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![Dmitry Kasatkin](/assets/img/avatar_default.png)
EVM uses the same key for all file systems to calculate the HMAC, making it possible to paste inodes from one file system on to another one, without EVM being able to detect it. To prevent such an attack, it is necessary to make the EVM HMAC file system specific. This patch uses the file system UUID, a file system unique identifier, to bind the EVM HMAC to the file system. The value inode->i_sb->s_uuid is used for the HMAC hash calculation, instead of using it for deriving the file system specific key. Initializing the key for every inode HMAC calculation is a bit more expensive operation than adding the uuid to the HMAC hash. Changing the HMAC calculation method or adding additional info to the calculation, requires existing EVM labeled file systems to be relabeled. This patch adds a Kconfig HMAC version option for backwards compatability. Changelog v1: - squash "hmac version setting" Changelog v0: - add missing Kconfig depends (Mimi) Signed-off-by: Dmitry Kasatkin <dmitry.kasatkin@intel.com> Signed-off-by: Mimi Zohar <zohar@linux.vnet.ibm.com>
447 lines
12 KiB
C
447 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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#include <linux/module.h>
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#include <linux/crypto.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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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 || !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 - 1;
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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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xattr_data->digest, 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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return -EPERM;
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}
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evm_status = evm_verify_current_integrity(dentry);
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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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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 = kstrdup(XATTR_EVM_SUFFIX, GFP_NOFS);
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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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printk(KERN_INFO "EVM: 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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printk(KERN_INFO "EVM: %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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