463 lines
12 KiB
C
463 lines
12 KiB
C
/*
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* Copyright (C) 2005-2010 IBM Corporation
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*
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* Author:
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* Mimi Zohar <zohar@us.ibm.com>
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* Kylene Hall <kjhall@us.ibm.com>
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation, version 2 of the License.
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*
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* File: evm_main.c
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* implements evm_inode_setxattr, evm_inode_post_setxattr,
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* evm_inode_removexattr, and evm_verifyxattr
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*/
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#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
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#include <linux/module.h>
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#include <linux/crypto.h>
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#include <linux/audit.h>
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#include <linux/xattr.h>
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#include <linux/integrity.h>
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#include <linux/evm.h>
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#include <crypto/hash.h>
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#include "evm.h"
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int evm_initialized;
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static char *integrity_status_msg[] = {
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"pass", "fail", "no_label", "no_xattrs", "unknown"
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};
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char *evm_hmac = "hmac(sha1)";
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char *evm_hash = "sha1";
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int evm_hmac_version = CONFIG_EVM_HMAC_VERSION;
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char *evm_config_xattrnames[] = {
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#ifdef CONFIG_SECURITY_SELINUX
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XATTR_NAME_SELINUX,
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#endif
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#ifdef CONFIG_SECURITY_SMACK
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XATTR_NAME_SMACK,
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#endif
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#ifdef CONFIG_IMA_APPRAISE
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XATTR_NAME_IMA,
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#endif
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XATTR_NAME_CAPS,
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NULL
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};
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static int evm_fixmode;
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static int __init evm_set_fixmode(char *str)
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{
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if (strncmp(str, "fix", 3) == 0)
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evm_fixmode = 1;
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return 0;
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}
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__setup("evm=", evm_set_fixmode);
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static int evm_find_protected_xattrs(struct dentry *dentry)
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{
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struct inode *inode = dentry->d_inode;
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char **xattr;
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int error;
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int count = 0;
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if (!inode->i_op->getxattr)
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return -EOPNOTSUPP;
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for (xattr = evm_config_xattrnames; *xattr != NULL; xattr++) {
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error = inode->i_op->getxattr(dentry, *xattr, NULL, 0);
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if (error < 0) {
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if (error == -ENODATA)
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continue;
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return error;
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}
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count++;
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}
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return count;
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}
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/*
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* evm_verify_hmac - calculate and compare the HMAC with the EVM xattr
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*
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* Compute the HMAC on the dentry's protected set of extended attributes
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* and compare it against the stored security.evm xattr.
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*
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* For performance:
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* - use the previoulsy retrieved xattr value and length to calculate the
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* HMAC.)
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* - cache the verification result in the iint, when available.
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*
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* Returns integrity status
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*/
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static enum integrity_status evm_verify_hmac(struct dentry *dentry,
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const char *xattr_name,
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char *xattr_value,
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size_t xattr_value_len,
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struct integrity_iint_cache *iint)
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{
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struct evm_ima_xattr_data *xattr_data = NULL;
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struct evm_ima_xattr_data calc;
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enum integrity_status evm_status = INTEGRITY_PASS;
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int rc, xattr_len;
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if (iint && iint->evm_status == INTEGRITY_PASS)
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return iint->evm_status;
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/* if status is not PASS, try to check again - against -ENOMEM */
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/* first need to know the sig type */
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rc = vfs_getxattr_alloc(dentry, XATTR_NAME_EVM, (char **)&xattr_data, 0,
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GFP_NOFS);
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if (rc <= 0) {
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if (rc == 0)
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evm_status = INTEGRITY_FAIL; /* empty */
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else if (rc == -ENODATA) {
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rc = evm_find_protected_xattrs(dentry);
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if (rc > 0)
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evm_status = INTEGRITY_NOLABEL;
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else if (rc == 0)
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evm_status = INTEGRITY_NOXATTRS; /* new file */
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}
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goto out;
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}
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xattr_len = rc;
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/* check value type */
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switch (xattr_data->type) {
