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0c7774abb4
Special kernel keys, such as those used to hold DNS results for AFS, CIFS and
NFS and those used to hold idmapper results for NFS, used to be
'invalidateable' with key_revoke(). However, since the default permissions for
keys were reduced:
Commit: 96b5c8fea6
KEYS: Reduce initial permissions on keys
it has become impossible to do this.
Add a key flag (KEY_FLAG_ROOT_CAN_INVAL) that will permit a key to be
invalidated by root. This should not be used for system keyrings as the
garbage collector will try and remove any invalidate key. For system keyrings,
KEY_FLAG_ROOT_CAN_CLEAR can be used instead.
After this, from userspace, keyctl_invalidate() and "keyctl invalidate" can be
used by any possessor of CAP_SYS_ADMIN (typically root) to invalidate DNS and
idmapper keys. Invalidated keys are immediately garbage collected and will be
immediately rerequested if needed again.
Signed-off-by: David Howells <dhowells@redhat.com>
Tested-by: Steve Dickson <steved@redhat.com>
168 lines
4.6 KiB
C
168 lines
4.6 KiB
C
/* Upcall routine, designed to work as a key type and working through
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* /sbin/request-key to contact userspace when handling DNS queries.
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*
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* See Documentation/networking/dns_resolver.txt
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*
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* Copyright (c) 2007 Igor Mammedov
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* Author(s): Igor Mammedov (niallain@gmail.com)
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* Steve French (sfrench@us.ibm.com)
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* Wang Lei (wang840925@gmail.com)
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* David Howells (dhowells@redhat.com)
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*
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* The upcall wrapper used to make an arbitrary DNS query.
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*
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* This function requires the appropriate userspace tool dns.upcall to be
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* installed and something like the following lines should be added to the
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* /etc/request-key.conf file:
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*
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* create dns_resolver * * /sbin/dns.upcall %k
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*
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* For example to use this module to query AFSDB RR:
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*
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* create dns_resolver afsdb:* * /sbin/dns.afsdb %k
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*
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* This library is free software; you can redistribute it and/or modify
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* it under the terms of the GNU Lesser General Public License as published
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* by the Free Software Foundation; either version 2.1 of the License, or
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* (at your option) any later version.
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*
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* This library is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See
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* the GNU Lesser General Public License for more details.
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*
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* You should have received a copy of the GNU Lesser General Public License
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* along with this library; if not, see <http://www.gnu.org/licenses/>.
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*/
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#include <linux/module.h>
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#include <linux/slab.h>
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#include <linux/dns_resolver.h>
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#include <linux/err.h>
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#include <keys/dns_resolver-type.h>
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#include <keys/user-type.h>
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#include "internal.h"
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/**
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* dns_query - Query the DNS
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* @type: Query type (or NULL for straight host->IP lookup)
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* @name: Name to look up
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* @namelen: Length of name
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* @options: Request options (or NULL if no options)
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* @_result: Where to place the returned data.
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* @_expiry: Where to store the result expiry time (or NULL)
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*
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* The data will be returned in the pointer at *result, and the caller is
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* responsible for freeing it.
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*
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* The description should be of the form "[<query_type>:]<domain_name>", and
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* the options need to be appropriate for the query type requested. If no
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* query_type is given, then the query is a straight hostname to IP address
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* lookup.
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*
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* The DNS resolution lookup is performed by upcalling to userspace by way of
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* requesting a key of type dns_resolver.
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*
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* Returns the size of the result on success, -ve error code otherwise.
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*/
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int dns_query(const char *type, const char *name, size_t namelen,
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const char *options, char **_result, time_t *_expiry)
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{
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struct key *rkey;
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struct user_key_payload *upayload;
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const struct cred *saved_cred;
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size_t typelen, desclen;
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char *desc, *cp;
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int ret, len;
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kenter("%s,%*.*s,%zu,%s",
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type, (int)namelen, (int)namelen, name, namelen, options);
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if (!name || namelen == 0 || !_result)
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return -EINVAL;
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/* construct the query key description as "[<type>:]<name>" */
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typelen = 0;
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desclen = 0;
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if (type) {
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typelen = strlen(type);
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if (typelen < 1)
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return -EINVAL;
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desclen += typelen + 1;
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}
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if (!namelen)
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namelen = strnlen(name, 256);
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if (namelen < 3 || namelen > 255)
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return -EINVAL;
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desclen += namelen + 1;
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desc = kmalloc(desclen, GFP_KERNEL);
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if (!desc)
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return -ENOMEM;
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cp = desc;
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if (type) {
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memcpy(cp, type, typelen);
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cp += typelen;
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*cp++ = ':';
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}
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memcpy(cp, name, namelen);
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cp += namelen;
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*cp = '\0';
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if (!options)
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options = "";
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kdebug("call request_key(,%s,%s)", desc, options);
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/* make the upcall, using special credentials to prevent the use of
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* add_key() to preinstall malicious redirections
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*/
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saved_cred = override_creds(dns_resolver_cache);
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rkey = request_key(&key_type_dns_resolver, desc, options);
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revert_creds(saved_cred);
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kfree(desc);
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if (IS_ERR(rkey)) {
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ret = PTR_ERR(rkey);
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goto out;
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}
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down_read(&rkey->sem);
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set_bit(KEY_FLAG_ROOT_CAN_INVAL, &rkey->flags);
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rkey->perm |= KEY_USR_VIEW;
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ret = key_validate(rkey);
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if (ret < 0)
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goto put;
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/* If the DNS server gave an error, return that to the caller */
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ret = rkey->type_data.x[0];
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if (ret)
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goto put;
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upayload = rcu_dereference_protected(rkey->payload.data,
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lockdep_is_held(&rkey->sem));
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len = upayload->datalen;
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ret = -ENOMEM;
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*_result = kmalloc(len + 1, GFP_KERNEL);
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if (!*_result)
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goto put;
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memcpy(*_result, upayload->data, len);
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*_result[len] = '\0';
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if (_expiry)
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*_expiry = rkey->expiry;
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ret = len;
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put:
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up_read(&rkey->sem);
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key_put(rkey);
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out:
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kleave(" = %d", ret);
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return ret;
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}
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EXPORT_SYMBOL(dns_query);
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