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

Christian Brauner
2021-12-09T14:34:38Z

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
>
>