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case EVM_XATTR_HMAC:
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rc = evm_calc_hmac(dentry, xattr_name, xattr_value,
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xattr_value_len, calc.digest);
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if (rc)
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break;
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rc = memcmp(xattr_data->digest, calc.digest,
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sizeof(calc.digest));
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if (rc)
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rc = -EINVAL;
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break;
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case EVM_IMA_XATTR_DIGSIG:
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rc = evm_calc_hash(dentry, xattr_name, xattr_value,
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xattr_value_len, calc.digest);
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if (rc)
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break;
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rc = integrity_digsig_verify(INTEGRITY_KEYRING_EVM,
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(const char *)xattr_data, xattr_len,
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calc.digest, sizeof(calc.digest));
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if (!rc) {
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/* we probably want to replace rsa with hmac here */
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evm_update_evmxattr(dentry, xattr_name, xattr_value,
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xattr_value_len);
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}
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break;
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default:
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rc = -EINVAL;
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break;
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}
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if (rc)
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evm_status = (rc == -ENODATA) ?
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INTEGRITY_NOXATTRS : INTEGRITY_FAIL;
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out:
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if (iint)
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iint->evm_status = evm_status;
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kfree(xattr_data);
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return evm_status;
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}
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static int evm_protected_xattr(const char *req_xattr_name)
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{
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char **xattrname;
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int namelen;
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int found = 0;
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namelen = strlen(req_xattr_name);
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for (xattrname = evm_config_xattrnames; *xattrname != NULL; xattrname++) {
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if ((strlen(*xattrname) == namelen)
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&& (strncmp(req_xattr_name, *xattrname, namelen) == 0)) {
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found = 1;
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break;
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}
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if (strncmp(req_xattr_name,
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*xattrname + XATTR_SECURITY_PREFIX_LEN,
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strlen(req_xattr_name)) == 0) {
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found = 1;
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break;
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}
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}
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return found;
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}
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/**
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* evm_verifyxattr - verify the integrity of the requested xattr
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* @dentry: object of the verify xattr
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* @xattr_name: requested xattr
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* @xattr_value: requested xattr value
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* @xattr_value_len: requested xattr value length
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*
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* Calculate the HMAC for the given dentry and verify it against the stored
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* security.evm xattr. For performance, use the xattr value and length
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* previously retrieved to calculate the HMAC.
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*
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* Returns the xattr integrity status.
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*
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* This function requires the caller to lock the inode's i_mutex before it
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* is executed.
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*/
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enum integrity_status evm_verifyxattr(struct dentry *dentry,
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const char *xattr_name,
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void *xattr_value, size_t xattr_value_len,
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struct integrity_iint_cache *iint)
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{
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if (!evm_initialized || !evm_protected_xattr(xattr_name))
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return INTEGRITY_UNKNOWN;
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if (!iint) {
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iint = integrity_iint_find(dentry->d_inode);
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if (!iint)
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return INTEGRITY_UNKNOWN;
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}
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return evm_verify_hmac(dentry, xattr_name, xattr_value,
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xattr_value_len, iint);
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}
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EXPORT_SYMBOL_GPL(evm_verifyxattr);
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/*
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* evm_verify_current_integrity - verify the dentry's metadata integrity
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* @dentry: pointer to the affected dentry
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*
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* Verify and return the dentry's metadata integrity. The exceptions are
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* before EVM is initialized or in 'fix' mode.
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*/
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static enum integrity_status evm_verify_current_integrity(struct dentry *dentry)
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{
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struct inode *inode = dentry->d_inode;
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if (!evm_initialized || !S_ISREG(inode->i_mode) || evm_fixmode)
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return 0;
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return evm_verify_hmac(dentry, NULL, NULL, 0, NULL);
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}
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/*
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* evm_protect_xattr - protect the EVM extended attribute
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*
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* Prevent security.evm from being modified or removed without the
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* necessary permissions or when the existing value is invalid.
