linux/security/integrity/ima/ima_appraise.c
Dmitry Kasatkin 0e5a247cb3 ima: added policy support for 'security.ima' type
The 'security.ima' extended attribute may contain either the file data's
hash or a digital signature.  This patch adds support for requiring a
specific extended attribute type.  It extends the IMA policy with a new
keyword 'appraise_type=imasig'.  (Default is hash.)

Changelog v2:
- Fixed Documentation/ABI/testing/ima_policy option syntax
Changelog v1:
- Differentiate between 'required' vs. 'actual' extended attribute

Signed-off-by: Dmitry Kasatkin <dmitry.kasatkin@intel.com>
Signed-off-by: Mimi Zohar <zohar@linux.vnet.ibm.com>
2013-01-22 16:10:31 -05:00

265 lines
6.3 KiB
C

/*
* Copyright (C) 2011 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.
*/
#include <linux/module.h>
#include <linux/file.h>
#include <linux/fs.h>
#include <linux/xattr.h>
#include <linux/magic.h>
#include <linux/ima.h>
#include <linux/evm.h>
#include "ima.h"
static int __init default_appraise_setup(char *str)
{
if (strncmp(str, "off", 3) == 0)
ima_appraise = 0;
else if (strncmp(str, "fix", 3) == 0)
ima_appraise = IMA_APPRAISE_FIX;
return 1;
}
__setup("ima_appraise=", default_appraise_setup);
/*
* ima_must_appraise - set appraise flag
*
* Return 1 to appraise
*/
int ima_must_appraise(struct inode *inode, int mask, enum ima_hooks func)
{
if (!ima_appraise)
return 0;
return ima_match_policy(inode, func, mask, IMA_APPRAISE);
}
static int ima_fix_xattr(struct dentry *dentry,
struct integrity_iint_cache *iint)
{
iint->ima_xattr.type = IMA_XATTR_DIGEST;
return __vfs_setxattr_noperm(dentry, XATTR_NAME_IMA,
(u8 *)&iint->ima_xattr,
sizeof(iint->ima_xattr), 0);
}
/*
* ima_appraise_measurement - appraise file measurement
*
* Call evm_verifyxattr() to verify the integrity of 'security.ima'.
* Assuming success, compare the xattr hash with the collected measurement.
*
* Return 0 on success, error code otherwise
*/
int ima_appraise_measurement(struct integrity_iint_cache *iint,
struct file *file, const unsigned char *filename)
{
struct dentry *dentry = file->f_dentry;
struct inode *inode = dentry->d_inode;
struct evm_ima_xattr_data *xattr_value = NULL;
enum integrity_status status = INTEGRITY_UNKNOWN;
const char *op = "appraise_data";
char *cause = "unknown";
int rc;
if (!ima_appraise)
return 0;
if (!inode->i_op->getxattr)
return INTEGRITY_UNKNOWN;
if (iint->flags & IMA_APPRAISED)
return iint->ima_status;
rc = vfs_getxattr_alloc(dentry, XATTR_NAME_IMA, (char **)&xattr_value,
0, GFP_NOFS);
if (rc <= 0) {
if (rc && rc != -ENODATA)
goto out;
cause = "missing-hash";
status =
(inode->i_size == 0) ? INTEGRITY_PASS : INTEGRITY_NOLABEL;
goto out;
}
status = evm_verifyxattr(dentry, XATTR_NAME_IMA, xattr_value, rc, iint);
if ((status != INTEGRITY_PASS) && (status != INTEGRITY_UNKNOWN)) {
if ((status == INTEGRITY_NOLABEL)
|| (status == INTEGRITY_NOXATTRS))
cause = "missing-HMAC";
else if (status == INTEGRITY_FAIL)
cause = "invalid-HMAC";
goto out;
}
switch (xattr_value->type) {
case IMA_XATTR_DIGEST:
if (iint->flags & IMA_DIGSIG_REQUIRED) {
cause = "IMA signature required";
status = INTEGRITY_FAIL;
break;
}
rc = memcmp(xattr_value->digest, iint->ima_xattr.digest,
IMA_DIGEST_SIZE);
if (rc) {
cause = "invalid-hash";
