Re: [PATCH v12 21/26] ima: Setup securityfs for IMA namespace

Stefan Berger <stefanb@xxxxxxxxxxxxx> · Tue, 31 May 2022 15:26:21 -0400

On 5/29/22 21:16, Serge E. Hallyn wrote:
On Wed, Apr 20, 2022 at 10:06:28AM -0400, Stefan Berger wrote:
Setup securityfs with symlinks, directories, and files for IMA
namespacing support. The same directory structure that IMA uses on the
host is also created for the namespacing case.

The securityfs file and directory ownerships cannot be set when the
IMA namespace is initialized. Therefore, delay the setup of the file
system to a later point when securityfs is in securityfs_fill_super.

Introduce a variable ima_policy_removed in ima_namespace that is used to
remember whether the policy file has previously been removed and thus
should not be created again in case of unmounting and again mounting
securityfs inside an IMA namespace.

This filesystem can now be mounted as follows:

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

The following directories, symlinks, and files are available
when IMA namespacing is enabled, otherwise it will be empty:

$ ls -l sys/kernel/security/
total 0
lr--r--r--. 1 root root 0 Dec  2 00:18 ima -> integrity/ima
drwxr-xr-x. 3 root root 0 Dec  2 00:18 integrity

$ ls -l sys/kernel/security/ima/
total 0
-r--r-----. 1 root root 0 Dec  2 00:18 ascii_runtime_measurements
-r--r-----. 1 root root 0 Dec  2 00:18 binary_runtime_measurements
-rw-------. 1 root root 0 Dec  2 00:18 policy
-r--r-----. 1 root root 0 Dec  2 00:18 runtime_measurements_count
-r--r-----. 1 root root 0 Dec  2 00:18 violations

Signed-off-by: Stefan Berger <stefanb@xxxxxxxxxxxxx>
Signed-off-by: James Bottomley <James.Bottomley@xxxxxxxxxxxxxxxxxxxxx>
Acked-by: Christian Brauner <brauner@xxxxxxxxxx>
Reviewed-by: Mimi Zohar <zohar@xxxxxxxxxxxxx>

Acked-by: Serge Hallyn <serge@xxxxxxxxxx>

but a nit below

Thanks for all the tags, I took all of them.
Would I need to worry about the other reviewerss' tags regardig the nit 
below? I'd rather leave it as-is otherwise.

   Stefan




---

v9:
  - rename policy_dentry_removed to ima_policy_removed
---
  include/linux/ima.h             | 13 ++++++++++
  security/inode.c                |  6 ++++-
  security/integrity/ima/ima.h    |  1 +
  security/integrity/ima/ima_fs.c | 46 +++++++++++++++++++++++----------
  4 files changed, 52 insertions(+), 14 deletions(-)

diff --git a/include/linux/ima.h b/include/linux/ima.h
index b9301e2aaa8b..0cbf0434bc93 100644
--- a/include/linux/ima.h
+++ b/include/linux/ima.h
@@ -41,6 +41,7 @@ extern int ima_measure_critical_data(const char *event_label,
  				     const char *event_name,
  				     const void *buf, size_t buf_len,
  				     bool hash, u8 *digest, size_t digest_len);
+extern int ima_fs_ns_init(struct user_namespace *user_ns, struct dentry *root);
  
  #ifdef CONFIG_IMA_APPRAISE_BOOTPARAM
  extern void ima_appraise_parse_cmdline(void);
@@ -227,6 +228,12 @@ void free_ima_ns(struct user_namespace *ns);
  
  void ima_free_ns_status_list(struct list_head *head, rwlock_t *ns_list_lock);
  
+static inline int ima_securityfs_init(struct user_namespace *user_ns,
+				      struct dentry *root)
+{
+	return ima_fs_ns_init(user_ns, root);
+}
+
  #else
  
  static inline void free_ima_ns(struct user_namespace *user_ns)
@@ -238,6 +245,12 @@ static inline void ima_free_ns_status_list(struct list_head *head,
  {
  }
  
+static inline int ima_securityfs_init(struct user_namespace *ns,
+				      struct dentry *root)
+{
+	return 0;
+}
+
  #endif /* CONFIG_IMA_NS */
  
  #endif /* _LINUX_IMA_H */
diff --git a/security/inode.c b/security/inode.c
index 84c9396792a9..e81f55f054dc 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>
@@ -82,7 +83,10 @@ static int securityfs_fill_super(struct super_block *sb, struct fs_context *fc)
  	sb->s_op = &securityfs_super_operations;
  	sb->s_root->d_inode->i_op = &securityfs_dir_inode_operations;
  
