linux/net/dns_resolver/dns_key.c
David Howells 5ac7eace2d KEYS: Add a facility to restrict new links into a keyring
Add a facility whereby proposed new links to be added to a keyring can be
vetted, permitting them to be rejected if necessary.  This can be used to
block public keys from which the signature cannot be verified or for which
the signature verification fails.  It could also be used to provide
blacklisting.

This affects operations like add_key(), KEYCTL_LINK and KEYCTL_INSTANTIATE.

To this end:

 (1) A function pointer is added to the key struct that, if set, points to
     the vetting function.  This is called as:

	int (*restrict_link)(struct key *keyring,
			     const struct key_type *key_type,
			     unsigned long key_flags,
			     const union key_payload *key_payload),

     where 'keyring' will be the keyring being added to, key_type and
     key_payload will describe the key being added and key_flags[*] can be
     AND'ed with KEY_FLAG_TRUSTED.

     [*] This parameter will be removed in a later patch when
     	 KEY_FLAG_TRUSTED is removed.

     The function should return 0 to allow the link to take place or an
     error (typically -ENOKEY, -ENOPKG or -EKEYREJECTED) to reject the
     link.

     The pointer should not be set directly, but rather should be set
     through keyring_alloc().

     Note that if called during add_key(), preparse is called before this
     method, but a key isn't actually allocated until after this function
     is called.

 (2) KEY_ALLOC_BYPASS_RESTRICTION is added.  This can be passed to
     key_create_or_update() or key_instantiate_and_link() to bypass the
     restriction check.

 (3) KEY_FLAG_TRUSTED_ONLY is removed.  The entire contents of a keyring
     with this restriction emplaced can be considered 'trustworthy' by
     virtue of being in the keyring when that keyring is consulted.

 (4) key_alloc() and keyring_alloc() take an extra argument that will be
     used to set restrict_link in the new key.  This ensures that the
     pointer is set before the key is published, thus preventing a window
     of unrestrictedness.  Normally this argument will be NULL.

 (5) As a temporary affair, keyring_restrict_trusted_only() is added.  It
     should be passed to keyring_alloc() as the extra argument instead of
     setting KEY_FLAG_TRUSTED_ONLY on a keyring.  This will be replaced in
     a later patch with functions that look in the appropriate places for
     authoritative keys.

Signed-off-by: David Howells <dhowells@redhat.com>
Reviewed-by: Mimi Zohar <zohar@linux.vnet.ibm.com>
2016-04-11 22:37:37 +01:00

