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 static long ue_zero = 0; 62 static long ue_int_max = INT_MAX; 63 64 #define UCOUNT_ENTRY(name) \ 65 { \ 66 .procname = name, \ 67 .maxlen = sizeof(long), \ 68 .mode = 0644, \ 69 .proc_handler = proc_doulongvec_minmax, \ 70 .extra1 = &ue_zero, \ 71 .extra2 = &ue_int_max, \ 72 } 73 static struct ctl_table user_table[] = { 74 UCOUNT_ENTRY("max_user_namespaces"), 75 UCOUNT_ENTRY("max_pid_namespaces"), 76 UCOUNT_ENTRY("max_uts_namespaces"), 77 UCOUNT_ENTRY("max_ipc_namespaces"), 78 UCOUNT_ENTRY("max_net_namespaces"), 79 UCOUNT_ENTRY("max_mnt_namespaces"), 80 UCOUNT_ENTRY("max_cgroup_namespaces"), 81 UCOUNT_ENTRY("max_time_namespaces"), 82 #ifdef CONFIG_INOTIFY_USER 83 UCOUNT_ENTRY("max_inotify_instances"), 84 UCOUNT_ENTRY("max_inotify_watches"), 85 #endif 86 #ifdef CONFIG_FANOTIFY 87 UCOUNT_ENTRY("max_fanotify_groups"), 88 UCOUNT_ENTRY("max_fanotify_marks"), 89 #endif 90 { }, 91 { }, 92 { }, 93 { }, 94 { } 95 }; 96 #endif /* CONFIG_SYSCTL */ 97 98 bool setup_userns_sysctls(struct user_namespace *ns) 99 { 100 #ifdef CONFIG_SYSCTL 101 struct ctl_table *tbl; 102 103 BUILD_BUG_ON(ARRAY_SIZE(user_table) != UCOUNT_COUNTS + 1); 104 setup_sysctl_set(&ns->set, &set_root, set_is_seen); 105 tbl = kmemdup(user_table, sizeof(user_table), GFP_KERNEL); 106 if (tbl) { 107 int i; 108 for (i = 0; i < UCOUNT_COUNTS; i++) { 109 tbl[i].data = &ns->ucount_max[i]; 110 } 111 ns->sysctls = __register_sysctl_table(&ns->set, "user", tbl); 112 } 113 if (!ns->sysctls) { 114 kfree(tbl); 115 retire_sysctl_set(&ns->set); 116 return false; 117 } 118 #endif 119 return true; 120 } 121 122 void retire_userns_sysctls(struct user_namespace *ns) 123 { 124 #ifdef CONFIG_SYSCTL 125 struct ctl_table *tbl; 126 127 tbl = ns->sysctls->ctl_table_arg; 128 unregister_sysctl_table(ns->sysctls); 129 retire_sysctl_set(&ns->set); 130 kfree(tbl); 131 #endif 132 } 133 134 static struct ucounts *find_ucounts(struct user_namespace *ns, kuid_t uid, struct hlist_head *hashent) 135 { 136 struct ucounts *ucounts; 137 138 hlist_for_each_entry(ucounts, hashent, node) { 139 if (uid_eq(ucounts->uid, uid) && (ucounts->ns == ns)) 140 return ucounts; 141 } 142 return NULL; 143 } 144 145 static void hlist_add_ucounts(struct ucounts *ucounts) 146 { 147 struct hlist_head *hashent = ucounts_hashentry(ucounts->ns, ucounts->uid); 148 spin_lock_irq(&ucounts_lock); 149 hlist_add_head(&ucounts->node, hashent); 150 spin_unlock_irq(&ucounts_lock); 151 } 152 153 static inline bool get_ucounts_or_wrap(struct ucounts *ucounts) 154 { 155 /* Returns true on a successful get, false if the count wraps. */ 156 return !atomic_add_negative(1, &ucounts->count); 157 } 158 159 struct ucounts *get_ucounts(struct ucounts *ucounts) 160 { 161 if (!get_ucounts_or_wrap(ucounts)) { 162 put_ucounts(ucounts); 163 ucounts = NULL; 164 } 165 return ucounts; 166 } 167 168 