security/integrity/evm/evm_secfs.c

   1 // SPDX-License-Identifier: GPL-2.0-only
   2 /*
   3  * Copyright (C) 2010 IBM Corporation
   4  *
   5  * Authors:
   6  * Mimi Zohar <zohar@us.ibm.com>
   7  *
   8  * File: evm_secfs.c
   9  *      - Used to signal when key is on keyring
  10  *      - Get the key and enable EVM
  11  */
  12
  13 #include <linux/audit.h>
  14 #include <linux/uaccess.h>
  15 #include <linux/init.h>
  16 #include <linux/mutex.h>
  17 #include "evm.h"
  18
  19 static struct dentry *evm_dir;
  20 static struct dentry *evm_init_tpm;
  21 static struct dentry *evm_symlink;
  22
  23 #ifdef CONFIG_EVM_ADD_XATTRS
  24 static struct dentry *evm_xattrs;
  25 static DEFINE_MUTEX(xattr_list_mutex);
  26 static int evm_xattrs_locked;
  27 #endif
  28
  29 /**
  30  * evm_read_key - read() for <securityfs>/evm
  31  *
  32  * @filp: file pointer, not actually used
  33  * @buf: where to put the result
  34  * @count: maximum to send along
  35  * @ppos: where to start
  36  *
  37  * Returns number of bytes read or error code, as appropriate
  38  */
  39 static ssize_t evm_read_key(struct file *filp, char __user *buf,
  40                             size_t count, loff_t *ppos)
  41 {
  42         char temp[80];
  43         ssize_t rc;
  44
  45         if (*ppos != 0)
  46                 return 0;
  47
  48         sprintf(temp, "%d", (evm_initialized & ~EVM_SETUP_COMPLETE));
  49         rc = simple_read_from_buffer(buf, count, ppos, temp, strlen(temp));
  50
  51         return rc;
  52 }
  53
  54 /**
  55  * evm_write_key - write() for <securityfs>/evm
  56  * @file: file pointer, not actually used
  57  * @buf: where to get the data from
  58  * @count: bytes sent
  59  * @ppos: where to start
  60  *
  61  * Used to signal that key is on the kernel key ring.
  62  * - get the integrity hmac key from the kernel key ring
  63  * - create list of hmac protected extended attributes
  64  * Returns number of bytes written or error code, as appropriate
  65  */
  66 static ssize_t evm_write_key(struct file *file, const char __user *buf,
  67                              size_t count, loff_t *ppos)
  68 {
  69         int i, ret;
  70
  71         if (!capable(CAP_SYS_ADMIN) || (evm_initialized & EVM_SETUP_COMPLETE))
  72                 return -EPERM;
  73
  74         ret = kstrtoint_from_user(buf, count, 0, &i);
  75
  76         if (ret)
  77                 return ret;
  78
  79         /* Reject invalid values */
  80         if (!i || (i & ~EVM_INIT_MASK) != 0)
  81                 return -EINVAL;
  82
  83         /* Don't allow a request to freshly enable metadata writes if
  84          * keys are loaded.
