/net/dccp/feat.c

   1// SPDX-License-Identifier: GPL-2.0-or-later
   2/*
   3 *  net/dccp/feat.c
   4 *
   5 *  Feature negotiation for the DCCP protocol (RFC 4340, section 6)
   6 *
   7 *  Copyright (c) 2008 Gerrit Renker <gerrit@erg.abdn.ac.uk>
   8 *  Rewrote from scratch, some bits from earlier code by
   9 *  Copyright (c) 2005 Andrea Bittau <a.bittau@cs.ucl.ac.uk>
  10 *
  11 *  ASSUMPTIONS
  12 *  -----------
  13 *  o Feature negotiation is coordinated with connection setup (as in TCP), wild
  14 *    changes of parameters of an established connection are not supported.
  15 *  o Changing non-negotiable (NN) values is supported in state OPEN/PARTOPEN.
  16 *  o All currently known SP features have 1-byte quantities. If in the future
  17 *    extensions of RFCs 4340..42 define features with item lengths larger than
  18 *    one byte, a feature-specific extension of the code will be required.
  19 */
  20#include <linux/module.h>
  21#include <linux/slab.h>
  22#include "ccid.h"
  23#include "feat.h"
  24
  25/* feature-specific sysctls - initialised to the defaults from RFC 4340, 6.4 */
  26unsigned long	sysctl_dccp_sequence_window __read_mostly = 100;
  27int		sysctl_dccp_rx_ccid	    __read_mostly = 2,
  28		sysctl_dccp_tx_ccid	    __read_mostly = 2;
  29
  30/*
  31 * Feature activation handlers.
  32 *
  33 * These all use an u64 argument, to provide enough room for NN/SP features. At
  34 * this stage the negotiated values have been checked to be within their range.
  35 */
  36static int dccp_hdlr_ccid(struct sock *sk, u64 ccid, bool rx)
  37{
  38	struct dccp_sock *dp = dccp_sk(sk);
  39	struct ccid *new_ccid = ccid_new(ccid, sk, rx);
  40
  41	if (new_ccid == NULL)
  42		return -ENOMEM;
  43
  44	if (rx) {
  45		ccid_hc_rx_delete(dp->dccps_hc_rx_ccid, sk);
  46		dp->dccps_hc_rx_ccid = new_ccid;
  47	} else {
  48		ccid_hc_tx_delete(dp->dccps_hc_tx_ccid, sk);
  49		dp->dccps_hc_tx_ccid = new_ccid;
  50	}
  51	return 0;
  52}
  53
  54static int dccp_hdlr_seq_win(struct sock *sk, u64 seq_win, bool rx)
  55{
  56	struct dccp_sock *dp = dccp_sk(sk);
  57
  58	if (rx) {
  59		dp->dccps_r_seq_win = seq_win;
  60		/* propagate changes to update SWL/SWH */
  61		dccp_update_gsr(sk, dp->dccps_gsr);
  62	} else {
  63		dp->dccps_l_seq_win = seq_win;
  64		/* propagate changes to update AWL */
  65		dccp_update_gss(sk, dp->dccps_gss);
  66	}
  67	return 0;
  68}
  69
  70static int dccp_hdlr_ack_ratio(struct sock *sk, u64 ratio, bool rx)
  71{
  72	if (rx)
  73		dccp_sk(sk)->dccps_r_ack_ratio = ratio;
  74	else
  75		dccp_sk(sk)->dccps_l_ack_ratio = ratio;
  76	return 0;
  77}
  78
  79static int dccp_hdlr_ackvec(struct sock *sk, u64 enable, bool rx)
  80{
  81	struct dccp_sock *dp = dccp_sk(sk);
  82
  83	if (rx) {
  84		if (enable && dp->dccps_hc_rx_ackvec == NULL) {
  85			dp->dccps_hc_rx_ackvec = dccp_ackvec_alloc(gfp_any());
  86			if (dp->dccps_hc_rx_ackvec == NULL)
  87				return -ENOMEM;
  88		} else if (!enable) {
  89			dccp_ackvec_free(dp->dccps_hc_rx_ackvec);
  90			dp->dccps_hc_rx_ackvec = NULL;
  91		}
  92	}
  93	return 0;
  94}
  95
  96static int dccp_hdlr_ndp(struct sock *sk, u64 enable, bool rx)
  97{
  98	if (!rx)
  99		dccp_sk(sk)->dccps_send_ndp_count = (enable > 0);
 100	return 0;
 101}
 102
 103/*
 104 * Minimum Checksum Coverage is located at the RX side (9.2.1). This means that
 105 * `rx' holds when the sending peer informs about his partial coverage via a
 106 * ChangeR() option. In the other case, we are the sender and the receiver
 107 * announces its coverage via ChangeL() options. The policy here is to honour
 108 * such communication by enabling the corresponding partial coverage - but only
 109 * if it has not been set manually before; the warning here means that all
 110 * packets will be dropped.
