dns: Allow the dns resolver to retrieve a server set

Allow the DNS resolver to retrieve a set of servers and their associated addresses, ports, preference and weight ratings. In terms of communication with userspace, "srv=1" is added to the callout string (the '1' indicating the maximum data version supported by the kernel) to ask the userspace side for this. If the userspace side doesn't recognise it, it will ignore the option and return the usual text address list. If the userspace side does recognise it, it will return some binary data that begins with a zero byte that would cause the string parsers to give an error. The second byte contains the version of the data in the blob (this may be between 1 and the version specified in the callout data). The remainder of the payload is version-specific. In version 1, the payload looks like (note that this is packed): u8 Non-string marker (ie. 0) u8 Content (0 => Server list) u8 Version (ie. 1) u8 Source (eg. DNS_RECORD_FROM_DNS_SRV) u8 Status (eg. DNS_LOOKUP_GOOD) u8 Number of servers foreach-server { u16 Name length (LE) u16 Priority (as per SRV record) (LE) u16 Weight (as per SRV record) (LE) u16 Port (LE) u8 Source (eg. DNS_RECORD_FROM_NSS) u8 Status (eg. DNS_LOOKUP_GOT_NOT_FOUND) u8 Protocol (eg. DNS_SERVER_PROTOCOL_UDP) u8 Number of addresses char[] Name (not NUL-terminated) foreach-address { u8 Family (AF_INET{,6}) union { u8[4] ipv4_addr u8[16] ipv6_addr } } } This can then be used to fetch a whole cell's VL-server configuration for AFS, for example.

David Howells committed 8 years ago

Commit bbb4c431 parent 0aa63eb4 files · +182 −10Browse files

Unified · Split

4 files

include/linux/dns_resolver.h +1 −3
include/uapi/linux/dns_resolver.h +116 −0
net/dns_resolver/dns_key.c +64 −3
net/dns_resolver/dns_query.c +1 −4

include/linux/dns_resolver.h+1−3

@@ -24,11 +24,9 @@ · 23 unmodified lines
24	#ifndef _LINUX_DNS_RESOLVER_H	24	#ifndef _LINUX_DNS_RESOLVER_H
25	#define _LINUX_DNS_RESOLVER_H	25	#define _LINUX_DNS_RESOLVER_H
26		26
27	#ifdef __KERNEL__	27	#include <uapi/linux/dns_resolver.h>
28		28
29	extern int dns_query(const char type, const char name, size_t namelen,	29	extern int dns_query(const char type, const char name, size_t namelen,
30	const char options, char _result, time64_t _expiry);	30	const char options, char _result, time64_t _expiry);
31		31
32	#endif /* KERNEL */
33
34	#endif /* _LINUX_DNS_RESOLVER_H */	32	#endif /* _LINUX_DNS_RESOLVER_H */

