/* * 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 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 #define DEVCG_LIST 3 #define MAJMINLEN 10 #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) { memset(str, 0, MAJMINLEN); if (m == ~0) sprintf(str, "*"); else snprintf(str, MAJMINLEN, "%d", 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]; spin_lock(&devcgroup->lock); list_for_each_entry(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); } spin_unlock(&devcgroup->lock); 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 | 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", .write = devcgroup_access_write, .private = DEVCG_ALLOW, }, { .name = "deny", .write = 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 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; }