/*
 * Copyright (C) 2008 IBM Corporation
 *
 * Author: Mimi Zohar <zohar@us.ibm.com>
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License as
 * published by the Free Software Foundation, version 2 of the
 * License.
 *
 * File: ima_api.c
 *      Implements must_measure, collect_measurement, store_measurement,
 *      and store_template.
 */
#include <linux/module.h>

#include "ima.h"
static const char *IMA_TEMPLATE_NAME = "ima";

/*
 * ima_store_template - store ima template measurements
 *
 * Calculate the hash of a template entry, add the template entry
 * to an ordered list of measurement entries maintained inside the kernel,
 * and also update the aggregate integrity value (maintained inside the
 * configured TPM PCR) over the hashes of the current list of measurement
 * entries.
 *
 * Applications retrieve the current kernel-held measurement list through
 * the securityfs entries in /sys/kernel/security/ima. The signed aggregate
 * TPM PCR (called quote) can be retrieved using a TPM user space library
 * and is used to validate the measurement list.
 *
 * Returns 0 on success, error code otherwise
 */
int ima_store_template(struct ima_template_entry *entry,
                       int violation, struct inode *inode)
{
        const char *op = "add_template_measure";
        const char *audit_cause = "hashing_error";
        int result;

        memset(entry->digest, 0, sizeof(entry->digest));
        entry->template_name = IMA_TEMPLATE_NAME;
        entry->template_len = sizeof(entry->template);

        if (!violation) {
                result = ima_calc_template_hash(entry->template_len,
                                                &entry->template,
                                                entry->digest);
                if (result < 0) {
                        integrity_audit_msg(AUDIT_INTEGRITY_PCR, inode,
                                            entry->template_name, op,
                                            audit_cause, result, 0);
                        return result;
                }
        }
        result = ima_add_template_entry(entry, violation, op, inode);
        return result;
}

/*
 * ima_add_violation - add violation to measurement list.
 *
 * Violations are flagged in the measurement list with zero hash values.
 * By extending the PCR with 0xFF's instead of with zeroes, the PCR
 * value is invalidated.
 */
void ima_add_violation(struct inode *inode, const unsigned char *filename,
                       const char *op, const char *cause)
{
        struct ima_template_entry *entry;
        int violation = 1;
        int result;

        /* can overflow, only indicator */
        atomic_long_inc(&ima_htable.violations);

        entry = kmalloc(sizeof(*entry), GFP_KERNEL);
        if (!entry) {
                result = -ENOMEM;
                goto err_out;
        }
        memset(&entry->template, 0, sizeof(entry->template));
        strncpy(entry->template.file_name, filename, IMA_EVENT_NAME_LEN_MAX);
        result = ima_store_template(entry, violation, inode);
        if (result < 0)
                kfree(entry);
err_out:
        integrity_audit_msg(AUDIT_INTEGRITY_PCR, inode, filename,
                            op, cause, result, 0);
}

/**
 * ima_must_measure - measure decision based on policy.
 * @inode: pointer to inode to measure
 * @mask: contains the permission mask (MAY_READ, MAY_WRITE, MAY_EXECUTE)
 * @function: calling function (PATH_CHECK, BPRM_CHECK, FILE_MMAP)
 *
 * The policy is defined in terms of keypairs:
 *              subj=, obj=, type=, func=, mask=, fsmagic=
 *      subj,obj, and type: are LSM specific.
 *      func: PATH_CHECK | BPRM_CHECK | FILE_MMAP
 *      mask: contains the permission mask
 *      fsmagic: hex value
 *
 * Must be called with iint->mutex held.
 *
 * Return 0 to measure. Return 1 if already measured.
 * For matching a DONT_MEASURE policy, no policy, or other
 * error, return an error code.
*/
int ima_must_measure(struct ima_iint_cache *iint, struct inode *inode,
                     int mask, int function)
{
        int must_measure;

        if (iint->flags & IMA_MEASURED)
                return 1;

        must_measure = ima_match_policy(inode, function, mask);
        return must_measure ? 0 : -EACCES;
}

/*
 * ima_collect_measurement - collect file measurement
 *
 * Calculate the file hash, if it doesn't already exist,
 * storing the measurement and i_version in the iint.
 *
 * Must be called with iint->mutex held.
 *
 * Return 0 on success, error code otherwise
 */
int ima_collect_measurement(struct ima_iint_cache *iint, struct file *file)
{
        int result = -EEXIST;

        if (!(iint->flags & IMA_MEASURED)) {
                u64 i_version = file->f_dentry->d_inode->i_version;

                memset(iint->digest, 0, IMA_DIGEST_SIZE);
                result = ima_calc_hash(file, iint->digest);
                if (!result)
                        iint->version = i_version;
        }
        return result;
}

/*
 * ima_store_measurement - store file measurement
 *
 * Create an "ima" template and then store the template by calling
 * ima_store_template.
 *
 * We only get here if the inode has not already been measured,
 * but the measurement could already exist:
 *      - multiple copies of the same file on either the same or
 *        different filesystems.
 *      - the inode was previously flushed as well as the iint info,
 *        containing the hashing info.
 *
 * Must be called with iint->mutex held.
 */
void ima_store_measurement(struct ima_iint_cache *iint, struct file *file,
                           const unsigned char *filename)
{
        const char *op = "add_template_measure";
        const char *audit_cause = "ENOMEM";
        int result = -ENOMEM;
        struct inode *inode = file->f_dentry->d_inode;
        struct ima_template_entry *entry;
        int violation = 0;

        entry = kmalloc(sizeof(*entry), GFP_KERNEL);
        if (!entry) {
                integrity_audit_msg(AUDIT_INTEGRITY_PCR, inode, filename,
                                    op, audit_cause, result, 0);
                return;
        }
        memset(&entry->template, 0, sizeof(entry->template));
        memcpy(entry->template.digest, iint->digest, IMA_DIGEST_SIZE);
        strncpy(entry->template.file_name, filename, IMA_EVENT_NAME_LEN_MAX);

        result = ima_store_template(entry, violation, inode);
        if (!result)
                iint->flags |= IMA_MEASURED;
        else
                kfree(entry);
}