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 #define UCOUNTS_HASHTABLE_BITS 10 12 static struct hlist_head ucounts_hashtable[(1 << UCOUNTS_HASHTABLE_BITS)]; 13 static DEFINE_SPINLOCK(ucounts_lock); 14 15 #define ucounts_hashfn(ns, uid) \ 16 hash_long((unsigned long)__kuid_val(uid) + (unsigned long)(ns), \ 17 UCOUNTS_HASHTABLE_BITS) 18 #define ucounts_hashentry(ns, uid) \ 19 (ucounts_hashtable + ucounts_hashfn(ns, uid)) 20 21 22 #ifdef CONFIG_SYSCTL 23 static struct ctl_table_set * 24 set_lookup(struct ctl_table_root *root) 25 { 26 return ¤t_user_ns()->set; 27 } 28 29 static int set_is_seen(struct ctl_table_set *set) 30 { 31 return ¤t_user_ns()->set == set; 32 } 33 34 static int set_permissions(struct ctl_table_header *head, 35 struct ctl_table *table) 36 { 37 struct user_namespace *user_ns = 38 container_of(head->set, struct user_namespace, set); 39 int mode; 40 41 /* Allow users with CAP_SYS_RESOURCE unrestrained access */ 42 if (ns_capable(user_ns, CAP_SYS_RESOURCE)) 43 mode = (table->mode & S_IRWXU) >> 6; 44 else 45 /* Allow all others at most read-only access */ 46 mode = table->mode & S_IROTH; 47 return (mode << 6) | (mode << 3) | mode; 48 } 49 50 static struct ctl_table_root set_root = { 51 .lookup = set_lookup, 52 .permissions = set_permissions, 53 }; 54 55 #define UCOUNT_ENTRY(name) \ 56 { \ 57 .procname = name, \ 58 .maxlen = sizeof(int), \ 59 .mode = 0644, \ 60 .proc_handler = proc_dointvec_minmax, \ 61 .extra1 = SYSCTL_ZERO, \ 62 .extra2 = SYSCTL_INT_MAX, \ 63 } 64 static struct ctl_table user_table[] = { 65 UCOUNT_ENTRY("max_user_namespaces"), 66 UCOUNT_ENTRY("max_pid_namespaces"), 67 UCOUNT_ENTRY("max_uts_namespaces"), 68 UCOUNT_ENTRY("max_ipc_namespaces"), 69 UCOUNT_ENTRY("max_net_namespaces"), 70 UCOUNT_ENTRY("max_mnt_namespaces"), 71 UCOUNT_ENTRY("max_cgroup_namespaces"), 72 UCOUNT_ENTRY("max_time_namespaces"), 73 #ifdef CONFIG_INOTIFY_USER 74 UCOUNT_ENTRY("max_inotify_instances"), 75 UCOUNT_ENTRY("max_inotify_watches"), 76 #endif 77 { } 78 }; 79 #endif /* CONFIG_SYSCTL */ 80 81 bool setup_userns_sysctls(struct user_namespace *ns) 82 { 83 #ifdef CONFIG_SYSCTL 84 struct ctl_table *tbl; 85 86 BUILD_BUG_ON(ARRAY_SIZE(user_table) != UCOUNT_COUNTS + 1); 87 setup_sysctl_set(&ns->set, &set_root, set_is_seen); 88 tbl = kmemdup(user_table, sizeof(user_table), GFP_KERNEL); 89 if (tbl) { 90 int i; 91 for (i = 0; i < UCOUNT_COUNTS; i++) { 92 tbl[i].data = &ns->ucount_max[i]; 93 } 94 ns->sysctls = __register_sysctl_table(&ns->set, "user", tbl); 95 } 96 if (!ns->sysctls) { 97 kfree(tbl); 98 retire_sysctl_set(&ns->set); 99 return false; 100 } 101 #endif 102 return true; 103 } 104 105 void retire_userns_sysctls(struct user_namespace *ns) 106 { 107 #ifdef CONFIG_SYSCTL 108 struct ctl_table *tbl; 109 110 tbl = ns->sysctls->ctl_table_arg; 111 unregister_sysctl_table(ns->sysctls); 112 retire_sysctl_set(&ns->set); 113 kfree(tbl); 114 #endif 115 } 116 117 static struct ucounts *find_ucounts(struct user_namespace *ns, kuid_t uid, struct hlist_head *hashent) 118 { 119 struct ucounts *ucounts; 120 121 hlist_for_each_entry(ucounts, hashent, node) { 122 if (uid_eq(ucounts->uid, uid) && (ucounts->ns == ns)) 123 return ucounts; 124 } 125 return NULL; 126 } 127 128 static struct ucounts *get_ucounts(struct user_namespace *ns, kuid_t uid) 129 { 130 struct hlist_head *hashent = ucounts_hashentry(ns, uid); 131 struct ucounts *ucounts, *new; 132 133 spin_lock_irq(&ucounts_lock); 134 ucounts = find_ucounts(ns, uid, hashent); 135 if (!ucounts) { 136 spin_unlock_irq(&ucounts_lock); 137 138 new = kzalloc(sizeof(*new), GFP_KERNEL); 139 if (!new) 140 return NULL; 141 142 new->ns = ns; 143 new->uid = uid; 144 new->count = 0; 145 146 spin_lock_irq(&ucounts_lock); 147 ucounts = find_ucounts(ns, uid, hashent); 148 if (ucounts) { 149 kfree(new); 150 } else { 151 hlist_add_head(&new->node, hashent); 152 ucounts = new; 153 } 154 } 155 if (ucounts->count == INT_MAX) 156 ucounts = NULL; 157 else 158 ucounts->count += 1; 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 spin_lock_irqsave(&ucounts_lock, flags); 168 ucounts->count -= 1; 169 if (!ucounts->count) 170 hlist_del_init(&ucounts->node); 171 else 172 ucounts = NULL; 173 spin_unlock_irqrestore(&ucounts_lock, flags); 174 175 kfree(ucounts); 176 } 177 178 static inline bool atomic_inc_below(atomic_t *v, int u) 179 { 180 int c, old; 181 c = atomic_read(v); 182 for (;;) { 183 if (unlikely(c >= u)) 184 return false; 185 old = atomic_cmpxchg(v, c, c+1); 186 if (likely(old == c)) 187 return true; 188 c = old; 189 } 190 } 191 192 struct ucounts *inc_ucount(struct user_namespace *ns, kuid_t uid, 193 enum ucount_type type) 194 { 195 struct ucounts *ucounts, *iter, *bad; 196 struct user_namespace *tns; 197 ucounts = get_ucounts(ns, uid); 198 for (iter = ucounts; iter; iter = tns->ucounts) { 199 int max; 200 tns = iter->ns; 201 max = READ_ONCE(tns->ucount_max[type]); 202 if (!atomic_inc_below(&iter->ucount[type], max)) 203 goto fail; 204 } 205 return ucounts; 206 fail: 207 bad = iter; 208 for (iter = ucounts; iter != bad; iter = iter->ns->ucounts) 209 atomic_dec(&iter->ucount[type]); 210 211 put_ucounts(ucounts); 212 return NULL; 213 } 214 215 void dec_ucount(struct ucounts *ucounts, enum ucount_type type) 216 { 217 struct ucounts *iter; 218 for (iter = ucounts; iter; iter = iter->ns->ucounts) { 219 int dec = atomic_dec_if_positive(&iter->ucount[type]); 220 WARN_ON_ONCE(dec < 0); 221 } 222 put_ucounts(ucounts); 223 } 224 225 static __init int user_namespace_sysctl_init(void) 226 { 227 #ifdef CONFIG_SYSCTL 228 static struct ctl_table_header *user_header; 229 static struct ctl_table empty[1]; 230 /* 231 * It is necessary to register the user directory in the 232 * default set so that registrations in the child sets work 233 * properly. 234 */ 235 user_header = register_sysctl("user", empty); 236 kmemleak_ignore(user_header); 237 BUG_ON(!user_header); 238 BUG_ON(!setup_userns_sysctls(&init_user_ns)); 239 #endif 240 return 0; 241 } 242 subsys_initcall(user_namespace_sysctl_init); 243