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) 2003-2013 Thomas Graf <tgraf@suug.ch>
10 */
11
12 #include <netlink-private/netlink.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 * Related sections in the development guide:
26 * - @core_doc{core_attr,Netlink Attributes}
27 *
28 * @{
29 *
30 * Header
31 * ------
32 * ~~~~{.c}
33 * #include <netlink/attr.h>
34 * ~~~~
35 */
36
37 /**
38 * @name Attribute Size Calculation
39 * @{
40 */
41
42 /**
43 * Return size of attribute whithout padding.
44 * @arg payload Payload length of attribute.
45 *
46 * @code
47 * <-------- nla_attr_size(payload) --------->
48 * +------------------+- - -+- - - - - - - - - +- - -+
49 * | Attribute Header | Pad | Payload | Pad |
50 * +------------------+- - -+- - - - - - - - - +- - -+
51 * @endcode
52 *
53 * @return Size of attribute in bytes without padding.
54 */
nla_attr_size(int payload)55 int nla_attr_size(int payload)
56 {
57 return NLA_HDRLEN + payload;
58 }
59
60 /**
61 * Return size of attribute including padding.
62 * @arg payload Payload length of attribute.
63 *
64 * @code
65 * <----------- nla_total_size(payload) ----------->
66 * +------------------+- - -+- - - - - - - - - +- - -+
67 * | Attribute Header | Pad | Payload | Pad |
68 * +------------------+- - -+- - - - - - - - - +- - -+
69 * @endcode
70 *
71 * @return Size of attribute in bytes.
72 */
nla_total_size(int payload)73 int nla_total_size(int payload)
74 {
75 return NLA_ALIGN(nla_attr_size(payload));
76 }
77
78 /**
79 * Return length of padding at the tail of the attribute.
80 * @arg payload Payload length of attribute.
81 *
82 * @code
83 * +------------------+- - -+- - - - - - - - - +- - -+
84 * | Attribute Header | Pad | Payload | Pad |
85 * +------------------+- - -+- - - - - - - - - +- - -+
86 * <--->
87 * @endcode
88 *
89 * @return Length of padding in bytes.
90 */
nla_padlen(int payload)91 int nla_padlen(int payload)
92 {
93 return nla_total_size(payload) - nla_attr_size(payload);
94 }
95
96 /** @} */
97
98 /**
99 * @name Parsing Attributes
100 * @{
101 */
102
103 /**
104 * Return type of the attribute.
105 * @arg nla Attribute.
106 *
107 * @return Type of attribute.
108 */
nla_type(const struct nlattr * nla)109 int nla_type(const struct nlattr *nla)
110 {
111 return nla->nla_type & NLA_TYPE_MASK;
112 }
113
114 /**
115 * Return pointer to the payload section.
116 * @arg nla Attribute.
117 *
118 * @return Pointer to start of payload section.
119 */
nla_data(const struct nlattr * nla)120 void *nla_data(const struct nlattr *nla)
121 {
122 return (char *) nla + NLA_HDRLEN;
123 }
124
125 /**
126 * Return length of the payload .
127 * @arg nla Attribute
128 *
129 * @return Length of payload in bytes.
130 */
nla_len(const struct nlattr * nla)131 int nla_len(const struct nlattr *nla)
132 {
133 return nla->nla_len - NLA_HDRLEN;
134 }
135
136 /**
137 * Check if the attribute header and payload can be accessed safely.
138 * @arg nla Attribute of any kind.
139 * @arg remaining Number of bytes remaining in attribute stream.
140 *
141 * Verifies that the header and payload do not exceed the number of
142 * bytes left in the attribute stream. This function must be called
143 * before access the attribute header or payload when iterating over
144 * the attribute stream using nla_next().
145 *
146 * @return True if the attribute can be accessed safely, false otherwise.
147 */
nla_ok(const struct nlattr * nla,int remaining)148 int nla_ok(const struct nlattr *nla, int remaining)
149 {
150 return remaining >= sizeof(*nla) &&
151 nla->nla_len >= sizeof(*nla) &&
152 nla->nla_len <= remaining;
153 }
154
155 /**
156 * Return next attribute in a stream of attributes.
157 * @arg nla Attribute of any kind.
158 * @arg remaining Variable to count remaining bytes in stream.