 111 */
 112static int dccp_hdlr_min_cscov(struct sock *sk, u64 cscov, bool rx)
 113{
 114	struct dccp_sock *dp = dccp_sk(sk);
 115
 116	if (rx)
 117		dp->dccps_pcrlen = cscov;
 118	else {
 119		if (dp->dccps_pcslen == 0)
 120			dp->dccps_pcslen = cscov;
 121		else if (cscov > dp->dccps_pcslen)
 122			DCCP_WARN("CsCov %u too small, peer requires >= %u\n",
 123				  dp->dccps_pcslen, (u8)cscov);
 124	}
 125	return 0;
 126}
 127
 128static const struct {
 129	u8			feat_num;		/* DCCPF_xxx */
 130	enum dccp_feat_type	rxtx;			/* RX or TX  */
 131	enum dccp_feat_type	reconciliation;		/* SP or NN  */
 132	u8			default_value;		/* as in 6.4 */
 133	int (*activation_hdlr)(struct sock *sk, u64 val, bool rx);
 134/*
 135 *    Lookup table for location and type of features (from RFC 4340/4342)
 136 *  +--------------------------+----+-----+----+----+---------+-----------+
 137 *  | Feature                  | Location | Reconc. | Initial |  Section  |
 138 *  |                          | RX | TX  | SP | NN |  Value  | Reference |
 139 *  +--------------------------+----+-----+----+----+---------+-----------+
 140 *  | DCCPF_CCID               |    |  X  | X  |    |   2     | 10        |
 141 *  | DCCPF_SHORT_SEQNOS       |    |  X  | X  |    |   0     |  7.6.1    |
 142 *  | DCCPF_SEQUENCE_WINDOW    |    |  X  |    | X  | 100     |  7.5.2    |
 143 *  | DCCPF_ECN_INCAPABLE      | X  |     | X  |    |   0     | 12.1      |
 144 *  | DCCPF_ACK_RATIO          |    |  X  |    | X  |   2     | 11.3      |
 145 *  | DCCPF_SEND_ACK_VECTOR    | X  |     | X  |    |   0     | 11.5      |
 146 *  | DCCPF_SEND_NDP_COUNT     |    |  X  | X  |    |   0     |  7.7.2    |
 147 *  | DCCPF_MIN_CSUM_COVER     | X  |     | X  |    |   0     |  9.2.1    |
 148 *  | DCCPF_DATA_CHECKSUM      | X  |     | X  |    |   0     |  9.3.1    |
 149 *  | DCCPF_SEND_LEV_RATE      | X  |     | X  |    |   0     | 4342/8.4  |
 150 *  +--------------------------+----+-----+----+----+---------+-----------+
 151 */
 152} dccp_feat_table[] = {
 153	{ DCCPF_CCID,		 FEAT_AT_TX, FEAT_SP, 2,   dccp_hdlr_ccid     },
 154	{ DCCPF_SHORT_SEQNOS,	 FEAT_AT_TX, FEAT_SP, 0,   NULL },
 155	{ DCCPF_SEQUENCE_WINDOW, FEAT_AT_TX, FEAT_NN, 100, dccp_hdlr_seq_win  },
 156	{ DCCPF_ECN_INCAPABLE,	 FEAT_AT_RX, FEAT_SP, 0,   NULL },
 157	{ DCCPF_ACK_RATIO,	 FEAT_AT_TX, FEAT_NN, 2,   dccp_hdlr_ack_ratio},
 158	{ DCCPF_SEND_ACK_VECTOR, FEAT_AT_RX, FEAT_SP, 0,   dccp_hdlr_ackvec   },
 159	{ DCCPF_SEND_NDP_COUNT,  FEAT_AT_TX, FEAT_SP, 0,   dccp_hdlr_ndp      },
 160	{ DCCPF_MIN_CSUM_COVER,  FEAT_AT_RX, FEAT_SP, 0,   dccp_hdlr_min_cscov},
 161	{ DCCPF_DATA_CHECKSUM,	 FEAT_AT_RX, FEAT_SP, 0,   NULL },
 162	{ DCCPF_SEND_LEV_RATE,	 FEAT_AT_RX, FEAT_SP, 0,   NULL },
 163};
 164#define DCCP_FEAT_SUPPORTED_MAX		ARRAY_SIZE(dccp_feat_table)
 165
 166/**
 167 * dccp_feat_index  -  Hash function to map feature number into array position
 168 * Returns consecutive array index or -1 if the feature is not understood.
