Re: [PATCH v5 15/16] ima: Move dentries into ima_namespace

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

On Wed, Dec 08, 2021 at 05:18:17PM -0500, Stefan Berger wrote:
> Move the dentries into the ima_namespace for reuse by virtualized
> SecurityFS. Implement function freeing the dentries in order of
> files and symlinks before directories.
> 
> Signed-off-by: Stefan Berger <stefanb@linux.ibm.com>
> ---

This doesn't work as implemented, I think.

What I would have preferred and what I tried to explain in the earlier
review was:
Keep the dentry stashing global since it is only needed for init_ima_ns.
Then struct ima_namespace becomes way smaller and simpler.
If you do that then it makes sense to remove the additional dget() in
securityfs_create_dentry() for non-init_ima_ns.
Then you can rely on auto-cleanup in .kill_sb() or on
ima_securityfs_init() failure and you only need to call
ima_fs_ns_free_dentries() if ns != init_ima_ns.

IIuc, it seems you're currently doing one dput() too many since you're
calling securityfs_remove() in the error path for non-init_ima_ns which
relies on the previous increased dget() which we removed.

>  include/linux/ima.h             | 13 ++++++
>  security/integrity/ima/ima_fs.c | 72 ++++++++++++++++++---------------
>  2 files changed, 52 insertions(+), 33 deletions(-)
> 
> diff --git a/include/linux/ima.h b/include/linux/ima.h
> index 3aaf6e806db4..4dd64e318b15 100644
> --- a/include/linux/ima.h
> +++ b/include/linux/ima.h
> @@ -220,6 +220,17 @@ struct ima_h_table {
>  	struct hlist_head queue[IMA_MEASURE_HTABLE_SIZE];
>  };
>  
> +enum {
> +	IMAFS_DENTRY_DIR = 0,
> +	IMAFS_DENTRY_SYMLINK,
> +	IMAFS_DENTRY_BINARY_RUNTIME_MEASUREMENTS,
> +	IMAFS_DENTRY_ASCII_RUNTIME_MEASUREMENTS,
> +	IMAFS_DENTRY_RUNTIME_MEASUREMENTS_COUNT,
> +	IMAFS_DENTRY_VIOLATIONS,
> +	IMAFS_DENTRY_IMA_POLICY,
> +	IMAFS_DENTRY_LAST
> +};
> +
>  struct ima_namespace {
>  	struct kref kref;
>  	struct user_namespace *user_ns;
> @@ -266,6 +277,8 @@ struct ima_namespace {
>  	struct mutex ima_write_mutex;
>  	unsigned long ima_fs_flags;
>  	int valid_policy;
> +
> +	struct dentry *dentry[IMAFS_DENTRY_LAST];
>  };
>  
>  extern struct ima_namespace init_ima_ns;
> diff --git a/security/integrity/ima/ima_fs.c b/security/integrity/ima/ima_fs.c
> index a749a3e79304..3810d11fb463 100644
> --- a/security/integrity/ima/ima_fs.c
> +++ b/security/integrity/ima/ima_fs.c
> @@ -360,14 +360,6 @@ static ssize_t ima_write_policy(struct file *file, const char __user *buf,
>  	return result;
>  }
>  
> -static struct dentry *ima_dir;
> -static struct dentry *ima_symlink;
> -static struct dentry *binary_runtime_measurements;
> -static struct dentry *ascii_runtime_measurements;
> -static struct dentry *runtime_measurements_count;
> -static struct dentry *violations;
> -static struct dentry *ima_policy;
> -
>  enum ima_fs_flags {
>  	IMA_FS_BUSY,
>  };
> @@ -437,8 +429,8 @@ static int ima_release_policy(struct inode *inode, struct file *file)
>  
>  	ima_update_policy(ns);
>  #if !defined(CONFIG_IMA_WRITE_POLICY) && !defined(CONFIG_IMA_READ_POLICY)
> -	securityfs_remove(ima_policy);
> -	ima_policy = NULL;
> +	securityfs_remove(ns->dentry[IMAFS_DENTRY_IMA_POLICY]);
> +	ns->dentry[IMAFS_DENTRY_IMA_POLICY] = NULL;
>  #elif defined(CONFIG_IMA_WRITE_POLICY)
>  	clear_bit(IMA_FS_BUSY, &ns->ima_fs_flags);
