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; 163 164 spin_lock_irq(&ucounts_lock); 165 ucounts = find_ucounts(ns, uid, hashent); 166 if (!ucounts) { 167 spin_unlock_irq(&ucounts_lock); 168 169 new = kzalloc(sizeof(*new), GFP_KERNEL); 170 if (!new) 171 return NULL; 172 173 new->ns = ns; 174 new->uid = uid; 175 atomic_set(&new->count, 1); 176 177 spin_lock_irq(&ucounts_lock); 178 ucounts = find_ucounts(ns, uid, hashent); 179 if (ucounts) { 180 kfree(new); 181 } else { 182 hlist_add_head(&new->node, hashent); 183 spin_unlock_irq(&ucounts_lock); 184 return new; 185 } 186 } 187 spin_unlock_irq(&ucounts_lock); 188 ucounts = get_ucounts(ucounts); 189 return ucounts; 190 } 191 192 void put_ucounts(struct ucounts *ucounts) 193 { 194 unsigned long flags; 195 196 if (atomic_dec_and_test(&ucounts->count)) { 197 spin_lock_irqsave(&ucounts_lock, flags); 198 hlist_del_init(&ucounts->node); 199 spin_unlock_irqrestore(&ucounts_lock, flags); 200 kfree(ucounts); 201 } 202 } 203 204 static inline bool atomic_long_inc_below(atomic_long_t *v, int u) 205 { 206 long c, old; 207 c = atomic_long_read(v); 208 for (;;) { 209 if (unlikely(c >= u)) 210 return false; 211 old = atomic_long_cmpxchg(v, c, c+1); 212 if (likely(old == c)) 213 return true; 214 c = old; 215 } 216 } 217 218 struct ucounts *inc_ucount(struct user_namespace *ns, kuid_t uid, 219 enum ucount_type type) 220 { 221 struct ucounts *ucounts, *iter, *bad; 222 struct user_namespace *tns; 223 ucounts = alloc_ucounts(ns, uid); 224 for (iter = ucounts; iter; iter = tns->ucounts) { 225 long max; 226 tns = iter->ns; 227 max = READ_ONCE(tns->ucount_max[type]); 228 if (!atomic_long_inc_below(&iter->ucount[type], max)) 229 goto fail; 230 } 231 return ucounts; 232 fail: 233 bad = iter; 234 for (iter = ucounts; iter != bad; iter = iter->ns->ucounts) 235 atomic_long_dec(&iter->ucount[type]); 236 237 put_ucounts(ucounts); 238 return NULL; 239 } 240 241 void dec_ucount(struct ucounts *ucounts, enum ucount_type type) 242 { 243 struct ucounts *iter; 244 for (iter = ucounts; iter; iter = iter->ns->ucounts) { 245 long dec = atomic_long_dec_if_positive(&iter->ucount[type]); 246 WARN_ON_ONCE(dec < 0); 247 } 248 put_ucounts(ucounts); 249 } 250 251 long inc_rlimit_ucounts(struct ucounts *ucounts, enum ucount_type type, long v) 252 { 253 struct ucounts *iter; 254 long ret = 0; 255 256 for (iter = ucounts; iter; iter = iter->ns->ucounts) { 257 long max = READ_ONCE(iter->ns->ucount_max[type]); 258 long new = atomic_long_add_return(v, &iter->ucount[type]); 259 if (new < 0 || new > max) 260 ret = LONG_MAX; 261 else if (iter == ucounts) 262 ret = new; 263 } 264 return ret; 265 } 266 267 bool dec_rlimit_ucounts(struct ucounts *ucounts, enum ucount_type type, long v) 268 { 269 struct ucounts *iter; 270 long new = -1; /* Silence compiler warning */ 271 for (iter = ucounts; iter; iter = iter->ns->ucounts) { 272 long dec = atomic_long_add_return(-v, &iter->ucount[type]); 273 WARN_ON_ONCE(dec < 0); 274 if (iter == ucounts) 275 new = dec; 276 } 277 return (new == 0); 278 } 279 280 bool is_ucounts_overlimit(struct ucounts *ucounts, enum ucount_type type, unsigned long max) 281 { 282 struct ucounts *iter; 283 if (get_ucounts_value(ucounts, type) > max) 284 return true; 285 for (iter = ucounts; iter; iter = iter->ns->ucounts) { 286 max = READ_ONCE(iter->ns->ucount_max[type]); 287 if (get_ucounts_value(iter, type) > max) 288 return true; 289 } 290 return false; 291 } 292 293 static __init int user_namespace_sysctl_init(void) 294 { 295 #ifdef CONFIG_SYSCTL 296 static struct ctl_table_header *user_header; 297 static struct ctl_table empty[1]; 298 /* 299 * It is necessary to register the user directory in the 300 * default set so that registrations in the child sets work 301 * properly. 302 */ 303 user_header = register_sysctl("user", empty); 304 kmemleak_ignore(user_header); 305 BUG_ON(!user_header); 306 BUG_ON(!setup_userns_sysctls(&init_user_ns)); 307 #endif 308 hlist_add_ucounts(&init_ucounts); 309 inc_rlimit_ucounts(&init_ucounts, UCOUNT_RLIMIT_NPROC, 1); 310 return 0; 311 } 312 subsys_initcall(user_namespace_sysctl_init); 313