struct ucounts *alloc_ucounts(struct user_namespace *ns, kuid_t uid) 169 { 170 struct hlist_head *hashent = ucounts_hashentry(ns, uid); 171 struct ucounts *ucounts, *new; 172 bool wrapped; 173 174 spin_lock_irq(&ucounts_lock); 175 ucounts = find_ucounts(ns, uid, hashent); 176 if (!ucounts) { 177 spin_unlock_irq(&ucounts_lock); 178 179 new = kzalloc(sizeof(*new), GFP_KERNEL); 180 if (!new) 181 return NULL; 182 183 new->ns = ns; 184 new->uid = uid; 185 atomic_set(&new->count, 1); 186 187 spin_lock_irq(&ucounts_lock); 188 ucounts = find_ucounts(ns, uid, hashent); 189 if (ucounts) { 190 kfree(new); 191 } else { 192 hlist_add_head(&new->node, hashent); 193 spin_unlock_irq(&ucounts_lock); 194 return new; 195 } 196 } 197 wrapped = !get_ucounts_or_wrap(ucounts); 198 spin_unlock_irq(&ucounts_lock); 199 if (wrapped) { 200 put_ucounts(ucounts); 201 return NULL; 202 } 203 return ucounts; 204 } 205 206 void put_ucounts(struct ucounts *ucounts) 207 { 208 unsigned long flags; 209 210 if (atomic_dec_and_lock_irqsave(&ucounts->count, &ucounts_lock, flags)) { 211 hlist_del_init(&ucounts->node); 212 spin_unlock_irqrestore(&ucounts_lock, flags); 213 kfree(ucounts); 214 } 215 } 216 217 static inline bool atomic_long_inc_below(atomic_long_t *v, int u) 218 { 219 long c, old; 220 c = atomic_long_read(v); 221 for (;;) { 222 if (unlikely(c >= u)) 223 return false; 224 old = atomic_long_cmpxchg(v, c, c+1); 225 if (likely(old == c)) 226 return true; 227 c = old; 228 } 229 } 230 231 struct ucounts *inc_ucount(struct user_namespace *ns, kuid_t uid, 232 enum ucount_type type) 233 { 234 struct ucounts *ucounts, *iter, *bad; 235 struct user_namespace *tns; 236 ucounts = alloc_ucounts(ns, uid); 237 for (iter = ucounts; iter; iter = tns->ucounts) { 238 long max; 239 tns = iter->ns; 240 max = READ_ONCE(tns->ucount_max[type]); 241 if (!atomic_long_inc_below(&iter->ucount[type], max)) 242 goto fail; 243 } 244 return ucounts; 245 fail: 246 bad = iter; 247 for (iter = ucounts; iter != bad; iter = iter->ns->ucounts) 248 atomic_long_dec(&iter->ucount[type]); 249 250 put_ucounts(ucounts); 251 return NULL; 252 } 253 254 void dec_ucount(struct ucounts *ucounts, enum ucount_type type) 255 { 256 struct ucounts *iter; 257 for (iter = ucounts; iter; iter = iter->ns->ucounts) { 258 long dec = atomic_long_dec_if_positive(&iter->ucount[type]); 259 WARN_ON_ONCE(dec < 0); 260 } 261 put_ucounts(ucounts); 262 } 263 264 long inc_rlimit_ucounts(struct ucounts *ucounts, enum ucount_type type, long v) 265 { 266 struct ucounts *iter; 267 long max = LONG_MAX; 268 long ret = 0; 269 270 for (iter = ucounts; iter; iter = iter->ns->ucounts) { 271 long new = atomic_long_add_return(v, &iter->ucount[type]); 272 if (new < 0 || new > max) 273 ret = LONG_MAX; 274 else if (iter == ucounts) 275 ret = new; 276 max = READ_ONCE(iter->ns->ucount_max[type]); 277 } 278 return ret; 279 } 280 281 bool