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1 office 1 /*
2 * lib/attr.c Netlink Attributes
3 *
4 * This library is free software; you can redistribute it and/or
5 * modify it under the terms of the GNU Lesser General Public
6 * License as published by the Free Software Foundation version 2.1
7 * of the License.
8 *
9 * Copyright (c) 2003-2008 Thomas Graf <tgraf@suug.ch>
10 */
11  
12 #include <netlink-local.h>
13 #include <netlink/netlink.h>
14 #include <netlink/utils.h>
15 #include <netlink/addr.h>
16 #include <netlink/attr.h>
17 #include <netlink/msg.h>
18 #include <linux/socket.h>
19  
20 /**
21 * @ingroup msg
22 * @defgroup attr Attributes
23 * Netlink Attributes Construction/Parsing Interface
24 *
25 * \section attr_sec Netlink Attributes
26 * Netlink attributes allow for data chunks of arbitary length to be
27 * attached to a netlink message. Each attribute is encoded with a
28 * type and length field, both 16 bits, stored in the attribute header
29 * preceding the attribute data. The main advantage of using attributes
30 * over packing everything into the family header is that the interface
31 * stays extendable as new attributes can supersede old attributes while
32 * remaining backwards compatible. Also attributes can be defined optional
33 * thus avoiding the transmission of unnecessary empty data blocks.
34 * Special nested attributes allow for more complex data structures to
35 * be transmitted, e.g. trees, lists, etc.
36 *
37 * While not required, netlink attributes typically follow the family
38 * header of a netlink message and must be properly aligned to NLA_ALIGNTO:
39 * @code
40 * +----------------+- - -+---------------+- - -+------------+- - -+
41 * | Netlink Header | Pad | Family Header | Pad | Attributes | Pad |
42 * +----------------+- - -+---------------+- - -+------------+- - -+
43 * @endcode
44 *
45 * The actual attributes are chained together each separately aligned to
46 * NLA_ALIGNTO. The position of an attribute is defined based on the
47 * length field of the preceding attributes:
48 * @code
49 * +-------------+- - -+-------------+- - -+------
50 * | Attribute 1 | Pad | Attribute 2 | Pad | ...
51 * +-------------+- - -+-------------+- - -+------
52 * nla_next(attr1)------^
53 * @endcode
54 *
55 * The attribute itself consists of the attribute header followed by
56 * the actual payload also aligned to NLA_ALIGNTO. The function nla_data()
57 * returns a pointer to the start of the payload while nla_len() returns
58 * the length of the payload in bytes.
59 *
60 * \b Note: Be aware, NLA_ALIGNTO equals to 4 bytes, therefore it is not
61 * safe to dereference any 64 bit data types directly.
62 *
63 * @code
64 * <----------- nla_total_size(payload) ----------->
65 * <-------- nla_attr_size(payload) --------->
66 * +------------------+- - -+- - - - - - - - - +- - -+
67 * | Attribute Header | Pad | Payload | Pad |
68 * +------------------+- - -+- - - - - - - - - +- - -+
69 * nla_data(nla)-------------^
70 * <- nla_len(nla) ->
71 * @endcode
72 *
73 * @subsection attr_datatypes Attribute Data Types
74 * A number of basic data types are supported to simplify access and
75 * validation of netlink attributes. This data type information is
76 * not encoded in the attribute, both the kernel and userspace part
77 * are required to share this information on their own.
78 *
79 * One of the major advantages of these basic types is the automatic
80 * validation of each attribute based on an attribute policy. The
81 * validation covers most of the checks required to safely use
82 * attributes and thus keeps the individual sanity check to a minimum.
83 *
84 * Never access attribute payload without ensuring basic validation
85 * first, attributes may:
86 * - not be present even though required
87 * - contain less actual payload than expected
88 * - fake a attribute length which exceeds the end of the message
89 * - contain unterminated character strings
90 *
91 * Policies are defined as array of the struct nla_policy. The array is
92 * indexed with the attribute type, therefore the array must be sized
93 * accordingly.
94 * @code
95 * static struct nla_policy my_policy[ATTR_MAX+1] = {
96 * [ATTR_FOO] = { .type = ..., .minlen = ..., .maxlen = ... },
97 * };
98 *
99 * err = nla_validate(attrs, attrlen, ATTR_MAX, &my_policy);
100 * @endcode
101 *
102 * Some basic validations are performed on every attribute, regardless of type.
