1 // SPDX-License-Identifier: GPL-2.0-only 2 3 #include <linux/stat.h> 4 #include <linux/sysctl.h> 5 #include <linux/slab.h> 6 #include <linux/cred.h> 7 #include <linux/hash.h> 8 #include <linux/kmemleak.h> 9 #include <linux/user_namespace.h> 10 11 struct ucounts init_ucounts = { 12 .ns = &init_user_ns, 13 .uid = GLOBAL_ROOT_UID, 14 .count = ATOMIC_INIT(1), 15 }; 16 17 #define UCOUNTS_HASHTABLE_BITS 10 18 static struct hlist_head ucounts_hashtable[(1 << UCOUNTS_HASHTABLE_BITS)]; 19 static DEFINE_SPINLOCK(ucounts_lock); 20 21 #define ucounts_hashfn(ns, uid) \ 22 hash_long((unsigned long)__kuid_val(uid) + (unsigned long)(ns), \ 23 UCOUNTS_HASHTABLE_BITS) 24 #define ucounts_hashentry(ns, uid) \ 25 (ucounts_hashtable + ucounts_hashfn(ns, uid)) 26 27 28 #ifdef CONFIG_SYSCTL 29 static struct ctl_table_set * 30 set_lookup(struct ctl_table_root *root) 31 { 32 return ¤t_user_ns()->set; 33 } 34 35 static int set_is_seen(struct ctl_table_set *set) 36 { 37 return ¤t_user_ns()->set == set; 38 } 39 40 static int set_permissions(struct ctl_table_header *head, 41 struct ctl_table *table) 42 { 43 struct user_namespace *user_ns = 44 container_of(head->set, struct user_namespace, set); 45 int mode; 46 47 /* Allow users with CAP_SYS_RESOURCE unrestrained access */ 48 if (ns_capable(user_ns, CAP_SYS_RESOURCE)) 49 mode = (table->mode & S_IRWXU) >> 6; 50 else 51 /* Allow all others at most read-only access */ 52 mode = table->mode & S_IROTH; 53 return (mode << 6) | (mode << 3) | mode; 54 } 55 56 static struct ctl_table_root set_root = { 57 .lookup = set_lookup, 58 .permissions = set_permissions, 59 }; 60 61 #define UCOUNT_ENTRY(name) \ 62 { \ 63 .procname = name, \ 64 .maxlen = sizeof(int), \ 65 .mode = 0644, \ 66 .proc_handler = proc_dointvec_minmax, \ 67 .extra1 = SYSCTL_ZERO, \ 68 .extra2 = SYSCTL_INT_MAX, \ 69 } 70 static struct ctl_table user_table[] = { 71 UCOUNT_ENTRY("max_user_namespaces"), 72 UCOUNT_ENTRY("max_pid_namespaces"), 73 UCOUNT_ENTRY("max_uts_namespaces"), 74 UCOUNT_ENTRY("max_ipc_namespaces"), 75 UCOUNT_ENTRY("max_net_namespaces"), 76 UCOUNT_ENTRY("max_mnt_namespaces"), 77 UCOUNT_ENTRY("max_cgroup_namespaces"), 78 UCOUNT_ENTRY("max_time_namespaces"), 79 #ifdef CONFIG_INOTIFY_USER 80 UCOUNT_ENTRY("max_inotify_instances"), 81 UCOUNT_ENTRY("max_inotify_watches"), 82 #endif 83 #ifdef CONFIG_FANOTIFY 84 UCOUNT_ENTRY("max_fanotify_groups"), 85 UCOUNT_ENTRY("max_fanotify_marks"), 86 #endif 87 { }, 88 { }, 89 { }, 90 { }, 91 { } 92 }; 93 #endif /* CONFIG_SYSCTL */ 94 95 bool setup_userns_sysctls(struct user_namespace *ns) 96 { 97 #ifdef CONFIG_SYSCTL 98 struct ctl_table *tbl; 99 100 BUILD_BUG_ON(ARRAY_SIZE(user_table) != UCOUNT_COUNTS + 1); 101 setup_sysctl_set(&ns->set, &set_root, set_is_seen); 102 tbl = kmemdup(user_table, sizeof(user_table), GFP_KERNEL); 103 if (tbl) { 104 int i; 105 for (i = 0; i < UCOUNT_COUNTS; i++) { 106 tbl[i].data = &ns->ucount_max[i]; 107 } 108 ns->sysctls = __register_sysctl_table(&ns->set, "user", tbl); 109 } 110 if (!ns->sysctls) { 111 kfree(tbl); 112 retire_sysctl_set(&ns->set); 113 return false; 114 } 115 #endif 116 return true; 117 } 118 119 void retire_userns_sysctls(struct user_namespace *ns) 120 { 121 #ifdef CONFIG_SYSCTL 122 struct ctl_table *tbl; 123 124 tbl = ns->sysctls->ctl_table_arg; 125 unregister_sysctl_table(ns->sysctls); 126 retire_sysctl_set(&ns->set); 127 kfree(tbl); 128 #endif 129 } 130 131 static struct ucounts *find_ucounts(struct user_namespace *ns, kuid_t uid, struct hlist_head *hashent) 132 { 133 struct ucounts *ucounts; 134 135 hlist_for_each_entry(ucounts, hashent, node) { 136 if (uid_eq(ucounts->uid, uid) && (ucounts->ns == ns)) 137 return ucounts; 138 } 139 return NULL; 140 } 141 142 static void hlist_add_ucounts(struct ucounts *ucounts) 143 { 144 struct hlist_head *hashent = ucounts_hashentry(ucounts->ns, ucounts->uid); 145 spin_lock_irq(&ucounts_lock); 146 hlist_add_head(&ucounts->node, hashent); 147 spin_unlock_irq(&ucounts_lock); 148 } 149 150 struct ucounts *get_ucounts(struct ucounts *ucounts) 151 { 152 if (ucounts && atomic_add_negative(1, &ucounts->count)) { 153 put_ucounts(ucounts); 154 ucounts = NULL; 155 } 156 return ucounts; 157 } 158 159 struct ucounts *alloc_ucounts(struct user_namespace *ns, kuid_t uid) 160 { 161 struct hlist_head *hashent = ucounts_hashentry(ns, uid); 162 struct ucounts *ucounts, *new; 163 long overflow; 164 165 spin_lock_irq(&ucounts_lock); 166 ucounts = find_ucounts(ns, uid, hashent); 167 if (!ucounts) { 168 spin_unlock_irq(&ucounts_lock); 169 170 new = kzalloc(sizeof(*new), GFP_KERNEL); 171 if (!new) 172 return NULL; 173 174 new->ns = ns; 175 new->uid = uid; 176 atomic_set(&new->count, 1); 177 178 spin_lock_irq(&ucounts_lock); 179 ucounts = find_ucounts(ns, uid, hashent); 180 if (ucounts) { 181 kfree(new); 182 } else { 183 hlist_add_head(&new->node, hashent); 184 spin_unlock_irq(&ucounts_lock); 185 return new; 186 } 187 } 188 overflow = atomic_add_negative(1, &ucounts->count); 189 spin_unlock_irq(&ucounts_lock); 190 if (overflow) { 191 put_ucounts(ucounts); 192 return NULL; 193 } 194 return ucounts; 195 } 196 197 void put_ucounts(struct ucounts *ucounts) 198 { 199 unsigned long flags; 200 201 if (atomic_dec_and_lock_irqsave(&ucounts->count, &ucounts_lock, flags)) { 202 hlist_del_init(&ucounts->node); 203 spin_unlock_irqrestore(&ucounts_lock, flags); 204 kfree(ucounts); 205 } 206 } 207 208 static inline bool atomic_long_inc_below(atomic_long_t *v, int u) 209 { 210 long c, old; 211 c = atomic_long_read(v); 212 for (;;) { 213 if (unlikely(c >= u)) 214 return false; 215 old = atomic_long_cmpxchg(v, c, c+1); 216 if (likely(old == c)) 217 return true; 218 c = old; 219 } 220 } 221 