userns: Generalize the user namespace count into ucount

The same kind of recursive sane default limit and policy
countrol that has been implemented for the user namespace
is desirable for the other namespaces, so generalize
the user namespace refernce count into a ucount.

Acked-by: Kees Cook <keescook@chromium.org>
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>

include/linux/user_namespace.h

@@ -23,6 +23,12 @@ struct uid_gid_map {	/* 64 bytes -- 1 cache line */
 #define USERNS_INIT_FLAGS USERNS_SETGROUPS_ALLOWED
 
 struct ucounts;
+
+enum ucount_type {
+	UCOUNT_USER_NAMESPACES,
+	UCOUNT_COUNTS,
+};
+
 struct user_namespace {
 	struct uid_gid_map	uid_map;
 	struct uid_gid_map	gid_map;
@@ -46,23 +52,23 @@ struct user_namespace {
 	struct ctl_table_header *sysctls;
 #endif
 	struct ucounts		*ucounts;
-	int max_user_namespaces;
+	int ucount_max[UCOUNT_COUNTS];
 };
 
 struct ucounts {
 	struct hlist_node node;
 	struct user_namespace *ns;
 	kuid_t uid;
 	atomic_t count;
-	atomic_t user_namespaces;
+	atomic_t ucount[UCOUNT_COUNTS];
 };
 
 extern struct user_namespace init_user_ns;
 
 bool setup_userns_sysctls(struct user_namespace *ns);
 void retire_userns_sysctls(struct user_namespace *ns);
-struct ucounts *inc_user_namespaces(struct user_namespace *ns, kuid_t uid);
-void dec_user_namespaces(struct ucounts *ucounts);
+struct ucounts *inc_ucount(struct user_namespace *ns, kuid_t uid, enum ucount_type type);
+void dec_ucount(struct ucounts *ucounts, enum ucount_type type);
 
 #ifdef CONFIG_USER_NS
 

kernel/fork.c

@@ -302,6 +302,7 @@ int arch_task_struct_size __read_mostly;
 
 void __init fork_init(void)
 {
+	int i;
 #ifndef CONFIG_ARCH_TASK_STRUCT_ALLOCATOR
 #ifndef ARCH_MIN_TASKALIGN
 #define ARCH_MIN_TASKALIGN	L1_CACHE_BYTES
@@ -322,7 +323,9 @@ void __init fork_init(void)
 	init_task.signal->rlim[RLIMIT_SIGPENDING] =
 		init_task.signal->rlim[RLIMIT_NPROC];
 
-	init_user_ns.max_user_namespaces = max_threads/2;
+	for (i = 0; i < UCOUNT_COUNTS; i++) {
+		init_user_ns.ucount_max[i] = max_threads/2;
+	}
 }
 
 int __weak arch_dup_task_struct(struct task_struct *dst,

kernel/ucount.c

@@ -57,16 +57,17 @@ static struct ctl_table_root set_root = {
 
 static int zero = 0;
 static int int_max = INT_MAX;
+#define UCOUNT_ENTRY(name) 				\
+	{						\
+		.procname	= name,			\
+		.maxlen		= sizeof(int),		\
+		.mode		= 0644,			\
+		.proc_handler	= proc_dointvec_minmax,	\
+		.extra1		= &zero,		\
+		.extra2		= &int_max,		\
+	}
 static struct ctl_table user_table[] = {
-	{
-		.procname	= "max_user_namespaces",
-		.data		= &init_user_ns.max_user_namespaces,
-		.maxlen		= sizeof(init_user_ns.max_user_namespaces),
-		.mode		= 0644,
-		.proc_handler	= proc_dointvec_minmax,
-		.extra1		= &zero,
-		.extra2		= &int_max,
-	},
+	UCOUNT_ENTRY("max_user_namespaces"),
 	{ }
 };
 #endif /* CONFIG_SYSCTL */
@@ -78,8 +79,10 @@ bool setup_userns_sysctls(struct user_namespace *ns)
 	setup_sysctl_set(&ns->set, &set_root, set_is_seen);
 	tbl = kmemdup(user_table, sizeof(user_table), GFP_KERNEL);
 	if (tbl) {
-		tbl[0].data = &ns->max_user_namespaces;
-
+		int i;
+		for (i = 0; i < UCOUNT_COUNTS; i++) {
+			tbl[i].data = &ns->ucount_max[i];
+		}
 		ns->sysctls = __register_sysctl_table(&ns->set, "user", tbl);
 	}
 	if (!ns->sysctls) {
@@ -172,39 +175,39 @@ static inline bool atomic_inc_below(atomic_t *v, int u)
 	}
 }
 
-struct ucounts *inc_user_namespaces(struct user_namespace *ns, kuid_t uid)
+struct ucounts *inc_ucount(struct user_namespace *ns, kuid_t uid,
+			   enum ucount_type type)
 {
 	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))
+		max = READ_ONCE(tns->ucount_max[type]);
+		if (!atomic_inc_below(&iter->ucount[type], max))
 			goto fail;
 	}
 	return ucounts;
 fail:
 	bad = iter;
 	for (iter = ucounts; iter != bad; iter = iter->ns->ucounts)
-		atomic_dec(&iter->user_namespaces);
+		atomic_dec(&iter->ucount[type]);
 
 	put_ucounts(ucounts);
 	return NULL;
 }
 
-void dec_user_namespaces(struct ucounts *ucounts)
+void dec_ucount(struct ucounts *ucounts, enum ucount_type type)
 {
 	struct ucounts *iter;
 	for (iter = ucounts; iter; iter = iter->ns->ucounts) {
-		int dec = atomic_dec_if_positive(&iter->user_namespaces);
+		int dec = atomic_dec_if_positive(&iter->ucount[type]);
 		WARN_ON_ONCE(dec < 0);
 	}
 	put_ucounts(ucounts);
 }
 
-
 static __init int user_namespace_sysctl_init(void)
 {
 #ifdef CONFIG_SYSCTL

kernel/user_namespace.c

@@ -31,6 +31,16 @@ static bool new_idmap_permitted(const struct file *file,
 				struct uid_gid_map *map);
 static void free_user_ns(struct work_struct *work);
 
+static struct ucounts *inc_user_namespaces(struct user_namespace *ns, kuid_t uid)
+{
+	return inc_ucount(ns, uid, UCOUNT_USER_NAMESPACES);
+}
+
+static void dec_user_namespaces(struct ucounts *ucounts)
+{
+	return dec_ucount(ucounts, UCOUNT_USER_NAMESPACES);
+}
+
 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
@@ -64,7 +74,7 @@ int create_user_ns(struct cred *new)
 	kuid_t owner = new->euid;
 	kgid_t group = new->egid;
 	struct ucounts *ucounts;
-	int ret;
+	int ret, i;
 
 	ret = -EUSERS;
 	if (parent_ns->level > 32)
@@ -110,7 +120,9 @@ int create_user_ns(struct cred *new)
 	ns->owner = owner;
 	ns->group = group;
 	INIT_WORK(&ns->work, free_user_ns);
-	ns->max_user_namespaces = INT_MAX;
+	for (i = 0; i < UCOUNT_COUNTS; i++) {
+		ns->ucount_max[i] = INT_MAX;
+	}
 	ns->ucounts = ucounts;
 
 	/* Inherit USERNS_SETGROUPS_ALLOWED from our parent */