/* * device_cgroup.c - device cgroup subsystem * * Copyright 2007 IBM Corp */ #include #include #include #include #include #include #include #include #include #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); /* * 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; bool deny_all; }; 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 *new_cgrp, struct cgroup_taskset *set) { struct task_struct *task = cgroup_taskset_first(set); if (current != task && !capable(CAP_SYS_ADMIN)) return -EPERM; return 0; } /* * called under devcgroup_mutex */ static int dev_exceptions_copy(struct list_head *dest, struct list_head *orig) { struct dev_exception_item *ex, *tmp, *new; 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; 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; 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); } } } /** * 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) { struct dev_exception_item *ex, *tmp; list_for_each_entry_safe(ex, tmp, &dev_cgroup->exceptions, list) { list_del(&ex->list); kfree(ex); } } /* * called from kernel/cgroup.c with cgroup_lock() held. */ static struct cgroup_subsys_state *devcgroup_create(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->exceptions); parent_cgroup = cgroup->parent; if (parent_cgroup == NULL) dev_cgroup->deny_all = false; else { parent_dev_cgroup = cgroup_to_devcgroup(parent_cgroup); mutex_lock(&devcgroup_mutex); ret = dev_exceptions_copy(&dev_cgroup->exceptions, &parent_dev_cgroup->exceptions); dev_cgroup->deny_all = parent_dev_cgroup->deny_all; mutex_unlock(&devcgroup_mutex); if (ret) { kfree(dev_cgroup); return ERR_PTR(ret); } } return &dev_cgroup->css; } static void devcgroup_destroy(struct cgroup *cgroup) { struct dev_cgroup *dev_cgroup; dev_cgroup = cgroup_to_devcgroup(cgroup); 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_read(struct cgroup *cgroup, struct cftype *cft, struct seq_file *m) { struct dev_cgroup *devcgroup = cgroup_to_devcgroup(cgroup); 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->deny_all == false) { 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; } /** * may_access - verifies if a new exception is part of what is allowed * by a dev cgroup based on the default policy + * exceptions. This is used to make sure a child cgroup * won't have more privileges than its parent or to * verify if a certain access is allowed. * @dev_cgroup: dev cgroup to be tested against * @refex: new exception */ static int may_access(struct dev_cgroup *dev_cgroup, struct dev_exception_item *refex) { struct dev_exception_item *ex; bool match = false; list_for_each_entry(ex, &dev_cgroup->exceptions, list) { if ((refex->type & DEV_BLOCK) && !(ex->type & DEV_BLOCK)) continue; if ((refex->type & DEV_CHAR) && !(ex->type & DEV_CHAR)) continue; if (ex->major != ~0 && ex->major != refex->major) continue; if (ex->minor != ~0 && ex->minor != refex->minor) continue; if (refex->access & (~ex->access)) continue; match = true; break; } /* * In two cases we'll consider this new exception valid: * - the dev cgroup has its default policy to allow + exception list: * the new exception should *not* match any of the exceptions * (!deny_all, !match) * - the dev cgroup has its default policy to deny + exception list: * the new exception *should* match the exceptions * (deny_all, match) */ if (dev_cgroup->deny_all == match) return 1; return 0; } /* * 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 cgroup *pcg = childcg->css.cgroup->parent; struct dev_cgroup *parent; if (!pcg) return 1; parent = cgroup_to_devcgroup(pcg); return may_access(parent, ex); } /* * 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, const char *buffer) { const char *b; char *endp; int count; struct dev_exception_item ex; if (!capable(CAP_SYS_ADMIN)) return -EPERM; memset(&ex, 0, sizeof(ex)); b = buffer; switch (*b) { case 'a': switch (filetype) { case DEVCG_ALLOW: if (!parent_has_perm(devcgroup, &ex)) return -EPERM; dev_exception_clean(devcgroup); devcgroup->deny_all = false; break; case DEVCG_DENY: dev_exception_clean(devcgroup); devcgroup->deny_all = true; 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)) { ex.major = simple_strtoul(b, &endp, 10); b = endp; } else { return -EINVAL; } if (*b != ':') return -EINVAL; b++; /* read minor */ if (*b == '*') { ex.minor = ~0; b++; } else if (isdigit(*b)) { ex.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': 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 (!parent_has_perm(devcgroup, &ex)) return -EPERM; /* * 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->deny_all == false) { dev_exception_rm(devcgroup, &ex); return 0; } return dev_exception_add(devcgroup, &ex); 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->deny_all == true) { dev_exception_rm(devcgroup, &ex); return 0; } return dev_exception_add(devcgroup, &ex); default: return -EINVAL; } return 0; } static int devcgroup_access_write(struct cgroup *cgrp, struct cftype *cft, const char *buffer) { int retval; mutex_lock(&devcgroup_mutex); retval = devcgroup_update_access(cgroup_to_devcgroup(cgrp), cft->private, buffer); mutex_unlock(&devcgroup_mutex); 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, }, { } /* terminate */ }; struct cgroup_subsys devices_subsys = { .name = "devices", .can_attach = devcgroup_can_attach, .create = devcgroup_create, .destroy = devcgroup_destroy, .subsys_id = devices_subsys_id, .base_cftypes = dev_cgroup_files, /* * While devices cgroup has the rudimentary hierarchy support which * checks the parent's restriction, it doesn't properly propagates * config changes in ancestors to their descendents. A child * should only be allowed to add more restrictions to the parent's * configuration. Fix it and remove the following. */ .broken_hierarchy = true, }; /** * __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(struct dev_cgroup *dev_cgroup, short type, u32 major, u32 minor, short access) { struct dev_exception_item ex; int rc; memset(&ex, 0, sizeof(ex)); ex.type = type; ex.major = major; ex.minor = minor; ex.access = access; rcu_read_lock(); rc = may_access(dev_cgroup, &ex); rcu_read_unlock(); if (!rc) return -EPERM; return 0; } int __devcgroup_inode_permission(struct inode *inode, int mask) { struct dev_cgroup *dev_cgroup = task_devcgroup(current); 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(dev_cgroup, type, imajor(inode), iminor(inode), access); } int devcgroup_inode_mknod(int mode, dev_t dev) { struct dev_cgroup *dev_cgroup = task_devcgroup(current); 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(dev_cgroup, type, MAJOR(dev), MINOR(dev), ACC_MKNOD); }