1// SPDX-License-Identifier: LGPL-2.1
  2
  3/*
  4 * NETLINK      Netlink attributes
  5 *
  6 *	This library is free software; you can redistribute it and/or
  7 *	modify it under the terms of the GNU Lesser General Public
  8 *	License as published by the Free Software Foundation version 2.1
  9 *	of the License.
 10 *
 11 * Copyright (c) 2003-2013 Thomas Graf <tgraf@suug.ch>
 12 */
 13
 14#include <errno.h>
 15#include "nlattr.h"
 16#include <linux/rtnetlink.h>
 17#include <string.h>
 18#include <stdio.h>
 19
 20static uint16_t nla_attr_minlen[NLA_TYPE_MAX+1] = {
 21	[NLA_U8]	= sizeof(uint8_t),
 22	[NLA_U16]	= sizeof(uint16_t),
 23	[NLA_U32]	= sizeof(uint32_t),
 24	[NLA_U64]	= sizeof(uint64_t),
 25	[NLA_STRING]	= 1,
 26	[NLA_FLAG]	= 0,
 27};
 28
 29static int nla_len(const struct nlattr *nla)
 30{
 31	return nla->nla_len - NLA_HDRLEN;
 32}
 33
 34static struct nlattr *nla_next(const struct nlattr *nla, int *remaining)
 35{
 36	int totlen = NLA_ALIGN(nla->nla_len);
 37
 38	*remaining -= totlen;
 39	return (struct nlattr *) ((char *) nla + totlen);
 40}
 41
 42static int nla_ok(const struct nlattr *nla, int remaining)
 43{
 44	return remaining >= sizeof(*nla) &&
 45	       nla->nla_len >= sizeof(*nla) &&
 46	       nla->nla_len <= remaining;
 47}
 48
 49static void *nla_data(const struct nlattr *nla)
 50{
 51	return (char *) nla + NLA_HDRLEN;
 52}
 53
 54static int nla_type(const struct nlattr *nla)
 55{
 56	return nla->nla_type & NLA_TYPE_MASK;
 57}
 58
 59static int validate_nla(struct nlattr *nla, int maxtype,
 60			struct nla_policy *policy)
 61{
 62	struct nla_policy *pt;
 63	unsigned int minlen = 0;
 64	int type = nla_type(nla);
 65
 66	if (type < 0 || type > maxtype)
 67		return 0;
 68
 69	pt = &policy[type];
 70
 71	if (pt->type > NLA_TYPE_MAX)
 72		return 0;
 73
 74	if (pt->minlen)
 75		minlen = pt->minlen;
 76	else if (pt->type != NLA_UNSPEC)
 77		minlen = nla_attr_minlen[pt->type];
 78
 79	if (nla_len(nla) < minlen)
 80		return -1;
 81
 82	if (pt->maxlen && nla_len(nla) > pt->maxlen)
 83		return -1;
 84
 85	if (pt->type == NLA_STRING) {
 86		char *data = nla_data(nla);
 87		if (data[nla_len(nla) - 1] != '\0')
 88			return -1;
 89	}
 90
 91	return 0;
 92}
 93
 94static inline int nlmsg_len(const struct nlmsghdr *nlh)
 95{
 96	return nlh->nlmsg_len - NLMSG_HDRLEN;
 97}
 98
 99/**
100 * Create attribute index based on a stream of attributes.
101 * @arg tb		Index array to be filled (maxtype+1 elements).
102 * @arg maxtype		Maximum attribute type expected and accepted.
103 * @arg head		Head of attribute stream.
104 * @arg len		Length of attribute stream.
105 * @arg policy		Attribute validation policy.
106 *
107 * Iterates over the stream of attributes and stores a pointer to each
108 * attribute in the index array using the attribute type as index to
109 * the array. Attribute with a type greater than the maximum type
110 * specified will be silently ignored in order to maintain backwards
111 * compatibility. If \a policy is not NULL, the attribute will be
112 * validated using the specified policy.
113 *
114 * @see nla_validate
115 * @return 0 on success or a negative error code.
116 */
117static int nla_parse(struct nlattr *tb[], int maxtype, struct nlattr *head, int len,
118		     struct nla_policy *policy)
119{
120	struct nlattr *nla;
121	int rem, err;
122
123	memset(tb, 0, sizeof(struct nlattr *) * (maxtype + 1));
124
125	nla_for_each_attr(nla, head, len, rem) {
126		int type = nla_type(nla);
127
128		if (type > maxtype)
129			continue;
130
131		if (policy) {
132			err = validate_nla(nla, maxtype, policy);
133			if (err < 0)
134				goto errout;
135		}
136
137		if (tb[type])
138			fprintf(stderr, "Attribute of type %#x found multiple times in message, "
139				  "previous attribute is being ignored.\n", type);
140
141		tb[type] = nla;
142	}
143
144	err = 0;
145errout:
146	return err;
147}
148
149/* dump netlink extended ack error message */
150int nla_dump_errormsg(struct nlmsghdr *nlh)
151{
152	struct nla_policy extack_policy[NLMSGERR_ATTR_MAX + 1] = {
153		[NLMSGERR_ATTR_MSG]	= { .type = NLA_STRING },
154		[NLMSGERR_ATTR_OFFS]	= { .type = NLA_U32 },
155	};
156	struct nlattr *tb[NLMSGERR_ATTR_MAX + 1], *attr;
157	struct nlmsgerr *err;
158	char *errmsg = NULL;
159	int hlen, alen;
160
161	/* no TLVs, nothing to do here */
162	if (!(nlh->nlmsg_flags & NLM_F_ACK_TLVS))
163		return 0;
164
165	err = (struct nlmsgerr *)NLMSG_DATA(nlh);
166	hlen = sizeof(*err);
167
168	/* if NLM_F_CAPPED is set then the inner err msg was capped */
169	if (!(nlh->nlmsg_flags & NLM_F_CAPPED))
170		hlen += nlmsg_len(&err->msg);
171
172	attr = (struct nlattr *) ((void *) err + hlen);
173	alen = nlh->nlmsg_len - hlen;
174
175	if (nla_parse(tb, NLMSGERR_ATTR_MAX, attr, alen, extack_policy) != 0) {
176		fprintf(stderr,
177			"Failed to parse extended error attributes\n");
178		return 0;
179	}
180
181	if (tb[NLMSGERR_ATTR_MSG])
182		errmsg = (char *) nla_data(tb[NLMSGERR_ATTR_MSG]);
183
184	fprintf(stderr, "Kernel error message: %s\n", errmsg);
185
186	return 0;
187}