 169 */
 170static int dccp_feat_index(u8 feat_num)
 171{
 172	/* The first 9 entries are occupied by the types from RFC 4340, 6.4 */
 173	if (feat_num > DCCPF_RESERVED && feat_num <= DCCPF_DATA_CHECKSUM)
 174		return feat_num - 1;
 175
 176	/*
 177	 * Other features: add cases for new feature types here after adding
 178	 * them to the above table.
 179	 */
 180	switch (feat_num) {
 181	case DCCPF_SEND_LEV_RATE:
 182			return DCCP_FEAT_SUPPORTED_MAX - 1;
 183	}
 184	return -1;
 185}
 186
 187static u8 dccp_feat_type(u8 feat_num)
 188{
 189	int idx = dccp_feat_index(feat_num);
 190
 191	if (idx < 0)
 192		return FEAT_UNKNOWN;
 193	return dccp_feat_table[idx].reconciliation;
 194}
 195
 196static int dccp_feat_default_value(u8 feat_num)
 197{
 198	int idx = dccp_feat_index(feat_num);
 199	/*
 200	 * There are no default values for unknown features, so encountering a
 201	 * negative index here indicates a serious problem somewhere else.
 202	 */
 203	DCCP_BUG_ON(idx < 0);
 204
 205	return idx < 0 ? 0 : dccp_feat_table[idx].default_value;
 206}
 207
 208/*
 209 *	Debugging and verbose-printing section
 210 */
 211static const char *dccp_feat_fname(const u8 feat)
 212{
 213	static const char *const feature_names[] = {
 214		[DCCPF_RESERVED]	= "Reserved",
 215		[DCCPF_CCID]		= "CCID",
 216		[DCCPF_SHORT_SEQNOS]	= "Allow Short Seqnos",
 217		[DCCPF_SEQUENCE_WINDOW]	= "Sequence Window",
 218		[DCCPF_ECN_INCAPABLE]	= "ECN Incapable",
 219		[DCCPF_ACK_RATIO]	= "Ack Ratio",
 220		[DCCPF_SEND_ACK_VECTOR]	= "Send ACK Vector",
 221		[DCCPF_SEND_NDP_COUNT]	= "Send NDP Count",
 222		[DCCPF_MIN_CSUM_COVER]	= "Min. Csum Coverage",
 223		[DCCPF_DATA_CHECKSUM]	= "Send Data Checksum",
 224	};
 225	if (feat > DCCPF_DATA_CHECKSUM && feat < DCCPF_MIN_CCID_SPECIFIC)
 226		return feature_names[DCCPF_RESERVED];
 227
 228	if (feat ==  DCCPF_SEND_LEV_RATE)
 229		return "Send Loss Event Rate";
 230	if (feat >= DCCPF_MIN_CCID_SPECIFIC)
 231		return "CCID-specific";
 232
 233	return feature_names[feat];
 234}
 235
 236static const char *const dccp_feat_sname[] = {
 237	"DEFAULT", "INITIALISING", "CHANGING", "UNSTABLE", "STABLE",
 238};
 239
 240#ifdef CONFIG_IP_DCCP_DEBUG
 241static const char *dccp_feat_oname(const u8 opt)
 242{
 243	switch (opt) {
 244	case DCCPO_CHANGE_L:  return "Change_L";
 245	case DCCPO_CONFIRM_L: return "Confirm_L";
 246	case DCCPO_CHANGE_R:  return "Change_R";
 247	case DCCPO_CONFIRM_R: return "Confirm_R";
 248	}
 249	return NULL;
 250}
 251
 252static void dccp_feat_printval(u8 feat_num, dccp_feat_val const *val)
