7 files changed, 686 insertions, 0 deletions

diff --git a/Documentation/controllers/devices.txt b/Documentation/controllers/devices.txt
new file mode 100644
index 000000000000..4dcea42432c2
--- /dev/null
+++ b/Documentation/controllers/devices.txt
@@ -0,0 +1,48 @@
+Device Whitelist Controller
+
+1. Description:
+
+Implement a cgroup to track and enforce open and mknod restrictions
+on device files.  A device cgroup associates a device access
+whitelist with each cgroup.  A whitelist entry has 4 fields.
+'type' is a (all), c (char), or b (block).  'all' means it applies
+to all types and all major and minor numbers.  Major and minor are
+either an integer or * for all.  Access is a composition of r
+(read), w (write), and m (mknod).
+
+The root device cgroup starts with rwm to 'all'.  A child device
+cgroup gets a copy of the parent.  Administrators can then remove
+devices from the whitelist or add new entries.  A child cgroup can
+never receive a device access which is denied its parent.  However
+when a device access is removed from a parent it will not also be
+removed from the child(ren).
+
+2. User Interface
+
+An entry is added using devices.allow, and removed using
+devices.deny.  For instance
+
+        echo 'c 1:3 mr' > /cgroups/1/devices.allow
+
+allows cgroup 1 to read and mknod the device usually known as
+/dev/null.  Doing
+
+        echo a > /cgroups/1/devices.deny
+
+will remove the default 'a *:* mrw' entry.
+
+3. Security
+
+Any task can move itself between cgroups.  This clearly won't
+suffice, but we can decide the best way to adequately restrict
+movement as people get some experience with this.  We may just want
+to require CAP_SYS_ADMIN, which at least is a separate bit from
+CAP_MKNOD.  We may want to just refuse moving to a cgroup which
+isn't a descendent of the current one.  Or we may want to use
+CAP_MAC_ADMIN, since we really are trying to lock down root.
+
+CAP_SYS_ADMIN is needed to modify the whitelist or move another
+task to a new cgroup.  (Again we'll probably want to change that).
+
+A cgroup may not be granted more permissions than the cgroup's
+parent has.
diff --git a/fs/namei.c b/fs/namei.c
index e179f71bfcb0..32fd9655485b 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -30,6 +30,7 @@
 #include <linux/capability.h>
 #include <linux/file.h>
 #include <linux/fcntl.h>
+#include <linux/device_cgroup.h>
 #include <asm/namei.h>
 #include <asm/uaccess.h>
 
@@ -281,6 +282,10 @@ int permission(struct inode *inode, int mask, struct nameidata *nd)
         if (retval)
                 return retval;
 
+        retval = devcgroup_inode_permission(inode, mask);
+        if (retval)
+                return retval;
+
         return security_inode_permission(inode, mask, nd);
 }
 
@@ -2028,6 +2033,10 @@ int vfs_mknod(struct inode *dir, struct dentry *dentry, int mode, dev_t dev)
         if (!dir->i_op || !dir->i_op->mknod)
                 return -EPERM;
 
+        error = devcgroup_inode_mknod(mode, dev);
+        if (error)
+                return error;
+
         error = security_inode_mknod(dir, dentry, mode, dev);
         if (error)
                 return error;
diff --git a/include/linux/cgroup_subsys.h b/include/linux/cgroup_subsys.h
index 1ddebfc52565..e2877454ec82 100644
--- a/include/linux/cgroup_subsys.h
+++ b/include/linux/cgroup_subsys.h
@@ -42,3 +42,9 @@ SUBSYS(mem_cgroup)
 #endif
 
 /* */
+
+#ifdef CONFIG_CGROUP_DEVICE
+SUBSYS(devices)
+#endif
+
+/* */
diff --git a/include/linux/device_cgroup.h b/include/linux/device_cgroup.h
new file mode 100644
index 000000000000..0b0d9c39ed67
--- /dev/null
+++ b/include/linux/device_cgroup.h
@@ -0,0 +1,12 @@
+#include <linux/module.h>
+#include <linux/fs.h>
+
+#ifdef CONFIG_CGROUP_DEVICE
+extern int devcgroup_inode_permission(struct inode *inode, int mask);
+extern int devcgroup_inode_mknod(int mode, dev_t dev);
+#else
+static inline int devcgroup_inode_permission(struct inode *inode, int mask)
+{ return 0; }
+static inline int devcgroup_inode_mknod(int mode, dev_t dev)
+{ return 0; }
+#endif
diff --git a/init/Kconfig b/init/Kconfig
index 6ce16bdbec76..a3457926342a 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -298,6 +298,13 @@ config CGROUP_NS
           for instance virtual servers and checkpoint/restart
           jobs.
 
