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 static int zero = 0; 56 static int int_max = INT_MAX; 57 #define UCOUNT_ENTRY(name) \ 58 { \ 59 .procname = name, \ 60 .maxlen = sizeof(int), \ 61 .mode = 0644, \ 62 .proc_handler = proc_dointvec_minmax, \ 63 .extra1 = &zero, \ 64 .extra2 = &int_max, \ 65 } 66 static struct ctl_table user_table[] = { 67 UCOUNT_ENTRY("max_user_namespaces"), 68 UCOUNT_ENTRY("max_pid_namespaces"), 69 UCOUNT_ENTRY("max_uts_namespaces"), 70 UCOUNT_ENTRY("max_ipc_namespaces"), 71 UCOUNT_ENTRY("max_net_namespaces"), 72 UCOUNT_ENTRY("max_mnt_namespaces"), 73 UCOUNT_ENTRY("max_cgroup_namespaces"), 74 #ifdef CONFIG_INOTIFY_USER 75 UCOUNT_ENTRY("max_inotify_instances"), 76 UCOUNT_ENTRY("max_inotify_watches"), 77 #endif 78 { } 79 }; 80 #endif /* CONFIG_SYSCTL */ 81 82 bool setup_userns_sysctls(struct user_namespace *ns) 83 { 84 #ifdef CONFIG_SYSCTL 85 struct ctl_table *tbl; 86 setup_sysctl_set(&ns->set, &set_root, set_is_seen); 87 tbl = kmemdup(user_table, sizeof(user_table), GFP_KERNEL); 88 if (tbl) { 89 int i; 90 for (i = 0; i < UCOUNT_COUNTS; i++) { 91 tbl[i].data = &ns->ucount_max[i]; 92 } 93 ns->sysctls = __register_sysctl_table(&ns->set, "user", tbl); 94 } 95 if (!ns->sysctls) { 96 kfree(tbl); 97 retire_sysctl_set(&ns->set); 98 return false; 99 } 100 #endif 101 return true; 102 } 103 104 void retire_userns_sysctls(struct user_namespace *ns) 105 { 106 #ifdef CONFIG_SYSCTL 107 struct ctl_table *tbl; 108 109 tbl = ns->sysctls->ctl_table_arg; 110 unregister_sysctl_table(ns->sysctls); 111 retire_sysctl_set(&ns->set); 112 kfree(tbl); 113 #endif 114 } 115 116 static struct ucounts *find_ucounts(struct user_namespace *ns, kuid_t uid, struct hlist_head *hashent) 117 { 118 struct ucounts *ucounts; 119 120 hlist_for_each_entry(ucounts, hashent, node) { 121 if (uid_eq(ucounts->uid, uid) && (ucounts->ns == ns)) 122 return ucounts; 123 } 124 return NULL; 125 } 126 127 static struct ucounts *get_ucounts(struct user_namespace *ns, kuid_t uid) 128 { 129 struct hlist_head *hashent = ucounts_hashentry(ns, uid); 130 struct ucounts *ucounts, *new; 131 132 spin_lock_irq(&ucounts_lock); 133 ucounts = find_ucounts(ns, uid, hashent); 134 if (!ucounts) { 135 spin_unlock_irq(&ucounts_lock); 136 137 new = kzalloc(sizeof(*new), GFP_KERNEL); 138 if (!new) 139 return NULL; 140 141 new->ns = ns; 142 new->uid = uid; 143 new->count = 0; 144 145 spin_lock_irq(&ucounts_lock); 146 ucounts = find_ucounts(ns, uid, hashent); 147 if (ucounts) { 148 kfree(new); 149 } else { 150 hlist_add_head(&new->node, hashent); 151 ucounts = new; 152 } 153 } 154 if (ucounts->count == INT_MAX) 155 ucounts = NULL; 156 else 157 ucounts->count += 1; 158 spin_unlock_irq(&ucounts_lock); 159 return ucounts; 160 } 161 162 static void put_ucounts(struct ucounts *ucounts) 163 { 164 unsigned long flags; 165 166 spin_lock_irqsave(&ucounts_lock, flags); 167 ucounts->count -= 1; 168 if (!ucounts->count) 169 hlist_del_init(&ucounts->node); 170 else 171 ucounts = NULL; 172 spin_unlock_irqrestore(&ucounts_lock, flags); 173 174 kfree(ucounts); 175 } 176 177 static inline bool atomic_inc_below(atomic_t *v, int u) 178 { 179 int c, old; 180 c = atomic_read(v); 181 for (;;) { 182 if (unlikely(c >= u)) 183 return false; 184 old = atomic_cmpxchg(v, c, c+1); 185 if (likely(old == c)) 186 return true; 187 c = old; 188 } 189 } 190 191 struct ucounts *inc_ucount(struct user_namespace *ns, kuid_t uid, 192 enum ucount_type type) 193 { 194 struct ucounts *ucounts, *iter, *bad; 195 struct user_namespace *tns; 196 ucounts = get_ucounts(ns, uid); 197 for (iter = ucounts; iter; iter = tns->ucounts) { 198 int max; 199 tns = iter->ns; 200 max = READ_ONCE(tns->ucount_max[type]); 201 if (!atomic_inc_below(&iter->ucount[type], max)) 202 goto fail; 203 } 204 return ucounts; 205 fail: 206 bad = iter; 207 for (iter = ucounts; iter != bad; iter = iter->ns->ucounts) 208 atomic_dec(&iter->ucount[type]); 209 210 put_ucounts(ucounts); 211 return NULL; 212 } 213 214 void dec_ucount(struct ucounts *ucounts, enum ucount_type type) 215 { 216 struct ucounts *iter; 217 for (iter = ucounts; iter; iter = iter->ns->ucounts) { 218 int dec = atomic_dec_if_positive(&iter->ucount[type]); 219 WARN_ON_ONCE(dec < 0); 220 } 221 put_ucounts(ucounts); 222 } 223 224 static __init int user_namespace_sysctl_init(void) 225 { 226 #ifdef CONFIG_SYSCTL 227 static struct ctl_table_header *user_header; 228 static struct ctl_table empty[1]; 229 /* 230 * It is necessary to register the user directory in the 231 * default set so that registrations in the child sets work 232 * properly. 233 */ 234 user_header = register_sysctl("user", empty); 235 kmemleak_ignore(user_header); 236 BUG_ON(!user_header); 237 BUG_ON(!setup_userns_sysctls(&init_user_ns)); 238 #endif 239 return 0; 240 } 241 subsys_initcall(user_namespace_sysctl_init); 242