Re: [PATCH v3 00/16] ima: Namespace IMA with audit support in IMA-ns

[James Bottomley <jejb@linux.ibm.com>]

On Mon, 2021-12-06 at 12:25 -0500, Stefan Berger wrote:
[...]
> v3:
>  - Further modifications to virtualized SecurityFS following James's
> posted patch
>  - Dropping of early teardown for user_namespaces since not needed
> anymore

This is my incremental to this series that moves the namespaced
securityfs away from using a vfsmount and on to a root dentry instead,
meaning we can call the blocking notifier from fill_super as Christian
requested (and thus can remove the securityfs_notifier_sent indicator
since it's only called once).

James

---

From 07b680d5fd59f5d3cea5580be25a2c9e08a01c3b Mon Sep 17 00:00:00 2001
From: James Bottomley <James.Bottomley@HansenPartnership.com>
Date: Mon, 6 Dec 2021 20:27:00 +0000
Subject: [PATCH] Incremental for d_root

---
 include/linux/user_namespace.h |  3 +-
 security/inode.c               | 55 +++++++++++++---------------------
 2 files changed, 22 insertions(+), 36 deletions(-)

diff --git a/include/linux/user_namespace.h b/include/linux/user_namespace.h
index 6b8bd060d8c4..03a0879376a0 100644
--- a/include/linux/user_namespace.h
+++ b/include/linux/user_namespace.h
@@ -104,8 +104,7 @@ struct user_namespace {
 	struct ima_namespace	*ima_ns;
 #endif
 #ifdef CONFIG_SECURITYFS
-	struct vfsmount		*securityfs_mount;
-	bool			securityfs_notifier_sent;
+	struct dentry		*securityfs_root;
 #endif
 } __randomize_layout;
 
diff --git a/security/inode.c b/security/inode.c
index 45211845fc31..f8b6cb3dfb87 100644
--- a/security/inode.c
+++ b/security/inode.c
@@ -24,6 +24,7 @@
 #include <linux/magic.h>
 #include <linux/user_namespace.h>
 
+static struct vfsmount *securityfs_mount;
 static int securityfs_mount_count;
 
 static BLOCKING_NOTIFIER_HEAD(securityfs_ns_notifier);
@@ -40,43 +41,24 @@ 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[] = {{""}};
 	int error;
+	struct user_namespace *ns = fc->user_ns;
 
 	error = simple_fill_super(sb, SECURITYFS_MAGIC, files);
 	if (error)
 		return error;
 
+	ns->securityfs_root = dget(sb->s_root);
+
 	sb->s_op = &securityfs_super_operations;
 
+	if (ns != &init_user_ns)
+		blocking_notifier_call_chain(&securityfs_ns_notifier,
+					     SECURITYFS_NS_ADD, ns);
+
 	return 0;
 }
 
@@ -87,7 +69,6 @@ static int securityfs_get_tree(struct fs_context *fc)
 
 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)
@@ -104,8 +85,10 @@ static void securityfs_kill_super(struct super_block *sb)
 		blocking_notifier_call_chain(&securityfs_ns_notifier,
 					     SECURITYFS_NS_REMOVE,
 					     sb->s_fs_info);
-	ns->securityfs_notifier_sent = false;
-	ns->securityfs_mount = NULL;
+
+	dput(ns->securityfs_root);
+	ns->securityfs_root = NULL;
+
 	kill_litter_super(sb);
 }
 
@@ -174,14 +157,18 @@ static struct dentry *securityfs_create_dentry(const char *name, umode_t mode,
 	pr_debug("securityfs: creating file '%s'\n",name);
 
 	if (ns == &init_user_ns) {
-		error = simple_pin_fs(&fs_type, &ns->securityfs_mount,
+		error = simple_pin_fs(&fs_type, &securityfs_mount,
 				      &securityfs_mount_count);
 		if (error)
 			return ERR_PTR(error);
 	}
 
-	if (!parent)
-		parent = ns->securityfs_mount->mnt_root;
+	if (!parent) {
+		if (ns == &init_user_ns)
+			parent = securityfs_mount->mnt_root;
+		else
+			parent = ns->securityfs_root;
+	}
 
 	dir = d_inode(parent);
 
@@ -227,7 +214,7 @@ static struct dentry *securityfs_create_dentry(const char *name, umode_t mode,
 out:
 	inode_unlock(dir);
 	if (ns == &init_user_ns)
-		simple_release_fs(&ns->securityfs_mount,
+		simple_release_fs(&securityfs_mount,
 				  &securityfs_mount_count);
 	return dentry;
 }
@@ -371,7 +358,7 @@ void securityfs_remove(struct dentry *dentry)
 	}
 	inode_unlock(dir);
 	if (ns == &init_user_ns)
-		simple_release_fs(&ns->securityfs_mount,
+		simple_release_fs(&securityfs_mount,
 				  &securityfs_mount_count);
 }
 EXPORT_SYMBOL_GPL(securityfs_remove);
-- 
2.33.0