/* 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" /* * Instantiate a user defined key for dns_resolver. * * 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_instantiate(struct key *key, struct key_preparsed_payload *prep) { struct user_key_payload *upayload; unsigned long derrno; int ret; size_t datalen = prep->datalen, result_len = 0; const char *data = prep->data, *end, *opt; kenter("%%%d,%s,'%*.*s',%zu", key->serial, key->description, (int)datalen, (int)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 %d\n", key->serial); 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); key->type_data.x[0] = -derrno; continue; } bad_option_value: printk(KERN_WARNING "Option '%*.*s' to dns_resolver key %d:" " bad/missing value\n", opt_nlen, opt_nlen, opt, key->serial); 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 (key->type_data.x[0]) { kleave(" = 0 [h_error %ld]", key->type_data.x[0]); return 0; } kdebug("store result"); ret = key_payload_reserve(key, result_len); if (ret < 0) return -EINVAL; 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'; rcu_assign_pointer(key->payload.data, upayload); kleave(" = 0"); return 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 int dns_resolver_match(const struct key *key, const void *description) { int slen, dlen, ret = 0; const char *src = key->description, *dsp = description; 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; } /* * 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", .instantiate = dns_resolver_instantiate, .match = dns_resolver_match, .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");