322 lines
8.1 KiB
C

/* Key type used to cache DNS lookups made by the kernel
*
* See Documentation/networking/dns_resolver.txt
*
* Copyright (c) 2007 Igor Mammedov
* Author(s): Igor Mammedov (niallain@gmail.com)
* Steve French (sfrench@us.ibm.com)
* Wang Lei (wang840925@gmail.com)
* David Howells (dhowells@redhat.com)
*
* This library is free software; you can redistribute it and/or modify
* it under the terms of the GNU Lesser General Public License as published
* by the Free Software Foundation; either version 2.1 of the License, or
* (at your option) any later version.
*
* This library is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See
* the GNU Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public License
* along with this library; if not, see <http://www.gnu.org/licenses/>.
*/
#include <linux/module.h>
#include <linux/moduleparam.h>
#include <linux/slab.h>
#include <linux/string.h>
#include <linux/kernel.h>
#include <linux/keyctl.h>
#include <linux/err.h>
#include <linux/seq_file.h>
#include <keys/dns_resolver-type.h>
#include <keys/user-type.h>
#include "internal.h"
MODULE_DESCRIPTION("DNS Resolver");
MODULE_AUTHOR("Wang Lei");
MODULE_LICENSE("GPL");
unsigned int dns_resolver_debug;
module_param_named(debug, dns_resolver_debug, uint, S_IWUSR | S_IRUGO);
MODULE_PARM_DESC(debug, "DNS Resolver debugging mask");
const struct cred *dns_resolver_cache;
#define DNS_ERRORNO_OPTION "dnserror"
/*
* Preparse instantiation data for a dns_resolver key.
*
* The data must be a NUL-terminated string, with the NUL char accounted in
* datalen.
*
* If the data contains a '#' characters, then we take the clause after each
* one to be an option of the form 'key=value'. The actual data of interest is
* the string leading up to the first '#'. For instance:
*
* "ip1,ip2,...#foo=bar"
*/
static int
dns_resolver_preparse(struct key_preparsed_payload *prep)
{
struct user_key_payload *upayload;
unsigned long derrno;
int ret;
int datalen = prep->datalen, result_len = 0;
const char *data = prep->data, *end, *opt;
kenter("'%*.*s',%u", datalen, datalen, data, datalen);
if (datalen <= 1 || !data || data[datalen - 1] != '\0')
return -EINVAL;
datalen--;
/* deal with any options embedded in the data */
end = data + datalen;
opt = memchr(data, '#', datalen);
if (!opt) {
/* no options: the entire data is the result */
kdebug("no options");
result_len = datalen;
} else {
const char *next_opt;
result_len = opt - data;
opt++;
kdebug("options: '%s'", opt);
do {
const char *eq;
int opt_len, opt_nlen, opt_vlen, tmp;
next_opt = memchr(opt, '#', end - opt) ?: end;
opt_len = next_opt - opt;
if (!opt_len) {
printk(KERN_WARNING
"Empty option to dns_resolver key\n");
return -EINVAL;
}
eq = memchr(opt, '=', opt_len) ?: end;
opt_nlen = eq - opt;
eq++;
opt_vlen = next_opt - eq; /* will be -1 if no value */
tmp = opt_vlen >= 0 ? opt_vlen : 0;
kdebug("option '%*.*s' val '%*.*s'",
opt_nlen, opt_nlen, opt, tmp, tmp, eq);
/* see if it's an error number representing a DNS error
* that's to be recorded as the result in this key */
if (opt_nlen == sizeof(DNS_ERRORNO_OPTION) - 1 &&
memcmp(opt, DNS_ERRORNO_OPTION, opt_nlen) == 0) {
kdebug("dns error number option");
if (opt_vlen <= 0)
goto bad_option_value;
ret = kstrtoul(eq, 10, &derrno);
if (ret < 0)
goto bad_option_value;
if (derrno < 1 || derrno > 511)
goto bad_option_value;
kdebug("dns error no. = %lu", derrno);
prep->payload.data[dns_key_error] = ERR_PTR(-derrno);
continue;
}
bad_option_value:
printk(KERN_WARNING
"Option '%*.*s' to dns_resolver key:"
" bad/missing value\n",
opt_nlen, opt_nlen, opt);
return -EINVAL;
} while (opt = next_opt + 1, opt < end);
}
/* don't cache the result if we're caching an error saying there's no
* result */
if (prep->payload.data[dns_key_error]) {
kleave(" = 0 [h_error %ld]", PTR_ERR(prep->payload.data[dns_key_error]));