include/uapi/linux/dns_resolver.h+116−0

@@ -0,0 +1,116 @@
	1	/* SPDX-License-Identifier: GPL-2.0+ WITH Linux-syscall-note */
	2	/* DNS resolver interface definitions.
	3	*
	4	* Copyright (C) 2018 Red Hat, Inc. All Rights Reserved.
	5	* Written by David Howells (dhowells@redhat.com)
	6	*
	7	* This program is free software; you can redistribute it and/or
	8	* modify it under the terms of the GNU General Public Licence
	9	* as published by the Free Software Foundation; either version
	10	* 2 of the Licence, or (at your option) any later version.
	11	*/
	12
	13	#ifndef _UAPI_LINUX_DNS_RESOLVER_H
	14	#define _UAPI_LINUX_DNS_RESOLVER_H
	15
	16	#include <linux/types.h>
	17
	18	/*
	19	* Type of payload.
	20	*/
	21	enum dns_payload_content_type {
	22	DNS_PAYLOAD_IS_SERVER_LIST = 0, /* List of servers, requested by srv=1 */
	23	};
	24
	25	/*
	26	* Type of address that might be found in an address record.
	27	*/
	28	enum dns_payload_address_type {
	29	DNS_ADDRESS_IS_IPV4 = 0, /* 4-byte AF_INET address */
	30	DNS_ADDRESS_IS_IPV6 = 1, /* 16-byte AF_INET6 address */
	31	};
	32
	33	/*
	34	* Type of protocol used to access a server.
	35	*/
	36	enum dns_payload_protocol_type {
	37	DNS_SERVER_PROTOCOL_UNSPECIFIED = 0,
	38	DNS_SERVER_PROTOCOL_UDP = 1, /* Use UDP to talk to the server */
	39	DNS_SERVER_PROTOCOL_TCP = 2, /* Use TCP to talk to the server */
	40	};
	41
	42	/*
	43	* Source of record included in DNS resolver payload.
	44	*/
	45	enum dns_record_source {
	46	DNS_RECORD_UNAVAILABLE = 0, /* No source available (empty record) */
	47	DNS_RECORD_FROM_CONFIG = 1, /* From local configuration data */
	48	DNS_RECORD_FROM_DNS_A = 2, /* From DNS A or AAAA record */
	49	DNS_RECORD_FROM_DNS_AFSDB = 3, /* From DNS AFSDB record */
	50	DNS_RECORD_FROM_DNS_SRV = 4, /* From DNS SRV record */
	51	DNS_RECORD_FROM_NSS = 5, /* From NSS */
	52	NR__dns_record_source
	53	};
	54
	55	/*
	56	* Status of record included in DNS resolver payload.
	57	*/
	58	enum dns_lookup_status {
	59	DNS_LOOKUP_NOT_DONE = 0, /* No lookup has been made */
	60	DNS_LOOKUP_GOOD = 1, /* Good records obtained */
	61	DNS_LOOKUP_GOOD_WITH_BAD = 2, /* Good records, some decoding errors */
	62	DNS_LOOKUP_BAD = 3, /* Couldn't decode results */
	63	DNS_LOOKUP_GOT_NOT_FOUND = 4, /* Got a "Not Found" result */
	64	DNS_LOOKUP_GOT_LOCAL_FAILURE = 5, /* Local failure during lookup */
	65	DNS_LOOKUP_GOT_TEMP_FAILURE = 6, /* Temporary failure during lookup */
	66	DNS_LOOKUP_GOT_NS_FAILURE = 7, /* Name server failure */
	67	NR__dns_lookup_status
	68	};
	69
	70	/*
	71	* Header at the beginning of binary format payload.
	72	*/
	73	struct dns_payload_header {
	74	__u8 zero; /* Zero byte: marks this as not being text */
	75	__u8 content; /* enum dns_payload_content_type */
	76	__u8 version; /* Encoding version */
	77	} __packed;
	78
	79	/*
	80	* Header at the beginning of a V1 server list. This is followed directly by
	81	* the server records. Each server records begins with a struct of type
	82	* dns_server_list_v1_server.
	83	*/
	84	struct dns_server_list_v1_header {
	85	struct dns_payload_header hdr;
	86	__u8 source; /* enum dns_record_source */
	87	__u8 status; /* enum dns_lookup_status */
	88	__u8 nr_servers; /* Number of server records following this */
	89	} __packed;
	90
	91	/*
	92	* Header at the beginning of each V1 server record. This is followed by the
	93	* characters of the name with no NUL-terminator, followed by the address
	94	* records for that server. Each address record begins with a struct of type
	95	* struct dns_server_list_v1_address.
	96	*/
	97	struct dns_server_list_v1_server {
	98	__u16 name_len; /* Length of name (LE) */
	99	__u16 priority; /* Priority (as SRV record) (LE) */
	100	__u16 weight; /* Weight (as SRV record) (LE) */
	101	__u16 port; /* UDP/TCP port number (LE) */
	102	__u8 source; /* enum dns_record_source */
	103	__u8 status; /* enum dns_lookup_status */
	104	__u8 protocol; /* enum dns_payload_protocol_type */
	105	__u8 nr_addrs;
	106	} __packed;
	107
	108	/*
	109	* Header at the beginning of each V1 address record. This is followed by the
	110	* bytes of the address, 4 for IPV4 and 16 for IPV6.
	111	*/
	112	struct dns_server_list_v1_address {
	113	__u8 address_type; /* enum dns_payload_address_type */
	114	} __packed;
	115
	116	#endif /* _UAPI_LINUX_DNS_RESOLVER_H */