 253{
 254	u8 i, type = dccp_feat_type(feat_num);
 255
 256	if (val == NULL || (type == FEAT_SP && val->sp.vec == NULL))
 257		dccp_pr_debug_cat("(NULL)");
 258	else if (type == FEAT_SP)
 259		for (i = 0; i < val->sp.len; i++)
 260			dccp_pr_debug_cat("%s%u", i ? " " : "", val->sp.vec[i]);
 261	else if (type == FEAT_NN)
 262		dccp_pr_debug_cat("%llu", (unsigned long long)val->nn);
 263	else
 264		dccp_pr_debug_cat("unknown type %u", type);
 265}
 266
 267static void dccp_feat_printvals(u8 feat_num, u8 *list, u8 len)
 268{
 269	u8 type = dccp_feat_type(feat_num);
 270	dccp_feat_val fval = { .sp.vec = list, .sp.len = len };
 271
 272	if (type == FEAT_NN)
 273		fval.nn = dccp_decode_value_var(list, len);
 274	dccp_feat_printval(feat_num, &fval);
 275}
 276
 277static void dccp_feat_print_entry(struct dccp_feat_entry const *entry)
 278{
 279	dccp_debug("   * %s %s = ", entry->is_local ? "local" : "remote",
 280				    dccp_feat_fname(entry->feat_num));
 281	dccp_feat_printval(entry->feat_num, &entry->val);
 282	dccp_pr_debug_cat(", state=%s %s\n", dccp_feat_sname[entry->state],
 283			  entry->needs_confirm ? "(Confirm pending)" : "");
 284}
 285
 286#define dccp_feat_print_opt(opt, feat, val, len, mandatory)	do {	      \
 287	dccp_pr_debug("%s(%s, ", dccp_feat_oname(opt), dccp_feat_fname(feat));\
 288	dccp_feat_printvals(feat, val, len);				      \
 289	dccp_pr_debug_cat(") %s\n", mandatory ? "!" : "");	} while (0)
 290
 291#define dccp_feat_print_fnlist(fn_list)  {		\
 292	const struct dccp_feat_entry *___entry;		\
 293							\
 294	dccp_pr_debug("List Dump:\n");			\
 295	list_for_each_entry(___entry, fn_list, node)	\
 296		dccp_feat_print_entry(___entry);	\
 297}
 298#else	/* ! CONFIG_IP_DCCP_DEBUG */
 299#define dccp_feat_print_opt(opt, feat, val, len, mandatory)
 300#define dccp_feat_print_fnlist(fn_list)
 301#endif
 302
 303static int __dccp_feat_activate(struct sock *sk, const int idx,
 304				const bool is_local, dccp_feat_val const *fval)
 305{
 306	bool rx;
 307	u64 val;
 308
 309	if (idx < 0 || idx >= DCCP_FEAT_SUPPORTED_MAX)
 310		return -1;
 311	if (dccp_feat_table[idx].activation_hdlr == NULL)
 312		return 0;
 313
 314	if (fval == NULL) {
 315		val = dccp_feat_table[idx].default_value;
 316	} else if (dccp_feat_table[idx].reconciliation == FEAT_SP) {
 317		if (fval->sp.vec == NULL) {
 318			/*
 319			 * This can happen when an empty Confirm is sent
 320			 * for an SP (i.e. known) feature. In this case
 321			 * we would be using the default anyway.
