Re: [RFC 04/11] ima: add support to namespace securityfs file

[Mimi Zohar]

On Thu, 2017-05-11 at 10:59 -0300, Guilherme Magalhaes wrote:
> Creating the namespace securityfs file under ima folder. When a mount
> namespace id is written to the namespace file, a new folder is created and
> with a policy file for that specified namespace. Then, user defined policy
> for namespaces may be set by writing rules to this namespace policy file.
> With this interface, there is no need to give visibility for the securityfs
> inside mount namespaces or containers in userspace.
> 
> Signed-off-by: Guilherme Magalhaes <guilherme.magalhaes@xxxxxxx>

The design needs to be flexible enough for different types of
containers, not just for when the orchestration layer provides the
policy. ÂWith this design, the container owner has no control over the
policy.

One option is that we bind mount the securityfs/policy, so that root
in the container will be allowed to read/write the policy. ÂAt some
point, we might connect a vTPM to the container so that the container
owner would be able to get a quote. ÂFor now even without a vTPM, the
same mechanism would allow root within the container to read the
measurement list.

Mimi


> ---
>  security/integrity/ima/ima.h    |   4 +
>  security/integrity/ima/ima_fs.c | 183 ++++++++++++++++++++++++++++++++++++++++
>  2 files changed, 187 insertions(+)
> 
> diff --git a/security/integrity/ima/ima.h b/security/integrity/ima/ima.h
> index 42fb91ba..6e8ca8e 100644
> --- a/security/integrity/ima/ima.h
> +++ b/security/integrity/ima/ima.h
> @@ -326,4 +326,8 @@ static inline int security_filter_rule_match(u32 secid, u32 field, u32 op,
>  #define	POLICY_FILE_FLAGS	S_IWUSR
>  #endif /* CONFIG_IMA_WRITE_POLICY */
> 
> +#ifdef CONFIG_IMA_PER_NAMESPACE
> +#define NAMESPACES_FILE_FLAGS  S_IWUSR
> +#endif
> +
>  #endif /* __LINUX_IMA_H */
> diff --git a/security/integrity/ima/ima_fs.c b/security/integrity/ima/ima_fs.c
> index ca303e5..6456407 100644
> --- a/security/integrity/ima/ima_fs.c
> +++ b/security/integrity/ima/ima_fs.c
> @@ -23,6 +23,8 @@
>  #include <linux/rcupdate.h>
>  #include <linux/parser.h>
>  #include <linux/vmalloc.h>
> +#include <linux/proc_ns.h>
> +#include <linux/radix-tree.h>
> 
>  #include "ima.h"
> 
> @@ -272,6 +274,40 @@ static const struct file_operations ima_ascii_measurements_ops = {
>  	.release = seq_release,
>  };
> 
> +#ifdef CONFIG_IMA_PER_NAMESPACE
> +/*
> + * check_mntns: check a mount namespace is valid
> + *
> + * @ns_id: namespace id to be checked
> + * Returns 0 if the namespace is valid.
> + *
> + * Note: a better way to implement this check is needed. There are
> + * cases where the namespace id is valid but not in use by any process
> + * and then this implementation misses this case. Could we use an
> + * interface similar to what setns implements?
> + */
> +static int check_mntns(unsigned int ns_id)
> +{
> +	struct task_struct *p;
> +	int result = 1;
> +	struct ns_common *ns;
> +
> +	rcu_read_lock();
> +	for_each_process(p) {
> +		ns = mntns_operations.get(p);
> +		if (ns->inum == ns_id) {
> +			result = 0;
> +			mntns_operations.put(ns);
> +			break;
> +		}
> +		mntns_operations.put(ns);
> +	}
> +	rcu_read_unlock();
> +
> +	return result;
> +}
> +#endif
> +
>  static ssize_t ima_read_policy(char *path)
>  {
>  	void *data;
> @@ -366,6 +402,9 @@ static struct dentry *ascii_runtime_measurements;
>  static struct dentry *runtime_measurements_count;
>  static struct dentry *violations;
>  static struct dentry *ima_policy;
> +#ifdef CONFIG_IMA_PER_NAMESPACE
> +static struct dentry *ima_namespaces;
> +#endif
> 
>  enum ima_fs_flags {
>  	IMA_FS_BUSY,
> @@ -451,6 +490,139 @@ static const struct file_operations ima_measure_policy_ops = {
>  	.llseek = generic_file_llseek,
>  };
> 
> +#ifdef CONFIG_IMA_PER_NAMESPACE
