sysctl: Infrastructure for per namespace sysctls

This patch implements the basic infrastructure for per namespace sysctls.

A list of lists of sysctl headers is added, allowing each namespace to have
it's own list of sysctl headers.

Each list of sysctl headers has a lookup function to find the first
sysctl header in the list, allowing the lists to have a per namespace
instance.

register_sysct_root is added to tell sysctl.c about additional
lists of sysctl_headers.  As all of the users are expected to be in
kernel no unregister function is provided.

sysctl_head_next is updated to walk through the list of lists.

__register_sysctl_paths is added to add a new sysctl table on
a non-default sysctl list.

The only intrusive part of this patch is propagating the information
to decided which list of sysctls to use for sysctl_check_table.

Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
Cc: Serge Hallyn <serue@us.ibm.com>
Cc: Daniel Lezcano <dlezcano@fr.ibm.com>
Cc: Cedric Le Goater <clg@fr.ibm.com>
Cc: Pavel Emelyanov <xemul@openvz.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 82 insertions, 11 deletions

diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index 89b7d95..45e76f2 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -157,8 +157,16 @@ static int proc_dointvec_taint(struct ctl_table *table, int write, struct file *
 #endif
 
 static struct ctl_table root_table[];
-static struct ctl_table_header root_table_header =
-	{ root_table, LIST_HEAD_INIT(root_table_header.ctl_entry) };
+static struct ctl_table_root sysctl_table_root;
+static struct ctl_table_header root_table_header = {
+	.ctl_table = root_table,
+	.ctl_entry = LIST_HEAD_INIT(sysctl_table_root.header_list),
+	.root = &sysctl_table_root,
+};
+static struct ctl_table_root sysctl_table_root = {
+	.root_list = LIST_HEAD_INIT(sysctl_table_root.root_list),
+	.header_list = LIST_HEAD_INIT(root_table_header.ctl_entry),
+};
 
 static struct ctl_table kern_table[];
 static struct ctl_table vm_table[];
@@ -1371,12 +1379,27 @@ void sysctl_head_finish(struct ctl_table_header *head)
 	spin_unlock(&sysctl_lock);
 }
 
-struct ctl_table_header *sysctl_head_next(struct ctl_table_header *prev)
+static struct list_head *
+lookup_header_list(struct ctl_table_root *root, struct nsproxy *namespaces)
 {
+	struct list_head *header_list;
+	header_list = &root->header_list;
+	if (root->lookup)
+		header_list = root->lookup(root, namespaces);
+	return header_list;
+}
+
+struct ctl_table_header *__sysctl_head_next(struct nsproxy *namespaces,
+					    struct ctl_table_header *prev)
+{
+	struct ctl_table_root *root;
+	struct list_head *header_list;
 	struct ctl_table_header *head;
 	struct list_head *tmp;
+
 	spin_lock(&sysctl_lock);
 	if (prev) {
+		head = prev;
 		tmp = &prev->ctl_entry;
 		unuse_table(prev);
 		goto next;
@@ -1390,14 +1413,38 @@ struct ctl_table_header *sysctl_head_next(struct ctl_table_header *prev)
 		spin_unlock(&sysctl_lock);
 		return head;
 	next:
+		root = head->root;
 		tmp = tmp->next;
-		if (tmp == &root_table_header.ctl_entry)
-			break;
+		header_list = lookup_header_list(root, namespaces);
+		if (tmp != header_list)
+			continue;
+
+		do {
+			root = list_entry(root->root_list.next,
+					struct ctl_table_root, root_list);
+			if (root == &sysctl_table_root)
+				goto out;
+			header_list = lookup_header_list(root, namespaces);
+		} while (list_empty(header_list));
+		tmp = header_list->next;
 	}
+out:
 	spin_unlock(&sysctl_lock);
 	return NULL;
 }
 
+struct ctl_table_header *sysctl_head_next(struct ctl_table_header *prev)
+{
+	return __sysctl_head_next(current->nsproxy, prev);
+}
+
+void register_sysctl_root(struct ctl_table_root *root)
+{
+	spin_lock(&sysctl_lock);
+	list_add_tail(&root->root_list, &sysctl_table_root.root_list);
+	spin_unlock(&sysctl_lock);
+}
+
 #ifdef CONFIG_SYSCTL_SYSCALL
 int do_sysctl(int __user *name, int nlen, void __user *oldval, size_t __user *oldlenp,
 	       void __user *newval, size_t newlen)
@@ -1554,14 +1601,16 @@ static __init int sysctl_init(void)
 {
 	int err;
 	sysctl_set_parent(NULL, root_table);
-	err = sysctl_check_table(root_table);
+	err = sysctl_check_table(current->nsproxy, root_table);
 	return 0;
 }
 
 core_initcall(sysctl_init);
 
 /**
- * register_sysctl_paths - register a sysctl hierarchy
+ * __register_sysctl_paths - register a sysctl hierarchy
+ * @root: List of sysctl headers to register on
+ * @namespaces: Data to compute which lists of sysctl entries are visible
  * @path: The path to the directory the sysctl table is in.
  * @table: the top-level table structure
  *
@@ -1629,9 +1678,12 @@ core_initcall(sysctl_init);
  * This routine returns %NULL on a failure to register, and a pointer
  * to the table header on success.
  */
-struct ctl_table_header *register_sysctl_paths(const struct ctl_path *path,
-						struct ctl_table *table)
+struct ctl_table_header *__register_sysctl_paths(
+	struct ctl_table_root *root,
+	struct nsproxy *namespaces,
+	const struct ctl_path *path, struct ctl_table *table)
 {
+	struct list_head *header_list;
 	struct ctl_table_header *header;
 	struct ctl_table *new, **prevp;
 	unsigned int n, npath;
@@ -1674,19 +1726,38 @@ struct ctl_table_header *register_sysctl_paths(const struct ctl_path *path,
 	INIT_LIST_HEAD(&header->ctl_entry);
 	header->used = 0;
 	header->unregistering = NULL;
+	header->root = root;
 	sysctl_set_parent(NULL, header->ctl_table);
-	if (sysctl_check_table(header->ctl_table)) {
+	if (sysctl_check_table(namespaces, header->ctl_table)) {
 		kfree(header);
 		return NULL;
 	}
 	spin_lock(&sysctl_lock);
-	list_add_tail(&header->ctl_entry, &root_table_header.ctl_entry);
+	header_list = lookup_header_list(root, namespaces);
+	list_add_tail(&header->ctl_entry, header_list);
 	spin_unlock(&sysctl_lock);
 
 	return header;
 }
 
 /**
+ * register_sysctl_table_path - register a sysctl table hierarchy
+ * @path: The path to the directory the sysctl table is in.
+ * @table: the top-level table structure
+ *
+ * Register a sysctl table hierarchy. @table should be a filled in ctl_table
+ * array. A completely 0 filled entry terminates the table.
+ *
+ * See __register_sysctl_paths for more details.
+ */
+struct ctl_table_header *register_sysctl_paths(const struct ctl_path *path,
+						struct ctl_table *table)
+{
+	return __register_sysctl_paths(&sysctl_table_root, current->nsproxy,
+					path, table);
+}
+
+/**
  * register_sysctl_table - register a sysctl table hierarchy
  * @table: the top-level table structure
  *