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 "ima.h"

int ima_initialized;

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);

struct ima_imbalance {
	struct hlist_node node;
	unsigned long fsmagic;
};

/*
 * ima_limit_imbalance - emit one imbalance message per filesystem type
 *
 * Maintain list of filesystem types that do not measure files properly.
 * Return false if unknown, true if known.
 */
static bool ima_limit_imbalance(struct file *file)
{
	static DEFINE_SPINLOCK(ima_imbalance_lock);
	static HLIST_HEAD(ima_imbalance_list);

	struct super_block *sb = file->f_dentry->d_sb;
	struct ima_imbalance *entry;
	struct hlist_node *node;
	bool found = false;

	rcu_read_lock();
	hlist_for_each_entry_rcu(entry, node, &ima_imbalance_list, node) {
		if (entry->fsmagic == sb->s_magic) {
			found = true;
			break;
		}
	}
	rcu_read_unlock();
	if (found)
		goto out;

	entry = kmalloc(sizeof(*entry), GFP_NOFS);
	if (!entry)
		goto out;
	entry->fsmagic = sb->s_magic;
	spin_lock(&ima_imbalance_lock);
	/*
	 * we could have raced and something else might have added this fs
	 * to the list, but we don't really care
	 */
	hlist_add_head_rcu(&entry->node, &ima_imbalance_list);
	spin_unlock(&ima_imbalance_lock);
	printk(KERN_INFO "IMA: unmeasured files on fsmagic: %lX\n",
	       entry->fsmagic);
out:
	return found;
}

/*
 * 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 rc;
	bool send_tomtou = false, send_writers = false;

	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;
	}

	rc = ima_must_measure(NULL, inode, MAY_READ, FILE_CHECK);
	if (rc < 0)
		goto out;

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

	if (send_tomtou)
		ima_add_violation(inode, dentry->d_name.name, "invalid_pcr",
				  "ToMToU");
	if (send_writers)
		ima_add_violation(inode, dentry->d_name.name, "invalid_pcr",
				  "open_writers");
}

/*
 * Decrement ima counts
 */
static void ima_dec_counts(struct inode *inode, struct file *file)
{
	mode_t mode = file->f_mode;

	assert_spin_locked(&inode->i_lock);

	if ((mode & (FMODE_READ | FMODE_WRITE)) == FMODE_READ) {
		if (unlikely(atomic_read(&inode->i_readcount) == 0)) {
			if (!ima_limit_imbalance(file)) {
				printk(KERN_INFO "%s: open/free imbalance (r:%u)\n",
				       __func__,
				       atomic_read(&inode->i_readcount));
				dump_stack();
			}
			return;
		}
	}
}

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

	BUG_ON(!mutex_is_locked(&iint->mutex));
	assert_spin_locked(&inode->i_lock);

	if (mode & FMODE_WRITE &&
	    atomic_read(&inode->i_writecount) == 1 &&
	    iint->version != inode->i_version)
		iint->flags &= ~IMA_MEASURED;
}

static void ima_file_free_iint(struct ima_iint_cache *iint, struct inode *inode,
			       struct file *file)
{
	mutex_lock(&iint->mutex);
	spin_lock(&inode->i_lock);

	ima_dec_counts(inode, file);
	ima_check_last_writer(iint, inode, file);

	spin_unlock(&inode->i_lock);
	mutex_unlock(&iint->mutex);
}

static void ima_file_free_noiint(struct inode *inode, struct file *file)
{
	spin_lock(&inode->i_lock);

	ima_dec_counts(inode, file);

	spin_unlock(&inode->i_lock);
}

/**
 * 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->f_dentry->d_inode;
	struct ima_iint_cache *iint;

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

	iint = ima_iint_find(inode);

	if (iint)
		ima_file_free_iint(iint, inode, file);
	else
		ima_file_free_noiint(inode, file);

}

static int process_measurement(struct file *file, const unsigned char *filename,
			       int mask, int function)
{
	struct inode *inode = file->f_dentry->d_inode;
	struct ima_iint_cache *iint;
	int rc = 0;

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

	rc = ima_must_measure(NULL, inode, mask, function);
	if (rc != 0)
		return rc;
retry:
	iint = ima_iint_find(inode);
	if (!iint) {
		rc = ima_inode_alloc(inode);
		if (!rc || rc == -EEXIST)
			goto retry;
		return rc;
	}

	mutex_lock(&iint->mutex);

	rc = ima_must_measure(iint, inode, mask, function);
	if (rc != 0)
		goto out;

	rc = ima_collect_measurement(iint, file);
	if (!rc)
		ima_store_measurement(iint, file, filename);
out:
	mutex_unlock(&iint->mutex);
	return rc;
}

/**
 * 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.
 *
 * Return 0 on success, an error code on failure.
 * (Based on the results of appraise_measurement().)
 */
int ima_file_mmap(struct file *file, unsigned long prot)
{
	int rc;

	if (!file)
		return 0;
	if (prot & PROT_EXEC)
		rc = process_measurement(file, file->f_dentry->d_name.name,
					 MAY_EXEC, FILE_MMAP);
	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.
 *
 * Return 0 on success, an error code on failure.
 * (Based on the results of appraise_measurement().)
 */
int ima_bprm_check(struct linux_binprm *bprm)
{
	int rc;

	rc = process_measurement(bprm->file, bprm->filename,
				 MAY_EXEC, BPRM_CHECK);
	return 0;
}

/**
 * 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.
 *
 * Always return 0 and audit dentry_open failures.
 * (Return code will be based upon measurement appraisal.)
 */
int ima_file_check(struct file *file, int mask)
{
	int rc;

	ima_rdwr_violation_check(file);
	rc = process_measurement(file, file->f_dentry->d_name.name,
				 mask & (MAY_READ | MAY_WRITE | MAY_EXEC),
				 FILE_CHECK);
	return 0;
}
EXPORT_SYMBOL_GPL(ima_file_check);

static int __init init_ima(void)
{
	int error;

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

static void __exit cleanup_ima(void)
{
	ima_cleanup();
}

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

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