ima_main.c

/*
 * Copyright (C) 2005,2006,2007,2008 IBM Corporation
 *
 * Authors:
 * Reiner Sailer <sailer@watson.ibm.com>
 * Serge Hallyn <serue@us.ibm.com>
 * Kylene Hall <kylene@us.ibm.com>
 * 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_main.c
 *	implements the IMA hooks: ima_bprm_check, ima_file_mmap,
 *	and ima_file_check.
 */
#include <linux/module.h>
#include <linux/file.h>
#include <linux/binfmts.h>
#include <linux/mount.h>
#include <linux/mman.h>
#include <linux/slab.h>
#include <linux/xattr.h>
#include <linux/ima.h>

#include "ima.h"

int ima_initialized;

#ifdef CONFIG_IMA_APPRAISE
int ima_appraise = IMA_APPRAISE_ENFORCE;
#else
int ima_appraise;
#endif

char *ima_hash = "sha1";
static int __init hash_setup(char *str)
{
	if (strncmp(str, "md5", 3) == 0)
		ima_hash = "md5";
	return 1;
}
__setup("ima_hash=", hash_setup);

/*
 * ima_rdwr_violation_check
 *
 * Only invalidate the PCR for measured files:
 * 	- Opening a file for write when already open for read,
 *	  results in a time of measure, time of use (ToMToU) error.
 *	- Opening a file for read when already open for write,
 * 	  could result in a file measurement error.
 *
 */
static void ima_rdwr_violation_check(struct file *file)
{
	struct dentry *dentry = file->f_path.dentry;
	struct inode *inode = dentry->d_inode;
	fmode_t mode = file->f_mode;
	int must_measure;
	bool send_tomtou = false, send_writers = false;
	char *pathbuf = NULL;
	const char *pathname;

	if (!S_ISREG(inode->i_mode) || !ima_initialized)
		return;

	mutex_lock(&inode->i_mutex);	/* file metadata: permissions, xattr */

	if (mode & FMODE_WRITE) {
		if (atomic_read(&inode->i_readcount) && IS_IMA(inode))
			send_tomtou = true;
		goto out;
	}

	must_measure = ima_must_measure(inode, MAY_READ, FILE_CHECK);
	if (!must_measure)
		goto out;

	if (atomic_read(&inode->i_writecount) > 0)
		send_writers = true;
out:
	mutex_unlock(&inode->i_mutex);

	if (!send_tomtou && !send_writers)
		return;

	pathname = ima_d_path(&file->f_path, &pathbuf);
	if (!pathname || strlen(pathname) > IMA_EVENT_NAME_LEN_MAX)
		pathname = dentry->d_name.name;

	if (send_tomtou)
		ima_add_violation(inode, pathname,
				  "invalid_pcr", "ToMToU");
	if (send_writers)
		ima_add_violation(inode, pathname,
				  "invalid_pcr", "open_writers");
	kfree(pathbuf);
}

static void ima_check_last_writer(struct integrity_iint_cache *iint,
				  struct inode *inode, struct file *file)
{
	fmode_t mode = file->f_mode;

	if (!(mode & FMODE_WRITE))
		return;

	mutex_lock(&inode->i_mutex);
	if (atomic_read(&inode->i_writecount) == 1 &&
	    iint->version != inode->i_version) {
		iint->flags &= ~IMA_DONE_MASK;
		if (iint->flags & IMA_APPRAISE)
			ima_update_xattr(iint, file);
	}
	mutex_unlock(&inode->i_mutex);
}

/**
 * ima_file_free - called on __fput()
 * @file: pointer to file structure being freed
 *
 * Flag files that changed, based on i_version
 */
void ima_file_free(struct file *file)
{
	struct inode *inode = file_inode(file);
	struct integrity_iint_cache *iint;

	if (!iint_initialized || !S_ISREG(inode->i_mode))
		return;

	iint = integrity_iint_find(inode);
	if (!iint)
		return;

	ima_check_last_writer(iint, inode, file);
}

static int process_measurement(struct file *file, const char *filename,
			       int mask, int function)
{
	struct inode *inode = file_inode(file);
	struct integrity_iint_cache *iint;
	char *pathbuf = NULL;
	const char *pathname = NULL;
	int rc = -ENOMEM, action, must_appraise, _func;

	if (!ima_initialized || !S_ISREG(inode->i_mode))
		return 0;

	/* Return an IMA_MEASURE, IMA_APPRAISE, IMA_AUDIT action
	 * bitmask based on the appraise/audit/measurement policy.
	 * Included is the appraise submask.
	 */
	action = ima_get_action(inode, mask, function);
	if (!action)
		return 0;

	must_appraise = action & IMA_APPRAISE;

	/*  Is the appraise rule hook specific?  */
	_func = (action & IMA_FILE_APPRAISE) ? FILE_CHECK : function;

	mutex_lock(&inode->i_mutex);

	iint = integrity_inode_get(inode);
	if (!iint)
		goto out;

