cregit-Linux how code gets into the kernel

Release 4.8 net/dns_resolver/dns_query.c

Directory: net/dns_resolver
/* Upcall routine, designed to work as a key type and working through
 * /sbin/request-key to contact userspace when handling DNS queries.
 * See Documentation/networking/dns_resolver.txt
 *   Copyright (c) 2007 Igor Mammedov
 *   Author(s): Igor Mammedov (
 *              Steve French (
 *              Wang Lei (
 *              David Howells (
 *   The upcall wrapper used to make an arbitrary DNS query.
 *   This function requires the appropriate userspace tool dns.upcall to be
 *   installed and something like the following lines should be added to the
 *   /etc/request-key.conf file:
 *      create dns_resolver * * /sbin/dns.upcall %k
 *   For example to use this module to query AFSDB RR:
 *      create dns_resolver afsdb:* * /sbin/dns.afsdb %k
 *   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
 *   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 <>.

#include <linux/module.h>
#include <linux/slab.h>
#include <linux/dns_resolver.h>
#include <linux/err.h>
#include <keys/dns_resolver-type.h>
#include <keys/user-type.h>

#include "internal.h"

 * dns_query - Query the DNS
 * @type: Query type (or NULL for straight host->IP lookup)
 * @name: Name to look up
 * @namelen: Length of name
 * @options: Request options (or NULL if no options)
 * @_result: Where to place the returned data.
 * @_expiry: Where to store the result expiry time (or NULL)
 * The data will be returned in the pointer at *result, and the caller is
 * responsible for freeing it.
 * The description should be of the form "[<query_type>:]<domain_name>", and
 * the options need to be appropriate for the query type requested.  If no
 * query_type is given, then the query is a straight hostname to IP address
 * lookup.
 * The DNS resolution lookup is performed by upcalling to userspace by way of
 * requesting a key of type dns_resolver.
 * Returns the size of the result on success, -ve error code otherwise.

int dns_query(const char *type, const char *name, size_t namelen, const char *options, char **_result, time64_t *_expiry) { struct key *rkey; const struct user_key_payload *upayload; const struct cred *saved_cred; size_t typelen, desclen; char *desc, *cp; int ret, len; kenter("%s,%*.*s,%zu,%s", type, (int)namelen, (int)namelen, name, namelen, options); if (!name || namelen == 0 || !_result) return -EINVAL; /* construct the query key description as "[<type>:]<name>" */ typelen = 0; desclen = 0; if (type) { typelen = strlen(type); if (typelen < 1) return -EINVAL; desclen += typelen + 1; } if (!namelen) namelen = strnlen(name, 256); if (namelen < 3 || namelen > 255) return -EINVAL; desclen += namelen + 1; desc = kmalloc(desclen, GFP_KERNEL); if (!desc) return -ENOMEM; cp = desc; if (type) { memcpy(cp, type, typelen); cp += typelen; *cp++ = ':'; } memcpy(cp, name, namelen); cp += namelen; *cp = '\0'; if (!options) options = ""; kdebug("call request_key(,%s,%s)", desc, options); /* make the upcall, using special credentials to prevent the use of * add_key() to preinstall malicious redirections */ saved_cred = override_creds(dns_resolver_cache); rkey = request_key(&key_type_dns_resolver, desc, options); revert_creds(saved_cred); kfree(desc); if (IS_ERR(rkey)) { ret = PTR_ERR(rkey); goto out; } down_read(&rkey->sem); set_bit(KEY_FLAG_ROOT_CAN_INVAL, &rkey->flags); rkey->perm |= KEY_USR_VIEW; ret = key_validate(rkey); if (ret < 0) goto put; /* If the DNS server gave an error, return that to the caller */ ret = PTR_ERR(rkey->[dns_key_error]); if (ret) goto put; upayload = user_key_payload(rkey); len = upayload->datalen; ret = -ENOMEM; *_result = kmalloc(len + 1, GFP_KERNEL); if (!*_result) goto put; memcpy(*_result, upayload->data, len); (*_result)[len] = '\0'; if (_expiry) *_expiry = rkey->expiry; ret = len; put: up_read(&rkey->sem); key_put(rkey); out: kleave(" = %d", ret); return ret; }


wang leiwang lei43892.41%225.00%
david howellsdavid howells183.80%225.00%
manuel schollingmanuel scholling153.16%225.00%
ben hutchingsben hutchings20.42%112.50%
aya mahfouzaya mahfouz10.21%112.50%


Overall Contributors

wang leiwang lei46191.83%218.18%
david howellsdavid howells193.78%327.27%
manuel schollingmanuel scholling152.99%218.18%
stephen rothwellstephen rothwell30.60%19.09%
ben hutchingsben hutchings20.40%19.09%
aya mahfouzaya mahfouz10.20%19.09%
jeff kirsherjeff kirsher10.20%19.09%
Directory: net/dns_resolver
Information contained on this website is for historical information purposes only and does not indicate or represent copyright ownership.