 322			 */
 323			DCCP_CRIT("Feature #%d undefined: using default", idx);
 324			val = dccp_feat_table[idx].default_value;
 325		} else {
 326			val = fval->sp.vec[0];
 327		}
 328	} else {
 329		val = fval->nn;
 330	}
 331
 332	/* Location is RX if this is a local-RX or remote-TX feature */
 333	rx = (is_local == (dccp_feat_table[idx].rxtx == FEAT_AT_RX));
 334
 335	dccp_debug("   -> activating %s %s, %sval=%llu\n", rx ? "RX" : "TX",
 336		   dccp_feat_fname(dccp_feat_table[idx].feat_num),
 337		   fval ? "" : "default ",  (unsigned long long)val);
 338
 339	return dccp_feat_table[idx].activation_hdlr(sk, val, rx);
 340}
 341
 342/**
 343 * dccp_feat_activate  -  Activate feature value on socket
 344 * @sk: fully connected DCCP socket (after handshake is complete)
 345 * @feat_num: feature to activate, one of %dccp_feature_numbers
 346 * @local: whether local (1) or remote (0) @feat_num is meant
 347 * @fval: the value (SP or NN) to activate, or NULL to use the default value
 348 *
 349 * For general use this function is preferable over __dccp_feat_activate().
 350 */
 351static int dccp_feat_activate(struct sock *sk, u8 feat_num, bool local,
 352			      dccp_feat_val const *fval)
 353{
 354	return __dccp_feat_activate(sk, dccp_feat_index(feat_num), local, fval);
 355}
 356
 357/* Test for "Req'd" feature (RFC 4340, 6.4) */
 358static inline int dccp_feat_must_be_understood(u8 feat_num)
 359{
 360	return	feat_num == DCCPF_CCID || feat_num == DCCPF_SHORT_SEQNOS ||
 361		feat_num == DCCPF_SEQUENCE_WINDOW;
 362}
 363
 364/* copy constructor, fval must not already contain allocated memory */
 365static int dccp_feat_clone_sp_val(dccp_feat_val *fval, u8 const *val, u8 len)
 366{
 367	fval->sp.len = len;
 368	if (fval->sp.len > 0) {
 369		fval->sp.vec = kmemdup(val, len, gfp_any());
 370		if (fval->sp.vec == NULL) {
 371			fval->sp.len = 0;
 372			return -ENOBUFS;
 373		}
 374	}
 375	return 0;
 376}
 377
 378static void dccp_feat_val_destructor(u8 feat_num, dccp_feat_val *val)
 379{
 380	if (unlikely(val == NULL))
 381		return;
 382	if (dccp_feat_type(feat_num) == FEAT_SP)
 383		kfree(val->sp.vec);
 384	memset(val, 0, sizeof(*val));
 385}
 386
 387static struct dccp_feat_entry *
 388	      dccp_feat_clone_entry(struct dccp_feat_entry const *original)
 389{
 390	struct dccp_feat_entry *new;
 391	u8 type = dccp_feat_type(original->feat_num);
 392
 393	if (type == FEAT_UNKNOWN)
 394		return NULL;
 395
 396	new = kmemdup(original, sizeof(struct dccp_feat_entry), gfp_any());
 397	if (new == NULL)
 398		return NULL;
 399
 400	if (type == FEAT_SP && dccp_feat_clone_sp_val(&new->val,
 401						      original->val.sp.vec,
 402						      original->val.sp.len)) {
 403		kfree(new);
 404		return NULL;
 405	}
 406	return new;
 407}
 408
 409static void dccp_feat_entry_destructor(struct dccp_feat_entry *entry)
 410{
 411	if (entry != NULL) {
 412		dccp_feat_val_destructor(entry->feat_num, &entry->val);
 413		kfree(entry);
 414	}
 415}
 416
 417/*
 418 * List management functions
 419 *
 420 * Feature negotiation lists rely on and maintain the following invariants:
 421 * - each feat_num in the list is known, i.e. we know its type and default value
 422 * - each feat_num/is_local combination is unique (old entries are overwritten)
 423 * - SP values are always freshly allocated
 424 * - list is sorted in increasing order of feature number (faster lookup)
 425 */
 426static struct dccp_feat_entry *dccp_feat_list_lookup(struct list_head *fn_list,
 427						     u8 feat_num, bool is_local)
 428{
 429	struct dccp_feat_entry *entry;
 430
 431	list_for_each_entry(entry, fn_list, node) {
 432		if (entry->feat_num == feat_num && entry->is_local == is_local)
 433			return entry;
 434		else if (entry->feat_num > feat_num)
 435			break;
 436	}
 437	return NULL;
 438}
 439
 440/**
 441 * dccp_feat_entry_new  -  Central list update routine (called by all others)
 442 * @head:  list to add to
 443 * @feat:  feature number
 444 * @local: whether the local (1) or remote feature with number @feat is meant
 445 *
 446 * This is the only constructor and serves to ensure the above invariants.
