ima_api.c

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/*
 * Copyright (C) 2008 IBM Corporation
 *
 * Author: Mimi Zohar <[email protected]>
 *
 * 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_appraise_or_measure, collect_measurement,
 *  appraise_measurement, store_measurement and store_template.
 */
#include <linux/module.h>
#include <linux/slab.h>
#include <linux/file.h>
#include <linux/fs.h>
#include <linux/xattr.h>
#include <linux/evm.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);
}

int ima_get_action(struct inode *inode, int mask, int function)
{
    int flags = IMA_MEASURE | IMA_AUDIT | IMA_APPRAISE;

    if (!ima_appraise)
        flags &= ~IMA_APPRAISE;

    return ima_match_policy(inode, function, mask, flags);
}

int ima_must_measure(struct inode *inode, int mask, int function)
{
    return ima_match_policy(inode, function, mask, IMA_MEASURE);
}

/*
 * 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 integrity_iint_cache *iint,
                struct file *file)
{
    struct inode *inode = file->f_dentry->d_inode;
    const char *filename = file->f_dentry->d_name.name;
    int result = 0;

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

        iint->ima_xattr.type = IMA_XATTR_DIGEST;
        result = ima_calc_hash(file, iint->ima_xattr.digest);
        if (!result) {
            iint->version = i_version;
            iint->flags |= IMA_COLLECTED;
        }
    }
    if (result)
        integrity_audit_msg(AUDIT_INTEGRITY_DATA, inode,
                    filename, "collect_data", "failed",
                    result, 0);
    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 integrity_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;

    if (iint->flags & IMA_MEASURED)
        return;

    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->ima_xattr.digest, IMA_DIGEST_SIZE);
    strcpy(entry->template.file_name,
           (strlen(filename) > IMA_EVENT_NAME_LEN_MAX) ?
           file->f_dentry->d_name.name : filename);

    result = ima_store_template(entry, violation, inode);
    if (!result || result == -EEXIST)
        iint->flags |= IMA_MEASURED;
    if (result < 0)
        kfree(entry);
}

void ima_audit_measurement(struct integrity_iint_cache *iint,
               const unsigned char *filename)
{
    struct audit_buffer *ab;
    char hash[(IMA_DIGEST_SIZE * 2) + 1];
    int i;

    if (iint->flags & IMA_AUDITED)
        return;

    for (i = 0; i < IMA_DIGEST_SIZE; i++)
        hex_byte_pack(hash + (i * 2), iint->ima_xattr.digest[i]);
    hash[i * 2] = '\0';

    ab = audit_log_start(current->audit_context, GFP_KERNEL,
                 AUDIT_INTEGRITY_RULE);
    if (!ab)
        return;

    audit_log_format(ab, "file=");
    audit_log_untrustedstring(ab, filename);
    audit_log_format(ab, " hash=");
    audit_log_untrustedstring(ab, hash);

    audit_log_task_info(ab, current);
    audit_log_end(ab);

    iint->flags |= IMA_AUDITED;
}