159 *
160 * Calculates the offset to the next attribute based on the attribute
161 * given. The attribute provided is assumed to be accessible, the
162 * caller is responsible to use nla_ok() beforehand. The offset (length
163 * of specified attribute including padding) is then subtracted from
164 * the remaining bytes variable and a pointer to the next attribute is
165 * returned.
166 *
167 * nla_next() can be called as long as remainig is >0.
168 *
169 * @return Pointer to next attribute.
170 */
nla_next(const struct nlattr * nla,int * remaining)171 struct nlattr *nla_next(const struct nlattr *nla, int *remaining)
172 {
173 int totlen = NLA_ALIGN(nla->nla_len);
174
175 *remaining -= totlen;
176 return (struct nlattr *) ((char *) nla + totlen);
177 }
178
179 static uint16_t nla_attr_minlen[NLA_TYPE_MAX+1] = {
180 [NLA_U8] = sizeof(uint8_t),
181 [NLA_U16] = sizeof(uint16_t),
182 [NLA_U32] = sizeof(uint32_t),
183 [NLA_U64] = sizeof(uint64_t),
184 [NLA_STRING] = 1,
185 [NLA_FLAG] = 0,
186 };
187
validate_nla(struct nlattr * nla,int maxtype,struct nla_policy * policy)188 static int validate_nla(struct nlattr *nla, int maxtype,
189 struct nla_policy *policy)
190 {
191 struct nla_policy *pt;
192 unsigned int minlen = 0;
193 int type = nla_type(nla);
194
195 if (type < 0 || type > maxtype)
196 return 0;
197
198 pt = &policy[type];
199
200 if (pt->type > NLA_TYPE_MAX)
201 BUG();
202
203 if (pt->minlen)
204 minlen = pt->minlen;
205 else if (pt->type != NLA_UNSPEC)
206 minlen = nla_attr_minlen[pt->type];
207
208 if (nla_len(nla) < minlen)
209 return -NLE_RANGE;
210
211 if (pt->maxlen && nla_len(nla) > pt->maxlen)
212 return -NLE_RANGE;
213
214 if (pt->type == NLA_STRING) {
215 char *data = nla_data(nla);
216 if (data[nla_len(nla) - 1] != '\0')
217 return -NLE_INVAL;
218 }
219
220 return 0;
221 }
222
223
224 /**
225 * Create attribute index based on a stream of attributes.
226 * @arg tb Index array to be filled (maxtype+1 elements).
227 * @arg maxtype Maximum attribute type expected and accepted.
228 * @arg head Head of attribute stream.
229 * @arg len Length of attribute stream.
230 * @arg policy Attribute validation policy.
231 *
232 * Iterates over the stream of attributes and stores a pointer to each
233 * attribute in the index array using the attribute type as index to
234 * the array. Attribute with a type greater than the maximum type
235 * specified will be silently ignored in order to maintain backwards
236 * compatibility. If \a policy is not NULL, the attribute will be
237 * validated using the specified policy.
238 *
239 * @see nla_validate
240 * @return 0 on success or a negative error code.
241 */
nla_parse(struct nlattr * tb[],int maxtype,struct nlattr * head,int len,struct nla_policy * policy)242 int nla_parse(struct nlattr *tb[], int maxtype, struct nlattr *head, int len,
243 struct nla_policy *policy)
244 {
245 struct nlattr *nla;
246 int rem, err;
247
248 memset(tb, 0, sizeof(struct nlattr *) * (maxtype + 1));
249
250 nla_for_each_attr(nla, head, len, rem) {
251 int type = nla_type(nla);
252
253 if (type > maxtype)
254 continue;
255
256 if (policy) {
257 err = validate_nla(nla, maxtype, policy);
258 if (err < 0)
259 goto errout;
260 }
261
262 if (tb[type])
263 NL_DBG(1, "Attribute of type %#x found multiple times in message, "
264 "previous attribute is being ignored.\n", type);
265
266 tb[type] = nla;
267 }
268
269 if (rem > 0)
270 NL_DBG(1, "netlink: %d bytes leftover after parsing "
271 "attributes.\n", rem);
272
273 err = 0;
274 errout:
275 return err;
276 }
277
278 /**
279 * Validate a stream of attributes.
280 * @arg head Head of attributes stream.
281 * @arg len Length of attributes stream.
282 * @arg maxtype Maximum attribute type expected and accepted.
283 * @arg policy Validation policy.
