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1 office 1 /*
2 * lib/msg.c Netlink Messages Interface
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 /**
13 * @ingroup core
14 * @defgroup msg Messages
15 * Netlink Message Construction/Parsing Interface
16 *
17 * The following information is partly extracted from RFC3549
18 * (ftp://ftp.rfc-editor.org/in-notes/rfc3549.txt)
19 *
20 * @par Message Format
21 * Netlink messages consist of a byte stream with one or multiple
22 * Netlink headers and an associated payload. If the payload is too big
23 * to fit into a single message it, can be split over multiple Netlink
24 * messages, collectively called a multipart message. For multipart
25 * messages, the first and all following headers have the \c NLM_F_MULTI
26 * Netlink header flag set, except for the last header which has the
27 * Netlink header type \c NLMSG_DONE.
28 *
29 * @par
30 * The Netlink message header (\link nlmsghdr struct nlmsghdr\endlink) is shown below.
31 * @code
32 * 0 1 2 3
33 * 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
34 * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
35 * | Length |
36 * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
37 * | Type | Flags |
38 * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
39 * | Sequence Number |
40 * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
41 * | Process ID (PID) |
42 * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
43 * @endcode
44 *
45 * @par
46 * The netlink message header and payload must be aligned properly:
47 * @code
48 * <------- NLMSG_ALIGN(hlen) ------> <---- NLMSG_ALIGN(len) --->
49 * +----------------------------+- - -+- - - - - - - - - - -+- - -+
50 * | Header | Pad | Payload | Pad |
51 * | struct nlmsghdr | | | |
52 * +----------------------------+- - -+- - - - - - - - - - -+- - -+
53 * @endcode
54 * @par
55 * Message Format:
56 * @code
57 * <--- nlmsg_total_size(payload) --->
58 * <-- nlmsg_msg_size(payload) ->
59 * +----------+- - -+-------------+- - -+-------- - -
60 * | nlmsghdr | Pad | Payload | Pad | nlmsghdr
61 * +----------+- - -+-------------+- - -+-------- - -
62 * nlmsg_data(nlh)---^ ^
63 * nlmsg_next(nlh)-----------------------+
64 * @endcode
65 * @par
66 * The payload may consist of arbitary data but may have strict
67 * alignment and formatting rules depening on the specific netlink
68 * families.
69 * @par
70 * @code
71 * <---------------------- nlmsg_len(nlh) --------------------->
72 * <------ hdrlen ------> <- nlmsg_attrlen(nlh, hdrlen) ->
73 * +----------------------+- - -+--------------------------------+
74 * | Family Header | Pad | Attributes |
75 * +----------------------+- - -+--------------------------------+
76 * nlmsg_attrdata(nlh, hdrlen)---^
77 * @endcode
78 * @par The ACK Netlink Message
79 * This message is actually used to denote both an ACK and a NACK.
80 * Typically, the direction is from FEC to CPC (in response to an ACK
81 * request message). However, the CPC should be able to send ACKs back
82 * to FEC when requested.
83 * @code
84 * 0 1 2 3
85 * 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
86 * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
87 * | Netlink message header |
88 * | type = NLMSG_ERROR |
89 * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
90 * | Error code |
91 * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
92 * | OLD Netlink message header |
93 * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
94 * @endcode
95 *
96 * @par Example
97 * @code
98 * // Various methods exist to create/allocate a new netlink
99 * // message.
100 * //
101 * // nlmsg_alloc() will allocate an empty netlink message with
102 * // a maximum payload size which defaults to the page size of
103 * // the system. This default size can be modified using the
104 * // function nlmsg_set_default_size().
105 * struct nl_msg *msg = nlmsg_alloc();
106 *
107 * // Very often, the message type and message flags are known
108 * // at allocation time while the other fields are auto generated:
109 * struct nl_msg *msg = nlmsg_alloc_simple(MY_TYPE, MY_FLAGS);
110 *
111 * // Alternatively an existing netlink message header can be used
112 * // to inherit the header values:
113 * struct nlmsghdr hdr = {
114 * .nlmsg_type = MY_TYPE,
115 * .nlmsg_flags = MY_FLAGS,
116 * };
117 * struct nl_msg *msg = nlmsg_inherit(&hdr);
118 *
119 * // Last but not least, netlink messages received from netlink sockets
120 * // can be converted into nl_msg objects using nlmsg_convert(). This
121 * // will create a message with a maximum payload size which equals the
122 * // length of the existing netlink message, therefore no more data can
123 * // be appened without calling nlmsg_expand() first.
124 * struct nl_msg *msg = nlmsg_convert(nlh_from_nl_sock);
125 *
126 * // Payload may be added to the message via nlmsg_append(). The fourth
127 * // parameter specifies the number of alignment bytes the data should
128 * // be padding with at the end. Common values are 0 to disable it or
129 * // NLMSG_ALIGNTO to ensure proper netlink message padding.
