xref: /openbmc/linux/tools/lib/bpf/nlattr.c (revision 17bcd27a)
1 // SPDX-License-Identifier: (LGPL-2.1 OR BSD-2-Clause)
2 
3 /*
4  * NETLINK      Netlink attributes
5  *
6  * Copyright (c) 2003-2013 Thomas Graf <tgraf@suug.ch>
7  */
8 
9 #include <errno.h>
10 #include <string.h>
11 #include <stdio.h>
12 #include <linux/rtnetlink.h>
13 #include "nlattr.h"
14 #include "libbpf_internal.h"
15 
16 static uint16_t nla_attr_minlen[LIBBPF_NLA_TYPE_MAX+1] = {
17 	[LIBBPF_NLA_U8]		= sizeof(uint8_t),
18 	[LIBBPF_NLA_U16]	= sizeof(uint16_t),
19 	[LIBBPF_NLA_U32]	= sizeof(uint32_t),
20 	[LIBBPF_NLA_U64]	= sizeof(uint64_t),
21 	[LIBBPF_NLA_STRING]	= 1,
22 	[LIBBPF_NLA_FLAG]	= 0,
23 };
24 
nla_next(const struct nlattr * nla,int * remaining)25 static struct nlattr *nla_next(const struct nlattr *nla, int *remaining)
26 {
27 	int totlen = NLA_ALIGN(nla->nla_len);
28 
29 	*remaining -= totlen;
30 	return (struct nlattr *)((void *)nla + totlen);
31 }
32 
nla_ok(const struct nlattr * nla,int remaining)33 static int nla_ok(const struct nlattr *nla, int remaining)
34 {
35 	return remaining >= (int)sizeof(*nla) &&
36 	       nla->nla_len >= sizeof(*nla) &&
37 	       nla->nla_len <= remaining;
38 }
39 
nla_type(const struct nlattr * nla)40 static int nla_type(const struct nlattr *nla)
41 {
42 	return nla->nla_type & NLA_TYPE_MASK;
43 }
44 
validate_nla(struct nlattr * nla,int maxtype,struct libbpf_nla_policy * policy)45 static int validate_nla(struct nlattr *nla, int maxtype,
46 			struct libbpf_nla_policy *policy)
47 {
48 	struct libbpf_nla_policy *pt;
49 	unsigned int minlen = 0;
50 	int type = nla_type(nla);
51 
52 	if (type < 0 || type > maxtype)
53 		return 0;
54 
55 	pt = &policy[type];
56 
57 	if (pt->type > LIBBPF_NLA_TYPE_MAX)
58 		return 0;
59 
60 	if (pt->minlen)
61 		minlen = pt->minlen;
62 	else if (pt->type != LIBBPF_NLA_UNSPEC)
63 		minlen = nla_attr_minlen[pt->type];
64 
65 	if (libbpf_nla_len(nla) < minlen)
66 		return -1;
67 
68 	if (pt->maxlen && libbpf_nla_len(nla) > pt->maxlen)
69 		return -1;
70 
71 	if (pt->type == LIBBPF_NLA_STRING) {
72 		char *data = libbpf_nla_data(nla);
73 
74 		if (data[libbpf_nla_len(nla) - 1] != '\0')
75 			return -1;
76 	}
77 
78 	return 0;
79 }
80 
nlmsg_len(const struct nlmsghdr * nlh)81 static inline int nlmsg_len(const struct nlmsghdr *nlh)
82 {
83 	return nlh->nlmsg_len - NLMSG_HDRLEN;
84 }
85 
86 /**
87  * Create attribute index based on a stream of attributes.
88  * @arg tb		Index array to be filled (maxtype+1 elements).
89  * @arg maxtype		Maximum attribute type expected and accepted.
90  * @arg head		Head of attribute stream.
91  * @arg len		Length of attribute stream.
92  * @arg policy		Attribute validation policy.
93  *
94  * Iterates over the stream of attributes and stores a pointer to each
95  * attribute in the index array using the attribute type as index to
96  * the array. Attribute with a type greater than the maximum type
97  * specified will be silently ignored in order to maintain backwards
98  * compatibility. If \a policy is not NULL, the attribute will be
99  * validated using the specified policy.
