Re: [PATCH v7 14/14] ima: Setup securityfs for IMA namespace

[Christian Brauner <christian.brauner@ubuntu.com>]

On Thu, Dec 16, 2021 at 12:43:23AM -0500, Stefan Berger wrote:
> From: Stefan Berger <stefanb@linux.ibm.com>
> 
> 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.
> 
> This filesystem can now be mounted as follows:
> 
> mount -t securityfs /sys/kernel/security/ /sys/kernel/security/
> 
> The following directories, symlinks, and files are then available.
> 
> $ 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@linux.ibm.com>
> Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>
> ---
>  include/linux/ima.h             | 14 ++++++++++++
>  security/inode.c                |  6 ++++-
>  security/integrity/ima/ima.h    |  1 +
>  security/integrity/ima/ima_fs.c | 40 ++++++++++++++++++++++++---------
>  4 files changed, 49 insertions(+), 12 deletions(-)
> 
> diff --git a/include/linux/ima.h b/include/linux/ima.h
> index f9e592bb9560..a2705aa5242a 100644
> --- a/include/linux/ima.h
> +++ b/include/linux/ima.h
> @@ -40,6 +40,7 @@ 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);
> @@ -232,6 +233,12 @@ static inline struct ima_namespace *get_current_ns(void)
>  	return current_user_ns()->ima_ns;
>  }
>  
> +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)
> @@ -250,6 +257,13 @@ static inline struct ima_namespace *get_current_ns(void)
>  {
>  	return &init_ima_ns;
>  }
> +
> +static inline int ima_securityfs_init(struct user_namespace *ns,
> +				      struct dentry *root)
> +{
> +	return 0;
> +}
> +
>  #endif /* CONFIG_IMA_NS */
>  
>  #if defined(CONFIG_IMA_APPRAISE) && defined(CONFIG_INTEGRITY_TRUSTED_KEYRING)
> diff --git a/security/inode.c b/security/inode.c
> index a0d9f086e3d5..ad9395d121f2 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>
> @@ -77,7 +78,10 @@ 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 d51703290e25..9b0f6a3763f9 100644
> --- a/security/integrity/ima/ima.h
> +++ b/security/integrity/ima/ima.h
> @@ -148,6 +148,7 @@ struct ima_namespace {
>  	int valid_policy;
>  
>  	struct dentry *policy_dentry;
> +	bool policy_dentry_removed;
>  } __randomize_layout;
>  
>  extern const int read_idmap[];
> diff --git a/security/integrity/ima/ima_fs.c b/security/integrity/ima/ima_fs.c
> index 7c5a721f4f3d..3b8001ba62e3 100644
> --- a/security/integrity/ima/ima_fs.c
> +++ b/security/integrity/ima/ima_fs.c
> @@ -431,6 +431,7 @@ 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->policy_dentry);
>  	ns->policy_dentry = NULL;
> +	ns->policy_dentry_removed = true;
>  #elif defined(CONFIG_IMA_WRITE_POLICY)
>  	clear_bit(IMA_FS_BUSY, &ns->ima_fs_flags);
>  #elif defined(CONFIG_IMA_READ_POLICY)
> @@ -447,21 +448,31 @@ static const struct file_operations ima_measure_policy_ops = {
>  	.llseek = generic_file_llseek,
>  };
>  
> -static int __init ima_fs_ns_init(struct user_namespace *user_ns)
> +int ima_fs_ns_init(struct user_namespace *user_ns, struct dentry *root)
>  {
>  	struct ima_namespace *ns = user_ns->ima_ns;
> -	struct dentry *ima_dir;
> +	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;
>  	struct dentry *runtime_measurements_count = NULL;
>  	struct dentry *violations = NULL;
>  
> -	ima_dir = securityfs_create_dir("ima", integrity_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 -1;

That should probably be return PTR_ERR(int_dir)