130 * nlmsg_append(msg, &mydata, sizeof(mydata), 0);
131 *
132 * // Sometimes it may be necessary to reserve room for data but defer
133 * // the actual copying to a later point, nlmsg_reserve() can be used
134 * // for this purpose:
135 * void *data = nlmsg_reserve(msg, sizeof(mydata), NLMSG_ALIGNTO);
136 *
137 * // Attributes may be added using the attributes interface.
138 *
139 * // After successful use of the message, the memory must be freed
140 * // using nlmsg_free()
141 * nlmsg_free(msg);
142 * @endcode
143 *
144 * @par 4) Parsing messages
145 * @code
146 * int n;
147 * unsigned char *buf;
148 * struct nlmsghdr *hdr;
149 *
150 * n = nl_recv(handle, NULL, &buf);
151 *
152 * hdr = (struct nlmsghdr *) buf;
153 * while (nlmsg_ok(hdr, n)) {
154 * // Process message here...
155 * hdr = nlmsg_next(hdr, &n);
156 * }
157 * @endcode
158 * @{
159 */
160  
161 #include <netlink-local.h>
162 #include <netlink/netlink.h>
163 #include <netlink/utils.h>
164 #include <netlink/cache.h>
165 #include <netlink/attr.h>
166 #include <netlink/msg.h>
167 #include <linux/socket.h>
168  
169 static size_t default_msg_size = 4096;
170  
171 /**
172 * @name Attribute Access
173 * @{
174 */
175  
176 //** @} */
177  
178 /**
179 * @name Message Parsing
180 * @{
181 */
182  
183 /**
184 * check if the netlink message fits into the remaining bytes
185 * @arg nlh netlink message header
186 * @arg remaining number of bytes remaining in message stream
187 */
188 int nlmsg_ok(const struct nlmsghdr *nlh, int remaining)
189 {
190 return (remaining >= sizeof(struct nlmsghdr) &&
191 nlh->nlmsg_len >= sizeof(struct nlmsghdr) &&
192 nlh->nlmsg_len <= remaining);
193 }
194  
195 /**
196 * next netlink message in message stream
197 * @arg nlh netlink message header
198 * @arg remaining number of bytes remaining in message stream
199 *
200 * @returns the next netlink message in the message stream and
201 * decrements remaining by the size of the current message.
202 */
203 struct nlmsghdr *nlmsg_next(struct nlmsghdr *nlh, int *remaining)
204 {
205 int totlen = NLMSG_ALIGN(nlh->nlmsg_len);
206  
207 *remaining -= totlen;
208  
209 return (struct nlmsghdr *) ((unsigned char *) nlh + totlen);
210 }
211  
212 /**
213 * parse attributes of a netlink message
214 * @arg nlh netlink message header
215 * @arg hdrlen length of family specific header
216 * @arg tb destination array with maxtype+1 elements
217 * @arg maxtype maximum attribute type to be expected
218 * @arg policy validation policy
219 *
220 * See nla_parse()
221 */
222 int nlmsg_parse(struct nlmsghdr *nlh, int hdrlen, struct nlattr *tb[],
223 int maxtype, struct nla_policy *policy)
224 {
225 if (!nlmsg_valid_hdr(nlh, hdrlen))
226 return -NLE_MSG_TOOSHORT;
227  
228 return nla_parse(tb, maxtype, nlmsg_attrdata(nlh, hdrlen),
229 nlmsg_attrlen(nlh, hdrlen), policy);
230 }
231  
232 /**
233 * nlmsg_validate - validate a netlink message including attributes
234 * @arg nlh netlinket message header
235 * @arg hdrlen length of familiy specific header
236 * @arg maxtype maximum attribute type to be expected
237 * @arg policy validation policy
238 */
239 int nlmsg_validate(struct nlmsghdr *nlh, int hdrlen, int maxtype,
240 struct nla_policy *policy)
241 {
242 if (!nlmsg_valid_hdr(nlh, hdrlen))
243 return -NLE_MSG_TOOSHORT;
244  
245 return nla_validate(nlmsg_attrdata(nlh, hdrlen),
246 nlmsg_attrlen(nlh, hdrlen), maxtype, policy);
247 }
248  
249 /** @} */
250  
251 /**
252 * @name Message Building/Access
253 * @{
254 */
255  
256 static struct nl_msg *__nlmsg_alloc(size_t len)
257 {
258 struct nl_msg *nm;
259  
260 nm = calloc(1, sizeof(*nm));
261 if (!nm)
262 goto errout;
263  
264 nm->nm_refcnt = 1;
265  
266 nm->nm_nlh = malloc(len);
267 if (!nm->nm_nlh)
268 goto errout;
269  
270 memset(nm->nm_nlh, 0, sizeof(struct nlmsghdr));
271  
272 nm->nm_protocol = -1;
273 nm->nm_size = len;
274 nm->nm_nlh->nlmsg_len = nlmsg_total_size(0);
275  
276 NL_DBG(2, "msg %p: Allocated new message, maxlen=%zu\n", nm, len);
277  
278 return nm;
279 errout:
280 free(nm);
281 return NULL;
282 }
283  
284 /**
285 * Allocate a new netlink message with the default maximum payload size.
