5 files changed, 650 insertions, 0 deletions

diff --git a/net/dns_resolver/Kconfig b/net/dns_resolver/Kconfig
new file mode 100644
index 000000000..255df9b6e
--- /dev/null
+++ b/net/dns_resolver/Kconfig
@@ -0,0 +1,28 @@
+# SPDX-License-Identifier: GPL-2.0-only
+#
+# Configuration for DNS Resolver
+#
+config DNS_RESOLVER
+	tristate "DNS Resolver support"
+	depends on NET && KEYS
+	help
+	  Saying Y here will include support for the DNS Resolver key type
+	  which can be used to make upcalls to perform DNS lookups in
+	  userspace.
+
+	  DNS Resolver is used to query DNS server for information.  Examples
+	  being resolving a UNC hostname element to an IP address for CIFS or
+	  performing a DNS query for AFSDB records so that AFS can locate a
+	  cell's volume location database servers.
+
+	  DNS Resolver is used by the CIFS and AFS modules, and would support
+	  SMB2 later.  DNS Resolver is supported by the userspace upcall
+	  helper "/sbin/dns.resolver" via /etc/request-key.conf.
+
+	  See <file:Documentation/networking/dns_resolver.rst> for further
+	  information.
+
+	  To compile this as a module, choose M here: the module will be called
+	  dnsresolver.
+
+	  If unsure, say N.
diff --git a/net/dns_resolver/Makefile b/net/dns_resolver/Makefile
new file mode 100644
index 000000000..877532d66
--- /dev/null
+++ b/net/dns_resolver/Makefile
@@ -0,0 +1,8 @@
+# SPDX-License-Identifier: GPL-2.0-only
+#
+# Makefile for the Linux DNS Resolver.
+#
+
+obj-$(CONFIG_DNS_RESOLVER) += dns_resolver.o
+
+dns_resolver-y :=  dns_key.o dns_query.o
diff --git a/net/dns_resolver/dns_key.c b/net/dns_resolver/dns_key.c
new file mode 100644
index 000000000..26a9d8434
--- /dev/null
+++ b/net/dns_resolver/dns_key.c
@@ -0,0 +1,391 @@
+/* Key type used to cache DNS lookups made by the kernel
+ *
+ * See Documentation/networking/dns_resolver.rst
+ *
+ *   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 <linux/dns_resolver.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, 0644);
+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.
+ *
+ * For normal hostname lookups, 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"
+ *
+ * For server list requests, the data must begin with a NUL char and be
+ * followed by a byte indicating the version of the data format.  Version 1
+ * looks something like (note this is packed):
+ *
+ *	u8      Non-string marker (ie. 0)
+ *	u8	Content (DNS_PAYLOAD_IS_*)
+ *	u8	Version (e.g. 1)
+ *	u8	Source of server list
+ *	u8	Lookup status of server list
+ *	u8	Number of servers
+ *	foreach-server {
+ *		__le16	Name length
+ *		__le16	Priority (as per SRV record, low first)
+ *		__le16	Weight (as per SRV record, higher first)
+ *		__le16	Port
+ *		u8	Source of address list
+ *		u8	Lookup status of address list
+ *		u8	Protocol (DNS_SERVER_PROTOCOL_*)
+ *		u8	Number of addresses
+ *		char[]	Name (not NUL-terminated)
+ *		foreach-address {
+ *			u8		Family (DNS_ADDRESS_IS_*)
+ *			union {
+ *				u8[4]	ipv4_addr
+ *				u8[16]	ipv6_addr
+ *			}
+ *		}
+ *	}
+ *
+ */
+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;
+
+	if (datalen <= 1 || !data)
+		return -EINVAL;
+
+	if (data[0] == 0) {
+		const struct dns_server_list_v1_header *v1;
+
+		/* It may be a server list. */
+		if (datalen < sizeof(*v1))
+			return -EINVAL;
+
+		v1 = (const struct dns_server_list_v1_header *)data;
+		kenter("[%u,%u],%u", v1->hdr.content, v1->hdr.version, datalen);
+		if (v1->hdr.content != DNS_PAYLOAD_IS_SERVER_LIST) {
+			pr_warn_ratelimited(
+				"dns_resolver: Unsupported content type (%u)\n",
+				v1->hdr.content);
+			return -EINVAL;
+		}
+
+		if (v1->hdr.version != 1) {
+			pr_warn_ratelimited(
+				"dns_resolver: Unsupported server list version (%u)\n",
+				v1->hdr.version);
+			return -EINVAL;
+		}
+
+		if ((v1->status != DNS_LOOKUP_GOOD &&
+		     v1->status != DNS_LOOKUP_GOOD_WITH_BAD)) {
+			if (prep->expiry == TIME64_MAX)
+				prep->expiry = ktime_get_real_seconds() + 1;
+		}
+
+		result_len = datalen;
+		goto store_result;
+	}
+
+	kenter("'%*.*s',%u", datalen, datalen, data, datalen);
+
+	if (!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 {
+			int opt_len, opt_nlen;