  85          */
  86         if ((i & EVM_ALLOW_METADATA_WRITES) &&
  87             ((evm_initialized & EVM_KEY_MASK) != 0) &&
  88             !(evm_initialized & EVM_ALLOW_METADATA_WRITES))
  89                 return -EPERM;
  90
  91         if (i & EVM_INIT_HMAC) {
  92                 ret = evm_init_key();
  93                 if (ret != 0)
  94                         return ret;
  95                 /* Forbid further writes after the symmetric key is loaded */
  96                 i |= EVM_SETUP_COMPLETE;
  97         }
  98
  99         evm_initialized |= i;
 100
 101         /* Don't allow protected metadata modification if a symmetric key
 102          * is loaded
 103          */
 104         if (evm_initialized & EVM_INIT_HMAC)
 105                 evm_initialized &= ~(EVM_ALLOW_METADATA_WRITES);
 106
 107         return count;
 108 }
 109
 110 static const struct file_operations evm_key_ops = {
 111         .read           = evm_read_key,
 112         .write          = evm_write_key,
 113 };
 114
 115 #ifdef CONFIG_EVM_ADD_XATTRS
 116 /**
 117  * evm_read_xattrs - read() for <securityfs>/evm_xattrs
 118  *
 119  * @filp: file pointer, not actually used
 120  * @buf: where to put the result
 121  * @count: maximum to send along
 122  * @ppos: where to start
 123  *
 124  * Returns number of bytes read or error code, as appropriate
 125  */
 126 static ssize_t evm_read_xattrs(struct file *filp, char __user *buf,
 127                                size_t count, loff_t *ppos)
 128 {
 129         char *temp;
 130         int offset = 0;
 131         ssize_t rc, size = 0;
 132         struct xattr_list *xattr;
 133
 134         if (*ppos != 0)
 135                 return 0;
 136
 137         rc = mutex_lock_interruptible(&xattr_list_mutex);
 138         if (rc)
 139                 return -ERESTARTSYS;
 140
 141         list_for_each_entry(xattr, &evm_config_xattrnames, list)
 142                 size += strlen(xattr->name) + 1;
 143
 144         temp = kmalloc(size + 1, GFP_KERNEL);
 145         if (!temp) {
 146                 mutex_unlock(&xattr_list_mutex);
 147                 return -ENOMEM;
 148         }
 149
 150         list_for_each_entry(xattr, &evm_config_xattrnames, list) {
 151                 sprintf(temp + offset, "%s\n", xattr->name);
 152                 offset += strlen(xattr->name) + 1;
 153         }
 154
 155         mutex_unlock(&xattr_list_mutex);
 156         rc = simple_read_from_buffer(buf, count, ppos, temp, strlen(temp));
 157
 158         kfree(temp);
 159
 160         return rc;
 161 }
 162
 163 /**
 164  * evm_write_xattrs - write() for <securityfs>/evm_xattrs
 165  * @file: file pointer, not actually used
 166  * @buf: where to get the data from
 167  * @count: bytes sent
 168  * @ppos: where to start
 169  *
 170  * Returns number of bytes written or error code, as appropriate
 171  */
 172 static ssize_t evm_write_xattrs(struct file *file, const char __user *buf,
 173                                 size_t count, loff_t *ppos)
 174 {
 175         int len, err;
 176         struct xattr_list *xattr, *tmp;
 177         struct audit_buffer *ab;
 178         struct iattr newattrs;
 179         struct inode *inode;
 180
 181         if (!capable(CAP_SYS_ADMIN) || evm_xattrs_locked)
 182                 return -EPERM;
 183
 184         if (*ppos != 0)
 185                 return -EINVAL;
 186
 187         if (count > XATTR_NAME_MAX)
 188                 return -E2BIG;
 189
 190         ab = audit_log_start(audit_context(), GFP_KERNEL,
 191                              AUDIT_INTEGRITY_EVM_XATTR);
 192         if (!ab)
 193                 return -ENOMEM;
 194
 195         xattr = kmalloc(sizeof(struct xattr_list), GFP_KERNEL);
 196         if (!xattr) {
 197                 err = -ENOMEM;
 198                 goto out;
 199         }
 200
 201         xattr->name = memdup_user_nul(buf, count);
 202         if (IS_ERR(xattr->name)) {
 203                 err = PTR_ERR(xattr->name);
 204                 xattr->name = NULL;
 205                 goto out;
 206         }
 207
 208         /* Remove any trailing newline */
 209         len = strlen(xattr->name);
 210         if (len && xattr->name[len-1] == '\n')
 211                 xattr->name[len-1] = '\0';
 212
 213         audit_log_format(ab, "xattr=");
 214         audit_log_untrustedstring(ab, xattr->name);
 215
 216         if (strcmp(xattr->name, ".") == 0) {
 217                 evm_xattrs_locked = 1;
 218                 newattrs.ia_mode = S_IFREG | 0440;
 219                 newattrs.ia_valid = ATTR_MODE;
 220                 inode = evm_xattrs->d_inode;
 221                 inode_lock(inode);
 222                 err = simple_setattr(evm_xattrs, &newattrs);
 223                 inode_unlock(inode);
 224                 if (!err)
 225                         err = count;
 226                 goto out;
 227         }
 228
 229         if (strncmp(xattr->name, XATTR_SECURITY_PREFIX,
 230                     XATTR_SECURITY_PREFIX_LEN) != 0) {
 231                 err = -EINVAL;
 232                 goto out;
 233         }
 234
 235         /*
 236          * xattr_list_mutex guards against races in evm_read_xattrs().
