userns: Make the count of user namespaces per user
Add a structure that is per user and per user ns and use it to hold
the count of user namespaces. This makes prevents one user from
creating denying service to another user by creating the maximum
number of user namespaces.
Rename the sysctl export of the maximum count from
/proc/sys/userns/max_user_namespaces to /proc/sys/user/max_user_namespaces
to reflect that the count is now per user.
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
diff --git a/kernel/fork.c b/kernel/fork.c
index daa6a82..d8cde53 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -322,7 +322,7 @@
init_task.signal->rlim[RLIMIT_SIGPENDING] =
init_task.signal->rlim[RLIMIT_NPROC];
- init_user_ns.max_user_namespaces = max_threads;
+ init_user_ns.max_user_namespaces = max_threads/2;
}
int __weak arch_dup_task_struct(struct task_struct *dst,
diff --git a/kernel/ucount.c b/kernel/ucount.c
index 6c2205c..33c4187 100644
--- a/kernel/ucount.c
+++ b/kernel/ucount.c
@@ -8,8 +8,20 @@
#include <linux/stat.h>
#include <linux/sysctl.h>
#include <linux/slab.h>
+#include <linux/hash.h>
#include <linux/user_namespace.h>
+#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))
+
+
#ifdef CONFIG_SYSCTL
static struct ctl_table_set *
set_lookup(struct ctl_table_root *root)
@@ -45,7 +57,7 @@
static int zero = 0;
static int int_max = INT_MAX;
-static struct ctl_table userns_table[] = {
+static struct ctl_table user_table[] = {
{
.procname = "max_user_namespaces",
.data = &init_user_ns.max_user_namespaces,
@@ -64,11 +76,11 @@
#ifdef CONFIG_SYSCTL
struct ctl_table *tbl;
setup_sysctl_set(&ns->set, &set_root, set_is_seen);
- tbl = kmemdup(userns_table, sizeof(userns_table), GFP_KERNEL);
+ tbl = kmemdup(user_table, sizeof(user_table), GFP_KERNEL);
if (tbl) {
tbl[0].data = &ns->max_user_namespaces;
- ns->sysctls = __register_sysctl_table(&ns->set, "userns", tbl);
+ ns->sysctls = __register_sysctl_table(&ns->set, "user", tbl);
}
if (!ns->sysctls) {
kfree(tbl);
@@ -91,6 +103,61 @@
#endif
}
+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;
+
+ spin_lock(&ucounts_lock);
+ ucounts = find_ucounts(ns, uid, hashent);
+ if (!ucounts) {
+ spin_unlock(&ucounts_lock);
+
+ new = kzalloc(sizeof(*new), GFP_KERNEL);
+ if (!new)
+ return NULL;
+
+ new->ns = ns;
+ new->uid = uid;
+ atomic_set(&new->count, 0);
+
+ spin_lock(&ucounts_lock);
+ ucounts = find_ucounts(ns, uid, hashent);
+ if (ucounts) {
+ kfree(new);
+ } else {
+ hlist_add_head(&new->node, hashent);
+ ucounts = new;
+ }
+ }
+ if (!atomic_add_unless(&ucounts->count, 1, INT_MAX))
+ ucounts = NULL;
+ spin_unlock(&ucounts_lock);
+ return ucounts;
+}
+
+static void put_ucounts(struct ucounts *ucounts)
+{
+ if (atomic_dec_and_test(&ucounts->count)) {
+ spin_lock(&ucounts_lock);
+ hlist_del_init(&ucounts->node);
+ spin_unlock(&ucounts_lock);
+
+ kfree(ucounts);
+ }
+}
+
static inline bool atomic_inc_below(atomic_t *v, int u)
{
int c, old;
@@ -105,44 +172,51 @@
}
}
-bool inc_user_namespaces(struct user_namespace *ns)
+struct ucounts *inc_user_namespaces(struct user_namespace *ns, kuid_t uid)
{
- struct user_namespace *pos, *bad;
- for (pos = ns; pos; pos = pos->parent) {