-	return 0;
+	if (ns != &init_user_ns)
+		error = ima_securityfs_init(ns, sb->s_root);
+
+	return error;
  }
  
  static int securityfs_get_tree(struct fs_context *fc)
diff --git a/security/integrity/ima/ima.h b/security/integrity/ima/ima.h
index cb48fc1d5b80..801dc3c8bfde 100644
--- a/security/integrity/ima/ima.h
+++ b/security/integrity/ima/ima.h
@@ -152,6 +152,7 @@ struct ima_namespace {
  	int valid_policy;
  
  	struct dentry *ima_policy;
+	bool ima_policy_removed;
  
  	struct notifier_block ima_lsm_policy_notifier;
  } __randomize_layout;
diff --git a/security/integrity/ima/ima_fs.c b/security/integrity/ima/ima_fs.c
index c41aa61b7393..84cd02a9e19b 100644
--- a/security/integrity/ima/ima_fs.c
+++ b/security/integrity/ima/ima_fs.c
@@ -21,6 +21,7 @@
  #include <linux/rcupdate.h>
  #include <linux/parser.h>
  #include <linux/vmalloc.h>
+#include <linux/ima.h>
  
  #include "ima.h"
  
@@ -433,6 +434,7 @@ static int ima_release_policy(struct inode *inode, struct file *file)
  #if !defined(CONFIG_IMA_WRITE_POLICY) && !defined(CONFIG_IMA_READ_POLICY)
  	securityfs_remove(ns->ima_policy);
  	ns->ima_policy = NULL;
+	ns->ima_policy_removed = true;
  #elif defined(CONFIG_IMA_WRITE_POLICY)
  	clear_bit(IMA_FS_BUSY, &ns->ima_fs_flags);
  #elif defined(CONFIG_IMA_READ_POLICY)
@@ -449,9 +451,11 @@ static const struct file_operations ima_measure_policy_ops = {
  	.llseek = generic_file_llseek,
  };
  
-static int __init ima_fs_ns_init(struct ima_namespace *ns)
+int ima_fs_ns_init(struct user_namespace *user_ns, struct dentry *root)
  {
-	struct dentry *ima_dir;
+	struct ima_namespace *ns = ima_ns_from_user_ns(user_ns);
+	struct dentry *int_dir;
+	struct dentry *ima_dir = NULL;
  	struct dentry *ima_symlink = NULL;
  	struct dentry *binary_runtime_measurements = NULL;
  	struct dentry *ascii_runtime_measurements = NULL;
@@ -459,11 +463,22 @@ static int __init ima_fs_ns_init(struct ima_namespace *ns)
  	struct dentry *violations = NULL;
  	int ret;
  
-	ima_dir = securityfs_create_dir("ima", integrity_dir);
-	if (IS_ERR(ima_dir))
-		return PTR_ERR(ima_dir);
+	/* FIXME: update when evm and integrity are namespaced */
+	if (user_ns != &init_user_ns) {
+		int_dir = securityfs_create_dir("integrity", root);
+		if (IS_ERR(int_dir))
+			return PTR_ERR(int_dir);
+	} else {
+		int_dir = integrity_dir;
+	}
  
-	ima_symlink = securityfs_create_symlink("ima", NULL, "integrity/ima",
+	ima_dir = securityfs_create_dir("ima", int_dir);
+	if (IS_ERR(ima_dir)) {
+		ret = PTR_ERR(ima_dir);
+		goto out;
+	}
+
+	ima_symlink = securityfs_create_symlink("ima", root, "integrity/ima",
  						NULL);
  	if (IS_ERR(ima_symlink)) {
  		ret = PTR_ERR(ima_symlink);
@@ -505,12 +520,15 @@ static int __init ima_fs_ns_init(struct ima_namespace *ns)
  		goto out;
  	}
  
-	ns->ima_policy = securityfs_create_file("policy", POLICY_FILE_FLAGS,
-						ima_dir, NULL,
-						&ima_measure_policy_ops);
-	if (IS_ERR(ns->ima_policy)) {
-		ret = PTR_ERR(ns->ima_policy);
-		goto out;
+	if (!ns->ima_policy_removed) {

It would be nicer to avoid this indent level by just doing

	if (ns->ima_policy_removed)
		return 0;

above the securityfs_create_file().

+		ns->ima_policy =
+		    securityfs_create_file("policy", POLICY_FILE_FLAGS,
+					   ima_dir, NULL,
+					   &ima_measure_policy_ops);
+		if (IS_ERR(ns->ima_policy)) {
+			ret = PTR_ERR(ns->ima_policy);
+			goto out;
+		}
  	}
  
  	return 0;
@@ -522,11 +540,13 @@ static int __init ima_fs_ns_init(struct ima_namespace *ns)
  	securityfs_remove(binary_runtime_measurements);
  	securityfs_remove(ima_symlink);
  	securityfs_remove(ima_dir);
+	if (user_ns != &init_user_ns)
+		securityfs_remove(int_dir);
  
  	return ret;
  }
  
  int __init ima_fs_init(void)
  {
-	return ima_fs_ns_init(&init_ima_ns);
+	return ima_fs_ns_init(&init_user_ns, NULL);
  }
--
2.34.1