+config CGROUP_DEVICE
+        bool "Device controller for cgroups"
+        depends on CGROUPS && EXPERIMENTAL
+        help
+          Provides a cgroup implementing whitelists for devices which
+          a process in the cgroup can mknod or open.
+
 config CPUSETS
         bool "Cpuset support"
         depends on SMP && CGROUPS
diff --git a/security/Makefile b/security/Makefile
index 9e8b02525014..7ef1107a7287 100644
--- a/security/Makefile
+++ b/security/Makefile
@@ -18,3 +18,4 @@ obj-$(CONFIG_SECURITY_SELINUX)		+= selinux/built-in.o
 obj-$(CONFIG_SECURITY_SMACK)            += commoncap.o smack/built-in.o
 obj-$(CONFIG_SECURITY_CAPABILITIES)     += commoncap.o capability.o
 obj-$(CONFIG_SECURITY_ROOTPLUG)         += commoncap.o root_plug.o
+obj-$(CONFIG_CGROUP_DEVICE)             += device_cgroup.o
diff --git a/security/device_cgroup.c b/security/device_cgroup.c
new file mode 100644
index 000000000000..4237b19e8fb3
--- /dev/null
+++ b/security/device_cgroup.c
@@ -0,0 +1,603 @@
+/*
+ * 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>
+
+#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 dev_cgroup {
+        struct cgroup_subsys_state css;
+        struct list_head whitelist;
+        spinlock_t lock;
+};
+
+static inline struct dev_cgroup *cgroup_to_devcgroup(struct cgroup *cgroup)
+{
+        return container_of(cgroup_subsys_state(cgroup, devices_subsys_id),
+                            struct dev_cgroup, css);
+}
+
+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;
+
+        whcopy = kmalloc(sizeof(*whcopy), GFP_KERNEL);
+        if (!whcopy)
+                return -ENOMEM;
+
+        memcpy(whcopy, wh, sizeof(*whcopy));
+        spin_lock(&dev_cgroup->lock);
+        list_add_tail(&whcopy->list, &dev_cgroup->whitelist);
+        spin_unlock(&dev_cgroup->lock);
+        return 0;
+}
+
+/*
+ * 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(&walk->list);
+                        kfree(walk);
+                }
+        }
+        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_MKNOD | ACC_READ | ACC_WRITE;
+                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
+
+static void set_access(char *acc, short access)
+{
+        int idx = 0;
+        memset(acc, 0, 4);
+        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, int len, unsigned m)
+{
+        memset(str, 0, len);
+        if (m == ~0)
+                sprintf(str, "*");
+        else
+                snprintf(str, len, "%d", m);
+}
+
+static char *print_whitelist(struct dev_cgroup *devcgroup, int *len)
+{
+        char *buf, *s, acc[4];
+        struct dev_whitelist_item *wh;
+        int ret;
+        int count = 0;
+        char maj[10], min[10];
+
+        buf = kmalloc(4096, GFP_KERNEL);
+        if (!buf)
+                return ERR_PTR(-ENOMEM);
+        s = buf;
+        *s = '\0';
+        *len = 0;
+
+        spin_lock(&devcgroup->lock);
+        list_for_each_entry(wh, &devcgroup->whitelist, list) {
+                set_access(acc, wh->access);
+                set_majmin(maj, 10, wh->major);
+                set_majmin(min, 10, wh->minor);
+                ret = snprintf(s, 4095-(s-buf), "%c %s:%s %s\n",
+                        type_to_char(wh->type), maj, min, acc);
+                if (s+ret >= buf+4095) {
+                        kfree(buf);
+                        buf = ERR_PTR(-ENOMEM);
+                        break;
+                }
+                s += ret;
+                *len += ret;
+                count++;
+        }
+        spin_unlock(&devcgroup->lock);
+
+        return buf;
+}
+
+static ssize_t devcgroup_access_read(struct cgroup *cgroup,
+                        struct cftype *cft, struct file *file,
+                        char __user *userbuf, size_t nbytes, loff_t *ppos)
+{
+        struct dev_cgroup *devcgroup = cgroup_to_devcgroup(cgroup);
+        int filetype = cft->private;
+        char *buffer;
+        int uninitialized_var(len);
+        int retval;
+
+        if (filetype != DEVCG_ALLOW)
+                return -EINVAL;
+        buffer = print_whitelist(devcgroup, &len);
+        if (IS_ERR(buffer))
+                return PTR_ERR(buffer);
+
+        retval = simple_read_from_buffer(userbuf, nbytes, ppos, buffer, len);
+        kfree(buffer);
+        return retval;
+}
+
+/*
+ * 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 | ACC_MASK)))
+                        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 cgroup *childcg,
+                                  struct dev_whitelist_item *wh)
+{
+        struct cgroup *pcg = childcg->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 ssize_t devcgroup_access_write(struct cgroup *cgroup, struct cftype *cft,
+                                struct file *file, const char __user *userbuf,
+                                size_t nbytes, loff_t *ppos)
+{
+        struct cgroup *cur_cgroup;