103 * - If the attribute type exceeds the maximum attribute type specified or
104 * the attribute type is lesser-or-equal than zero, the attribute will
105 * be silently ignored.
106 * - If the payload length falls below the \a minlen value the attribute
107 * will be rejected.
108 * - If \a maxlen is non-zero and the payload length exceeds the \a maxlen
109 * value the attribute will be rejected.
110 *
111 *
112 * @par Unspecific Attribute (NLA_UNSPEC)
113 * This is the standard type if no type is specified. It is used for
114 * binary data of arbitary length. Typically this attribute carries
115 * a binary structure or a stream of bytes.
116 * @par
117 * @code
118 * // In this example, we will assume a binary structure requires to
119 * // be transmitted. The definition of the structure will typically
120 * // go into a header file available to both the kernel and userspace
121 * // side.
122 * //
123 * // Note: Be careful when putting 64 bit data types into a structure.
124 * // The attribute payload is only aligned to 4 bytes, dereferencing
125 * // the member may fail.
126 * struct my_struct {
127 * int a;
128 * int b;
129 * };
130 *
131 * // The validation function will not enforce an exact length match to
132 * // allow structures to grow as required. Note: While it is allowed
133 * // to add members to the end of the structure, changing the order or
134 * // inserting members in the middle of the structure will break your
135 * // binary interface.
136 * static struct nla_policy my_policy[ATTR_MAX+1] = {
137 * [ATTR_MY_STRICT] = { .type = NLA_UNSPEC,
138 * .minlen = sizeof(struct my_struct) },
139 *
140 * // The binary structure is appened to the message using nla_put()
141 * struct my_struct foo = { .a = 1, .b = 2 };
142 * nla_put(msg, ATTR_MY_STRUCT, sizeof(foo), &foo);
143 *
144 * // On the receiving side, a pointer to the structure pointing inside
145 * // the message payload is returned by nla_get().
146 * if (attrs[ATTR_MY_STRUCT])
147 * struct my_struct *foo = nla_get(attrs[ATTR_MY_STRUCT]);
148 * @endcode
149 *
150 * @par Integers (NLA_U8, NLA_U16, NLA_U32, NLA_U64)
151 * Integers come in different sizes from 8 bit to 64 bit. However, since the
152 * payload length is aligned to 4 bytes, integers smaller than 32 bit are
153 * only useful to enforce the maximum range of values.
154 * @par
155 * \b Note: There is no difference made between signed and unsigned integers.
156 * The validation only enforces the minimal payload length required to store
157 * an integer of specified type.
158 * @par
159 * @code
160 * // Even though possible, it does not make sense to specify .minlen or
161 * // .maxlen for integer types. The data types implies the corresponding
162 * // minimal payload length.
163 * static struct nla_policy my_policy[ATTR_MAX+1] = {
164 * [ATTR_FOO] = { .type = NLA_U32 },
165 *
166 * // Numeric values can be appended directly using the respective
167 * // nla_put_uxxx() function
168 * nla_put_u32(msg, ATTR_FOO, 123);
169 *
170 * // Same for the receiving side.
171 * if (attrs[ATTR_FOO])
172 * uint32_t foo = nla_get_u32(attrs[ATTR_FOO]);
173 * @endcode
174 *
175 * @par Character string (NLA_STRING)
176 * This data type represents a NUL terminated character string of variable
177 * length. For binary data streams the type NLA_UNSPEC is recommended.
178 * @par
179 * @code
180 * // Enforce a NUL terminated character string of at most 4 characters
181 * // including the NUL termination.
182 * static struct nla_policy my_policy[ATTR_MAX+1] = {
183 * [ATTR_BAR] = { .type = NLA_STRING, maxlen = 4 },
184 *
185 * // nla_put_string() creates a string attribute of the necessary length
186 * // and appends it to the message including the NUL termination.
187 * nla_put_string(msg, ATTR_BAR, "some text");
188 *
189 * // It is safe to use the returned character string directly if the
190 * // attribute has been validated as the validation enforces the proper
191 * // termination of the string.
192 * if (attrs[ATTR_BAR])
193 * char *text = nla_get_string(attrs[ATTR_BAR]);
194 * @endcode
195 *
196 * @par Flag (NLA_FLAG)
197 * This attribute type may be used to indicate the presence of a flag. The
198 * attribute is only valid if the payload length is zero. The presence of
199 * the attribute header indicates the presence of the flag.