284 *
285 * Iterates over the stream of attributes and validates each attribute
286 * one by one using the specified policy. Attributes with a type greater
287 * than the maximum type specified will be silently ignored in order to
288 * maintain backwards compatibility.
289 *
290 * See section @core_doc{core_attr_parse,Attribute Parsing} for more details.
291 *
292 * @return 0 on success or a negative error code.
293 */
nla_validate(struct nlattr * head,int len,int maxtype,struct nla_policy * policy)294 int nla_validate(struct nlattr *head, int len, int maxtype,
295 struct nla_policy *policy)
296 {
297 struct nlattr *nla;
298 int rem, err;
299
300 nla_for_each_attr(nla, head, len, rem) {
301 err = validate_nla(nla, maxtype, policy);
302 if (err < 0)
303 goto errout;
304 }
305
306 err = 0;
307 errout:
308 return err;
309 }
310
311 /**
312 * Find a single attribute in a stream of attributes.
313 * @arg head Head of attributes stream.
314 * @arg len Length of attributes stream.
315 * @arg attrtype Attribute type to look for.
316 *
317 * Iterates over the stream of attributes and compares each type with
318 * the type specified. Returns the first attribute which matches the
319 * type.
320 *
321 * @return Pointer to attribute found or NULL.
322 */
nla_find(struct nlattr * head,int len,int attrtype)323 struct nlattr *nla_find(struct nlattr *head, int len, int attrtype)
324 {
325 struct nlattr *nla;
326 int rem;
327
328 nla_for_each_attr(nla, head, len, rem)
329 if (nla_type(nla) == attrtype)
330 return nla;
331
332 return NULL;
333 }
334
335 /** @} */
336
337 /**
338 * @name Helper Functions
339 * @{
340 */
341
342 /**
343 * Copy attribute payload to another memory area.
344 * @arg dest Pointer to destination memory area.
345 * @arg src Attribute
346 * @arg count Number of bytes to copy at most.
347 *
348 * Note: The number of bytes copied is limited by the length of
349 * the attribute payload.
350 *
351 * @return The number of bytes copied to dest.
352 */
nla_memcpy(void * dest,struct nlattr * src,int count)353 int nla_memcpy(void *dest, struct nlattr *src, int count)
354 {
355 int minlen;
356
357 if (!src)
358 return 0;
359
360 minlen = min_t(int, count, nla_len(src));
361 memcpy(dest, nla_data(src), minlen);
362
363 return minlen;
364 }
365
366 /**
367 * Copy string attribute payload to a buffer.
368 * @arg dst Pointer to destination buffer.
369 * @arg nla Attribute of type NLA_STRING.
370 * @arg dstsize Size of destination buffer in bytes.
371 *
372 * Copies at most dstsize - 1 bytes to the destination buffer.
373 * The result is always a valid NUL terminated string. Unlike
374 * strlcpy the destination buffer is always padded out.
375 *
376 * @return The length of string attribute without the terminating NUL.
377 */
nla_strlcpy(char * dst,const struct nlattr * nla,size_t dstsize)378 size_t nla_strlcpy(char *dst, const struct nlattr *nla, size_t dstsize)
379 {
380 size_t srclen = nla_len(nla);
381 char *src = nla_data(nla);
382
383 if (srclen > 0 && src[srclen - 1] == '\0')
384 srclen--;
385
386 if (dstsize > 0) {
387 size_t len = (srclen >= dstsize) ? dstsize - 1 : srclen;
388
389 memset(dst, 0, dstsize);
390 memcpy(dst, src, len);
391 }
392
393 return srclen;
394 }
395
396 /**
397 * Compare attribute payload with memory area.
398 * @arg nla Attribute.
399 * @arg data Memory area to compare to.
400 * @arg size Number of bytes to compare.
401 *
402 * @see memcmp(3)
403 * @return An integer less than, equal to, or greater than zero.
404 */
nla_memcmp(const struct nlattr * nla,const void * data,size_t size)405 int nla_memcmp(const struct nlattr *nla, const void *data, size_t size)
406 {
407 int d = nla_len(nla) - size;
408
409 if (d == 0)
410 d = memcmp(nla_data(nla), data, size);
411
412 return d;
413 }
414
415 /**
416 * Compare string attribute payload with string
417 * @arg nla Attribute of type NLA_STRING.
418 * @arg str NUL terminated string.
