380 строки
9.1 KiB
C
380 строки
9.1 KiB
C
// SPDX-License-Identifier: GPL-2.0-only
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#include <linux/stat.h>
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#include <linux/sysctl.h>
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#include <linux/slab.h>
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#include <linux/cred.h>
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#include <linux/hash.h>
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#include <linux/kmemleak.h>
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#include <linux/user_namespace.h>
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struct ucounts init_ucounts = {
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.ns = &init_user_ns,
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.uid = GLOBAL_ROOT_UID,
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.count = ATOMIC_INIT(1),
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};
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#define UCOUNTS_HASHTABLE_BITS 10
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static struct hlist_head ucounts_hashtable[(1 << UCOUNTS_HASHTABLE_BITS)];
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static DEFINE_SPINLOCK(ucounts_lock);
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#define ucounts_hashfn(ns, uid) \
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hash_long((unsigned long)__kuid_val(uid) + (unsigned long)(ns), \
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UCOUNTS_HASHTABLE_BITS)
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#define ucounts_hashentry(ns, uid) \
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(ucounts_hashtable + ucounts_hashfn(ns, uid))
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#ifdef CONFIG_SYSCTL
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static struct ctl_table_set *
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set_lookup(struct ctl_table_root *root)
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{
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return ¤t_user_ns()->set;
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}
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static int set_is_seen(struct ctl_table_set *set)
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{
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return ¤t_user_ns()->set == set;
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}
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static int set_permissions(struct ctl_table_header *head,
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struct ctl_table *table)
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{
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struct user_namespace *user_ns =
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container_of(head->set, struct user_namespace, set);
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int mode;
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/* Allow users with CAP_SYS_RESOURCE unrestrained access */
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if (ns_capable(user_ns, CAP_SYS_RESOURCE))
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mode = (table->mode & S_IRWXU) >> 6;
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else
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/* Allow all others at most read-only access */
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mode = table->mode & S_IROTH;
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return (mode << 6) | (mode << 3) | mode;
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}
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static struct ctl_table_root set_root = {
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.lookup = set_lookup,
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.permissions = set_permissions,
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};
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static long ue_zero = 0;
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static long ue_int_max = INT_MAX;
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#define UCOUNT_ENTRY(name) \
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{ \
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.procname = name, \
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.maxlen = sizeof(long), \
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.mode = 0644, \
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.proc_handler = proc_doulongvec_minmax, \
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.extra1 = &ue_zero, \
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.extra2 = &ue_int_max, \
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}
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static struct ctl_table user_table[] = {
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UCOUNT_ENTRY("max_user_namespaces"),
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UCOUNT_ENTRY("max_pid_namespaces"),
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UCOUNT_ENTRY("max_uts_namespaces"),
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UCOUNT_ENTRY("max_ipc_namespaces"),
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UCOUNT_ENTRY("max_net_namespaces"),
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UCOUNT_ENTRY("max_mnt_namespaces"),
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UCOUNT_ENTRY("max_cgroup_namespaces"),
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UCOUNT_ENTRY("max_time_namespaces"),
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#ifdef CONFIG_INOTIFY_USER
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UCOUNT_ENTRY("max_inotify_instances"),
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UCOUNT_ENTRY("max_inotify_watches"),
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#endif
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#ifdef CONFIG_FANOTIFY
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UCOUNT_ENTRY("max_fanotify_groups"),
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UCOUNT_ENTRY("max_fanotify_marks"),
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#endif
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{ },
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{ },
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{ },
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{ },
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{ }
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};
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#endif /* CONFIG_SYSCTL */
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bool setup_userns_sysctls(struct user_namespace *ns)
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{
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#ifdef CONFIG_SYSCTL
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struct ctl_table *tbl;
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BUILD_BUG_ON(ARRAY_SIZE(user_table) != UCOUNT_COUNTS + 1);
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setup_sysctl_set(&ns->set, &set_root, set_is_seen);
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tbl = kmemdup(user_table, sizeof(user_table), GFP_KERNEL);
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if (tbl) {
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int i;
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for (i = 0; i < UCOUNT_COUNTS; i++) {
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tbl[i].data = &ns->ucount_max[i];
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}
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ns->sysctls = __register_sysctl_table(&ns->set, "user", tbl);
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}
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if (!ns->sysctls) {
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kfree(tbl);
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retire_sysctl_set(&ns->set);
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return false;
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}
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#endif
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return true;
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}
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void retire_userns_sysctls(struct user_namespace *ns)
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{
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#ifdef CONFIG_SYSCTL
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struct ctl_table *tbl;
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tbl = ns->sysctls->ctl_table_arg;
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unregister_sysctl_table(ns->sysctls);
