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kernel/ucount.c
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// SPDX-License-Identifier: GPL-2.0-only |
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#include <linux/stat.h> #include <linux/sysctl.h> #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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#define UCOUNTS_HASHTABLE_BITS 10 static struct hlist_head ucounts_hashtable[(1 << UCOUNTS_HASHTABLE_BITS)]; static DEFINE_SPINLOCK(ucounts_lock); #define ucounts_hashfn(ns, uid) \ hash_long((unsigned long)__kuid_val(uid) + (unsigned long)(ns), \ UCOUNTS_HASHTABLE_BITS) #define ucounts_hashentry(ns, uid) \ (ucounts_hashtable + ucounts_hashfn(ns, uid)) |
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#ifdef CONFIG_SYSCTL static struct ctl_table_set * set_lookup(struct ctl_table_root *root) { return ¤t_user_ns()->set; } static int set_is_seen(struct ctl_table_set *set) { return ¤t_user_ns()->set == set; } static int set_permissions(struct ctl_table_header *head, struct ctl_table *table) { struct user_namespace *user_ns = container_of(head->set, struct user_namespace, set); int mode; /* Allow users with CAP_SYS_RESOURCE unrestrained access */ if (ns_capable(user_ns, CAP_SYS_RESOURCE)) mode = (table->mode & S_IRWXU) >> 6; else /* Allow all others at most read-only access */ mode = table->mode & S_IROTH; return (mode << 6) | (mode << 3) | mode; } static struct ctl_table_root set_root = { .lookup = set_lookup, .permissions = set_permissions, }; |
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#define UCOUNT_ENTRY(name) \ |
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{ \ .procname = name, \ .maxlen = sizeof(int), \ .mode = 0644, \ .proc_handler = proc_dointvec_minmax, \ |
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.extra1 = SYSCTL_ZERO, \ .extra2 = SYSCTL_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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#ifdef CONFIG_INOTIFY_USER UCOUNT_ENTRY("max_inotify_instances"), UCOUNT_ENTRY("max_inotify_watches"), #endif |
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{ } }; #endif /* CONFIG_SYSCTL */ bool setup_userns_sysctls(struct user_namespace *ns) { #ifdef CONFIG_SYSCTL struct ctl_table *tbl; 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; for (i = 0; i < UCOUNT_COUNTS; i++) { tbl[i].data = &ns->ucount_max[i]; } |
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ns->sysctls = __register_sysctl_table(&ns->set, "user", tbl); |
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} if (!ns->sysctls) { kfree(tbl); retire_sysctl_set(&ns->set); return false; } #endif return true; } void retire_userns_sysctls(struct user_namespace *ns) { #ifdef CONFIG_SYSCTL struct ctl_table *tbl; tbl = ns->sysctls->ctl_table_arg; unregister_sysctl_table(ns->sysctls); retire_sysctl_set(&ns->set); kfree(tbl); #endif } |
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static struct ucounts *find_ucounts(struct user_namespace *ns, kuid_t uid, struct hlist_head *hashent) { struct ucounts *ucounts; hlist_for_each_entry(ucounts, hashent, node) { if (uid_eq(ucounts->uid, uid) && (ucounts->ns == ns)) return ucounts; } return NULL; } static struct ucounts *get_ucounts(struct user_namespace *ns, kuid_t uid) { struct hlist_head *hashent = ucounts_hashentry(ns, uid); struct ucounts *ucounts, *new; |
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spin_lock_irq(&ucounts_lock); |
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ucounts = find_ucounts(ns, uid, hashent); if (!ucounts) { |
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spin_unlock_irq(&ucounts_lock); |
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new = kzalloc(sizeof(*new), GFP_KERNEL); if (!new) return NULL; new->ns = ns; new->uid = uid; |
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new->count = 0; |
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spin_lock_irq(&ucounts_lock); |
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ucounts = find_ucounts(ns, uid, hashent); if (ucounts) { kfree(new); } else { hlist_add_head(&new->node, hashent); ucounts = new; } } |
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if (ucounts->count == INT_MAX) |
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ucounts = NULL; |
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else ucounts->count += 1; |
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spin_unlock_irq(&ucounts_lock); |
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return ucounts; } static void put_ucounts(struct ucounts *ucounts) { |
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unsigned long flags; |
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spin_lock_irqsave(&ucounts_lock, flags); ucounts->count -= 1; if (!ucounts->count) |
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hlist_del_init(&ucounts->node); |
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else ucounts = NULL; spin_unlock_irqrestore(&ucounts_lock, flags); |
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kfree(ucounts); |
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} |
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static inline bool atomic_inc_below(atomic_t *v, int u) { int c, old; c = atomic_read(v); for (;;) { if (unlikely(c >= u)) return false; old = atomic_cmpxchg(v, c, c+1); if (likely(old == c)) return true; c = old; } } |
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struct ucounts *inc_ucount(struct user_namespace *ns, kuid_t uid, enum ucount_type type) |
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{ |
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struct ucounts *ucounts, *iter, *bad; struct user_namespace *tns; ucounts = get_ucounts(ns, uid); for (iter = ucounts; iter; iter = tns->ucounts) { int max; tns = iter->ns; |
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max = READ_ONCE(tns->ucount_max[type]); if (!atomic_inc_below(&iter->ucount[type], max)) |
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goto fail; } |
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return ucounts; |
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fail: |
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bad = iter; for (iter = ucounts; iter != bad; iter = iter->ns->ucounts) |
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atomic_dec(&iter->ucount[type]); |
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put_ucounts(ucounts); 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; for (iter = ucounts; iter; iter = iter->ns->ucounts) { |
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int dec = atomic_dec_if_positive(&iter->ucount[type]); |
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WARN_ON_ONCE(dec < 0); } |
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put_ucounts(ucounts); |
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} |
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static __init int user_namespace_sysctl_init(void) { #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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* It is necessary to register the user directory in the |
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* default set so that registrations in the child sets work * properly. */ |
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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)); #endif return 0; } subsys_initcall(user_namespace_sysctl_init); |