return 0;
}
kdebug("store result");
prep->quotalen = result_len;
upayload = kmalloc(sizeof(*upayload) + result_len + 1, GFP_KERNEL);
if (!upayload) {
kleave(" = -ENOMEM");
return -ENOMEM;
}
upayload->datalen = result_len;
memcpy(upayload->data, data, result_len);
upayload->data[result_len] = '\0';
prep->payload.data[dns_key_data] = upayload;
kleave(" = 0");
return 0;
}
/*
* Clean up the preparse data
*/
static void dns_resolver_free_preparse(struct key_preparsed_payload *prep)
{
pr_devel("==>%s()\n", __func__);
kfree(prep->payload.data[dns_key_data]);
}
/*
* The description is of the form "[<type>:]<domain_name>"
*
* The domain name may be a simple name or an absolute domain name (which
* should end with a period). The domain name is case-independent.
*/
static bool dns_resolver_cmp(const struct key *key,
const struct key_match_data *match_data)
{
int slen, dlen, ret = 0;
const char *src = key->description, *dsp = match_data->raw_data;
kenter("%s,%s", src, dsp);
if (!src || !dsp)
goto no_match;
if (strcasecmp(src, dsp) == 0)
goto matched;
slen = strlen(src);
dlen = strlen(dsp);
if (slen <= 0 || dlen <= 0)
goto no_match;
if (src[slen - 1] == '.')
slen--;
if (dsp[dlen - 1] == '.')
dlen--;
if (slen != dlen || strncasecmp(src, dsp, slen) != 0)
goto no_match;
matched:
ret = 1;
no_match:
kleave(" = %d", ret);
return ret;
}
/*
* Preparse the match criterion.
*/
static int dns_resolver_match_preparse(struct key_match_data *match_data)
{
match_data->lookup_type = KEYRING_SEARCH_LOOKUP_ITERATE;
match_data->cmp = dns_resolver_cmp;
return 0;
}
/*
* Describe a DNS key
*/
static void dns_resolver_describe(const struct key *key, struct seq_file *m)
{
seq_puts(m, key->description);
if (key_is_instantiated(key)) {
int err = PTR_ERR(key->payload.data[dns_key_error]);
if (err)
seq_printf(m, ": %d", err);
else
seq_printf(m, ": %u", key->datalen);
}
}
/*
* read the DNS data
* - the key's semaphore is read-locked
*/
static long dns_resolver_read(const struct key *key,
char __user *buffer, size_t buflen)
{
int err = PTR_ERR(key->payload.data[dns_key_error]);
if (err)
return err;
return user_read(key, buffer, buflen);
}
struct key_type key_type_dns_resolver = {
.name = "dns_resolver",
.preparse = dns_resolver_preparse,
.free_preparse = dns_resolver_free_preparse,
.instantiate = generic_key_instantiate,
.match_preparse = dns_resolver_match_preparse,
.revoke = user_revoke,
.destroy = user_destroy,
.describe = dns_resolver_describe,
.read = dns_resolver_read,
};
static int __init init_dns_resolver(void)
{
struct cred *cred;
struct key *keyring;
int ret;
/* create an override credential set with a special thread keyring in
* which DNS requests are cached
*
* this is used to prevent malicious redirections from being installed
* with add_key().
*/
cred = prepare_kernel_cred(NULL);
if (!cred)
return -ENOMEM;
keyring = keyring_alloc(".dns_resolver",
GLOBAL_ROOT_UID, GLOBAL_ROOT_GID, cred,
(KEY_POS_ALL & ~KEY_POS_SETATTR) |
KEY_USR_VIEW | KEY_USR_READ,
KEY_ALLOC_NOT_IN_QUOTA, NULL, NULL);
if (IS_ERR(keyring)) {
ret = PTR_ERR(keyring);
goto failed_put_cred;
}
ret = register_key_type(&key_type_dns_resolver);
if (ret < 0)
goto failed_put_key;
/* instruct request_key() to use this special keyring as a cache for
* the results it looks up */
set_bit(KEY_FLAG_ROOT_CAN_CLEAR, &keyring->flags);
cred->thread_keyring = keyring;
cred->jit_keyring = KEY_REQKEY_DEFL_THREAD_KEYRING;
dns_resolver_cache = cred;
kdebug("DNS resolver keyring: %d\n", key_serial(keyring));
return 0;
failed_put_key:
key_put(keyring);
failed_put_cred:
put_cred(cred);
return ret;
}
static void __exit exit_dns_resolver(void)
{
key_revoke(dns_resolver_cache->thread_keyring);
unregister_key_type(&key_type_dns_resolver);
put_cred(dns_resolver_cache);
}
module_init(init_dns_resolver)
module_exit(exit_dns_resolver)
MODULE_LICENSE("GPL");