integrity: IMA as an integrity service provider

IMA provides hardware (TPM) based measurement and attestation for
file measurements. As the Trusted Computing (TPM) model requires,
IMA measures all files before they are accessed in any way (on the
integrity_bprm_check, integrity_path_check and integrity_file_mmap
hooks), and commits the measurements to the TPM. Once added to the
TPM, measurements can not be removed.

In addition, IMA maintains a list of these file measurements, which
can be used to validate the aggregate value stored in the TPM.  The
TPM can sign these measurements, and thus the system can prove, to
itself and to a third party, the system's integrity in a way that
cannot be circumvented by malicious or compromised software.

- alloc ima_template_entry before calling ima_store_template()
- log ima_add_boot_aggregate() failure
- removed unused IMA_TEMPLATE_NAME_LEN
- replaced hard coded string length with #define name

Signed-off-by: Mimi Zohar <zohar@us.ibm.com>
Signed-off-by: James Morris <jmorris@namei.org>

1 files changed, 280 insertions, 0 deletions

diff --git a/security/integrity/ima/ima_main.c b/security/integrity/ima/ima_main.c
new file mode 100644
index 0000000..53cee4c
--- /dev/null
+++ b/security/integrity/ima/ima_main.c
@@ -0,0 +1,280 @@
+/*
+ * 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_path_check.
+ */
+#include <linux/module.h>
+#include <linux/file.h>
+#include <linux/binfmts.h>
+#include <linux/mount.h>
+#include <linux/mman.h>
+
+#include "ima.h"
+
+int ima_initialized;
+
+char *ima_hash = "sha1";
+static int __init hash_setup(char *str)
+{
+	const char *op = "hash_setup";
+	const char *hash = "sha1";
+	int result = 0;
+	int audit_info = 0;
+
+	if (strncmp(str, "md5", 3) == 0) {
+		hash = "md5";
+		ima_hash = str;
+	} else if (strncmp(str, "sha1", 4) != 0) {
+		hash = "invalid_hash_type";
+		result = 1;
+	}
+	integrity_audit_msg(AUDIT_INTEGRITY_HASH, NULL, NULL, op, hash,
+			    result, audit_info);
+	return 1;
+}
+__setup("ima_hash=", hash_setup);
+
+/**
+ * ima_file_free - called on __fput()
+ * @file: pointer to file structure being freed
+ *
+ * Flag files that changed, based on i_version;
+ * and decrement the iint readcount/writecount.
+ */
+void ima_file_free(struct file *file)
+{
+	struct inode *inode = file->f_dentry->d_inode;
+	struct ima_iint_cache *iint;
+
+	if (!ima_initialized || !S_ISREG(inode->i_mode))
+		return;
+	iint = ima_iint_find_get(inode);
+	if (!iint)
+		return;
+
+	mutex_lock(&iint->mutex);
+	if ((file->f_mode & (FMODE_READ | FMODE_WRITE)) == FMODE_READ)
+		iint->readcount--;
+
+	if (file->f_mode & FMODE_WRITE) {
+		iint->writecount--;
+		if (iint->writecount == 0) {
+			if (iint->version != inode->i_version)
+				iint->flags &= ~IMA_MEASURED;
+		}
+	}
+	mutex_unlock(&iint->mutex);
+	kref_put(&iint->refcount, iint_free);
+}
+
+/* ima_read_write_check - reflect possible reading/writing errors in the PCR.
+ *
+ * When opening a file for read, if the file is already open for write,
+ * the file could change, resulting in a file measurement error.
+ *
+ * Opening a file for write, if the file is already open for read, results
+ * in a time of measure, time of use (ToMToU) error.
+ *
+ * In either case invalidate the PCR.
+ */
+enum iint_pcr_error { TOMTOU, OPEN_WRITERS };
+static void ima_read_write_check(enum iint_pcr_error error,
+				 struct ima_iint_cache *iint,
+				 struct inode *inode,
+				 const unsigned char *filename)
+{
+	switch (error) {
+	case TOMTOU:
+		if (iint->readcount > 0)
+			ima_add_violation(inode, filename, "invalid_pcr",
+					  "ToMToU");
+		break;
+	case OPEN_WRITERS:
+		if (iint->writecount > 0)
+			ima_add_violation(inode, filename, "invalid_pcr",
+					  "open_writers");
+		break;
+	}
+}
+
+static int get_path_measurement(struct ima_iint_cache *iint, struct file *file,
+				const unsigned char *filename)
+{
+	int rc = 0;
+
+	if (IS_ERR(file)) {
+		pr_info("%s dentry_open failed\n", filename);
+		return rc;
+	}
+	iint->readcount++;
+
+	rc = ima_collect_measurement(iint, file);
+	if (!rc)
+		ima_store_measurement(iint, file, filename);
+	return rc;
+}
+
+/**
+ * ima_path_check - based on policy, collect/store measurement.
+ * @path: contains a pointer to the path to be measured
+ * @mask: contains MAY_READ, MAY_WRITE or MAY_EXECUTE
+ *
+ * Measure the file being open for readonly, based on the
+ * ima_must_measure() policy decision.
+ *
+ * Keep read/write counters for all files, but 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.
+ *
+ * Return 0 on success, an error code on failure.
+ * (Based on the results of appraise_measurement().)
+ */
+int ima_path_check(struct path *path, int mask)
+{
+	struct inode *inode = path->dentry->d_inode;
+	struct ima_iint_cache *iint;
+	struct file *file = NULL;
+	int rc;
+
+	if (!ima_initialized || !S_ISREG(inode->i_mode))
+		return 0;
+	iint = ima_iint_find_insert_get(inode);
+	if (!iint)
+		return 0;
+
+	mutex_lock(&iint->mutex);
+	if ((mask & MAY_WRITE) || (mask == 0))
+		iint->writecount++;
+	else if (mask & (MAY_READ | MAY_EXEC))
+		iint->readcount++;
+
+	rc = ima_must_measure(iint, inode, MAY_READ, PATH_CHECK);
+	if (rc < 0)
+		goto out;
+
+	if ((mask & MAY_WRITE) || (mask == 0))
+		ima_read_write_check(TOMTOU, iint, inode,
+				     path->dentry->d_name.name);
+
+	if ((mask & (MAY_WRITE | MAY_READ | MAY_EXEC)) != MAY_READ)
+		goto out;
+
+	ima_read_write_check(OPEN_WRITERS, iint, inode,
+			     path->dentry->d_name.name);
+	if (!(iint->flags & IMA_MEASURED)) {
+		struct dentry *dentry = dget(path->dentry);
+		struct vfsmount *mnt = mntget(path->mnt);
+
+		file = dentry_open(dentry, mnt, O_RDONLY, current->cred);
+		rc = get_path_measurement(iint, file, dentry->d_name.name);
+	}
+out:
+	mutex_unlock(&iint->mutex);
+	if (file)
+		fput(file);
+	kref_put(&iint->refcount, iint_free);
+	return 0;
+}
+
+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;
+
+	if (!ima_initialized || !S_ISREG(inode->i_mode))
+		return 0;
+	iint = ima_iint_find_insert_get(inode);
+	if (!iint)
+		return -ENOMEM;
+
+	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);
+	kref_put(&iint->refcount, iint_free);
+	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;
+}
+
+static int __init init_ima(void)
+{
+	int error;
+
+	ima_iintcache_init();
+	error = ima_init();
+	ima_initialized = 1;
+	return error;
+}
+
+late_initcall(init_ima);	/* Start IMA after the TPM is available */
+
+MODULE_DESCRIPTION("Integrity Measurement Architecture");
+MODULE_LICENSE("GPL");