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