| /* |
| * This program is free software; you can redistribute it and/or |
| * modify it under the terms of the GNU General Public License as |
| * published by the Free Software Foundation, version 2 of the |
| * License. |
| */ |
| |
| #include <linux/stat.h> |
| #include <linux/sysctl.h> |
| #include <linux/slab.h> |
| #include <linux/user_namespace.h> |
| |
| #ifdef CONFIG_SYSCTL |
| static struct ctl_table_set * |
| set_lookup(struct ctl_table_root *root) |
| { |
| return ¤t_user_ns()->set; |
| } |
| |
| static int set_is_seen(struct ctl_table_set *set) |
| { |
| return ¤t_user_ns()->set == set; |
| } |
| |
| static int set_permissions(struct ctl_table_header *head, |
| struct ctl_table *table) |
| { |
| struct user_namespace *user_ns = |
| container_of(head->set, struct user_namespace, set); |
| int mode; |
| |
| /* Allow users with CAP_SYS_RESOURCE unrestrained access */ |
| if (ns_capable(user_ns, CAP_SYS_RESOURCE)) |
| mode = (table->mode & S_IRWXU) >> 6; |
| else |
| /* Allow all others at most read-only access */ |
| mode = table->mode & S_IROTH; |
| return (mode << 6) | (mode << 3) | mode; |
| } |
| |
| static struct ctl_table_root set_root = { |
| .lookup = set_lookup, |
| .permissions = set_permissions, |
| }; |
| |
| static int zero = 0; |
| static int int_max = INT_MAX; |
| static struct ctl_table userns_table[] = { |
| { |
| .procname = "max_user_namespaces", |
| .data = &init_user_ns.max_user_namespaces, |
| .maxlen = sizeof(init_user_ns.max_user_namespaces), |
| .mode = 0644, |
| .proc_handler = proc_dointvec_minmax, |
| .extra1 = &zero, |
| .extra2 = &int_max, |
| }, |
| { } |
| }; |
| #endif /* CONFIG_SYSCTL */ |
| |
| bool setup_userns_sysctls(struct user_namespace *ns) |
| { |
| #ifdef CONFIG_SYSCTL |
| struct ctl_table *tbl; |
| setup_sysctl_set(&ns->set, &set_root, set_is_seen); |
| tbl = kmemdup(userns_table, sizeof(userns_table), GFP_KERNEL); |
| if (tbl) { |
| tbl[0].data = &ns->max_user_namespaces; |
| |
| ns->sysctls = __register_sysctl_table(&ns->set, "userns", tbl); |
| } |
| if (!ns->sysctls) { |
| kfree(tbl); |
| retire_sysctl_set(&ns->set); |
| return false; |
| } |
| #endif |
| return true; |
| } |
| |
| void retire_userns_sysctls(struct user_namespace *ns) |
| { |
| #ifdef CONFIG_SYSCTL |
| struct ctl_table *tbl; |
| |
| tbl = ns->sysctls->ctl_table_arg; |
| unregister_sysctl_table(ns->sysctls); |
| retire_sysctl_set(&ns->set); |
| kfree(tbl); |
| #endif |
| } |
| |
| static inline bool atomic_inc_below(atomic_t *v, int u) |
| { |
| int c, old; |
| c = atomic_read(v); |
| for (;;) { |
| if (unlikely(c >= u)) |
| return false; |
| old = atomic_cmpxchg(v, c, c+1); |
| if (likely(old == c)) |
| return true; |
| c = old; |
| } |
| } |
| |
| bool inc_user_namespaces(struct user_namespace *ns) |
| { |
| struct user_namespace *pos, *bad; |
| for (pos = ns; pos; pos = pos->parent) { |
| int max = READ_ONCE(pos->max_user_namespaces); |
| if (!atomic_inc_below(&pos->user_namespaces, max)) |
| goto fail; |
| } |
| return true; |
| fail: |
| bad = pos; |
| for (pos = ns; pos != bad; pos = pos->parent) |
| atomic_dec(&pos->user_namespaces); |
| |
| return false; |
| } |
| |
| void dec_user_namespaces(struct user_namespace *ns) |
| { |
| struct user_namespace *pos; |
| for (pos = ns; pos; pos = pos->parent) { |
| int dec = atomic_dec_if_positive(&pos->user_namespaces); |
| WARN_ON_ONCE(dec < 0); |
| } |
| } |
| |
| static __init int user_namespace_sysctl_init(void) |
| { |
| #ifdef CONFIG_SYSCTL |
| static struct ctl_table_header *userns_header; |
| static struct ctl_table empty[1]; |
| /* |
| * It is necessary to register the userns directory in the |
| * default set so that registrations in the child sets work |
| * properly. |
| */ |
| userns_header = register_sysctl("userns", empty); |
| BUG_ON(!userns_header); |
| BUG_ON(!setup_userns_sysctls(&init_user_ns)); |
| #endif |
| return 0; |
| } |
| subsys_initcall(user_namespace_sysctl_init); |
| |
| |