+			const char *eq;
+			char optval[128];
+
+			next_opt = memchr(opt, '#', end - opt) ?: end;
+			opt_len = next_opt - opt;
+			if (opt_len <= 0 || opt_len > sizeof(optval)) {
+				pr_warn_ratelimited("Invalid option length (%d) for dns_resolver key\n",
+						    opt_len);
+				return -EINVAL;
+			}
+
+			eq = memchr(opt, '=', opt_len);
+			if (eq) {
+				opt_nlen = eq - opt;
+				eq++;
+				memcpy(optval, eq, next_opt - eq);
+				optval[next_opt - eq] = '\0';
+			} else {
+				opt_nlen = opt_len;
+				optval[0] = '\0';
+			}
+
+			kdebug("option '%*.*s' val '%s'",
+			       opt_nlen, opt_nlen, opt, optval);
+
+			/* 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");
+
+				ret = kstrtoul(optval, 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:
+			pr_warn_ratelimited("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;
+	}
+
+store_result:
+	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_positive(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 *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",
+	.flags		= KEY_TYPE_NET_DOMAIN | KEY_TYPE_INSTANT_REAP,
+	.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");
diff --git a/net/dns_resolver/dns_query.c b/net/dns_resolver/dns_query.c
new file mode 100644
index 000000000..82b084cc1
--- /dev/null
+++ b/net/dns_resolver/dns_query.c
@@ -0,0 +1,172 @@
+/* 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.rst
+ *
+ *   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)
+ *
+ *   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
+ *   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/slab.h>
+#include <linux/cred.h>
+#include <linux/dns_resolver.h>
+#include <linux/err.h>
+#include <net/net_namespace.h>
+
+#include <keys/dns_resolver-type.h>
+#include <keys/user-type.h>
+
+#include "internal.h"
+
+/**
+ * dns_query - Query the DNS
+ * @net: The network namespace to operate in.
+ * @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 (or NULL)
+ * @_expiry: Where to store the result expiry time (or NULL)
+ * @invalidate: Always invalidate the key after use
+ *
+ * The data will be returned in the pointer at *result, if provided, 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(struct net *net,
+	      const char *type, const char *name, size_t namelen,
+	      const char *options, char **_result, time64_t *_expiry,
+	      bool invalidate)
+{
+	struct key *rkey;
+	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)
+		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 < 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_net(&key_type_dns_resolver, desc, net, 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->payload.data[dns_key_error]);
+	if (ret)
+		goto put;
+
+	upayload = user_key_payload_locked(rkey);
+	len = upayload->datalen;
+
+	if (_result) {
+		ret = -ENOMEM;
+		*_result = kmemdup_nul(upayload->data, len, GFP_KERNEL);
+		if (!*_result)
+			goto put;
+	}
+
+	if (_expiry)
+		*_expiry = rkey->expiry;
+
+	ret = len;
+put:
+	up_read(&rkey->sem);
+	if (invalidate)
+		key_invalidate(rkey);
+	key_put(rkey);
+out:
+	kleave(" = %d", ret);
+	return ret;
+}
+EXPORT_SYMBOL(dns_query);
diff --git a/net/dns_resolver/internal.h b/net/dns_resolver/internal.h
new file mode 100644
index 000000000..0c570d40e
--- /dev/null
+++ b/net/dns_resolver/internal.h
@@ -0,0 +1,51 @@
+/*
+ *   Copyright (c) 2010 Wang Lei
+ *   Author(s): Wang Lei (wang840925@gmail.com). All Rights Reserved.
+ *
+ *   Internal DNS Rsolver stuff
+ *
+ *   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/compiler.h>
+#include <linux/kernel.h>
+#include <linux/sched.h>
+
+/*
+ * Layout of key payload words.
+ */
+enum {
+	dns_key_data,
+	dns_key_error,
+};
+
+/*
+ * dns_key.c
+ */
+extern const struct cred *dns_resolver_cache;
+
+/*
+ * debug tracing
+ */
+extern unsigned int dns_resolver_debug;
+
+#define	kdebug(FMT, ...)				\
+do {							\
+	if (unlikely(dns_resolver_debug))		\
+		printk(KERN_DEBUG "[%-6.6s] "FMT"\n",	\
+		       current->comm, ##__VA_ARGS__);	\
+} while (0)
+
+#define kenter(FMT, ...) kdebug("==> %s("FMT")", __func__, ##__VA_ARGS__)
+#define kleave(FMT, ...) kdebug("<== %s()"FMT"", __func__, ##__VA_ARGS__)