419 *
420 * @see strcmp(3)
421 * @return An integer less than, equal to, or greater than zero.
422 */
nla_strcmp(const struct nlattr * nla,const char * str)423 int nla_strcmp(const struct nlattr *nla, const char *str)
424 {
425 int len = strlen(str) + 1;
426 int d = nla_len(nla) - len;
427
428 if (d == 0)
429 d = memcmp(nla_data(nla), str, len);
430
431 return d;
432 }
433
434 /** @} */
435
436 /**
437 * @name Unspecific Attribute
438 * @{
439 */
440
441 /**
442 * Reserve space for a attribute.
443 * @arg msg Netlink Message.
444 * @arg attrtype Attribute Type.
445 * @arg attrlen Length of payload.
446 *
447 * Reserves room for a attribute in the specified netlink message and
448 * fills in the attribute header (type, length). Returns NULL if there
449 * is unsuficient space for the attribute.
450 *
451 * Any padding between payload and the start of the next attribute is
452 * zeroed out.
453 *
454 * @return Pointer to start of attribute or NULL on failure.
455 */
nla_reserve(struct nl_msg * msg,int attrtype,int attrlen)456 struct nlattr *nla_reserve(struct nl_msg *msg, int attrtype, int attrlen)
457 {
458 struct nlattr *nla;
459 int tlen;
460
461 if (attrlen < 0)
462 return NULL;
463
464 tlen = NLMSG_ALIGN(msg->nm_nlh->nlmsg_len) + nla_total_size(attrlen);
465
466 if (tlen > msg->nm_size)
467 return NULL;
468
469 nla = (struct nlattr *) nlmsg_tail(msg->nm_nlh);
470 nla->nla_type = attrtype;
471 nla->nla_len = nla_attr_size(attrlen);
472
473 if (attrlen)
474 memset((unsigned char *) nla + nla->nla_len, 0, nla_padlen(attrlen));
475 msg->nm_nlh->nlmsg_len = tlen;
476
477 NL_DBG(2, "msg %p: attr <%p> %d: Reserved %d (%d) bytes at offset +%td "
478 "nlmsg_len=%d\n", msg, nla, nla->nla_type,
479 nla_total_size(attrlen), attrlen,
480 (void *) nla - nlmsg_data(msg->nm_nlh),
481 msg->nm_nlh->nlmsg_len);
482
483 return nla;
484 }
485
486 /**
487 * Add a unspecific attribute to netlink message.
488 * @arg msg Netlink message.
489 * @arg attrtype Attribute type.
490 * @arg datalen Length of data to be used as payload.
491 * @arg data Pointer to data to be used as attribute payload.
492 *
493 * Reserves room for a unspecific attribute and copies the provided data
494 * into the message as payload of the attribute. Returns an error if there
495 * is insufficient space for the attribute.
496 *
497 * @see nla_reserve
498 * @return 0 on success or a negative error code.
499 */
nla_put(struct nl_msg * msg,int attrtype,int datalen,const void * data)500 int nla_put(struct nl_msg *msg, int attrtype, int datalen, const void *data)
501 {
502 struct nlattr *nla;
503
504 if (datalen < 0)
505 return -NLE_RANGE;
506
507 nla = nla_reserve(msg, attrtype, datalen);
508 if (!nla)
509 return -NLE_NOMEM;
510
511 if (datalen > 0) {
512 memcpy(nla_data(nla), data, datalen);
513 NL_DBG(2, "msg %p: attr <%p> %d: Wrote %d bytes at offset +%td\n",
514 msg, nla, nla->nla_type, datalen,
515 (void *) nla - nlmsg_data(msg->nm_nlh));
516 }
517
518 return 0;
519 }
520
521 /**
522 * Add abstract data as unspecific attribute to netlink message.
523 * @arg msg Netlink message.
524 * @arg attrtype Attribute type.
525 * @arg data Abstract data object.
526 *
527 * Equivalent to nla_put() except that the length of the payload is
528 * derived from the abstract data object.
529 *
530 * @see nla_put
531 * @return 0 on success or a negative error code.
532 */
nla_put_data(struct nl_msg * msg,int attrtype,struct nl_data * data)533 int nla_put_data(struct nl_msg *msg, int attrtype, struct nl_data *data)
534 {
535 return nla_put(msg, attrtype, nl_data_get_size(data),
536 nl_data_get(data));
537 }
538
539 /**
540 * Add abstract address as unspecific attribute to netlink message.
