[RFC PATCH 3/4] sysctl: userns: Do not use dynamic memory

[Alexey Gladkov <legion@xxxxxxxxxx>]

Dynamic memory allocation is needed to modify .data and specify the
per namespace parameter. The new sysctl API is allowed to get rid of
the need for such modification.

Signed-off-by: Alexey Gladkov <legion@xxxxxxxxxx>
---
 include/linux/user_namespace.h |   6 --
 kernel/ucount.c                | 116 +++++++++++++--------------------
 kernel/user_namespace.c        |  10 +--
 3 files changed, 46 insertions(+), 86 deletions(-)

diff --git a/include/linux/user_namespace.h b/include/linux/user_namespace.h
index 45f09bec02c4..7b134516e5cb 100644
--- a/include/linux/user_namespace.h
+++ b/include/linux/user_namespace.h
@@ -95,10 +95,6 @@ struct user_namespace {
 	struct key		*persistent_keyring_register;
 #endif
 	struct work_struct	work;
-#ifdef CONFIG_SYSCTL
-	struct ctl_table_set	set;
-	struct ctl_table_header *sysctls;
-#endif
 	struct ucounts		*ucounts;
 	long ucount_max[UCOUNT_COUNTS];
 	long rlimit_max[UCOUNT_RLIMIT_COUNTS];
@@ -116,8 +112,6 @@ struct ucounts {
 extern struct user_namespace init_user_ns;
 extern struct ucounts init_ucounts;
 
-bool setup_userns_sysctls(struct user_namespace *ns);
-void retire_userns_sysctls(struct user_namespace *ns);
 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);
 struct ucounts *alloc_ucounts(struct user_namespace *ns, kuid_t uid);
diff --git a/kernel/ucount.c b/kernel/ucount.c
index ee8e57fd6f90..4a5072671847 100644
--- a/kernel/ucount.c
+++ b/kernel/ucount.c
@@ -7,6 +7,7 @@
 #include <linux/hash.h>
 #include <linux/kmemleak.h>
 #include <linux/user_namespace.h>
+#include <linux/fs.h>
 
 struct ucounts init_ucounts = {
 	.ns    = &init_user_ns,
@@ -26,38 +27,20 @@ static DEFINE_SPINLOCK(ucounts_lock);
 
 
 #ifdef CONFIG_SYSCTL
-static struct ctl_table_set *
-set_lookup(struct ctl_table_root *root)
-{
-	return &current_user_ns()->set;
-}
-
-static int set_is_seen(struct ctl_table_set *set)
-{
-	return &current_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,
+static int user_sys_open(struct ctl_context *ctx, struct inode *inode,
+		        struct file *file);
+static ssize_t user_sys_read(struct ctl_context *ctx, struct file *file,
+			    char *buffer, size_t *lenp, loff_t *ppos);
+static ssize_t user_sys_write(struct ctl_context *ctx, struct file *file,
+			     char *buffer, size_t *lenp, loff_t *ppos);
+
+static struct ctl_fops user_sys_fops = {
+	.open	= user_sys_open,
+	.read	= user_sys_read,
+	.write	= user_sys_write,
 };
 
+static long ue_dummy = 0;
 static long ue_zero = 0;
 static long ue_int_max = INT_MAX;
 
@@ -66,9 +49,11 @@ static long ue_int_max = INT_MAX;
 		.procname	= name,				\
 		.maxlen		= sizeof(long),			\
 		.mode		= 0644,				\
+		.data		= &ue_dummy,			\
 		.proc_handler	= proc_doulongvec_minmax,	\
 		.extra1		= &ue_zero,			\
 		.extra2		= &ue_int_max,			\
+		.ctl_fops	= &user_sys_fops,		\
 	}
 static struct ctl_table user_table[] = {
 	UCOUNT_ENTRY("max_user_namespaces"),
@@ -89,44 +74,43 @@ static struct ctl_table user_table[] = {
 #endif
 	{ }
 };
-#endif /* CONFIG_SYSCTL */
 