100  *
101  * @see nla_validate
102  * @return 0 on success or a negative error code.
103  */
libbpf_nla_parse(struct nlattr * tb[],int maxtype,struct nlattr * head,int len,struct libbpf_nla_policy * policy)104 int libbpf_nla_parse(struct nlattr *tb[], int maxtype, struct nlattr *head,
105 		     int len, struct libbpf_nla_policy *policy)
106 {
107 	struct nlattr *nla;
108 	int rem, err;
109 
110 	memset(tb, 0, sizeof(struct nlattr *) * (maxtype + 1));
111 
112 	libbpf_nla_for_each_attr(nla, head, len, rem) {
113 		int type = nla_type(nla);
114 
115 		if (type > maxtype)
116 			continue;
117 
118 		if (policy) {
119 			err = validate_nla(nla, maxtype, policy);
120 			if (err < 0)
121 				goto errout;
122 		}
123 
124 		if (tb[type])
125 			pr_warn("Attribute of type %#x found multiple times in message, "
126 				"previous attribute is being ignored.\n", type);
127 
128 		tb[type] = nla;
129 	}
130 
131 	err = 0;
132 errout:
133 	return err;
134 }
135 
136 /**
137  * Create attribute index based on nested attribute
138  * @arg tb              Index array to be filled (maxtype+1 elements).
139  * @arg maxtype         Maximum attribute type expected and accepted.
140  * @arg nla             Nested Attribute.
141  * @arg policy          Attribute validation policy.
142  *
143  * Feeds the stream of attributes nested into the specified attribute
144  * to libbpf_nla_parse().
145  *
146  * @see libbpf_nla_parse
147  * @return 0 on success or a negative error code.
148  */
libbpf_nla_parse_nested(struct nlattr * tb[],int maxtype,struct nlattr * nla,struct libbpf_nla_policy * policy)149 int libbpf_nla_parse_nested(struct nlattr *tb[], int maxtype,
150 			    struct nlattr *nla,
151 			    struct libbpf_nla_policy *policy)
152 {
153 	return libbpf_nla_parse(tb, maxtype, libbpf_nla_data(nla),
154 				libbpf_nla_len(nla), policy);
155 }
156 
157 /* dump netlink extended ack error message */
libbpf_nla_dump_errormsg(struct nlmsghdr * nlh)158 int libbpf_nla_dump_errormsg(struct nlmsghdr *nlh)
159 {
160 	struct libbpf_nla_policy extack_policy[NLMSGERR_ATTR_MAX + 1] = {
161 		[NLMSGERR_ATTR_MSG]	= { .type = LIBBPF_NLA_STRING },
162 		[NLMSGERR_ATTR_OFFS]	= { .type = LIBBPF_NLA_U32 },
163 	};
164 	struct nlattr *tb[NLMSGERR_ATTR_MAX + 1], *attr;
165 	struct nlmsgerr *err;
166 	char *errmsg = NULL;
167 	int hlen, alen;
168 
169 	/* no TLVs, nothing to do here */
170 	if (!(nlh->nlmsg_flags & NLM_F_ACK_TLVS))
171 		return 0;
172 
173 	err = (struct nlmsgerr *)NLMSG_DATA(nlh);
174 	hlen = sizeof(*err);
175 
176 	/* if NLM_F_CAPPED is set then the inner err msg was capped */
177 	if (!(nlh->nlmsg_flags & NLM_F_CAPPED))
178 		hlen += nlmsg_len(&err->msg);
179 
180 	attr = (struct nlattr *) ((void *) err + hlen);
181 	alen = (void *)nlh + nlh->nlmsg_len - (void *)attr;
182 
183 	if (libbpf_nla_parse(tb, NLMSGERR_ATTR_MAX, attr, alen,
184 			     extack_policy) != 0) {
185 		pr_warn("Failed to parse extended error attributes\n");
186 		return 0;
187 	}
188 
189 	if (tb[NLMSGERR_ATTR_MSG])
190 		errmsg = (char *) libbpf_nla_data(tb[NLMSGERR_ATTR_MSG]);
191 
192 	pr_warn("Kernel error message: %s\n", errmsg);
193 
194 	return 0;
195 }
196