541 * @arg msg Netlink message.
542 * @arg attrtype Attribute type.
543 * @arg addr Abstract address object.
544 *
545 * @see nla_put
546 * @return 0 on success or a negative error code.
547 */
nla_put_addr(struct nl_msg * msg,int attrtype,struct nl_addr * addr)548 int nla_put_addr(struct nl_msg *msg, int attrtype, struct nl_addr *addr)
549 {
550 return nla_put(msg, attrtype, nl_addr_get_len(addr),
551 nl_addr_get_binary_addr(addr));
552 }
553
554 /** @} */
555
556 /**
557 * @name Integer Attributes
558 */
559
560 /**
561 * Add 8 bit integer attribute to netlink message.
562 * @arg msg Netlink message.
563 * @arg attrtype Attribute type.
564 * @arg value Numeric value to store as payload.
565 *
566 * @see nla_put
567 * @return 0 on success or a negative error code.
568 */
nla_put_u8(struct nl_msg * msg,int attrtype,uint8_t value)569 int nla_put_u8(struct nl_msg *msg, int attrtype, uint8_t value)
570 {
571 return nla_put(msg, attrtype, sizeof(uint8_t), &value);
572 }
573
574 /**
575 * Return value of 8 bit integer attribute.
576 * @arg nla 8 bit integer attribute
577 *
578 * @return Payload as 8 bit integer.
579 */
nla_get_u8(struct nlattr * nla)580 uint8_t nla_get_u8(struct nlattr *nla)
581 {
582 return *(uint8_t *) nla_data(nla);
583 }
584
585 /**
586 * Add 16 bit integer attribute to netlink message.
587 * @arg msg Netlink message.
588 * @arg attrtype Attribute type.
589 * @arg value Numeric value to store as payload.
590 *
591 * @see nla_put
592 * @return 0 on success or a negative error code.
593 */
nla_put_u16(struct nl_msg * msg,int attrtype,uint16_t value)594 int nla_put_u16(struct nl_msg *msg, int attrtype, uint16_t value)
595 {
596 return nla_put(msg, attrtype, sizeof(uint16_t), &value);
597 }
598
599 /**
600 * Return payload of 16 bit integer attribute.
601 * @arg nla 16 bit integer attribute
602 *
603 * @return Payload as 16 bit integer.
604 */
nla_get_u16(struct nlattr * nla)605 uint16_t nla_get_u16(struct nlattr *nla)
606 {
607 return *(uint16_t *) nla_data(nla);
608 }
609
610 /**
611 * Add 32 bit integer attribute to netlink message.
612 * @arg msg Netlink message.
613 * @arg attrtype Attribute type.
614 * @arg value Numeric value to store as payload.
615 *
616 * @see nla_put
617 * @return 0 on success or a negative error code.
618 */
nla_put_u32(struct nl_msg * msg,int attrtype,uint32_t value)619 int nla_put_u32(struct nl_msg *msg, int attrtype, uint32_t value)
620 {
621 return nla_put(msg, attrtype, sizeof(uint32_t), &value);
622 }
623
624 /**
625 * Return payload of 32 bit integer attribute.
626 * @arg nla 32 bit integer attribute.
627 *
628 * @return Payload as 32 bit integer.
629 */
nla_get_u32(struct nlattr * nla)630 uint32_t nla_get_u32(struct nlattr *nla)
631 {
632 return *(uint32_t *) nla_data(nla);
633 }
634
635 /**
636 * Add 64 bit integer attribute to netlink message.
637 * @arg msg Netlink message.
638 * @arg attrtype Attribute type.
639 * @arg value Numeric value to store as payload.
640 *
641 * @see nla_put
642 * @return 0 on success or a negative error code.
643 */
nla_put_u64(struct nl_msg * msg,int attrtype,uint64_t value)644 int nla_put_u64(struct nl_msg *msg, int attrtype, uint64_t value)
645 {
646 return nla_put(msg, attrtype, sizeof(uint64_t), &value);
647 }
648
649 /**
650 * Return payload of u64 attribute
651 * @arg nla u64 netlink attribute
652 *
653 * @return Payload as 64 bit integer.