>  #elif defined(CONFIG_IMA_READ_POLICY)
> @@ -455,58 +447,72 @@ static const struct file_operations ima_measure_policy_ops = {
>  	.llseek = generic_file_llseek,
>  };
>  
> -int __init ima_fs_init(void)
> +static void ima_fs_ns_free_dentries(struct ima_namespace *ns)
>  {
> -	ima_dir = securityfs_create_dir("ima", integrity_dir);
> -	if (IS_ERR(ima_dir))
> +	int i;
> +
> +	for (i = IMAFS_DENTRY_LAST - 1; i >= 0; i--)
> +		securityfs_remove(ns->dentry[i]);
> +
> +	memset(ns->dentry, 0, sizeof(ns->dentry));
> +}
> +
> +static int __init ima_securityfs_init(struct user_namespace *user_ns)
> +{
> +	struct ima_namespace *ns = user_ns->ima_ns;
> +	struct dentry *ima_dir;
> +
> +	ns->dentry[IMAFS_DENTRY_DIR] = securityfs_create_dir("ima", integrity_dir);
> +	if (IS_ERR(ns->dentry[IMAFS_DENTRY_DIR]))
>  		return -1;
> +	ima_dir = ns->dentry[IMAFS_DENTRY_DIR];
>  
> -	ima_symlink = securityfs_create_symlink("ima", NULL, "integrity/ima",
> -						NULL);
> -	if (IS_ERR(ima_symlink))
> +	ns->dentry[IMAFS_DENTRY_SYMLINK] =
> +	    securityfs_create_symlink("ima", NULL, "integrity/ima", NULL);
> +	if (IS_ERR(ns->dentry[IMAFS_DENTRY_SYMLINK]))
>  		goto out;
>  
> -	binary_runtime_measurements =
> +	ns->dentry[IMAFS_DENTRY_BINARY_RUNTIME_MEASUREMENTS] =
>  	    securityfs_create_file("binary_runtime_measurements",
>  				   S_IRUSR | S_IRGRP, ima_dir, NULL,
>  				   &ima_measurements_ops);
> -	if (IS_ERR(binary_runtime_measurements))
> +	if (IS_ERR(ns->dentry[IMAFS_DENTRY_BINARY_RUNTIME_MEASUREMENTS]))
>  		goto out;
>  
> -	ascii_runtime_measurements =
> +	ns->dentry[IMAFS_DENTRY_ASCII_RUNTIME_MEASUREMENTS] =
>  	    securityfs_create_file("ascii_runtime_measurements",
>  				   S_IRUSR | S_IRGRP, ima_dir, NULL,
>  				   &ima_ascii_measurements_ops);
> -	if (IS_ERR(ascii_runtime_measurements))
> +	if (IS_ERR(ns->dentry[IMAFS_DENTRY_ASCII_RUNTIME_MEASUREMENTS]))
>  		goto out;
>  
> -	runtime_measurements_count =
> +	ns->dentry[IMAFS_DENTRY_RUNTIME_MEASUREMENTS_COUNT] =
>  	    securityfs_create_file("runtime_measurements_count",
>  				   S_IRUSR | S_IRGRP, ima_dir, NULL,
>  				   &ima_measurements_count_ops);
> -	if (IS_ERR(runtime_measurements_count))
> +	if (IS_ERR(ns->dentry[IMAFS_DENTRY_RUNTIME_MEASUREMENTS_COUNT]))
>  		goto out;
>  
> -	violations =
> +	ns->dentry[IMAFS_DENTRY_VIOLATIONS] =
>  	    securityfs_create_file("violations", S_IRUSR | S_IRGRP,
>  				   ima_dir, NULL, &ima_htable_violations_ops);
> -	if (IS_ERR(violations))
> +	if (IS_ERR(ns->dentry[IMAFS_DENTRY_VIOLATIONS]))
>  		goto out;
>  
> -	ima_policy = securityfs_create_file("policy", POLICY_FILE_FLAGS,
> +	ns->dentry[IMAFS_DENTRY_IMA_POLICY] =
> +	    securityfs_create_file("policy", POLICY_FILE_FLAGS,
>  					    ima_dir, NULL,
>  					    &ima_measure_policy_ops);
> -	if (IS_ERR(ima_policy))
> +	if (IS_ERR(ns->dentry[IMAFS_DENTRY_IMA_POLICY]))
>  		goto out;
>  
>  	return 0;
>  out:
> -	securityfs_remove(violations);
> -	securityfs_remove(runtime_measurements_count);
> -	securityfs_remove(ascii_runtime_measurements);
> -	securityfs_remove(binary_runtime_measurements);
> -	securityfs_remove(ima_symlink);
> -	securityfs_remove(ima_dir);
> -	securityfs_remove(ima_policy);
> +	ima_fs_ns_free_dentries(ns);
>  	return -1;
>  }
> +
> +int __init ima_fs_init(void)
> +{
> +	return ima_securityfs_init(&init_user_ns);
> +}
> -- 
> 2.31.1
> 
>