286 *
287 * Allocates a new netlink message without any further payload. The
288 * maximum payload size defaults to PAGESIZE or as otherwise specified
289 * with nlmsg_set_default_size().
290 *
291 * @return Newly allocated netlink message or NULL.
292 */
293 struct nl_msg *nlmsg_alloc(void)
294 {
295 return __nlmsg_alloc(default_msg_size);
296 }
297  
298 /**
299 * Allocate a new netlink message with maximum payload size specified.
300 */
301 struct nl_msg *nlmsg_alloc_size(size_t max)
302 {
303 return __nlmsg_alloc(max);
304 }
305  
306 /**
307 * Allocate a new netlink message and inherit netlink message header
308 * @arg hdr Netlink message header template
309 *
310 * Allocates a new netlink message and inherits the original message
311 * header. If \a hdr is not NULL it will be used as a template for
312 * the netlink message header, otherwise the header is left blank.
313 *
314 * @return Newly allocated netlink message or NULL
315 */
316 struct nl_msg *nlmsg_inherit(struct nlmsghdr *hdr)
317 {
318 struct nl_msg *nm;
319  
320 nm = nlmsg_alloc();
321 if (nm && hdr) {
322 struct nlmsghdr *new = nm->nm_nlh;
323  
324 new->nlmsg_type = hdr->nlmsg_type;
325 new->nlmsg_flags = hdr->nlmsg_flags;
326 new->nlmsg_seq = hdr->nlmsg_seq;
327 new->nlmsg_pid = hdr->nlmsg_pid;
328 }
329  
330 return nm;
331 }
332  
333 /**
334 * Allocate a new netlink message
335 * @arg nlmsgtype Netlink message type
336 * @arg flags Message flags.
337 *
338 * @return Newly allocated netlink message or NULL.
339 */
340 struct nl_msg *nlmsg_alloc_simple(int nlmsgtype, int flags)
341 {
342 struct nl_msg *msg;
343 struct nlmsghdr nlh = {
344 .nlmsg_type = nlmsgtype,
345 .nlmsg_flags = flags,
346 };
347  
348 msg = nlmsg_inherit(&nlh);
349 if (msg)
350 NL_DBG(2, "msg %p: Allocated new simple message\n", msg);
351  
352 return msg;
353 }
354  
355 /**
356 * Set the default maximum message payload size for allocated messages
357 * @arg max Size of payload in bytes.
358 */
359 void nlmsg_set_default_size(size_t max)
360 {
361 if (max < nlmsg_total_size(0))
362 max = nlmsg_total_size(0);
363  
364 default_msg_size = max;
365 }
366  
367 /**
368 * Convert a netlink message received from a netlink socket to a nl_msg
369 * @arg hdr Netlink message received from netlink socket.
370 *
371 * Allocates a new netlink message and copies all of the data pointed to
372 * by \a hdr into the new message object.
373 *
374 * @return Newly allocated netlink message or NULL.
375 */
376 struct nl_msg *nlmsg_convert(struct nlmsghdr *hdr)
377 {
378 struct nl_msg *nm;
379  
380 nm = __nlmsg_alloc(NLMSG_ALIGN(hdr->nlmsg_len));
381 if (!nm)
382 goto errout;
383  
384 memcpy(nm->nm_nlh, hdr, hdr->nlmsg_len);
385  
386 return nm;
387 errout:
388 nlmsg_free(nm);
389 return NULL;
390 }
391  
392 /**
393 * Reserve room for additional data in a netlink message
394 * @arg n netlink message
395 * @arg len length of additional data to reserve room for
396 * @arg pad number of bytes to align data to
397 *
398 * Reserves room for additional data at the tail of the an
399 * existing netlink message. Eventual padding required will
400 * be zeroed out.
401 *
402 * @return Pointer to start of additional data tailroom or NULL.