-bool setup_userns_sysctls(struct user_namespace *ns)
+static int user_sys_open(struct ctl_context *ctx, struct inode *inode, struct file *file)
 {
-#ifdef CONFIG_SYSCTL
-	struct ctl_table *tbl;
-
-	BUILD_BUG_ON(ARRAY_SIZE(user_table) != UCOUNT_COUNTS + 1);
-	setup_sysctl_set(&ns->set, &set_root, set_is_seen);
-	tbl = kmemdup(user_table, sizeof(user_table), GFP_KERNEL);
-	if (tbl) {
-		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) {
-		kfree(tbl);
-		retire_sysctl_set(&ns->set);
-		return false;
-	}
-#endif
-	return true;
+	/* Allow users with CAP_SYS_RESOURCE unrestrained access */
+	if ((file->f_mode & FMODE_WRITE) &&
+	    !ns_capable(file->f_cred->user_ns, CAP_SYS_RESOURCE))
+		return -EPERM;
+	return 0;
 }
 
-void retire_userns_sysctls(struct user_namespace *ns)
+static ssize_t user_sys_read(struct ctl_context *ctx, struct file *file,
+		     char *buffer, size_t *lenp, loff_t *ppos)
 {
-#ifdef CONFIG_SYSCTL
-	struct ctl_table *tbl;
+	struct ctl_table table = *ctx->table;
+	table.data = &file->f_cred->user_ns->ucount_max[ctx->table - user_table];
+	return table.proc_handler(&table, 0, buffer, lenp, ppos);
+}
 
-	tbl = ns->sysctls->ctl_table_arg;
-	unregister_sysctl_table(ns->sysctls);
-	retire_sysctl_set(&ns->set);
-	kfree(tbl);
-#endif
+static ssize_t user_sys_write(struct ctl_context *ctx, struct file *file,
+		      char *buffer, size_t *lenp, loff_t *ppos)
+{
+	struct ctl_table table = *ctx->table;
+	table.data = &file->f_cred->user_ns->ucount_max[ctx->table - user_table];
+	return table.proc_handler(&table, 1, buffer, lenp, ppos);
 }
 
+static struct ctl_table user_root_table[] = {
+	{
+		.procname       = "user",
+		.mode           = 0555,
+		.child          = user_table,
+	},
+	{}
+};
+
+#endif /* CONFIG_SYSCTL */
+
 static struct ucounts *find_ucounts(struct user_namespace *ns, kuid_t uid, struct hlist_head *hashent)
 {
 	struct ucounts *ucounts;
@@ -357,17 +341,7 @@ bool is_rlimit_overlimit(struct ucounts *ucounts, enum rlimit_type type, unsigne
 static __init int user_namespace_sysctl_init(void)
 {
 #ifdef CONFIG_SYSCTL
-	static struct ctl_table_header *user_header;
-	static struct ctl_table empty[1];
-	/*
-	 * It is necessary to register the user directory in the
-	 * default set so that registrations in the child sets work
-	 * properly.
-	 */
-	user_header = register_sysctl("user", empty);
-	kmemleak_ignore(user_header);
-	BUG_ON(!user_header);
-	BUG_ON(!setup_userns_sysctls(&init_user_ns));
+	register_sysctl_table(user_root_table);
 #endif
 	hlist_add_ucounts(&init_ucounts);
 	inc_rlimit_ucounts(&init_ucounts, UCOUNT_RLIMIT_NPROC, 1);
diff --git a/kernel/user_namespace.c b/kernel/user_namespace.c
index 981bb2d10d83..c0e707bc9a31 100644
--- a/kernel/user_namespace.c
+++ b/kernel/user_namespace.c
@@ -149,17 +149,10 @@ int create_user_ns(struct cred *new)
 	INIT_LIST_HEAD(&ns->keyring_name_list);
 	init_rwsem(&ns->keyring_sem);
 #endif
-	ret = -ENOMEM;
-	if (!setup_userns_sysctls(ns))
-		goto fail_keyring;
 
 	set_cred_user_ns(new, ns);
 	return 0;
-fail_keyring:
-#ifdef CONFIG_PERSISTENT_KEYRINGS
-	key_put(ns->persistent_keyring_register);
-#endif
-	ns_free_inum(&ns->ns);
+
 fail_free:
 	kmem_cache_free(user_ns_cachep, ns);
 fail_dec:
@@ -208,7 +201,6 @@ static void free_user_ns(struct work_struct *work)
 			kfree(ns->projid_map.forward);
 			kfree(ns->projid_map.reverse);
 		}
-		retire_userns_sysctls(ns);
 		key_free_user_ns(ns);
 		ns_free_inum(&ns->ns);
 		kmem_cache_free(user_ns_cachep, ns);
-- 
2.33.3