- int max = READ_ONCE(pos->max_user_namespaces);
- if (!atomic_inc_below(&pos->user_namespaces, max))
+ 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;
+ max = READ_ONCE(tns->max_user_namespaces);
+ if (!atomic_inc_below(&iter->user_namespaces, max))
goto fail;
}
- return true;
+ return ucounts;
fail:
- bad = pos;
- for (pos = ns; pos != bad; pos = pos->parent)
- atomic_dec(&pos->user_namespaces);
+ bad = iter;
+ for (iter = ucounts; iter != bad; iter = iter->ns->ucounts)
+ atomic_dec(&iter->user_namespaces);
- return false;
+ put_ucounts(ucounts);
+ return NULL;
}
-void dec_user_namespaces(struct user_namespace *ns)
+void dec_user_namespaces(struct ucounts *ucounts)
{
- struct user_namespace *pos;
- for (pos = ns; pos; pos = pos->parent) {
- int dec = atomic_dec_if_positive(&pos->user_namespaces);
+ struct ucounts *iter;
+ for (iter = ucounts; iter; iter = iter->ns->ucounts) {
+ int dec = atomic_dec_if_positive(&iter->user_namespaces);
WARN_ON_ONCE(dec < 0);
}
+ put_ucounts(ucounts);
}
+
static __init int user_namespace_sysctl_init(void)
{
#ifdef CONFIG_SYSCTL
- static struct ctl_table_header *userns_header;
+ static struct ctl_table_header *user_header;
static struct ctl_table empty[1];
/*
- * It is necessary to register the userns directory in the
+ * It is necessary to register the user directory in the
* default set so that registrations in the child sets work
* properly.
*/
- userns_header = register_sysctl("userns", empty);
- BUG_ON(!userns_header);
+ user_header = register_sysctl("user", empty);
+ BUG_ON(!user_header);
BUG_ON(!setup_userns_sysctls(&init_user_ns));
#endif
return 0;
diff --git a/kernel/user_namespace.c b/kernel/user_namespace.c
index 7d87017..58c67e5 100644
--- a/kernel/user_namespace.c
+++ b/kernel/user_namespace.c
@@ -31,7 +31,6 @@
struct uid_gid_map *map);
static void free_user_ns(struct work_struct *work);
-
static void set_cred_user_ns(struct cred *cred, struct user_namespace *user_ns)
{
/* Start with the same capabilities as init but useless for doing
@@ -64,13 +63,15 @@
struct user_namespace *ns, *parent_ns = new->user_ns;
kuid_t owner = new->euid;
kgid_t group = new->egid;
+ struct ucounts *ucounts;
int ret;
ret = -EUSERS;
if (parent_ns->level > 32)
goto fail;
- if (!inc_user_namespaces(parent_ns))
+ ucounts = inc_user_namespaces(parent_ns, owner);
+ if (!ucounts)
goto fail;
/*
@@ -110,6 +111,7 @@
ns->group = group;
INIT_WORK(&ns->work, free_user_ns);
ns->max_user_namespaces = INT_MAX;
+ ns->ucounts = ucounts;
/* Inherit USERNS_SETGROUPS_ALLOWED from our parent */
mutex_lock(&userns_state_mutex);
@@ -133,7 +135,7 @@
fail_free:
kmem_cache_free(user_ns_cachep, ns);
fail_dec:
- dec_user_namespaces(parent_ns);
+ dec_user_namespaces(ucounts);
fail:
return ret;
}
@@ -164,6 +166,7 @@
container_of(work, struct user_namespace, work);
do {
+ struct ucounts *ucounts = ns->ucounts;
parent = ns->parent;
retire_userns_sysctls(ns);
#ifdef CONFIG_PERSISTENT_KEYRINGS
@@ -171,7 +174,7 @@
#endif
ns_free_inum(&ns->ns);
kmem_cache_free(user_ns_cachep, ns);
- dec_user_namespaces(parent);
+ dec_user_namespaces(ucounts);
ns = parent;
} while (atomic_dec_and_test(&parent->count));
}
