1 /* 2 * This program is free software; you can redistribute it and/or 3 * modify it under the terms of the GNU General Public License as 4 * published by the Free Software Foundation, version 2 of the 5 * License. 6 */ 7 8 #include <linux/stat.h> 9 #include <linux/sysctl.h> 10 #include <linux/slab.h> 11 #include <linux/hash.h> 12 #include <linux/user_namespace.h> 13 14 #define UCOUNTS_HASHTABLE_BITS 10 15 static struct hlist_head ucounts_hashtable[(1 << UCOUNTS_HASHTABLE_BITS)]; 16 static DEFINE_SPINLOCK(ucounts_lock); 17 18 #define ucounts_hashfn(ns, uid) \ 19 hash_long((unsigned long)__kuid_val(uid) + (unsigned long)(ns), \ 20 UCOUNTS_HASHTABLE_BITS) 21 #define ucounts_hashentry(ns, uid) \ 22 (ucounts_hashtable + ucounts_hashfn(ns, uid)) 23 24 25 #ifdef CONFIG_SYSCTL 26 static struct ctl_table_set * 27 set_lookup(struct ctl_table_root *root) 28 { 29 return ¤t_user_ns()->set; 30 } 31 32 static int set_is_seen(struct ctl_table_set *set) 33 { 34 return ¤t_user_ns()->set == set; 35 } 36 37 static int set_permissions(struct ctl_table_header *head, 38 struct ctl_table *table) 39 { 40 struct user_namespace *user_ns = 41 container_of(head->set, struct user_namespace, set); 42 int mode; 43 44 /* Allow users with CAP_SYS_RESOURCE unrestrained access */ 45 if (ns_capable(user_ns, CAP_SYS_RESOURCE)) 46 mode = (table->mode & S_IRWXU) >> 6; 47 else 48 /* Allow all others at most read-only access */ 49 mode = table->mode & S_IROTH; 50 return (mode << 6) | (mode << 3) | mode; 51 } 52 53 static struct ctl_table_root set_root = { 54 .lookup = set_lookup, 55 .permissions = set_permissions, 56 }; 57 58 static int zero = 0; 59 static int int_max = INT_MAX; 60 #define UCOUNT_ENTRY(name) \ 61 { \ 62 .procname = name, \ 63 .maxlen = sizeof(int), \ 64 .mode = 0644, \ 65 .proc_handler = proc_dointvec_minmax, \ 66 .extra1 = &zero, \ 67 .extra2 = &int_max, \ 68 } 69 static struct ctl_table user_table[] = { 70 UCOUNT_ENTRY("max_user_namespaces"), 71 UCOUNT_ENTRY("max_pid_namespaces"), 72 UCOUNT_ENTRY("max_uts_namespaces"), 73 UCOUNT_ENTRY("max_ipc_namespaces"), 74 UCOUNT_ENTRY("max_net_namespaces"), 75 UCOUNT_ENTRY("max_mnt_namespaces"), 76 UCOUNT_ENTRY("max_cgroup_namespaces"), 77 #ifdef CONFIG_INOTIFY_USER 78 UCOUNT_ENTRY("max_inotify_instances"), 79 UCOUNT_ENTRY("max_inotify_watches"), 80 #endif 81 { } 82 }; 83 #endif /* CONFIG_SYSCTL */ 84 85 bool setup_userns_sysctls(struct user_namespace *ns) 86 { 87 #ifdef CONFIG_SYSCTL 88 struct ctl_table *tbl; 89 setup_sysctl_set(&ns->set, &set_root, set_is_seen); 90 tbl = kmemdup(user_table, sizeof(user_table), GFP_KERNEL); 91 if (tbl) { 92 int i; 93 for (i = 0; i < UCOUNT_COUNTS; i++) { 94 tbl[i].data = &ns->ucount_max[i]; 95 } 96 ns->sysctls = __register_sysctl_table(&ns->set, "user", tbl); 97 } 98 if (!ns->sysctls) { 99 kfree(tbl); 100 retire_sysctl_set(&ns->set); 101 return false; 102 } 103 #endif 104 return true; 105 } 106 107 void retire_userns_sysctls(struct user_namespace *ns) 108 { 109 #ifdef CONFIG_SYSCTL 110 struct ctl_table *tbl; 111 112 tbl = ns->sysctls->ctl_table_arg; 113 unregister_sysctl_table(ns->sysctls); 114 retire_sysctl_set(&ns->set); 115 kfree(tbl); 116 #endif 117 } 118 119 static