Re: [PATCH v12 08/26] ima: Move IMA securityfs files into ima_namespace or onto stack

Serge E. Hallyn
2022-05-21T03:24:29Z

On Wed, Apr 20, 2022 at 10:06:15AM -0400, Stefan Berger wrote:
> Earlier we simplified how dentry creation and deletion is manged in
> securityfs. This allows us to move IMA securityfs files from global
> variables directly into ima_fs_ns_init() itself. We can now rely on
> those dentries to be cleaned up when the securityfs instance is cleaned
> when the last reference to it is dropped.
>
> Things are slightly different for the initial IMA namespace. In contrast
> to non-initial IMA namespaces it has pinning logic binding the lifetime
> of the securityfs superblock to created dentries. We need to keep this
> behavior to not regress userspace. Since IMA never removes most of the
> securityfs files the initial securityfs instance stays pinned. This also
> means even for the initial IMA namespace we don't need to keep
> references to these dentries anywhere.
>
> The ima_policy file is the exception since IMA can end up removing it
> on systems that don't allow reading or extending the IMA custom policy.
>
> Signed-off-by: Stefan Berger <stefanb@linux.ibm.com>
> Acked-by: Christian Brauner <brauner@kernel.org>
> Reviewed-by: Mimi Zohar <zohar@linux.ibm.com>

Acked-by: Serge Hallyn <serge@hallyn.com>

>
> ---
>
> v9:
> - Revert renaming of ima_policy to policy_dentry
> ---
> security/integrity/ima/ima.h | 2 ++
> security/integrity/ima/ima_fs.c | 37 ++++++++++++++++++---------------
> 2 files changed, 22 insertions(+), 17 deletions(-)
>
> diff --git a/security/integrity/ima/ima.h b/security/integrity/ima/ima.h
> index a144edfdb9a1..b35c8504ef87 100644
> --- a/security/integrity/ima/ima.h
> +++ b/security/integrity/ima/ima.h
> @@ -142,6 +142,8 @@ struct ima_namespace {
> struct mutex ima_write_mutex;
> unsigned long ima_fs_flags;
> int valid_policy;
> +
> + struct dentry *ima_policy;
> } __randomize_layout;
> extern struct ima_namespace init_ima_ns;
>
> diff --git a/security/integrity/ima/ima_fs.c b/security/integrity/ima/ima_fs.c
> index 4cf786f0bba8..89d3113ceda1 100644
> --- a/security/integrity/ima/ima_fs.c
> +++ b/security/integrity/ima/ima_fs.c
> @@ -359,14 +359,6 @@ 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,
> };
> @@ -436,8 +428,8 @@ 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->ima_policy);
> + ns->ima_policy = NULL;
> #elif defined(CONFIG_IMA_WRITE_POLICY)
> clear_bit(IMA_FS_BUSY, &ns->ima_fs_flags);
> #elif defined(CONFIG_IMA_READ_POLICY)
> @@ -454,8 +446,14 @@ static const struct file_operations ima_measure_policy_ops = {
> .llseek = generic_file_llseek,
> };
>
> -int __init ima_fs_init(void)
> +static int __init ima_fs_ns_init(struct ima_namespace *ns)
> {
> + struct dentry *ima_dir;
> + 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;
> int ret;
>
> ima_dir = securityfs_create_dir("ima", integrity_dir);
> @@ -504,17 +502,17 @@ int __init ima_fs_init(void)
> goto out;
> }
>
> - ima_policy = securityfs_create_file("policy", POLICY_FILE_FLAGS,
> - ima_dir, NULL,
> - &ima_measure_policy_ops);
> - if (IS_ERR(ima_policy)) {
> - ret = PTR_ERR(ima_policy);
> + 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;
> out:
> - securityfs_remove(ima_policy);
> + securityfs_remove(ns->ima_policy);
> securityfs_remove(violations);
> securityfs_remove(runtime_measurements_count);
> securityfs_remove(ascii_runtime_measurements);
> @@ -524,3 +522,8 @@ int __init ima_fs_init(void)
>
> return ret;
> }
> +
> +int __init ima_fs_init(void)
> +{
> + return ima_fs_ns_init(&init_ima_ns);
> +}
> --
> 2.34.1