1 /* 2 * This program is free software; you can redistribute it and/or 3 * modify it under the terms of the GNU General Public License as 4 * published by the Free Software Foundation, version 2 of the 5 * License. 6 */ 7 8 #include <linux/stat.h> 9 #include <linux/sysctl.h> 10 #include <linux/slab.h> 11 #include <linux/hash.h> 12 #include <linux/user_namespace.h> 13 14 #define UCOUNTS_HASHTABLE_BITS 10 15 static struct hlist_head ucounts_hashtable[(1 << UCOUNTS_HASHTABLE_BITS)]; 16 static DEFINE_SPINLOCK(ucounts_lock); 17 18 #define ucounts_hashfn(ns, uid) \ 19 hash_long((unsigned long)__kuid_val(uid) + (unsigned long)(ns), \ 20 UCOUNTS_HASHTABLE_BITS) 21 #define ucounts_hashentry(ns, uid) \ 22 (ucounts_hashtable + ucounts_hashfn(ns, uid)) 23 24 25 #ifdef CONFIG_SYSCTL 26 static struct ctl_table_set * 27 set_lookup(struct ctl_table_root *root) 28 { 29 return ¤t_user_ns()->set; 30 } 31 32 static int set_is_seen(struct ctl_table_set *set) 33 { 34 return ¤t_user_ns()->set == set; 35 } 36 37 static int set_permissions(struct ctl_table_header *head, 38 struct ctl_table *table) 39 { 40 struct user_namespace *user_ns = 41 container_of(head->set, struct user_namespace, set); 42 int mode; 43 44 /* Allow users with CAP_SYS_RESOURCE unrestrained access */ 45 if (ns_capable(user_ns, CAP_SYS_RESOURCE)) 46 mode = (table->mode & S_IRWXU) >> 6; 47 else 48 /* Allow all others at most read-only access */ 49 mode = table->mode & S_IROTH; 50 return (mode << 6) | (mode << 3) | mode; 51 } 52 53 static struct ctl_table_root set_root = { 54 .lookup = set_lookup, 55 .permissions = set_permissions, 56 }; 57 58 static int zero = 0; 59 static int int_max = INT_MAX; 60 #define UCOUNT_ENTRY(name) \ 61 { \ 62 .procname = name, \ 63 .maxlen = sizeof(int), \ 64 .mode = 0644, \ 65 .proc_handler = proc_dointvec_minmax, \ 66 .extra1 = &zero, \ 67 .extra2 = &int_max, \ 68 } 69 static struct ctl_table user_table[] = { 70 UCOUNT_ENTRY("max_user_namespaces"), 71 UCOUNT_ENTRY("max_pid_namespaces"), 72 UCOUNT_ENTRY("max_uts_namespaces"), 73 UCOUNT_ENTRY("max_ipc_namespaces"), 74 UCOUNT_ENTRY("max_net_namespaces"), 75 UCOUNT_ENTRY("max_mnt_namespaces"), 76 UCOUNT_ENTRY("max_cgroup_namespaces"), 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 setup_sysctl_set(&ns->set, &set_root, set_is_seen); 86 tbl = kmemdup(user_table, sizeof(user_table), GFP_KERNEL); 87 if (tbl) { 88 int i; 89 for (i = 0; i < UCOUNT_COUNTS; i++) { 90 tbl[i].data = &ns->ucount_max[i]; 91 } 92 ns->sysctls = __register_sysctl_table(&ns->set, "user", tbl); 93 } 94 if (!ns->sysctls) { 95 kfree(tbl); 96 retire_sysctl_set(&ns->set); 97 return false; 98 } 99 #endif 100 return true; 101 } 102 103 void retire_userns_sysctls(struct user_namespace *ns) 104 { 105 #ifdef CONFIG_SYSCTL 106 struct ctl_table *tbl; 107 108 tbl = ns->sysctls->ctl_table_arg; 109 unregister_sysctl_table(ns->sysctls); 110 retire_sysctl_set(&ns->set); 111 kfree(tbl); 112 #endif 113 } 114 115 static struct ucounts *find_ucounts(struct user_namespace *ns, kuid_t