 237          * Entries are only added to the evm_config_xattrnames list
 238          * and never deleted. Therefore, the list is traversed
 239          * using list_for_each_entry_lockless() without holding
 240          * the mutex in evm_calc_hmac_or_hash(), evm_find_protected_xattrs()
 241          * and evm_protected_xattr().
 242          */
 243         mutex_lock(&xattr_list_mutex);
 244         list_for_each_entry(tmp, &evm_config_xattrnames, list) {
 245                 if (strcmp(xattr->name, tmp->name) == 0) {
 246                         err = -EEXIST;
 247                         mutex_unlock(&xattr_list_mutex);
 248                         goto out;
 249                 }
 250         }
 251         list_add_tail_rcu(&xattr->list, &evm_config_xattrnames);
 252         mutex_unlock(&xattr_list_mutex);
 253
 254         audit_log_format(ab, " res=0");
 255         audit_log_end(ab);
 256         return count;
 257 out:
 258         audit_log_format(ab, " res=%d", err);
 259         audit_log_end(ab);
 260         if (xattr) {
 261                 kfree(xattr->name);
 262                 kfree(xattr);
 263         }
 264         return err;
 265 }
 266
 267 static const struct file_operations evm_xattr_ops = {
 268         .read           = evm_read_xattrs,
 269         .write          = evm_write_xattrs,
 270 };
 271
 272 static int evm_init_xattrs(void)
 273 {
 274         evm_xattrs = securityfs_create_file("evm_xattrs", 0660, evm_dir, NULL,
 275                                             &evm_xattr_ops);
 276         if (!evm_xattrs || IS_ERR(evm_xattrs))
 277                 return -EFAULT;
 278
 279         return 0;
 280 }
 281 #else
 282 static int evm_init_xattrs(void)
 283 {
 284         return 0;
 285 }
 286 #endif
 287
 288 int __init evm_init_secfs(void)
 289 {
 290         int error = 0;
 291
 292         evm_dir = securityfs_create_dir("evm", integrity_dir);
 293         if (!evm_dir || IS_ERR(evm_dir))
 294                 return -EFAULT;
 295
 296         evm_init_tpm = securityfs_create_file("evm", 0660,
 297                                               evm_dir, NULL, &evm_key_ops);
 298         if (!evm_init_tpm || IS_ERR(evm_init_tpm)) {
 299                 error = -EFAULT;
 300                 goto out;
 301         }
 302
 303         evm_symlink = securityfs_create_symlink("evm", NULL,
 304                                                 "integrity/evm/evm", NULL);
 305         if (!evm_symlink || IS_ERR(evm_symlink)) {
 306                 error = -EFAULT;
 307                 goto out;
 308         }
 309
 310         if (evm_init_xattrs() != 0) {
 311                 error = -EFAULT;
 312                 goto out;
 313         }
 314
 315         return 0;
 316 out:
 317         securityfs_remove(evm_symlink);
 318         securityfs_remove(evm_init_tpm);
 319         securityfs_remove(evm_dir);
 320         return error;
 321 }