> +/*
> + * Assumes namespace id is in use by some process and this mapping
> + * does not exist in the map table.
> + */
> +static int create_mnt_ns_directory(unsigned int ns_id)
> +{
> +	int result;
> +	struct dentry *ns_dir, *ns_policy;
> +	char dir_name[64];
> +
> +	snprintf(dir_name, sizeof(dir_name), "%u", ns_id);
> +
> +	ns_dir = securityfs_create_dir(dir_name, ima_dir);
> +	if (IS_ERR(ns_dir)) {
> +		result = PTR_ERR(ns_dir);
> +		goto out;
> +	}
> +
> +	ns_policy = securityfs_create_file("policy", POLICY_FILE_FLAGS,
> +		                                ns_dir, NULL,
> +		                                &ima_measure_policy_ops);
> +	if (IS_ERR(ns_policy)) {
> +		result = PTR_ERR(ns_policy);
> +		securityfs_remove(ns_dir);
> +		goto out;
> +	}
> +
> +	result = 0;
> +
> +out:
> +	return result;
> +}
> +
> +static ssize_t handle_new_namespace_policy(const char *data, size_t datalen)
> +{
> +	unsigned int ns_id;
> +	ssize_t result;
> +
> +	result = -EINVAL;
> +
> +	if (sscanf(data, "%u", &ns_id) != 1) {
> +		pr_err("IMA: invalid namespace id: %s\n", data);
> +		goto out;
> +	}
> +
> +	if (check_mntns(ns_id)) {
> +		result = -ENOENT;
> +		pr_err("IMA: unused namespace id %u\n", ns_id);
> +		goto out;
> +	}
> +
> +	result = create_mnt_ns_directory(ns_id);
> +	if (result != 0) {
> +		pr_err("IMA: namespace id %u directory creation failed\n", ns_id);
> +		goto out;
> +	}
> +
> +	result = datalen;
> +	pr_info("IMA: directory created for namespace id %u\n", ns_id);
> +
> +out:
> +	return result;
> +}
> +
> +static ssize_t ima_write_namespaces(struct file *file, const char __user *buf,
> +		                            size_t datalen, loff_t *ppos)
> +{
> +	char *data;
> +	ssize_t result;
> +
> +	if (datalen >= PAGE_SIZE)
> +		datalen = PAGE_SIZE - 1;
> +
> +	/* No partial writes. */
> +	result = -EINVAL;
> +	if (*ppos != 0)
> +		goto out;
> +
> +	result = -ENOMEM;
> +	data = kmalloc(datalen + 1, GFP_KERNEL);
> +	if (!data)
> +		goto out;
> +
> +	*(data + datalen) = '\0';
> +
> +	result = -EFAULT;
> +	if (copy_from_user(data, buf, datalen))
> +		goto out_free;
> +
> +	result = mutex_lock_interruptible(&ima_write_mutex);
> +	if (result < 0)
> +		goto out_free;
> +
> +	result = handle_new_namespace_policy(data, datalen);
> +
> +	mutex_unlock(&ima_write_mutex);
> +
> +out_free:
> +	kfree(data);
> +out:
> +	return result;
> +}
> +
> +static int ima_open_namespaces(struct inode *inode, struct file *filp)
> +{
> +	if (!(filp->f_flags & O_WRONLY))
> +		return -EACCES;
> +
> +	if (!capable(CAP_SYS_ADMIN))
> +		return -EPERM;
> +
> +	if (test_and_set_bit(IMA_FS_BUSY, &ima_fs_flags))
> +		return -EBUSY;
> +	return 0;
> +}
> +
> +static int ima_release_namespaces(struct inode *inode, struct file *file)
> +{
> +	clear_bit(IMA_FS_BUSY, &ima_fs_flags);
> +
> +	return 0;
> +}
> +
> +static const struct file_operations ima_namespaces_ops = {
> +		.open = ima_open_namespaces,
> +		.write = ima_write_namespaces,
> +		.read = seq_read,
> +		.release = ima_release_namespaces,
> +		.llseek = generic_file_llseek,
> +};
> +#endif
> +
>  int __init ima_fs_init(void)
>  {
>  	ima_dir = securityfs_create_dir("ima", NULL);
> @@ -490,6 +662,14 @@ int __init ima_fs_init(void)
>  	if (IS_ERR(ima_policy))
>  		goto out;
> 
> +#ifdef CONFIG_IMA_PER_NAMESPACE
> +	ima_namespaces = securityfs_create_file("namespaces", NAMESPACES_FILE_FLAGS,
> +						ima_dir, NULL,
> +						&ima_namespaces_ops);
> +	if (IS_ERR(ima_namespaces))
> +		goto out;
> +#endif
> +
>  	return 0;
>  out:
>  	securityfs_remove(violations);
> @@ -498,5 +678,8 @@ int __init ima_fs_init(void)
>  	securityfs_remove(binary_runtime_measurements);
>  	securityfs_remove(ima_dir);
>  	securityfs_remove(ima_policy);
> +#ifdef CONFIG_IMA_PER_NAMESPACE
> +	securityfs_remove(ima_namespaces);
> +#endif
>  	return -1;
>  }