403 */
404 void *nlmsg_reserve(struct nl_msg *n, size_t len, int pad)
405 {
406 void *buf = n->nm_nlh;
407 size_t nlmsg_len = n->nm_nlh->nlmsg_len;
408 size_t tlen;
409  
410 tlen = pad ? ((len + (pad - 1)) & ~(pad - 1)) : len;
411  
412 if ((tlen + nlmsg_len) > n->nm_size)
413 return NULL;
414  
415 buf += nlmsg_len;
416 n->nm_nlh->nlmsg_len += tlen;
417  
418 if (tlen > len)
419 memset(buf + len, 0, tlen - len);
420  
421 NL_DBG(2, "msg %p: Reserved %zu bytes, pad=%d, nlmsg_len=%d\n",
422 n, len, pad, n->nm_nlh->nlmsg_len);
423  
424 return buf;
425 }
426  
427 /**
428 * Append data to tail of a netlink message
429 * @arg n netlink message
430 * @arg data data to add
431 * @arg len length of data
432 * @arg pad Number of bytes to align data to.
433 *
434 * Extends the netlink message as needed and appends the data of given
435 * length to the message.
436 *
437 * @return 0 on success or a negative error code
438 */
439 int nlmsg_append(struct nl_msg *n, void *data, size_t len, int pad)
440 {
441 void *tmp;
442  
443 tmp = nlmsg_reserve(n, len, pad);
444 if (tmp == NULL)
445 return -NLE_NOMEM;
446  
447 memcpy(tmp, data, len);
448 NL_DBG(2, "msg %p: Appended %zu bytes with padding %d\n", n, len, pad);
449  
450 return 0;
451 }
452  
453 /**
454 * Add a netlink message header to a netlink message
455 * @arg n netlink message
456 * @arg pid netlink process id or NL_AUTO_PID
457 * @arg seq sequence number of message or NL_AUTO_SEQ
458 * @arg type message type
459 * @arg payload length of message payload
460 * @arg flags message flags
461 *
462 * Adds or overwrites the netlink message header in an existing message
463 * object. If \a payload is greater-than zero additional room will be
464 * reserved, f.e. for family specific headers. It can be accesed via
465 * nlmsg_data().
466 *
467 * @return A pointer to the netlink message header or NULL.
468 */
469 struct nlmsghdr *nlmsg_put(struct nl_msg *n, uint32_t pid, uint32_t seq,
470 int type, int payload, int flags)
471 {
472 struct nlmsghdr *nlh;
473  
474 if (n->nm_nlh->nlmsg_len < NLMSG_HDRLEN)
475 BUG();
476  
477 nlh = (struct nlmsghdr *) n->nm_nlh;
478 nlh->nlmsg_type = type;
479 nlh->nlmsg_flags = flags;
480 nlh->nlmsg_pid = pid;
481 nlh->nlmsg_seq = seq;
482  
483 NL_DBG(2, "msg %p: Added netlink header type=%d, flags=%d, pid=%d, "
484 "seq=%d\n", n, type, flags, pid, seq);
485  
486 if (payload > 0 &&
487 nlmsg_reserve(n, payload, NLMSG_ALIGNTO) == NULL)
488 return NULL;
489  
490 return nlh;
491 }
492  
493 /**
494 * Release a reference from an netlink message
495 * @arg msg message to release reference from
496 *
497 * Frees memory after the last reference has been released.
498 */
499 void nlmsg_free(struct nl_msg *msg)
500 {
501 if (!msg)
502 return;
503  
504 msg->nm_refcnt--;
505 NL_DBG(4, "Returned message reference %p, %d remaining\n",
506 msg, msg->nm_refcnt);
507  
508 if (msg->nm_refcnt < 0)
509 BUG();
510  
511 if (msg->nm_refcnt <= 0) {
512 free(msg->nm_nlh);
513 free(msg);
514 NL_DBG(2, "msg %p: Freed\n", msg);
515 }
516 }
517  
518 /** @} */
519  
520 /**
521 * @name Direct Parsing
522 * @{
523 */
524  
525 /** @cond SKIP */
526 struct dp_xdata {
527 void (*cb)(struct nl_object *, void *);
528 void *arg;
529 };
530 /** @endcond */
531  
532 static int parse_cb(struct nl_object *obj, struct nl_parser_param *p)
533 {
534 struct dp_xdata *x = p->pp_arg;
535  
536 x->cb(obj, x->arg);
537 return 0;
538 }
539  
540 int nl_msg_parse(struct nl_msg *msg, void (*cb)(struct nl_object *, void *),
541 void *arg)
542 {
543 struct nl_cache_ops *ops;
544 struct nl_parser_param p = {
545 .pp_cb = parse_cb
546 };
547 struct dp_xdata x = {
548 .cb = cb,
549 .arg = arg,
550 };
551  
552 ops = nl_cache_ops_associate(nlmsg_get_proto(msg),
553 nlmsg_hdr(msg)->nlmsg_type);
554 if (ops == NULL)
555 return -NLE_MSGTYPE_NOSUPPORT;
556 p.pp_arg = &x;
557  
558 return nl_cache_parse(ops, NULL, nlmsg_hdr(msg), &p);
559 }
560  
561 /** @} */