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*
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* The posix xattr acls are 'system' prefixed, which normally would not
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* affect security.evm. An interesting side affect of writing posix xattr
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* acls is their modifying of the i_mode, which is included in security.evm.
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* For posix xattr acls only, permit security.evm, even if it currently
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* doesn't exist, to be updated.
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*/
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static int evm_protect_xattr(struct dentry *dentry, const char *xattr_name,
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const void *xattr_value, size_t xattr_value_len)
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{
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enum integrity_status evm_status;
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if (strcmp(xattr_name, XATTR_NAME_EVM) == 0) {
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if (!capable(CAP_SYS_ADMIN))
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return -EPERM;
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} else if (!evm_protected_xattr(xattr_name)) {
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if (!posix_xattr_acl(xattr_name))
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return 0;
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evm_status = evm_verify_current_integrity(dentry);
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if ((evm_status == INTEGRITY_PASS) ||
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(evm_status == INTEGRITY_NOXATTRS))
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return 0;
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goto out;
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}
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evm_status = evm_verify_current_integrity(dentry);
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out:
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if (evm_status != INTEGRITY_PASS)
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integrity_audit_msg(AUDIT_INTEGRITY_METADATA, dentry->d_inode,
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dentry->d_name.name, "appraise_metadata",
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integrity_status_msg[evm_status],
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-EPERM, 0);
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return evm_status == INTEGRITY_PASS ? 0 : -EPERM;
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}
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/**
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* evm_inode_setxattr - protect the EVM extended attribute
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* @dentry: pointer to the affected dentry
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* @xattr_name: pointer to the affected extended attribute name
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* @xattr_value: pointer to the new extended attribute value
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* @xattr_value_len: pointer to the new extended attribute value length
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*
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* Updating 'security.evm' requires CAP_SYS_ADMIN privileges and that
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* the current value is valid.
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*/
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int evm_inode_setxattr(struct dentry *dentry, const char *xattr_name,
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const void *xattr_value, size_t xattr_value_len)
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{
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return evm_protect_xattr(dentry, xattr_name, xattr_value,
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xattr_value_len);
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}
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/**
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* evm_inode_removexattr - protect the EVM extended attribute
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* @dentry: pointer to the affected dentry
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* @xattr_name: pointer to the affected extended attribute name
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*
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* Removing 'security.evm' requires CAP_SYS_ADMIN privileges and that
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* the current value is valid.
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*/
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int evm_inode_removexattr(struct dentry *dentry, const char *xattr_name)
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{
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return evm_protect_xattr(dentry, xattr_name, NULL, 0);
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}
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/**
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* evm_inode_post_setxattr - update 'security.evm' to reflect the changes
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* @dentry: pointer to the affected dentry
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* @xattr_name: pointer to the affected extended attribute name
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* @xattr_value: pointer to the new extended attribute value
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* @xattr_value_len: pointer to the new extended attribute value length
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*
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* Update the HMAC stored in 'security.evm' to reflect the change.
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*
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* No need to take the i_mutex lock here, as this function is called from
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* __vfs_setxattr_noperm(). The caller of which has taken the inode's
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* i_mutex lock.
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*/
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void evm_inode_post_setxattr(struct dentry *dentry, const char *xattr_name,
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const void *xattr_value, size_t xattr_value_len)
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{
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if (!evm_initialized || (!evm_protected_xattr(xattr_name)
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&& !posix_xattr_acl(xattr_name)))
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return;
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evm_update_evmxattr(dentry, xattr_name, xattr_value, xattr_value_len);
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return;
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}
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/**
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* evm_inode_post_removexattr - update 'security.evm' after removing the xattr
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* @dentry: pointer to the affected dentry
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* @xattr_name: pointer to the affected extended attribute name
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*
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* Update the HMAC stored in 'security.evm' to reflect removal of the xattr.
