325 lines
7.2 KiB
C
325 lines
7.2 KiB
C
// SPDX-License-Identifier: GPL-2.0-only
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/*
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* Copyright (C) 2010 IBM Corporation
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*
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* Authors:
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* Mimi Zohar <zohar@us.ibm.com>
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*
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* File: evm_secfs.c
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* - Used to signal when key is on keyring
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* - Get the key and enable EVM
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*/
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#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
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#include <linux/audit.h>
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#include <linux/uaccess.h>
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#include <linux/init.h>
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#include <linux/mutex.h>
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#include "evm.h"
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static struct dentry *evm_dir;
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static struct dentry *evm_init_tpm;
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static struct dentry *evm_symlink;
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#ifdef CONFIG_EVM_ADD_XATTRS
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static struct dentry *evm_xattrs;
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static DEFINE_MUTEX(xattr_list_mutex);
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static int evm_xattrs_locked;
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#endif
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/**
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* evm_read_key - read() for <securityfs>/evm
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*
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* @filp: file pointer, not actually used
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* @buf: where to put the result
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* @count: maximum to send along
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* @ppos: where to start
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*
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* Returns number of bytes read or error code, as appropriate
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*/
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static ssize_t evm_read_key(struct file *filp, char __user *buf,
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size_t count, loff_t *ppos)
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{
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char temp[80];
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ssize_t rc;
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if (*ppos != 0)
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return 0;
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sprintf(temp, "%d", (evm_initialized & ~EVM_SETUP_COMPLETE));
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rc = simple_read_from_buffer(buf, count, ppos, temp, strlen(temp));
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return rc;
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}
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/**
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* evm_write_key - write() for <securityfs>/evm
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* @file: file pointer, not actually used
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* @buf: where to get the data from
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* @count: bytes sent
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* @ppos: where to start
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*
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* Used to signal that key is on the kernel key ring.
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* - get the integrity hmac key from the kernel key ring
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* - create list of hmac protected extended attributes
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* Returns number of bytes written or error code, as appropriate
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*/
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static ssize_t evm_write_key(struct file *file, const char __user *buf,
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size_t count, loff_t *ppos)
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{
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unsigned int i;
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int ret;
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if (!capable(CAP_SYS_ADMIN) || (evm_initialized & EVM_SETUP_COMPLETE))
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return -EPERM;
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ret = kstrtouint_from_user(buf, count, 0, &i);
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if (ret)
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return ret;
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/* Reject invalid values */
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if (!i || (i & ~EVM_INIT_MASK) != 0)
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return -EINVAL;
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/*
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* Don't allow a request to enable metadata writes if
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* an HMAC key is loaded.
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*/
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if ((i & EVM_ALLOW_METADATA_WRITES) &&
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(evm_initialized & EVM_INIT_HMAC) != 0)
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return -EPERM;
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if (i & EVM_INIT_HMAC) {
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ret = evm_init_key();
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if (ret != 0)
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return ret;
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/* Forbid further writes after the symmetric key is loaded */
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i |= EVM_SETUP_COMPLETE;
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}
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evm_initialized |= i;
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/* Don't allow protected metadata modification if a symmetric key
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* is loaded
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*/
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if (evm_initialized & EVM_INIT_HMAC)
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evm_initialized &= ~(EVM_ALLOW_METADATA_WRITES);
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return count;
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}
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static const struct file_operations evm_key_ops = {
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.read = evm_read_key,
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.write = evm_write_key,
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};
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#ifdef CONFIG_EVM_ADD_XATTRS
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/**
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* evm_read_xattrs - read() for <securityfs>/evm_xattrs
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*
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* @filp: file pointer, not actually used
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* @buf: where to put the result
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* @count: maximum to send along
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* @ppos: where to start
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*
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* Returns number of bytes read or error code, as appropriate
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*/
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static ssize_t evm_read_xattrs(struct file *filp, char __user *buf,
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size_t count, loff_t *ppos)
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{
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char *temp;
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int offset = 0;
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ssize_t rc, size = 0;
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struct xattr_list *xattr;
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if (*ppos != 0)
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return 0;
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rc = mutex_lock_interruptible(&xattr_list_mutex);
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if (rc)
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return -ERESTARTSYS;
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list_for_each_entry(xattr, &evm_config_xattrnames, list)
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size += strlen(xattr->name) + 1;
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temp = kmalloc(size + 1, GFP_KERNEL);
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if (!temp) {
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mutex_unlock(&xattr_list_mutex);
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return -ENOMEM;
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}
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list_for_each_entry(xattr, &evm_config_xattrnames, list) {
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sprintf(temp + offset, "%s\n", xattr->name);
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offset += strlen(xattr->name) + 1;
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}
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mutex_unlock(&xattr_list_mutex);
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rc = simple_read_from_buffer(buf, count, ppos, temp, strlen(temp));
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kfree(temp);
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return rc;