 447 */
 448static struct dccp_feat_entry *
 449	      dccp_feat_entry_new(struct list_head *head, u8 feat, bool local)
 450{
 451	struct dccp_feat_entry *entry;
 452
 453	list_for_each_entry(entry, head, node)
 454		if (entry->feat_num == feat && entry->is_local == local) {
 455			dccp_feat_val_destructor(entry->feat_num, &entry->val);
 456			return entry;
 457		} else if (entry->feat_num > feat) {
 458			head = &entry->node;
 459			break;
 460		}
 461
 462	entry = kmalloc(sizeof(*entry), gfp_any());
 463	if (entry != NULL) {
 464		entry->feat_num = feat;
 465		entry->is_local = local;
 466		list_add_tail(&entry->node, head);
 467	}
 468	return entry;
 469}
 470
 471/**
 472 * dccp_feat_push_change  -  Add/overwrite a Change option in the list
 473 * @fn_list: feature-negotiation list to update
 474 * @feat: one of %dccp_feature_numbers
 475 * @local: whether local (1) or remote (0) @feat_num is meant
 476 * @mandatory: whether to use Mandatory feature negotiation options
 477 * @fval: pointer to NN/SP value to be inserted (will be copied)
 478 */
 479static int dccp_feat_push_change(struct list_head *fn_list, u8 feat, u8 local,
 480				 u8 mandatory, dccp_feat_val *fval)
 481{
 482	struct dccp_feat_entry *new = dccp_feat_entry_new(fn_list, feat, local);
 483
 484	if (new == NULL)
 485		return -ENOMEM;
 486
 487	new->feat_num	     = feat;
 488	new->is_local	     = local;
 489	new->state	     = FEAT_INITIALISING;
 490	new->needs_confirm   = false;
 491	new->empty_confirm   = false;
 492	new->val	     = *fval;
 493	new->needs_mandatory = mandatory;
 494
 495	return 0;
 496}
 497
 498/**
 499 * dccp_feat_push_confirm  -  Add a Confirm entry to the FN list
 500 * @fn_list: feature-negotiation list to add to
 501 * @feat: one of %dccp_feature_numbers
 502 * @local: whether local (1) or remote (0) @feat_num is being confirmed
 503 * @fval: pointer to NN/SP value to be inserted or NULL
 504 *
 505 * Returns 0 on success, a Reset code for further processing otherwise.