200 * @par
201 * @code
202 * // This attribute type is special as .minlen and .maxlen have no effect.
203 * static struct nla_policy my_policy[ATTR_MAX+1] = {
204 * [ATTR_FLAG] = { .type = NLA_FLAG },
205 *
206 * // nla_put_flag() appends a zero sized attribute to the message.
207 * nla_put_flag(msg, ATTR_FLAG);
208 *
209 * // There is no need for a receival function, the presence is the value.
210 * if (attrs[ATTR_FLAG])
211 * // flag is present
212 * @endcode
213 *
214 * @par Micro Seconds (NLA_MSECS)
215 *
216 * @par Nested Attribute (NLA_NESTED)
217 * Attributes can be nested and put into a container to create groups, lists
218 * or to construct trees of attributes. Nested attributes are often used to
219 * pass attributes to a subsystem where the top layer has no knowledge of the
220 * configuration possibilities of each subsystem.
221 * @par
222 * \b Note: When validating the attributes using nlmsg_validate() or
223 * nlmsg_parse() it will only affect the top level attributes. Each
224 * level of nested attributes must be validated seperately using
225 * nla_parse_nested() or nla_validate().
226 * @par
227 * @code
228 * // The minimal length policy may be used to enforce the presence of at
229 * // least one attribute.
230 * static struct nla_policy my_policy[ATTR_MAX+1] = {
231 * [ATTR_OPTS] = { .type = NLA_NESTED, minlen = NLA_HDRLEN },
232 *
233 * // Nested attributes are constructed by enclosing the attributes
234 * // to be nested with calls to nla_nest_start() respetively nla_nest_end().
235 * struct nlattr *opts = nla_nest_start(msg, ATTR_OPTS);
236 * nla_put_u32(msg, ATTR_FOO, 123);
237 * nla_put_string(msg, ATTR_BAR, "some text");
238 * nla_nest_end(msg, opts);
239 *
240 * // Various methods exist to parse nested attributes, the easiest being
241 * // nla_parse_nested() which also allows validation in the same step.
242 * if (attrs[ATTR_OPTS]) {
243 * struct nlattr *nested[ATTR_MAX+1];
244 *
245 * nla_parse_nested(nested, ATTR_MAX, attrs[ATTR_OPTS], &policy);
246 *
247 * if (nested[ATTR_FOO])
248 * uint32_t foo = nla_get_u32(nested[ATTR_FOO]);
249 * }
250 * @endcode
251 *
252 * @subsection attr_exceptions Exception Based Attribute Construction
253 * Often a large number of attributes are added to a message in a single
254 * function. In order to simplify error handling, a second set of
255 * construction functions exist which jump to a error label when they
256 * fail instead of returning an error code. This second set consists
257 * of macros which are named after their error code based counterpart
258 * except that the name is written all uppercase.
259 *
260 * All of the macros jump to the target \c nla_put_failure if they fail.
261 * @code
262 * void my_func(struct nl_msg *msg)
263 * {
264 * NLA_PUT_U32(msg, ATTR_FOO, 10);
265 * NLA_PUT_STRING(msg, ATTR_BAR, "bar");
266 *
267 * return 0;
268 *
269 * nla_put_failure:
270 * return -NLE_NOMEM;
271 * }
272 * @endcode
273 *
274 * @subsection attr_examples Examples
275 * @par Example 1.1 Constructing a netlink message with attributes.
