[PATCH v3 12/16] securityfs: Extend securityfs with namespacing support

[Stefan Berger <stefanb@xxxxxxxxxxxxx>]

Extend 'securityfs' for support of IMA namespacing so that each
IMA (user) namespace can have its own front-end for showing the currently
active policy, the measurement list, number of violations and so on.

The filesystem can be mounted to the usual securityfs mount point like
this:

mount -t securityfs /sys/kernel/security /sys/kernel/security

Signed-off-by: Stefan Berger <stefanb@xxxxxxxxxxxxx>
Signed-off-by: James Bottomley <James.Bottomley@xxxxxxxxxxxxxxxxxxxxx>
---
 include/linux/security.h       |  8 +++++
 include/linux/user_namespace.h |  1 +
 security/inode.c               | 58 ++++++++++++++++++++++++++++++++--
 3 files changed, 65 insertions(+), 2 deletions(-)

diff --git a/include/linux/security.h b/include/linux/security.h
index 7e0ba63b5dde..b5266bedef3f 100644
--- a/include/linux/security.h
+++ b/include/linux/security.h
@@ -1929,6 +1929,14 @@ struct dentry *securityfs_create_symlink(const char *name,
 					 const struct inode_operations *iops);
 extern void securityfs_remove(struct dentry *dentry);
 
+enum {
+	SECURITYFS_NS_ADD,
+	SECURITYFS_NS_REMOVE,
+};
+
+extern int securityfs_register_ns_notifier(struct notifier_block *nb);
+extern int securityfs_unregister_ns_notifier(struct notifier_block *nb);
+
 #else /* CONFIG_SECURITYFS */
 
 static inline struct dentry *securityfs_create_dir(const char *name,
diff --git a/include/linux/user_namespace.h b/include/linux/user_namespace.h
index 89663e6e0e85..6b8bd060d8c4 100644
--- a/include/linux/user_namespace.h
+++ b/include/linux/user_namespace.h
@@ -105,6 +105,7 @@ struct user_namespace {
 #endif
 #ifdef CONFIG_SECURITYFS
 	struct vfsmount		*securityfs_mount;
+	bool			securityfs_notifier_sent;
 #endif
 } __randomize_layout;
 
diff --git a/security/inode.c b/security/inode.c
index f1006cec6ce6..45211845fc31 100644
--- a/security/inode.c
+++ b/security/inode.c
@@ -18,6 +18,7 @@
 #include <linux/pagemap.h>
 #include <linux/init.h>
 #include <linux/namei.h>
+#include <linux/notifier.h>
 #include <linux/security.h>
 #include <linux/lsm_hooks.h>
 #include <linux/magic.h>
@@ -25,6 +26,8 @@
 
 static int securityfs_mount_count;
 
+static BLOCKING_NOTIFIER_HEAD(securityfs_ns_notifier);
+
 static void securityfs_free_inode(struct inode *inode)
 {
 	if (S_ISLNK(inode->i_mode))
@@ -37,6 +40,32 @@ static const struct super_operations securityfs_super_operations = {
 	.free_inode	= securityfs_free_inode,
 };
 
+static struct file_system_type fs_type;
+
+static void securityfs_free_context(struct fs_context *fc)
+{
+	struct user_namespace *ns = fc->user_ns;
+
+	if (ns == &init_user_ns ||
+	    ns->securityfs_notifier_sent)
+		return;
+
+	ns->securityfs_notifier_sent = true;
+
+	ns->securityfs_mount = vfs_kern_mount(&fs_type, SB_KERNMOUNT,
+					      fs_type.name, NULL);
+	if (IS_ERR(ns->securityfs_mount)) {
+		printk(KERN_ERR "kern mount on securityfs ERROR: %ld\n",
+		       PTR_ERR(ns->securityfs_mount));
+		ns->securityfs_mount = NULL;
+		return;
+	}
+
+	blocking_notifier_call_chain(&securityfs_ns_notifier,
+				     SECURITYFS_NS_ADD, fc->user_ns);
+	mntput(ns->securityfs_mount);
+}
+
 static int securityfs_fill_super(struct super_block *sb, struct fs_context *fc)
 {
 	static const struct tree_descr files[] = {{""}};
@@ -53,11 +82,12 @@ static int securityfs_fill_super(struct super_block *sb, struct fs_context *fc)
 
 static int securityfs_get_tree(struct fs_context *fc)
 {
-	return get_tree_single(fc, securityfs_fill_super);
+	return get_tree_keyed(fc, securityfs_fill_super, fc->user_ns);
 }
 
 static const struct fs_context_operations securityfs_context_ops = {
 	.get_tree	= securityfs_get_tree,
+	.free		= securityfs_free_context,
 };
 
 static int securityfs_init_fs_context(struct fs_context *fc)
@@ -66,13 +96,37 @@ static int securityfs_init_fs_context(struct fs_context *fc)
 	return 0;
 }
 
+static void securityfs_kill_super(struct super_block *sb)
+{
+	struct user_namespace *ns = sb->s_fs_info;
+
+	if (ns != &init_user_ns)
+		blocking_notifier_call_chain(&securityfs_ns_notifier,
+					     SECURITYFS_NS_REMOVE,
+					     sb->s_fs_info);
+	ns->securityfs_notifier_sent = false;
+	ns->securityfs_mount = NULL;
+	kill_litter_super(sb);
+}
+
 static struct file_system_type fs_type = {
 	.owner =	THIS_MODULE,
 	.name =		"securityfs",
 	.init_fs_context = securityfs_init_fs_context,
-	.kill_sb =	kill_litter_super,
+	.kill_sb =	securityfs_kill_super,
+	.fs_flags =	FS_USERNS_MOUNT,
 };
 
+int securityfs_register_ns_notifier(struct notifier_block *nb)
+{
+	return blocking_notifier_chain_register(&securityfs_ns_notifier, nb);
+}
+
+int securityfs_unregister_ns_notifier(struct notifier_block *nb)
+{
+	return blocking_notifier_chain_unregister(&securityfs_ns_notifier, nb);
+}
+
 /**
  * securityfs_create_dentry - create a dentry in the securityfs filesystem
  *
-- 
2.31.1