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}
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/**
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* evm_write_xattrs - write() for <securityfs>/evm_xattrs
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* @file: file pointer, not actually used
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* @buf: where to get the data from
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* @count: bytes sent
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* @ppos: where to start
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*
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* Returns number of bytes written or error code, as appropriate
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*/
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static ssize_t evm_write_xattrs(struct file *file, const char __user *buf,
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size_t count, loff_t *ppos)
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{
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int len, err;
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struct xattr_list *xattr, *tmp;
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struct audit_buffer *ab;
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struct iattr newattrs;
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struct inode *inode;
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if (!capable(CAP_SYS_ADMIN) || evm_xattrs_locked)
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return -EPERM;
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if (*ppos != 0)
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return -EINVAL;
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if (count > XATTR_NAME_MAX)
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return -E2BIG;
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ab = audit_log_start(audit_context(), GFP_KERNEL,
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AUDIT_INTEGRITY_EVM_XATTR);
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if (!ab)
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return -ENOMEM;
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xattr = kmalloc(sizeof(struct xattr_list), GFP_KERNEL);
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if (!xattr) {
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err = -ENOMEM;
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goto out;
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}
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xattr->name = memdup_user_nul(buf, count);
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if (IS_ERR(xattr->name)) {
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err = PTR_ERR(xattr->name);
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xattr->name = NULL;
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goto out;
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}
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/* Remove any trailing newline */
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len = strlen(xattr->name);
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if (len && xattr->name[len-1] == '\n')
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xattr->name[len-1] = '\0';
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audit_log_format(ab, "xattr=");
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audit_log_untrustedstring(ab, xattr->name);
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if (strcmp(xattr->name, ".") == 0) {
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evm_xattrs_locked = 1;
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newattrs.ia_mode = S_IFREG | 0440;
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newattrs.ia_valid = ATTR_MODE;
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inode = evm_xattrs->d_inode;
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inode_lock(inode);
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err = simple_setattr(evm_xattrs, &newattrs);
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inode_unlock(inode);
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if (!err)
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err = count;
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goto out;
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}
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if (strncmp(xattr->name, XATTR_SECURITY_PREFIX,
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XATTR_SECURITY_PREFIX_LEN) != 0) {
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err = -EINVAL;
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goto out;
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}
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/*
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* xattr_list_mutex guards against races in evm_read_xattrs().
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* Entries are only added to the evm_config_xattrnames list
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* and never deleted. Therefore, the list is traversed
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* using list_for_each_entry_lockless() without holding
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* the mutex in evm_calc_hmac_or_hash(), evm_find_protected_xattrs()
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* and evm_protected_xattr().
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*/
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mutex_lock(&xattr_list_mutex);
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list_for_each_entry(tmp, &evm_config_xattrnames, list) {
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if (strcmp(xattr->name, tmp->name) == 0) {
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err = -EEXIST;
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mutex_unlock(&xattr_list_mutex);
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goto out;
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}
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}
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list_add_tail_rcu(&xattr->list, &evm_config_xattrnames);
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mutex_unlock(&xattr_list_mutex);
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audit_log_format(ab, " res=0");
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audit_log_end(ab);
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return count;
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out:
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audit_log_format(ab, " res=%d", err);
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audit_log_end(ab);
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if (xattr) {
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kfree(xattr->name);
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kfree(xattr);
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}
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return err;
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}
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static const struct file_operations evm_xattr_ops = {
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.read = evm_read_xattrs,
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.write = evm_write_xattrs,
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};
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static int evm_init_xattrs(void)
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{
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evm_xattrs = securityfs_create_file("evm_xattrs", 0660, evm_dir, NULL,
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&evm_xattr_ops);
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if (!evm_xattrs || IS_ERR(evm_xattrs))
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return -EFAULT;
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return 0;
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}
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#else
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static int evm_init_xattrs(void)
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{
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return 0;
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}
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#endif
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int __init evm_init_secfs(void)
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{
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int error = 0;
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evm_dir = securityfs_create_dir("evm", integrity_dir);
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if (!evm_dir || IS_ERR(evm_dir))
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return -EFAULT;
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evm_init_tpm = securityfs_create_file("evm", 0660,
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evm_dir, NULL, &evm_key_ops);
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if (!evm_init_tpm || IS_ERR(evm_init_tpm)) {
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error = -EFAULT;
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goto out;
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}
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evm_symlink = securityfs_create_symlink("evm", NULL,
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"integrity/evm/evm", NULL);
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if (!evm_symlink || IS_ERR(evm_symlink)) {
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error = -EFAULT;
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goto out;
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}
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if (evm_init_xattrs() != 0) {
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error = -EFAULT;
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goto out;
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}
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return 0;
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out:
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securityfs_remove(evm_symlink);
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securityfs_remove(evm_init_tpm);
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securityfs_remove(evm_dir);
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return error;
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}
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