	/* Determine if already appraised/measured based on bitmask
	 * (IMA_MEASURE, IMA_MEASURED, IMA_XXXX_APPRAISE, IMA_XXXX_APPRAISED,
	 *  IMA_AUDIT, IMA_AUDITED)
	 */
	iint->flags |= action;
	action &= IMA_DO_MASK;
	action &= ~((iint->flags & IMA_DONE_MASK) >> 1);

	/* Nothing to do, just return existing appraised status */
	if (!action) {
		if (must_appraise)
			rc = ima_get_cache_status(iint, _func);
		goto out_digsig;
	}

	rc = ima_collect_measurement(iint, file);
	if (rc != 0)
		goto out_digsig;

	if (function != BPRM_CHECK)
		pathname = ima_d_path(&file->f_path, &pathbuf);

	if (!pathname)
		pathname = filename;

	if (action & IMA_MEASURE)
		ima_store_measurement(iint, file, pathname);
	if (action & IMA_APPRAISE_SUBMASK)
		rc = ima_appraise_measurement(_func, iint, file, pathname);
	if (action & IMA_AUDIT)
		ima_audit_measurement(iint, pathname);
	kfree(pathbuf);
out_digsig:
	if ((mask & MAY_WRITE) && (iint->flags & IMA_DIGSIG))
		rc = -EACCES;
out:
	mutex_unlock(&inode->i_mutex);
	if ((rc && must_appraise) && (ima_appraise & IMA_APPRAISE_ENFORCE))
		return -EACCES;
	return 0;
}

/**
 * ima_file_mmap - based on policy, collect/store measurement.
 * @file: pointer to the file to be measured (May be NULL)
 * @prot: contains the protection that will be applied by the kernel.
 *
 * Measure files being mmapped executable based on the ima_must_measure()
 * policy decision.
 *
 * On success return 0.  On integrity appraisal error, assuming the file
 * is in policy and IMA-appraisal is in enforcing mode, return -EACCES.
 */
int ima_file_mmap(struct file *file, unsigned long prot)
{
	if (file && (prot & PROT_EXEC))
		return process_measurement(file, file->f_dentry->d_name.name,
					   MAY_EXEC, MMAP_CHECK);
	return 0;
}

/**
 * ima_bprm_check - based on policy, collect/store measurement.
 * @bprm: contains the linux_binprm structure
 *
 * The OS protects against an executable file, already open for write,
 * from being executed in deny_write_access() and an executable file,
 * already open for execute, from being modified in get_write_access().
 * So we can be certain that what we verify and measure here is actually
 * what is being executed.
 *
 * On success return 0.  On integrity appraisal error, assuming the file
 * is in policy and IMA-appraisal is in enforcing mode, return -EACCES.
 */
int ima_bprm_check(struct linux_binprm *bprm)
{
	return process_measurement(bprm->file,
				 (strcmp(bprm->filename, bprm->interp) == 0) ?
				 bprm->filename : bprm->interp,
				 MAY_EXEC, BPRM_CHECK);
}

/**
 * ima_path_check - based on policy, collect/store measurement.
 * @file: pointer to the file to be measured
 * @mask: contains MAY_READ, MAY_WRITE or MAY_EXECUTE
 *
 * Measure files based on the ima_must_measure() policy decision.
 *
 * On success return 0.  On integrity appraisal error, assuming the file
 * is in policy and IMA-appraisal is in enforcing mode, return -EACCES.
 */
int ima_file_check(struct file *file, int mask)
{
	ima_rdwr_violation_check(file);
	return process_measurement(file, file->f_dentry->d_name.name,
				 mask & (MAY_READ | MAY_WRITE | MAY_EXEC),
				 FILE_CHECK);
}
EXPORT_SYMBOL_GPL(ima_file_check);

/**
 * ima_module_check - based on policy, collect/store/appraise measurement.
 * @file: pointer to the file to be measured/appraised
 *
 * Measure/appraise kernel modules based on policy.
 *
 * On success return 0.  On integrity appraisal error, assuming the file
 * is in policy and IMA-appraisal is in enforcing mode, return -EACCES.
 */
int ima_module_check(struct file *file)
{
	if (!file) {
#ifndef CONFIG_MODULE_SIG_FORCE
		if ((ima_appraise & IMA_APPRAISE_MODULES) &&
		    (ima_appraise & IMA_APPRAISE_ENFORCE))
			return -EACCES;	/* INTEGRITY_UNKNOWN */
#endif
		return 0;	/* We rely on module signature checking */
	}
	return process_measurement(file, file->f_dentry->d_name.name,
				   MAY_EXEC, MODULE_CHECK);
}

static int __init init_ima(void)
{
	int error;

	error = ima_init();
	if (!error)
		ima_initialized = 1;
	return error;
}

late_initcall(init_ima);	/* Start IMA after the TPM is available */

MODULE_DESCRIPTION("Integrity Measurement Architecture");
MODULE_LICENSE("GPL");