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retire_sysctl_set(&ns->set);
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kfree(tbl);
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#endif
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}
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static struct ucounts *find_ucounts(struct user_namespace *ns, kuid_t uid, struct hlist_head *hashent)
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{
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struct ucounts *ucounts;
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hlist_for_each_entry(ucounts, hashent, node) {
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if (uid_eq(ucounts->uid, uid) && (ucounts->ns == ns))
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return ucounts;
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}
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return NULL;
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}
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static void hlist_add_ucounts(struct ucounts *ucounts)
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{
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struct hlist_head *hashent = ucounts_hashentry(ucounts->ns, ucounts->uid);
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spin_lock_irq(&ucounts_lock);
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hlist_add_head(&ucounts->node, hashent);
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spin_unlock_irq(&ucounts_lock);
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}
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static inline bool get_ucounts_or_wrap(struct ucounts *ucounts)
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{
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/* Returns true on a successful get, false if the count wraps. */
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return !atomic_add_negative(1, &ucounts->count);
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}
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struct ucounts *get_ucounts(struct ucounts *ucounts)
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{
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if (!get_ucounts_or_wrap(ucounts)) {
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put_ucounts(ucounts);
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ucounts = NULL;
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}
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return ucounts;
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}
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struct ucounts *alloc_ucounts(struct user_namespace *ns, kuid_t uid)
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{
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struct hlist_head *hashent = ucounts_hashentry(ns, uid);
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struct ucounts *ucounts, *new;
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bool wrapped;
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spin_lock_irq(&ucounts_lock);
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ucounts = find_ucounts(ns, uid, hashent);
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if (!ucounts) {
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spin_unlock_irq(&ucounts_lock);
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new = kzalloc(sizeof(*new), GFP_KERNEL);
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if (!new)
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return NULL;
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new->ns = ns;
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new->uid = uid;
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atomic_set(&new->count, 1);
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spin_lock_irq(&ucounts_lock);
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ucounts = find_ucounts(ns, uid, hashent);
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if (ucounts) {
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kfree(new);
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} else {
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hlist_add_head(&new->node, hashent);
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get_user_ns(new->ns);
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spin_unlock_irq(&ucounts_lock);
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return new;
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}
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}
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wrapped = !get_ucounts_or_wrap(ucounts);
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spin_unlock_irq(&ucounts_lock);
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if (wrapped) {
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put_ucounts(ucounts);
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return NULL;
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}
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return ucounts;
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}
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void put_ucounts(struct ucounts *ucounts)
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{
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unsigned long flags;
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if (atomic_dec_and_lock_irqsave(&ucounts->count, &ucounts_lock, flags)) {
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hlist_del_init(&ucounts->node);
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spin_unlock_irqrestore(&ucounts_lock, flags);
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put_user_ns(ucounts->ns);
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kfree(ucounts);
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}
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}
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static inline bool atomic_long_inc_below(atomic_long_t *v, int u)
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{
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long c, old;
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c = atomic_long_read(v);
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for (;;) {
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if (unlikely(c >= u))
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return false;
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old = atomic_long_cmpxchg(v, c, c+1);
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if (likely(old == c))
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return true;
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c = old;
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}
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}
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struct ucounts *inc_ucount(struct user_namespace *ns, kuid_t uid,
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enum ucount_type type)
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{
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struct ucounts *ucounts, *iter, *bad;
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struct user_namespace *tns;
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ucounts = alloc_ucounts(ns, uid);
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for (iter = ucounts; iter; iter = tns->ucounts) {
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long max;
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tns = iter->ns;
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max = READ_ONCE(tns->ucount_max[type]);
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if (!atomic_long_inc_below(&iter->ucount[type], max))
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goto fail;
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}
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return ucounts;
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fail:
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bad = iter;
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for (iter = ucounts; iter != bad; iter = iter->ns->ucounts)
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atomic_long_dec(&iter->ucount[type]);
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put_ucounts(ucounts);
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return NULL;
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}
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void dec_ucount(struct ucounts *ucounts, enum ucount_type type)
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{
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struct ucounts *iter;
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for (iter = ucounts; iter; iter = iter->ns->ucounts) {