struct ucounts *find_ucounts(struct user_namespace *ns, kuid_t uid, struct hlist_head *hashent) 120 { 121 struct ucounts *ucounts; 122 123 hlist_for_each_entry(ucounts, hashent, node) { 124 if (uid_eq(ucounts->uid, uid) && (ucounts->ns == ns)) 125 return ucounts; 126 } 127 return NULL; 128 } 129 130 static struct ucounts *get_ucounts(struct user_namespace *ns, kuid_t uid) 131 { 132 struct hlist_head *hashent = ucounts_hashentry(ns, uid); 133 struct ucounts *ucounts, *new; 134 135 spin_lock_irq(&ucounts_lock); 136 ucounts = find_ucounts(ns, uid, hashent); 137 if (!ucounts) { 138 spin_unlock_irq(&ucounts_lock); 139 140 new = kzalloc(sizeof(*new), GFP_KERNEL); 141 if (!new) 142 return NULL; 143 144 new->ns = ns; 145 new->uid = uid; 146 atomic_set(&new->count, 0); 147 148 spin_lock_irq(&ucounts_lock); 149 ucounts = find_ucounts(ns, uid, hashent); 150 if (ucounts) { 151 kfree(new); 152 } else { 153 hlist_add_head(&new->node, hashent); 154 ucounts = new; 155 } 156 } 157 if (!atomic_add_unless(&ucounts->count, 1, INT_MAX)) 158 ucounts = NULL; 159 spin_unlock_irq(&ucounts_lock); 160 return ucounts; 161 } 162 163 static void put_ucounts(struct ucounts *ucounts) 164 { 165 unsigned long flags; 166 167 if (atomic_dec_and_test(&ucounts->count)) { 168 spin_lock_irqsave(&ucounts_lock, flags); 169 hlist_del_init(&ucounts->node); 170 spin_unlock_irqrestore(&ucounts_lock, flags); 171 172 kfree(ucounts); 173 } 174 } 175 176 static inline bool atomic_inc_below(atomic_t *v, int u) 177 { 178 int c, old; 179 c = atomic_read(v); 180 for (;;) { 181 if (unlikely(c >= u)) 182 return false; 183 old = atomic_cmpxchg(v, c, c+1); 184 if (likely(old == c)) 185 return true; 186 c = old; 187 } 188 } 189 190 struct ucounts *inc_ucount(struct user_namespace *ns, kuid_t uid, 191 enum ucount_type type) 192 { 193 struct ucounts *ucounts, *iter, *bad; 194 struct user_namespace *tns; 195 ucounts = get_ucounts(ns, uid); 196 for (iter = ucounts; iter; iter = tns->ucounts) { 197 int max; 198 tns = iter->ns; 199 max = READ_ONCE(tns->ucount_max[type]); 200 if (!atomic_inc_below(&iter->ucount[type], max)) 201 goto fail; 202 } 203 return ucounts; 204 fail: 205 bad = iter; 206 for (iter = ucounts; iter != bad; iter = iter->ns->ucounts) 207 atomic_dec(&iter->ucount[type]); 208 209 put_ucounts(ucounts); 210 return NULL; 211 } 212 213 void dec_ucount(struct ucounts *ucounts, enum ucount_type type) 214 { 215 struct ucounts *iter; 216 for (iter = ucounts; iter; iter = iter->ns->ucounts) { 217 int dec = atomic_dec_if_positive(&iter->ucount[type]); 218 WARN_ON_ONCE(dec < 0); 219 } 220 put_ucounts(ucounts); 221 } 222 223 static __init int user_namespace_sysctl_init(void) 224 { 225 #ifdef CONFIG_SYSCTL 226 static struct ctl_table_header *user_header; 227 static struct ctl_table empty[1]; 228 /* 229 * It is necessary to register the user directory in the 230 * default set so that registrations in the child sets work 231 * properly. 232 */ 233 user_header = register_sysctl("user", empty); 234 kmemleak_ignore(user_header); 235 BUG_ON(!user_header); 236 BUG_ON(!setup_userns_sysctls(&init_user_ns)); 237 #endif 238 return 0; 239 } 240 subsys_initcall(user_namespace_sysctl_init); 241