uid, struct hlist_head *hashent) 116 { 117 struct ucounts *ucounts; 118 119 hlist_for_each_entry(ucounts, hashent, node) { 120 if (uid_eq(ucounts->uid, uid) && (ucounts->ns == ns)) 121 return ucounts; 122 } 123 return NULL; 124 } 125 126 static struct ucounts *get_ucounts(struct user_namespace *ns, kuid_t uid) 127 { 128 struct hlist_head *hashent = ucounts_hashentry(ns, uid); 129 struct ucounts *ucounts, *new; 130 131 spin_lock(&ucounts_lock); 132 ucounts = find_ucounts(ns, uid, hashent); 133 if (!ucounts) { 134 spin_unlock(&ucounts_lock); 135 136 new = kzalloc(sizeof(*new), GFP_KERNEL); 137 if (!new) 138 return NULL; 139 140 new->ns = ns; 141 new->uid = uid; 142 atomic_set(&new->count, 0); 143 144 spin_lock(&ucounts_lock); 145 ucounts = find_ucounts(ns, uid, hashent); 146 if (ucounts) { 147 kfree(new); 148 } else { 149 hlist_add_head(&new->node, hashent); 150 ucounts = new; 151 } 152 } 153 if (!atomic_add_unless(&ucounts->count, 1, INT_MAX)) 154 ucounts = NULL; 155 spin_unlock(&ucounts_lock); 156 return ucounts; 157 } 158 159 static void put_ucounts(struct ucounts *ucounts) 160 { 161 if (atomic_dec_and_test(&ucounts->count)) { 162 spin_lock(&ucounts_lock); 163 hlist_del_init(&ucounts->node); 164 spin_unlock(&ucounts_lock); 165 166 kfree(ucounts); 167 } 168 } 169 170 static inline bool atomic_inc_below(atomic_t *v, int u) 171 { 172 int c, old; 173 c = atomic_read(v); 174 for (;;) { 175 if (unlikely(c >= u)) 176 return false; 177 old = atomic_cmpxchg(v, c, c+1); 178 if (likely(old == c)) 179 return true; 180 c = old; 181 } 182 } 183 184 struct ucounts *inc_ucount(struct user_namespace *ns, kuid_t uid, 185 enum ucount_type type) 186 { 187 struct ucounts *ucounts, *iter, *bad; 188 struct user_namespace *tns; 189 ucounts = get_ucounts(ns, uid); 190 for (iter = ucounts; iter; iter = tns->ucounts) { 191 int max; 192 tns = iter->ns; 193 max = READ_ONCE(tns->ucount_max[type]); 194 if (!atomic_inc_below(&iter->ucount[type], max)) 195 goto fail; 196 } 197 return ucounts; 198 fail: 199 bad = iter; 200 for (iter = ucounts; iter != bad; iter = iter->ns->ucounts) 201 atomic_dec(&iter->ucount[type]); 202 203 put_ucounts(ucounts); 204 return NULL; 205 } 206 207 void dec_ucount(struct ucounts *ucounts, enum ucount_type type) 208 { 209 struct ucounts *iter; 210 for (iter = ucounts; iter; iter = iter->ns->ucounts) { 211 int dec = atomic_dec_if_positive(&iter->ucount[type]); 212 WARN_ON_ONCE(dec < 0); 213 } 214 put_ucounts(ucounts); 215 } 216 217 static __init int user_namespace_sysctl_init(void) 218 { 219 #ifdef CONFIG_SYSCTL 220 static struct ctl_table_header *user_header; 221 static struct ctl_table empty[1]; 222 /* 223 * It is necessary to register the user directory in the 224 * default set so that registrations in the child sets work 225 * properly. 226 */ 227 user_header = register_sysctl("user", empty); 228 BUG_ON(!user_header); 229 BUG_ON(!setup_userns_sysctls(&init_user_ns)); 230 #endif 231 return 0; 232 } 233 subsys_initcall(user_namespace_sysctl_init); 234 235 236