222 struct ucounts *inc_ucount(struct user_namespace *ns, kuid_t uid, 223 enum ucount_type type) 224 { 225 struct ucounts *ucounts, *iter, *bad; 226 struct user_namespace *tns; 227 ucounts = alloc_ucounts(ns, uid); 228 for (iter = ucounts; iter; iter = tns->ucounts) { 229 long max; 230 tns = iter->ns; 231 max = READ_ONCE(tns->ucount_max[type]); 232 if (!atomic_long_inc_below(&iter->ucount[type], max)) 233 goto fail; 234 } 235 return ucounts; 236 fail: 237 bad = iter; 238 for (iter = ucounts; iter != bad; iter = iter->ns->ucounts) 239 atomic_long_dec(&iter->ucount[type]); 240 241 put_ucounts(ucounts); 242 return NULL; 243 } 244 245 void dec_ucount(struct ucounts *ucounts, enum ucount_type type) 246 { 247 struct ucounts *iter; 248 for (iter = ucounts; iter; iter = iter->ns->ucounts) { 249 long dec = atomic_long_dec_if_positive(&iter->ucount[type]); 250 WARN_ON_ONCE(dec < 0); 251 } 252 put_ucounts(ucounts); 253 } 254 255 long inc_rlimit_ucounts(struct ucounts *ucounts, enum ucount_type type, long v) 256 { 257 struct ucounts *iter; 258 long ret = 0; 259 260 for (iter = ucounts; iter; iter = iter->ns->ucounts) { 261 long max = READ_ONCE(iter->ns->ucount_max[type]); 262 long new = atomic_long_add_return(v, &iter->ucount[type]); 263 if (new < 0 || new > max) 264 ret = LONG_MAX; 265 else if (iter == ucounts) 266 ret = new; 267 } 268 return ret; 269 } 270 271 bool dec_rlimit_ucounts(struct ucounts *ucounts, enum ucount_type type, long v) 272 { 273 struct ucounts *iter; 274 long new = -1; /* Silence compiler warning */ 275 for (iter = ucounts; iter; iter = iter->ns->ucounts) { 276 long dec = atomic_long_add_return(-v, &iter->ucount[type]); 277 WARN_ON_ONCE(dec < 0); 278 if (iter == ucounts) 279 new = dec; 280 } 281 return (new == 0); 282 } 283 284 bool is_ucounts_overlimit(struct ucounts *ucounts, enum ucount_type type, unsigned long max) 285 { 286 struct ucounts *iter; 287 if (get_ucounts_value(ucounts, type) > max) 288 return true; 289 for (iter = ucounts; iter; iter = iter->ns->ucounts) { 290 max = READ_ONCE(iter->ns->ucount_max[type]); 291 if (get_ucounts_value(iter, type) > max) 292 return true; 293 } 294 return false; 295 } 296 297 static __init int user_namespace_sysctl_init(void) 298 { 299 #ifdef CONFIG_SYSCTL 300 static struct ctl_table_header *user_header; 301 static struct ctl_table empty[1]; 302 /* 303 * It is necessary to register the user directory in the 304 * default set so that registrations in the child sets work 305 * properly. 306 */ 307 user_header = register_sysctl("user", empty); 308 kmemleak_ignore(user_header); 309 BUG_ON(!user_header); 310 BUG_ON(!setup_userns_sysctls(&init_user_ns)); 311 #endif 312 hlist_add_ucounts(&init_ucounts); 313 inc_rlimit_ucounts(&init_ucounts, UCOUNT_RLIMIT_NPROC, 1); 314 return 0; 315 } 316 subsys_initcall(user_namespace_sysctl_init); 317