Re: [Linux-ima-devel] [PATCH 6/7] ima: add securityfs interface to restore a measurements list

From: Mimi Zohar <zohar@linux.vnet.ibm.com>
To: Roberto Sassu <roberto.sassu@huawei.com>,
	linux-ima-devel@lists.sourceforge.net
Cc: linux-security-module@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [Linux-ima-devel] [PATCH 6/7] ima: add securityfs interface to restore a measurements list
Date: Mon, 05 Jun 2017 01:56:52 -0400	[thread overview]
Message-ID: <1496642212.2998.98.camel@linux.vnet.ibm.com> (raw)
In-Reply-To: <20170516125347.10574-7-roberto.sassu@huawei.com>

On Tue, 2017-05-16 at 14:53 +0200, Roberto Sassu wrote:
> Through the new interface restore_kexec_list, it will be possible
> to restore a measurements list, previously read from
> binary_kexec_runtime_measurements.

For development, this was fine.  You were able to save and restore the
measurement list with the kexec hdr, but do we really need two
securityfs files, one for saving the measurement list and another for
restoring it?  Just like we can read and write the IMA policy, we
should be able to save and restore the kexec list using a single
securityfs file.

> The patch reuses the policy functions to create a buffer, read
> the measurements and call ima_restore_measurement_list().

Calling a function named ima_read_policy() for restoring the
measurement list is unusual.  Again, this was fine for development,
but to upstream this functionality it should be cleaned up.  Normally,
there would be a call to a common generic function from multiple
places.

Mimi

> Signed-off-by: Roberto Sassu <roberto.sassu@huawei.com>
> ---
>  security/integrity/ima/ima_fs.c | 38 ++++++++++++++++++++++++++++++++++----
>  1 file changed, 34 insertions(+), 4 deletions(-)
> 
> diff --git a/security/integrity/ima/ima_fs.c b/security/integrity/ima/ima_fs.c
> index a93f941..6e3f93f 100644
> --- a/security/integrity/ima/ima_fs.c
> +++ b/security/integrity/ima/ima_fs.c
> @@ -77,6 +77,7 @@ static const struct file_operations ima_measurements_count_ops = {
>  };
> 
>  static struct dentry *binary_kexec_runtime_measurements;
> +static struct dentry *restore_kexec_list;
> 
>  /* returns pointer to hlist_node */
>  static void *ima_measurements_start(struct seq_file *m, loff_t *pos)
> @@ -297,7 +298,7 @@ static const struct file_operations ima_ascii_measurements_ops = {
>  	.release = seq_release,
>  };
> 
> -static ssize_t ima_read_policy(char *path)
> +static ssize_t ima_read_policy(char *path, bool khdr)
>  {
>  	void *data;
>  	char *datap;
> @@ -317,6 +318,13 @@ static ssize_t ima_read_policy(char *path)
>  	}
> 
>  	datap = data;
> +
> +	if (khdr) {
> +		rc = ima_restore_measurement_list(size, data);
> +		size = 0;
> +		goto out;
> +	}
> +
>  	while (size > 0 && (p = strsep(&datap, "\n"))) {
>  		pr_debug("rule: %s\n", p);
>  		rc = ima_parse_add_rule(p);
> @@ -325,6 +333,7 @@ static ssize_t ima_read_policy(char *path)
>  		size -= rc;
>  	}
> 
> +out:
>  	vfree(data);
>  	if (rc < 0)
>  		return rc;
> @@ -337,6 +346,7 @@ static ssize_t ima_read_policy(char *path)
>  static ssize_t ima_write_policy(struct file *file, const char __user *buf,
>  				size_t datalen, loff_t *ppos)
>  {
> +	bool khdr = file->f_path.dentry == restore_kexec_list;
>  	char *data;
>  	ssize_t result;
> 
> @@ -363,8 +373,13 @@ static ssize_t ima_write_policy(struct file *file, const char __user *buf,
>  	if (result < 0)
>  		goto out_free;
> 
> +	if (khdr && data[0] != '/') {
> +		mutex_unlock(&ima_write_mutex);
> +		goto out_free;
> +	}
> +
>  	if (data[0] == '/') {
> -		result = ima_read_policy(data);
> +		result = ima_read_policy(data, khdr);
>  	} else if (ima_appraise & IMA_APPRAISE_POLICY) {
>  		pr_err("IMA: signed policy file (specified as an absolute pathname) required\n");
>  		integrity_audit_msg(AUDIT_INTEGRITY_STATUS, NULL, NULL,
> @@ -393,7 +408,7 @@ static struct dentry *violations;
>  static struct dentry *ima_policy;
> 
>  enum ima_fs_flags {
> -	IMA_FS_BUSY,
> +	IMA_FS_BUSY, IMA_RESTORE_LIST_BUSY,
>  };
> 
>  static unsigned long ima_fs_flags;
> @@ -412,6 +427,9 @@ static const struct seq_operations ima_policy_seqops = {
>   */
>  static int ima_open_policy(struct inode *inode, struct file *filp)
>  {
> +	bool khdr = filp->f_path.dentry == restore_kexec_list;
> +	unsigned long bit = khdr ? IMA_RESTORE_LIST_BUSY : IMA_FS_BUSY;
> +
>  	if (!(filp->f_flags & O_WRONLY)) {
>  #ifndef	CONFIG_IMA_READ_POLICY
>  		return -EACCES;
> @@ -423,7 +441,7 @@ static int ima_open_policy(struct inode *inode, struct file *filp)
>  		return seq_open(filp, &ima_policy_seqops);
>  #endif
>  	}
> -	if (test_and_set_bit(IMA_FS_BUSY, &ima_fs_flags))
> +	if (test_and_set_bit(bit, &ima_fs_flags))
>  		return -EBUSY;
>  	return 0;
>  }
> @@ -439,6 +457,11 @@ static int ima_release_policy(struct inode *inode, struct file *file)
>  {
>  	const char *cause = valid_policy ? "completed" : "failed";
> 
> +	if (file->f_path.dentry == restore_kexec_list) {
> +		clear_bit(IMA_RESTORE_LIST_BUSY, &ima_fs_flags);
> +		return 0;
> +	}
> +
>  	if ((file->f_flags & O_ACCMODE) == O_RDONLY)
>  		return seq_release(inode, file);
> 
> @@ -522,9 +545,16 @@ int __init ima_fs_init(void)
>  				   &ima_measurements_ops);
>  	if (IS_ERR(binary_kexec_runtime_measurements))
>  		goto out;
> +
> +	restore_kexec_list = securityfs_create_file("restore_kexec_list",
> +						    S_IWUSR, ima_dir, NULL,
> +						    &ima_measure_policy_ops);
> +	if (IS_ERR(restore_kexec_list))
> +		goto out;
>  #endif
>  	return 0;
>  out:
> +	securityfs_remove(restore_kexec_list);
>  	securityfs_remove(binary_kexec_runtime_measurements);
>  	securityfs_remove(violations);
>  	securityfs_remove(runtime_measurements_count);