+        struct dev_cgroup *devcgroup, *cur_devcgroup;
+        int filetype = cft->private;
+        char *buffer, *b;
+        int retval = 0, count;
+        struct dev_whitelist_item wh;
+
+        if (!capable(CAP_SYS_ADMIN))
+                return -EPERM;
+
+        devcgroup = cgroup_to_devcgroup(cgroup);
+        cur_cgroup = task_cgroup(current, devices_subsys.subsys_id);
+        cur_devcgroup = cgroup_to_devcgroup(cur_cgroup);
+
+        buffer = kmalloc(nbytes+1, GFP_KERNEL);
+        if (!buffer)
+                return -ENOMEM;
+
+        if (copy_from_user(buffer, userbuf, nbytes)) {
+                retval = -EFAULT;
+                goto out1;
+        }
+        buffer[nbytes] = 0;     /* nul-terminate */
+
+        cgroup_lock();
+        if (cgroup_is_removed(cgroup)) {
+                retval = -ENODEV;
+                goto out2;
+        }
+
+        memset(&wh, 0, sizeof(wh));
+        b = buffer;
+
+        switch (*b) {
+        case 'a':
+                wh.type = DEV_ALL;
+                wh.access = ACC_MASK;
+                goto handle;
+        case 'b':
+                wh.type = DEV_BLOCK;
+                break;
+        case 'c':
+                wh.type = DEV_CHAR;
+                break;
+        default:
+                retval = -EINVAL;
+                goto out2;
+        }
+        b++;
+        if (!isspace(*b)) {
+                retval = -EINVAL;
+                goto out2;
+        }
+        b++;
+        if (*b == '*') {
+                wh.major = ~0;
+                b++;
+        } else if (isdigit(*b)) {
+                wh.major = 0;
+                while (isdigit(*b)) {
+                        wh.major = wh.major*10+(*b-'0');
+                        b++;
+                }
+        } else {
+                retval = -EINVAL;
+                goto out2;
+        }
+        if (*b != ':') {
+                retval = -EINVAL;
+                goto out2;
+        }
+        b++;
+
+        /* read minor */
+        if (*b == '*') {
+                wh.minor = ~0;
+                b++;
+        } else if (isdigit(*b)) {
+                wh.minor = 0;
+                while (isdigit(*b)) {
+                        wh.minor = wh.minor*10+(*b-'0');
+                        b++;
+                }
+        } else {
+                retval = -EINVAL;
+                goto out2;
+        }
+        if (!isspace(*b)) {
+                retval = -EINVAL;
+                goto out2;
+        }
+        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:
+                        retval = -EINVAL;
+                        goto out2;
+                }
+        }
+
+handle:
+        retval = 0;
+        switch (filetype) {
+        case DEVCG_ALLOW:
+                if (!parent_has_perm(cgroup, &wh))
+                        retval = -EPERM;
+                else
+                        retval = dev_whitelist_add(devcgroup, &wh);
+                break;
+        case DEVCG_DENY:
+                dev_whitelist_rm(devcgroup, &wh);
+                break;
+        default:
+                retval = -EINVAL;
+                goto out2;
+        }
+
+        if (retval == 0)
+                retval = nbytes;
+
+out2:
+        cgroup_unlock();
+out1:
+        kfree(buffer);
+        return retval;
+}
+
+static struct cftype dev_cgroup_files[] = {
+        {
+                .name = "allow",
+                .read = devcgroup_access_read,
+                .write  = devcgroup_access_write,
+                .private = DEVCG_ALLOW,
+        },
+        {
+                .name = "deny",
+                .write = devcgroup_access_write,
+                .private = DEVCG_DENY,
+        },
+};
+
+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 cgroup *cgroup;
+        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;
+        cgroup = task_cgroup(current, devices_subsys.subsys_id);
+        dev_cgroup = cgroup_to_devcgroup(cgroup);
+        if (!dev_cgroup)
+                return 0;
+
+        spin_lock(&dev_cgroup->lock);
+        list_for_each_entry(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;
+                spin_unlock(&dev_cgroup->lock);
+                return 0;
+        }
+        spin_unlock(&dev_cgroup->lock);
+
+        return -EPERM;
+}
+
+int devcgroup_inode_mknod(int mode, dev_t dev)
+{
+        struct cgroup *cgroup;
+        struct dev_cgroup *dev_cgroup;
+        struct dev_whitelist_item *wh;
+
+        cgroup = task_cgroup(current, devices_subsys.subsys_id);
+        dev_cgroup = cgroup_to_devcgroup(cgroup);
+        if (!dev_cgroup)
+                return 0;
+
+        spin_lock(&dev_cgroup->lock);
+        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;
+                spin_unlock(&dev_cgroup->lock);
+                return 0;
+        }
+        spin_unlock(&dev_cgroup->lock);
+        return -EPERM;
+}