status = INTEGRITY_FAIL;
break;
}
status = INTEGRITY_PASS;
break;
case EVM_IMA_XATTR_DIGSIG:
iint->flags |= IMA_DIGSIG;
rc = integrity_digsig_verify(INTEGRITY_KEYRING_IMA,
xattr_value->digest, rc - 1,
iint->ima_xattr.digest,
IMA_DIGEST_SIZE);
if (rc == -EOPNOTSUPP) {
status = INTEGRITY_UNKNOWN;
} else if (rc) {
cause = "invalid-signature";
status = INTEGRITY_FAIL;
} else {
status = INTEGRITY_PASS;
}
break;
default:
status = INTEGRITY_UNKNOWN;
cause = "unknown-ima-data";
break;
}
out:
if (status != INTEGRITY_PASS) {
if ((ima_appraise & IMA_APPRAISE_FIX) &&
(!xattr_value ||
xattr_value->type != EVM_IMA_XATTR_DIGSIG)) {
if (!ima_fix_xattr(dentry, iint))
status = INTEGRITY_PASS;
}
integrity_audit_msg(AUDIT_INTEGRITY_DATA, inode, filename,
op, cause, rc, 0);
} else {
iint->flags |= IMA_APPRAISED;
}
iint->ima_status = status;
kfree(xattr_value);
return status;
}
/*
* ima_update_xattr - update 'security.ima' hash value
*/
void ima_update_xattr(struct integrity_iint_cache *iint, struct file *file)
{
struct dentry *dentry = file->f_dentry;
int rc = 0;
/* do not collect and update hash for digital signatures */
if (iint->flags & IMA_DIGSIG)
return;
rc = ima_collect_measurement(iint, file);
if (rc < 0)
return;
ima_fix_xattr(dentry, iint);
}
/**
* ima_inode_post_setattr - reflect file metadata changes
* @dentry: pointer to the affected dentry
*
* Changes to a dentry's metadata might result in needing to appraise.
*
* This function is called from notify_change(), which expects the caller
* to lock the inode's i_mutex.
*/
void ima_inode_post_setattr(struct dentry *dentry)
{
struct inode *inode = dentry->d_inode;
struct integrity_iint_cache *iint;
int must_appraise, rc;
if (!ima_initialized || !ima_appraise || !S_ISREG(inode->i_mode)
|| !inode->i_op->removexattr)
return;
must_appraise = ima_must_appraise(inode, MAY_ACCESS, POST_SETATTR);
iint = integrity_iint_find(inode);
if (iint) {
if (must_appraise)
iint->flags |= IMA_APPRAISE;
else
iint->flags &= ~(IMA_APPRAISE | IMA_APPRAISED);
}
if (!must_appraise)
rc = inode->i_op->removexattr(dentry, XATTR_NAME_IMA);
return;
}
/*
* ima_protect_xattr - protect 'security.ima'
*
* Ensure that not just anyone can modify or remove 'security.ima'.
*/
static int ima_protect_xattr(struct dentry *dentry, const char *xattr_name,
const void *xattr_value, size_t xattr_value_len)
{
if (strcmp(xattr_name, XATTR_NAME_IMA) == 0) {
if (!capable(CAP_SYS_ADMIN))
return -EPERM;
return 1;
}
return 0;
}
static void ima_reset_appraise_flags(struct inode *inode)
{
struct integrity_iint_cache *iint;
if (!ima_initialized || !ima_appraise || !S_ISREG(inode->i_mode))
return;
iint = integrity_iint_find(inode);
if (!iint)
return;
iint->flags &= ~IMA_DONE_MASK;
return;
}
int ima_inode_setxattr(struct dentry *dentry, const char *xattr_name,
const void *xattr_value, size_t xattr_value_len)
{
int result;
result = ima_protect_xattr(dentry, xattr_name, xattr_value,
xattr_value_len);
if (result == 1) {
ima_reset_appraise_flags(dentry->d_inode);
result = 0;
}
return result;
}
int ima_inode_removexattr(struct dentry *dentry, const char *xattr_name)
{
int result;
result = ima_protect_xattr(dentry, xattr_name, NULL, 0);
if (result == 1) {
ima_reset_appraise_flags(dentry->d_inode);
result = 0;
}
return result;
}