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long dec = atomic_long_dec_if_positive(&iter->ucount[type]);
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WARN_ON_ONCE(dec < 0);
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}
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put_ucounts(ucounts);
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}
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long inc_rlimit_ucounts(struct ucounts *ucounts, enum ucount_type type, long v)
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{
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struct ucounts *iter;
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long max = LONG_MAX;
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long ret = 0;
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for (iter = ucounts; iter; iter = iter->ns->ucounts) {
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long new = atomic_long_add_return(v, &iter->ucount[type]);
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if (new < 0 || new > max)
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ret = LONG_MAX;
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else if (iter == ucounts)
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ret = new;
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max = READ_ONCE(iter->ns->ucount_max[type]);
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}
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return ret;
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}
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bool dec_rlimit_ucounts(struct ucounts *ucounts, enum ucount_type type, long v)
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{
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struct ucounts *iter;
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long new = -1; /* Silence compiler warning */
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for (iter = ucounts; iter; iter = iter->ns->ucounts) {
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long dec = atomic_long_sub_return(v, &iter->ucount[type]);
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WARN_ON_ONCE(dec < 0);
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if (iter == ucounts)
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new = dec;
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}
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return (new == 0);
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}
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static void do_dec_rlimit_put_ucounts(struct ucounts *ucounts,
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struct ucounts *last, enum ucount_type type)
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{
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struct ucounts *iter, *next;
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for (iter = ucounts; iter != last; iter = next) {
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long dec = atomic_long_sub_return(1, &iter->ucount[type]);
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WARN_ON_ONCE(dec < 0);
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next = iter->ns->ucounts;
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if (dec == 0)
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put_ucounts(iter);
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}
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}
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void dec_rlimit_put_ucounts(struct ucounts *ucounts, enum ucount_type type)
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{
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do_dec_rlimit_put_ucounts(ucounts, NULL, type);
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}
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long inc_rlimit_get_ucounts(struct ucounts *ucounts, enum ucount_type type)
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{
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/* Caller must hold a reference to ucounts */
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struct ucounts *iter;
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long max = LONG_MAX;
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long dec, ret = 0;
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for (iter = ucounts; iter; iter = iter->ns->ucounts) {
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long new = atomic_long_add_return(1, &iter->ucount[type]);
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if (new < 0 || new > max)
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goto unwind;
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if (iter == ucounts)
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ret = new;
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max = READ_ONCE(iter->ns->ucount_max[type]);
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/*
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* Grab an extra ucount reference for the caller when
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* the rlimit count was previously 0.
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*/
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if (new != 1)
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continue;
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if (!get_ucounts(iter))
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goto dec_unwind;
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}
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return ret;
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dec_unwind:
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dec = atomic_long_sub_return(1, &iter->ucount[type]);
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WARN_ON_ONCE(dec < 0);
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unwind:
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do_dec_rlimit_put_ucounts(ucounts, iter, type);
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return 0;
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}
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bool is_ucounts_overlimit(struct ucounts *ucounts, enum ucount_type type, unsigned long rlimit)
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{
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struct ucounts *iter;
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long max = rlimit;
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if (rlimit > LONG_MAX)
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max = LONG_MAX;
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for (iter = ucounts; iter; iter = iter->ns->ucounts) {
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if (get_ucounts_value(iter, type) > max)
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return true;
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max = READ_ONCE(iter->ns->ucount_max[type]);
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}
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return false;
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}
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static __init int user_namespace_sysctl_init(void)
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{
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#ifdef CONFIG_SYSCTL
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static struct ctl_table_header *user_header;
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static struct ctl_table empty[1];
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/*
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* It is necessary to register the user directory in the
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* default set so that registrations in the child sets work
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* properly.
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*/
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user_header = register_sysctl("user", empty);
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kmemleak_ignore(user_header);
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BUG_ON(!user_header);
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BUG_ON(!setup_userns_sysctls(&init_user_ns));
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#endif
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hlist_add_ucounts(&init_ucounts);
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inc_rlimit_ucounts(&init_ucounts, UCOUNT_RLIMIT_NPROC, 1);
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return 0;
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}
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subsys_initcall(user_namespace_sysctl_init);
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