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