--- /dev/null
+/* 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->type_data[0] = 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->type_data[0]) {
+ kleave(" = 0 [h_error %ld]", PTR_ERR(prep->type_data[0]));
+ 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[0] = 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[0]);
+}
+
+/*
+ * 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)
+{
+ int err = key->type_data.x[0];
+
+ seq_puts(m, key->description);
+ if (key_is_instantiated(key)) {
+ 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)
+{
+ if (key->type_data.x[0])
+ return key->type_data.x[0];
+
+ 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);
+ 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");
+
Code Review / kvmfornfv.git / blobdiff