276 * @code
277 * struct nl_msg *build_msg(int ifindex, struct nl_addr *lladdr, int mtu)
278 * {
279 * struct nl_msg *msg;
280 * struct nlattr *info, *vlan;
281 * struct ifinfomsg ifi = {
282 * .ifi_family = AF_INET,
283 * .ifi_index = ifindex,
284 * };
285 *
286 * // Allocate a new netlink message, type=RTM_SETLINK, flags=NLM_F_ECHO
287 * if (!(msg = nlmsg_alloc_simple(RTM_SETLINK, NLM_F_ECHO)))
288 * return NULL;
289 *
290 * // Append the family specific header (struct ifinfomsg)
291 * if (nlmsg_append(msg, &ifi, sizeof(ifi), NLMSG_ALIGNTO) < 0)
292 * goto nla_put_failure
293 *
294 * // Append a 32 bit integer attribute to carry the MTU
295 * NLA_PUT_U32(msg, IFLA_MTU, mtu);
296 *
297 * // Append a unspecific attribute to carry the link layer address
298 * NLA_PUT_ADDR(msg, IFLA_ADDRESS, lladdr);
299 *
300 * // Append a container for nested attributes to carry link information
301 * if (!(info = nla_nest_start(msg, IFLA_LINKINFO)))
302 * goto nla_put_failure;
303 *
304 * // Put a string attribute into the container
305 * NLA_PUT_STRING(msg, IFLA_INFO_KIND, "vlan");
306 *
307 * // Append another container inside the open container to carry
308 * // vlan specific attributes
309 * if (!(vlan = nla_nest_start(msg, IFLA_INFO_DATA)))
310 * goto nla_put_failure;
311 *
312 * // add vlan specific info attributes here...
313 *
314 * // Finish nesting the vlan attributes and close the second container.
315 * nla_nest_end(msg, vlan);
316 *
317 * // Finish nesting the link info attribute and close the first container.
318 * nla_nest_end(msg, info);
319 *
320 * return msg;
321 *
322 * // If any of the construction macros fails, we end up here.
323 * nla_put_failure:
324 * nlmsg_free(msg);
325 * return NULL;
326 * }
327 * @endcode
328 *
329 * @par Example 2.1 Parsing a netlink message with attributes.
330 * @code
331 * int parse_message(struct nl_msg *msg)
332 * {
333 * // The policy defines two attributes: a 32 bit integer and a container
334 * // for nested attributes.
335 * struct nla_policy attr_policy[ATTR_MAX+1] = {
336 * [ATTR_FOO] = { .type = NLA_U32 },
337 * [ATTR_BAR] = { .type = NLA_NESTED },
338 * };
339 * struct nlattr *attrs[ATTR_MAX+1];
340 * int err;
341 *
342 * // The nlmsg_parse() function will make sure that the message contains
343 * // enough payload to hold the header (struct my_hdr), validates any
344 * // attributes attached to the messages and stores a pointer to each
345 * // attribute in the attrs[] array accessable by attribute type.
346 * if ((err = nlmsg_parse(nlmsg_hdr(msg), sizeof(struct my_hdr), attrs,
347 * ATTR_MAX, attr_policy)) < 0)
348 * goto errout;
349 *
350 * if (attrs[ATTR_FOO]) {
351 * // It is safe to directly access the attribute payload without
352 * // any further checks since nlmsg_parse() enforced the policy.
353 * uint32_t foo = nla_get_u32(attrs[ATTR_FOO]);
354 * }
355 *
356 * if (attrs[ATTR_BAR]) {
357 * struct nlattr *nested[NESTED_MAX+1];
358 *
359 * // Attributes nested in a container can be parsed the same way
360 * // as top level attributes.
361 * if ((err = nla_parse_nested(nested, NESTED_MAX, attrs[ATTR_BAR],
362 * nested_policy)) < 0)
363 * goto errout;
364 *
365 * // Process nested attributes here.
366 * }
367 *
368 * err = 0;
369 * errout:
370 * return err;
371 * }
372 * @endcode
373 *
374 * @{
375 */
376  
377 /**
378 * @name Attribute Size Calculation
379 * @{
380 */
381  
382 /** @} */
383  
384 /**
385 * @name Parsing Attributes
386 * @{
387 */
388  
389 /**
390 * Check if the attribute header and payload can be accessed safely.
391 * @arg nla Attribute of any kind.
392 * @arg remaining Number of bytes remaining in attribute stream.
393 *
394 * Verifies that the header and payload do not exceed the number of
395 * bytes left in the attribute stream. This function must be called
396 * before access the attribute header or payload when iterating over
397 * the attribute stream using nla_next().
398 *
399 * @return True if the attribute can be accessed safely, false otherwise.
400 */
401 int nla_ok(const struct nlattr *nla, int remaining)
402 {
403 return remaining >= sizeof(*nla) &&
404 nla->nla_len >= sizeof(*nla) &&
405 nla->nla_len <= remaining;
406 }
407  
408 /**
409 * Return next attribute in a stream of attributes.
410 * @arg nla Attribute of any kind.
411 * @arg remaining Variable to count remaining bytes in stream.