654 */
nla_get_u64(struct nlattr * nla)655 uint64_t nla_get_u64(struct nlattr *nla)
656 {
657 uint64_t tmp = 0;
658
659 if (nla && nla_len(nla) >= sizeof(tmp))
660 memcpy(&tmp, nla_data(nla), sizeof(tmp));
661
662 return tmp;
663 }
664
665 /** @} */
666
667 /**
668 * @name String Attribute
669 */
670
671 /**
672 * Add string attribute to netlink message.
673 * @arg msg Netlink message.
674 * @arg attrtype Attribute type.
675 * @arg str NUL terminated string.
676 *
677 * @see nla_put
678 * @return 0 on success or a negative error code.
679 */
nla_put_string(struct nl_msg * msg,int attrtype,const char * str)680 int nla_put_string(struct nl_msg *msg, int attrtype, const char *str)
681 {
682 return nla_put(msg, attrtype, strlen(str) + 1, str);
683 }
684
685 /**
686 * Return payload of string attribute.
687 * @arg nla String attribute.
688 *
689 * @return Pointer to attribute payload.
690 */
nla_get_string(struct nlattr * nla)691 char *nla_get_string(struct nlattr *nla)
692 {
693 return (char *) nla_data(nla);
694 }
695
nla_strdup(struct nlattr * nla)696 char *nla_strdup(struct nlattr *nla)
697 {
698 return strdup(nla_get_string(nla));
699 }
700
701 /** @} */
702
703 /**
704 * @name Flag Attribute
705 */
706
707 /**
708 * Add flag netlink attribute to netlink message.
709 * @arg msg Netlink message.
710 * @arg attrtype Attribute type.
711 *
712 * @see nla_put
713 * @return 0 on success or a negative error code.
714 */
nla_put_flag(struct nl_msg * msg,int attrtype)715 int nla_put_flag(struct nl_msg *msg, int attrtype)
716 {
717 return nla_put(msg, attrtype, 0, NULL);
718 }
719
720 /**
721 * Return true if flag attribute is set.
722 * @arg nla Flag netlink attribute.
723 *
724 * @return True if flag is set, otherwise false.
725 */
nla_get_flag(struct nlattr * nla)726 int nla_get_flag(struct nlattr *nla)
727 {
728 return !!nla;
729 }
730
731 /** @} */
732
733 /**
734 * @name Microseconds Attribute
735 */
736
737 /**
738 * Add a msecs netlink attribute to a netlink message
739 * @arg n netlink message
740 * @arg attrtype attribute type
741 * @arg msecs number of msecs
742 */
nla_put_msecs(struct nl_msg * n,int attrtype,unsigned long msecs)743 int nla_put_msecs(struct nl_msg *n, int attrtype, unsigned long msecs)
744 {
745 return nla_put_u64(n, attrtype, msecs);
746 }
747
748 /**
749 * Return payload of msecs attribute
750 * @arg nla msecs netlink attribute
751 *
752 * @return the number of milliseconds.
753 */
nla_get_msecs(struct nlattr * nla)754 unsigned long nla_get_msecs(struct nlattr *nla)
755 {
756 return nla_get_u64(nla);
757 }
758
759 /** @} */
760
761 /**
762 * @name Nested Attribute
763 */
764
765 /**
766 * Add nested attributes to netlink message.
767 * @arg msg Netlink message.
768 * @arg attrtype Attribute type.
769 * @arg nested Message containing attributes to be nested.
770 *
771 * Takes the attributes found in the \a nested message and appends them
772 * to the message \a msg nested in a container of the type \a attrtype.
773 * The \a nested message may not have a family specific header.
774 *
775 * @see nla_put
776 * @return 0 on success or a negative error code.
777 */
nla_put_nested(struct nl_msg * msg,int attrtype,struct nl_msg * nested)778 int nla_put_nested(struct nl_msg *msg, int attrtype, struct nl_msg *nested)
779 {
780 NL_DBG(2, "msg %p: attr <> %d: adding msg %p as nested attribute\n",
781 msg, attrtype, nested);
782
783 return nla_put(msg, attrtype, nlmsg_datalen(nested->nm_nlh),
784 nlmsg_data(nested->nm_nlh));
785 }
786
787
788 /**
789 * Start a new level of nested attributes.
790 * @arg msg Netlink message.
791 * @arg attrtype Attribute type of container.
792 *
793 * @return Pointer to container attribute.