dec_rlimit_ucounts(struct ucounts *ucounts, enum ucount_type type, long v) 282 { 283 struct ucounts *iter; 284 long new = -1; /* Silence compiler warning */ 285 for (iter = ucounts; iter; iter = iter->ns->ucounts) { 286 long dec = atomic_long_sub_return(v, &iter->ucount[type]); 287 WARN_ON_ONCE(dec < 0); 288 if (iter == ucounts) 289 new = dec; 290 } 291 return (new == 0); 292 } 293 294 static void do_dec_rlimit_put_ucounts(struct ucounts *ucounts, 295 struct ucounts *last, enum ucount_type type) 296 { 297 struct ucounts *iter, *next; 298 for (iter = ucounts; iter != last; iter = next) { 299 long dec = atomic_long_sub_return(1, &iter->ucount[type]); 300 WARN_ON_ONCE(dec < 0); 301 next = iter->ns->ucounts; 302 if (dec == 0) 303 put_ucounts(iter); 304 } 305 } 306 307 void dec_rlimit_put_ucounts(struct ucounts *ucounts, enum ucount_type type) 308 { 309 do_dec_rlimit_put_ucounts(ucounts, NULL, type); 310 } 311 312 long inc_rlimit_get_ucounts(struct ucounts *ucounts, enum ucount_type type) 313 { 314 /* Caller must hold a reference to ucounts */ 315 struct ucounts *iter; 316 long max = LONG_MAX; 317 long dec, ret = 0; 318 319 for (iter = ucounts; iter; iter = iter->ns->ucounts) { 320 long new = atomic_long_add_return(1, &iter->ucount[type]); 321 if (new < 0 || new > max) 322 goto unwind; 323 if (iter == ucounts) 324 ret = new; 325 max = READ_ONCE(iter->ns->ucount_max[type]); 326 /* 327 * Grab an extra ucount reference for the caller when 328 * the rlimit count was previously 0. 329 */ 330 if (new != 1) 331 continue; 332 if (!get_ucounts(iter)) 333 goto dec_unwind; 334 } 335 return ret; 336 dec_unwind: 337 dec = atomic_long_sub_return(1, &iter->ucount[type]); 338 WARN_ON_ONCE(dec < 0); 339 unwind: 340 do_dec_rlimit_put_ucounts(ucounts, iter, type); 341 return 0; 342 } 343 344 bool is_ucounts_overlimit(struct ucounts *ucounts, enum ucount_type type, unsigned long rlimit) 345 { 346 struct ucounts *iter; 347 long max = rlimit; 348 if (rlimit > LONG_MAX) 349 max = LONG_MAX; 350 for (iter = ucounts; iter; iter = iter->ns->ucounts) { 351 if (get_ucounts_value(iter, type) > max) 352 return true; 353 max = READ_ONCE(iter->ns->ucount_max[type]); 354 } 355 return false; 356 } 357 358 static __init int user_namespace_sysctl_init(void) 359 { 360 #ifdef CONFIG_SYSCTL 361 static struct ctl_table_header *user_header; 362 static struct ctl_table empty[1]; 363 /* 364 * It is necessary to register the user directory in the 365 * default set so that registrations in the child sets work 366 * properly. 367 */ 368 user_header = register_sysctl("user", empty); 369 kmemleak_ignore(user_header); 370 BUG_ON(!user_header); 371 BUG_ON(!setup_userns_sysctls(&init_user_ns)); 372 #endif 373 hlist_add_ucounts(&init_ucounts); 374 inc_rlimit_ucounts(&init_ucounts, UCOUNT_RLIMIT_NPROC, 1); 375 return 0; 376 } 377 subsys_initcall(user_namespace_sysctl_init); 378