net/dns_resolver/dns_key.c+64−3

@@ -29,6 +29,7 @@ · 28 unmodified lines
29	#include <linux/keyctl.h>	29	#include <linux/keyctl.h>
30	#include <linux/err.h>	30	#include <linux/err.h>
31	#include <linux/seq_file.h>	31	#include <linux/seq_file.h>
		32	#include <linux/dns_resolver.h>
32	#include <keys/dns_resolver-type.h>	33	#include <keys/dns_resolver-type.h>
33	#include <keys/user-type.h>	34	#include <keys/user-type.h>
34	#include "internal.h"	35	#include "internal.h"
@@ -48,27 +49,86 @@ const struct cred *dns_resolver_cache; · 13 unmodified lines
48	/*	49	/*
49	* Preparse instantiation data for a dns_resolver key.	50	* Preparse instantiation data for a dns_resolver key.
50	*	51	*
51	* The data must be a NUL-terminated string, with the NUL char accounted in	52	* For normal hostname lookups, the data must be a NUL-terminated string, with
52	* datalen.	53	* the NUL char accounted in datalen.
53	*	54	*
54	* If the data contains a '#' characters, then we take the clause after each	55	* If the data contains a '#' characters, then we take the clause after each
55	* one to be an option of the form 'key=value'. The actual data of interest is	56	* one to be an option of the form 'key=value'. The actual data of interest is
56	* the string leading up to the first '#'. For instance:	57	* the string leading up to the first '#'. For instance:
57	*	58	*
58	* "ip1,ip2,...#foo=bar"	59	* "ip1,ip2,...#foo=bar"
		60	*
		61	* For server list requests, the data must begin with a NUL char and be
		62	* followed by a byte indicating the version of the data format. Version 1
		63	* looks something like (note this is packed):
		64	*
		65	* u8 Non-string marker (ie. 0)
		66	* u8 Content (DNS_PAYLOAD_IS_*)
		67	* u8 Version (e.g. 1)
		68	* u8 Source of server list
		69	* u8 Lookup status of server list
		70	* u8 Number of servers
		71	* foreach-server {
		72	* __le16 Name length
		73	* __le16 Priority (as per SRV record, low first)
		74	* __le16 Weight (as per SRV record, higher first)
		75	* __le16 Port
		76	* u8 Source of address list
		77	* u8 Lookup status of address list
		78	* u8 Protocol (DNS_SERVER_PROTOCOL_*)
		79	* u8 Number of addresses
		80	* char[] Name (not NUL-terminated)
		81	* foreach-address {
		82	* u8 Family (DNS_ADDRESS_IS_*)
		83	* union {
		84	* u8[4] ipv4_addr
		85	* u8[16] ipv6_addr
		86	* }
		87	* }
		88	* }
		89	*
59	*/	90	*/
60	static int	91	static int
61	dns_resolver_preparse(struct key_preparsed_payload *prep)	92	dns_resolver_preparse(struct key_preparsed_payload *prep)
62	{	93	{
		94	const struct dns_payload_header *bin;
63	struct user_key_payload *upayload;	95	struct user_key_payload *upayload;
64	unsigned long derrno;	96	unsigned long derrno;
65	int ret;	97	int ret;
66	int datalen = prep->datalen, result_len = 0;	98	int datalen = prep->datalen, result_len = 0;
67	const char data = prep->data, end, *opt;	99	const char data = prep->data, end, *opt;
68		100
		101	if (datalen <= 1 \|\| !data)
		102	return -EINVAL;
		103
		104	if (data[0] == 0) {
		105	/* It may be a server list. */
		106	if (datalen <= sizeof(*bin))
		107	return -EINVAL;
		108
		109	bin = (const struct dns_payload_header *)data;
		110	kenter("[%u,%u],%u", bin->content, bin->version, datalen);
		111	if (bin->content != DNS_PAYLOAD_IS_SERVER_LIST) {
		112	pr_warn_ratelimited(
		113	"dns_resolver: Unsupported content type (%u)\n",
		114	bin->content);
		115	return -EINVAL;
		116	}
		117
		118	if (bin->version != 1) {
		119	pr_warn_ratelimited(
		120	"dns_resolver: Unsupported server list version (%u)\n",
		121	bin->version);
		122	return -EINVAL;
		123	}
		124
		125	result_len = datalen;
		126	goto store_result;
		127	}
		128
69	kenter("'%.s',%u", datalen, datalen, data, datalen);	129	kenter("'%.s',%u", datalen, datalen, data, datalen);
70		130
71	if (datalen <= 1 \|\| !data \|\| data[datalen - 1] != '\0')	131	if (!data \|\| data[datalen - 1] != '\0')
72	return -EINVAL;	132	return -EINVAL;
73	datalen--;	133	datalen--;
74		134
@@ -144,6 +204,7 @@ dns_resolver_preparse(struct key_preparsed_payload *prep) · 69 unmodified lines
144	return 0;	204	return 0;
145	}	205	}
146		206
		207	store_result:
147	kdebug("store result");	208	kdebug("store result");
148	prep->quotalen = result_len;	209	prep->quotalen = result_len;
149		210

net/dns_resolver/dns_query.c+1−4

 	if (_result) {
 		ret = -ENOMEM;
-		*_result = kmalloc(len + 1, GFP_KERNEL);
+		*_result = kmemdup_nul(upayload->data, len, GFP_KERNEL);
 		if (!*_result)
 			goto put;
-		memcpy(*_result, upayload->data, len);
-		(*_result)[len] = '\0';
 	}
 	if (_expiry)

dns: Allow the dns resolver to retrieve a server set

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