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*/
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void evm_inode_post_removexattr(struct dentry *dentry, const char *xattr_name)
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{
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struct inode *inode = dentry->d_inode;
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if (!evm_initialized || !evm_protected_xattr(xattr_name))
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return;
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mutex_lock(&inode->i_mutex);
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evm_update_evmxattr(dentry, xattr_name, NULL, 0);
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mutex_unlock(&inode->i_mutex);
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return;
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}
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/**
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* evm_inode_setattr - prevent updating an invalid EVM extended attribute
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* @dentry: pointer to the affected dentry
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*/
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int evm_inode_setattr(struct dentry *dentry, struct iattr *attr)
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{
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unsigned int ia_valid = attr->ia_valid;
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enum integrity_status evm_status;
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if (!(ia_valid & (ATTR_MODE | ATTR_UID | ATTR_GID)))
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return 0;
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evm_status = evm_verify_current_integrity(dentry);
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if ((evm_status == INTEGRITY_PASS) ||
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(evm_status == INTEGRITY_NOXATTRS))
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return 0;
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integrity_audit_msg(AUDIT_INTEGRITY_METADATA, dentry->d_inode,
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dentry->d_name.name, "appraise_metadata",
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integrity_status_msg[evm_status], -EPERM, 0);
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return -EPERM;
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}
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/**
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* evm_inode_post_setattr - update 'security.evm' after modifying metadata
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* @dentry: pointer to the affected dentry
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* @ia_valid: for the UID and GID status
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*
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* For now, update the HMAC stored in 'security.evm' to reflect UID/GID
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* changes.
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*
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* This function is called from notify_change(), which expects the caller
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* to lock the inode's i_mutex.
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*/
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void evm_inode_post_setattr(struct dentry *dentry, int ia_valid)
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{
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if (!evm_initialized)
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return;
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if (ia_valid & (ATTR_MODE | ATTR_UID | ATTR_GID))
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evm_update_evmxattr(dentry, NULL, NULL, 0);
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return;
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}
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/*
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* evm_inode_init_security - initializes security.evm
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*/
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int evm_inode_init_security(struct inode *inode,
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const struct xattr *lsm_xattr,
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struct xattr *evm_xattr)
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{
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struct evm_ima_xattr_data *xattr_data;
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int rc;
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if (!evm_initialized || !evm_protected_xattr(lsm_xattr->name))
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return 0;
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xattr_data = kzalloc(sizeof(*xattr_data), GFP_NOFS);
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if (!xattr_data)
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return -ENOMEM;
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xattr_data->type = EVM_XATTR_HMAC;
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rc = evm_init_hmac(inode, lsm_xattr, xattr_data->digest);
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if (rc < 0)
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goto out;
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evm_xattr->value = xattr_data;
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evm_xattr->value_len = sizeof(*xattr_data);
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evm_xattr->name = XATTR_EVM_SUFFIX;
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return 0;
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out:
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kfree(xattr_data);
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return rc;
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}
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EXPORT_SYMBOL_GPL(evm_inode_init_security);
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static int __init init_evm(void)
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{
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int error;
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error = evm_init_secfs();
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if (error < 0) {
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pr_info("Error registering secfs\n");
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goto err;
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}
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return 0;
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err:
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return error;
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}
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/*
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* evm_display_config - list the EVM protected security extended attributes
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*/
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static int __init evm_display_config(void)
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{
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char **xattrname;
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for (xattrname = evm_config_xattrnames; *xattrname != NULL; xattrname++)
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pr_info("%s\n", *xattrname);
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return 0;
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}
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pure_initcall(evm_display_config);
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late_initcall(init_evm);
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MODULE_DESCRIPTION("Extended Verification Module");
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MODULE_LICENSE("GPL");
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