412 *
413 * Calculates the offset to the next attribute based on the attribute
414 * given. The attribute provided is assumed to be accessible, the
415 * caller is responsible to use nla_ok() beforehand. The offset (length
416 * of specified attribute including padding) is then subtracted from
417 * the remaining bytes variable and a pointer to the next attribute is
418 * returned.
419 *
420 * nla_next() can be called as long as remainig is >0.
421 *
422 * @return Pointer to next attribute.
423 */
424 struct nlattr *nla_next(const struct nlattr *nla, int *remaining)
425 {
426 int totlen = NLA_ALIGN(nla->nla_len);
427  
428 *remaining -= totlen;
429 return (struct nlattr *) ((char *) nla + totlen);
430 }
431  
432 static uint16_t nla_attr_minlen[NLA_TYPE_MAX+1] = {
433 [NLA_U8] = sizeof(uint8_t),
434 [NLA_U16] = sizeof(uint16_t),
435 [NLA_U32] = sizeof(uint32_t),
436 [NLA_U64] = sizeof(uint64_t),
437 [NLA_STRING] = 1,
438 };
439  
440 static int validate_nla(struct nlattr *nla, int maxtype,
441 struct nla_policy *policy)
442 {
443 struct nla_policy *pt;
444 int minlen = 0, type = nla_type(nla);
445  
446 if (type <= 0 || type > maxtype)
447 return 0;
448  
449 pt = &policy[type];
450  
451 if (pt->type > NLA_TYPE_MAX)
452 BUG();
453  
454 if (pt->minlen)
455 minlen = pt->minlen;
456 else if (pt->type != NLA_UNSPEC)
457 minlen = nla_attr_minlen[pt->type];
458  
459 if (pt->type == NLA_FLAG && nla_len(nla) > 0)
460 return -NLE_RANGE;
461  
462 if (nla_len(nla) < minlen)
463 return -NLE_RANGE;
464  
465 if (pt->maxlen && nla_len(nla) > pt->maxlen)
466 return -NLE_RANGE;
467  
468 if (pt->type == NLA_STRING) {
469 char *data = nla_data(nla);
470 if (data[nla_len(nla) - 1] != '\0')
471 return -NLE_INVAL;
472 }
473  
474 return 0;
475 }
476  
477  
478 /**
479 * Create attribute index based on a stream of attributes.
480 * @arg tb Index array to be filled (maxtype+1 elements).
481 * @arg maxtype Maximum attribute type expected and accepted.
482 * @arg head Head of attribute stream.
483 * @arg len Length of attribute stream.
484 * @arg policy Attribute validation policy.
485 *
486 * Iterates over the stream of attributes and stores a pointer to each
487 * attribute in the index array using the attribute type as index to
488 * the array. Attribute with a type greater than the maximum type
489 * specified will be silently ignored in order to maintain backwards
490 * compatibility. If \a policy is not NULL, the attribute will be
491 * validated using the specified policy.
492 *
493 * @see nla_validate
494 * @return 0 on success or a negative error code.
495 */
496 int nla_parse(struct nlattr *tb[], int maxtype, struct nlattr *head, int len,
497 struct nla_policy *policy)
498 {
499 struct nlattr *nla;
500 int rem, err;
501  
502 memset(tb, 0, sizeof(struct nlattr *) * (maxtype + 1));
503  
504 nla_for_each_attr(nla, head, len, rem) {
505 int type = nla_type(nla);
506  
507 if (type == 0) {
508 fprintf(stderr, "Illegal nla->nla_type == 0\n");
509 continue;
510 }
511  
512 if (type <= maxtype) {
513 if (policy) {
514 err = validate_nla(nla, maxtype, policy);
515 if (err < 0)
516 goto errout;
517 }
518  
519 tb[type] = nla;
520 }
521 }
522  
523 if (rem > 0)
524 fprintf(stderr, "netlink: %d bytes leftover after parsing "
525 "attributes.\n", rem);
526  
527 err = 0;
528 errout:
529 return err;
530 }
531  
532 /**
533 * Validate a stream of attributes.
534 * @arg head Head of attributes stream.
535 * @arg len Length of attributes stream.
536 * @arg maxtype Maximum attribute type expected and accepted.
537 * @arg policy Validation policy.
