Re: [PATCH v4 16/16] ima: Setup securityfs for IMA namespace

On 12/8/21 07:58, Christian Brauner wrote:

On Tue, Dec 07, 2021 at 03:21:27PM -0500, Stefan Berger wrote:

quoted

  
  #if defined(CONFIG_IMA_APPRAISE) && defined(CONFIG_INTEGRITY_TRUSTED_KEYRING)

diff --git a/security/inode.c b/security/inode.c
index 121ac1874dde..10ee20917f42 100644
--- a/security/inode.c
+++ b/security/inode.c

@@ -16,6 +16,7 @@
  #include <linux/fs_context.h>
  #include <linux/mount.h>
  #include <linux/pagemap.h>
+#include <linux/ima.h>
  #include <linux/init.h>
  #include <linux/namei.h>
  #include <linux/security.h>

@@ -41,6 +42,7 @@ static const struct super_operations securityfs_super_operations = {
  static int securityfs_fill_super(struct super_block *sb, struct fs_context *fc)
  {
  	static const struct tree_descr files[] = {{""}};
+	struct user_namespace *ns = fc->user_ns;
  	int error;
  
  	error = simple_fill_super(sb, SECURITYFS_MAGIC, files);

@@ -49,7 +51,10 @@ static int securityfs_fill_super(struct super_block *sb, struct fs_context *fc)
  
  	sb->s_op = &securityfs_super_operations;
  
-	return 0;
+	if (ns != &init_user_ns)
+		error = ima_fs_ns_init(ns, sb->s_root);
+
+	return error;
  }
  
  static int securityfs_get_tree(struct fs_context *fc)

@@ -69,6 +74,11 @@ static int securityfs_init_fs_context(struct fs_context *fc)
  
  static void securityfs_kill_super(struct super_block *sb)
  {
+	struct user_namespace *ns = sb->s_fs_info;
+
+	if (ns != &init_user_ns)
+		ima_fs_ns_free_dentries(ns);

Say securityfs is unmounted. Then all the inodes and dentries become
invalid. It's not allowed to hold on to any dentries or inodes after the
super_block is shut down. So I just want to be sure that nothing in ima
can access these dentries after securityfs is unmounted.

To put it another way: why are they stored in struct ima_namespace in
the first place? If you don't pin a filesystem when creating files or
directories like you do for securityfs in init_ima_ns then you don't
need to hold on to them as they will be automatically be wiped during
umount.

The reason was so that securityfs for init_ima_ns and IMA namespaces could share the code assigning to dentries to keep around and can clean up if an error occurs while creating a dentry.

What about this: We keep the dentries in the ima_namespace, modify the code creating the dentries in securityfs_create_dentry() to only take the additional reference in case of init_user_ns (I suppose this is what you suggest) and then keep 'static void ima_fs_ns_free_dentries()' only for removing the dentries for the error case and never call it from securityfs_kill_super()? Would that be acceptable?