
if ((mask & MAY_WRITE) && !(wh->access & ACC_WRITE))
continue;
if ((mask & MAY_READ) && !(wh->access & ACC_READ))
continue;
rcu_read_unlock();
return 0;
}
rcu_read_unlock();
return -EPERM;
}
int devcgroup_inode_mknod(int mode, dev_t dev)
{
struct dev_cgroup *dev_cgroup;
struct dev_whitelist_item *wh;
rcu_read_lock();
dev_cgroup = task_devcgroup(current);
list_for_each_entry(wh, &dev_cgroup->whitelist, list) {
if (wh->type & DEV_ALL)
goto acc_check;
if ((wh->type & DEV_BLOCK) && !S_ISBLK(mode))
continue;
if ((wh->type & DEV_CHAR) && !S_ISCHR(mode))
continue;
if (wh->major != ~0 && wh->major != MAJOR(dev))
continue;
if (wh->minor != ~0 && wh->minor != MINOR(dev))
continue;
acc_check:
if (!(wh->access & ACC_MKNOD))
continue;
rcu_read_unlock();
return 0;
}
rcu_read_unlock();
return -EPERM;
}