794 */
nla_nest_start(struct nl_msg * msg,int attrtype)795 struct nlattr *nla_nest_start(struct nl_msg *msg, int attrtype)
796 {
797 struct nlattr *start = (struct nlattr *) nlmsg_tail(msg->nm_nlh);
798
799 if (nla_put(msg, attrtype, 0, NULL) < 0)
800 return NULL;
801
802 NL_DBG(2, "msg %p: attr <%p> %d: starting nesting\n",
803 msg, start, start->nla_type);
804
805 return start;
806 }
807
808 /**
809 * Finalize nesting of attributes.
810 * @arg msg Netlink message.
811 * @arg start Container attribute as returned from nla_nest_start().
812 *
813 * Corrects the container attribute header to include the appeneded attributes.
814 *
815 * @return 0
816 */
nla_nest_end(struct nl_msg * msg,struct nlattr * start)817 int nla_nest_end(struct nl_msg *msg, struct nlattr *start)
818 {
819 size_t pad, len;
820
821 len = (void *) nlmsg_tail(msg->nm_nlh) - (void *) start;
822
823 if (len == NLA_HDRLEN) {
824 /*
825 * Kernel can't handle empty nested attributes, trim the
826 * attribute header again
827 */
828 nla_nest_cancel(msg, start);
829
830 return 0;
831 }
832
833 start->nla_len = len;
834
835 pad = NLMSG_ALIGN(msg->nm_nlh->nlmsg_len) - msg->nm_nlh->nlmsg_len;
836 if (pad > 0) {
837 /*
838 * Data inside attribute does not end at a alignment boundry.
839 * Pad accordingly and accoun for the additional space in
840 * the message. nlmsg_reserve() may never fail in this situation,
841 * the allocate message buffer must be a multiple of NLMSG_ALIGNTO.
842 */
843 if (!nlmsg_reserve(msg, pad, 0))
844 BUG();
845
846 NL_DBG(2, "msg %p: attr <%p> %d: added %zu bytes of padding\n",
847 msg, start, start->nla_type, pad);
848 }
849
850 NL_DBG(2, "msg %p: attr <%p> %d: closing nesting, len=%u\n",
851 msg, start, start->nla_type, start->nla_len);
852
853 return 0;
854 }
855
856 /**
857 * Cancel the addition of a nested attribute
858 * @arg msg Netlink message
859 * @arg attr Nested netlink attribute
860 *
861 * Removes any partially added nested Netlink attribute from the message
862 * by resetting the message to the size before the call to nla_nest_start()
863 * and by overwriting any potentially touched message segments with 0.
864 */
nla_nest_cancel(struct nl_msg * msg,struct nlattr * attr)865 void nla_nest_cancel(struct nl_msg *msg, struct nlattr *attr)
866 {
867 ssize_t len;
868
869 len = (void *) nlmsg_tail(msg->nm_nlh) - (void *) attr;
870 if (len < 0)
871 BUG();
872 else if (len > 0) {
873 msg->nm_nlh->nlmsg_len -= len;
874 memset(nlmsg_tail(msg->nm_nlh), 0, len);
875 }
876 }
877
878 /**
879 * Create attribute index based on nested attribute
880 * @arg tb Index array to be filled (maxtype+1 elements).
881 * @arg maxtype Maximum attribute type expected and accepted.
882 * @arg nla Nested Attribute.
883 * @arg policy Attribute validation policy.
884 *
885 * Feeds the stream of attributes nested into the specified attribute
886 * to nla_parse().
887 *
888 * @see nla_parse
889 * @return 0 on success or a negative error code.
890 */
nla_parse_nested(struct nlattr * tb[],int maxtype,struct nlattr * nla,struct nla_policy * policy)891 int nla_parse_nested(struct nlattr *tb[], int maxtype, struct nlattr *nla,
892 struct nla_policy *policy)
893 {
894 return nla_parse(tb, maxtype, nla_data(nla), nla_len(nla), policy);
895 }
896
897 /**
898 * Return true if attribute has NLA_F_NESTED flag set
899 * @arg attr Netlink attribute
900 *
901 * @return True if attribute has NLA_F_NESTED flag set, oterhwise False.
902 */
nla_is_nested(struct nlattr * attr)903 int nla_is_nested(struct nlattr *attr)
904 {
905 return !!(attr->nla_type & NLA_F_NESTED);
906 }
907
908 /** @} */
909
910 /** @} */
911