/*
 * 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;

        if (!S_ISBLK(mode) && !S_ISCHR(mode))
                return 0;

        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;
}