538 *
539 * Iterates over the stream of attributes and validates each attribute
540 * one by one using the specified policy. Attributes with a type greater
541 * than the maximum type specified will be silently ignored in order to
542 * maintain backwards compatibility.
543 *
544 * See \ref attr_datatypes for more details on what kind of validation
545 * checks are performed on each attribute data type.
546 *
547 * @return 0 on success or a negative error code.
548 */
549 int nla_validate(struct nlattr *head, int len, int maxtype,
550 struct nla_policy *policy)
551 {
552 struct nlattr *nla;
553 int rem, err;
554  
555 nla_for_each_attr(nla, head, len, rem) {
556 err = validate_nla(nla, maxtype, policy);
557 if (err < 0)
558 goto errout;
559 }
560  
561 err = 0;
562 errout:
563 return err;
564 }
565  
566 /**
567 * Find a single attribute in a stream of attributes.
568 * @arg head Head of attributes stream.
569 * @arg len Length of attributes stream.
570 * @arg attrtype Attribute type to look for.
571 *
572 * Iterates over the stream of attributes and compares each type with
573 * the type specified. Returns the first attribute which matches the
574 * type.
575 *
576 * @return Pointer to attribute found or NULL.
577 */
578 struct nlattr *nla_find(struct nlattr *head, int len, int attrtype)
579 {
580 struct nlattr *nla;
581 int rem;
582  
583 nla_for_each_attr(nla, head, len, rem)
584 if (nla_type(nla) == attrtype)
585 return nla;
586  
587 return NULL;
588 }
589  
590 /** @} */
591  
592 /**
593 * @name Unspecific Attribute
594 * @{
595 */
596  
597 /**
598 * Reserve space for a attribute.
599 * @arg msg Netlink Message.
600 * @arg attrtype Attribute Type.
601 * @arg attrlen Length of payload.
602 *
603 * Reserves room for a attribute in the specified netlink message and
604 * fills in the attribute header (type, length). Returns NULL if there
605 * is unsuficient space for the attribute.
606 *
607 * Any padding between payload and the start of the next attribute is
608 * zeroed out.
609 *
610 * @return Pointer to start of attribute or NULL on failure.
611 */
612 struct nlattr *nla_reserve(struct nl_msg *msg, int attrtype, int attrlen)
613 {
614 struct nlattr *nla;
615 int tlen;
616  
617 tlen = NLMSG_ALIGN(msg->nm_nlh->nlmsg_len) + nla_total_size(attrlen);
618  
619 if ((tlen + msg->nm_nlh->nlmsg_len) > msg->nm_size)
620 return NULL;
621  
622 nla = (struct nlattr *) nlmsg_tail(msg->nm_nlh);
623 nla->nla_type = attrtype;
624 nla->nla_len = nla_attr_size(attrlen);
625  
626 memset((unsigned char *) nla + nla->nla_len, 0, nla_padlen(attrlen));
627 msg->nm_nlh->nlmsg_len = tlen;
628  
629 NL_DBG(2, "msg %p: Reserved %d bytes at offset +%td for attr %d "
630 "nlmsg_len=%d\n", msg, attrlen,
631 (void *) nla - nlmsg_data(msg->nm_nlh),
632 attrtype, msg->nm_nlh->nlmsg_len);
633  
634 return nla;
635 }
636  
637 /**
638 * Add a unspecific attribute to netlink message.
639 * @arg msg Netlink message.
640 * @arg attrtype Attribute type.
641 * @arg datalen Length of data to be used as payload.
642 * @arg data Pointer to data to be used as attribute payload.
643 *
644 * Reserves room for a unspecific attribute and copies the provided data
645 * into the message as payload of the attribute. Returns an error if there
646 * is insufficient space for the attribute.
647 *
648 * @see nla_reserve
649 * @return 0 on success or a negative error code.
650 */
651 int nla_put(struct nl_msg *msg, int attrtype, int datalen, const void *data)
652 {
653 struct nlattr *nla;
654  
655 nla = nla_reserve(msg, attrtype, datalen);
656 if (!nla)
657 return -NLE_NOMEM;
658  
659 memcpy(nla_data(nla), data, datalen);
660 NL_DBG(2, "msg %p: Wrote %d bytes at offset +%td for attr %d\n",
661 msg, datalen, (void *) nla - nlmsg_data(msg->nm_nlh), attrtype);
662  
663 return 0;
664 }
665  
666  
667  
668 /** @} */