 506 */
 507static int dccp_feat_push_confirm(struct list_head *fn_list, u8 feat, u8 local,
 508				  dccp_feat_val *fval)
 509{
 510	struct dccp_feat_entry *new = dccp_feat_entry_new(fn_list, feat, local);
 511
 512	if (new == NULL)
 513		return DCCP_RESET_CODE_TOO_BUSY;
 514
 515	new->feat_num	     = feat;
 516	new->is_local	     = local;
 517	new->state	     = FEAT_STABLE;	/* transition in 6.6.2 */
 518	new->needs_confirm   = true;
 519	new->empty_confirm   = (fval == NULL);
 520	new->val.nn	     = 0;		/* zeroes the whole structure */
 521	if (!new->empty_confirm)
 522		new->val     = *fval;
 523	new->needs_mandatory = false;
 524
 525	return 0;
 526}
 527
 528static int dccp_push_empty_confirm(struct list_head *fn_list, u8 feat, u8 local)
 529{
 530	return dccp_feat_push_confirm(fn_list, feat, local, NULL);
 531}
 532
 533static inline void dccp_feat_list_pop(struct dccp_feat_entry *entry)
 534{
 535	list_del(&entry->node);
 536	dccp_feat_entry_destructor(entry);
 537}
 538
 539void dccp_feat_list_purge(struct list_head *fn_list)
 540{
 541	struct dccp_feat_entry *entry, *next;
 542
 543	list_for_each_entry_safe(entry, next, fn_list, node)
 544		dccp_feat_entry_destructor(entry);
 545	INIT_LIST_HEAD(fn_list);
 546}
 547EXPORT_SYMBOL_GPL(dccp_feat_list_purge);
 548
 549/* generate @to as full clone of @from - @to must not contain any nodes */
 550int dccp_feat_clone_list(struct list_head const *from, struct list_head *to)
 551{
 552	struct dccp_feat_entry *entry, *new;
 553
 554	INIT_LIST_HEAD(to);
 555	list_for_each_entry(entry, from, node) {
 556		new = dccp_feat_clone_entry(entry);
 557		if (new == NULL)
 558			goto cloning_failed;
 559		list_add_tail(&new->node, to);
 560	}
 561	return 0;
 562
 563cloning_failed:
 564	dccp_feat_list_purge(to);
 565	return -ENOMEM;
 566}
 567
 568/**
 569 * dccp_feat_valid_nn_length  -  Enforce length constraints on NN options
 570 * Length is between 0 and %DCCP_OPTVAL_MAXLEN. Used for outgoing packets only,
 571 * incoming options are accepted as long as their values are valid.
 572 */
 573static u8 dccp_feat_valid_nn_length(u8 feat_num)
 574{
 575	if (feat_num == DCCPF_ACK_RATIO)	/* RFC 4340, 11.3 and 6.6.8 */
 576		return 2;
 577	if (feat_num == DCCPF_SEQUENCE_WINDOW)	/* RFC 4340, 7.5.2 and 6.5  */
 578		return 6;
 579	return 0;
 580}
 581
 582static u8 dccp_feat_is_valid_nn_val(u8 feat_num, u64 val)
 583{
 584	switch (feat_num) {
 585	case DCCPF_ACK_RATIO:
 586		return val <= DCCPF_ACK_RATIO_MAX;
 587	case DCCPF_SEQUENCE_WINDOW:
 588		return val >= DCCPF_SEQ_WMIN && val <= DCCPF_SEQ_WMAX;
 589	}
 590	return 0;	/* feature unknown - so we can't tell */
 591}
 592
 593/* check that SP values are within the ranges defined in RFC 4340 */
 594static u8 dccp_feat_is_valid_sp_val(u8 feat_num, u8 val)
 595{
 596	switch (feat_num) {
 597	case DCCPF_CCID:
 598		return val == DCCPC_CCID2 || val == DCCPC_CCID3;
 599	/* Type-check Boolean feature values: */
 600	case DCCPF_SHORT_SEQNOS:
 601	case DCCPF_ECN_INCAPABLE:
 602	case DCCPF_SEND_ACK_VECTOR:
 603	case DCCPF_SEND_NDP_COUNT:
 604	case DCCPF_DATA_CHECKSUM:
 605	case DCCPF_SEND_LEV_RATE:
 606		return val < 2;
 607	case DCCPF_MIN_CSUM_COVER:
 608		return val < 16;
 609	}
 610	return 0;			/* feature unknown */
 611}
 612
 613static u8 dccp_feat_sp_list_ok(u8 feat_num, u8 const *sp_list, u8 sp_len)
 614{
 615	if (sp_list == NULL || sp_len < 1)
 616		return 0;
 617	while (sp_len--)
 618		if (!dccp_feat_is_valid_sp_val(feat_num, *sp_list++))
 619			return 0;
 620	return 1;
 621}
 622
 623/**
 624 * dccp_feat_insert_opts  -  Generate FN options from current list state
 625 * @skb: next sk_buff to be sent to the peer
 626 * @dp: for client during handshake and general negotiation
 627 * @dreq: used by the server only (all Changes/Confirms in LISTEN/RESPOND)
 628 */
 629int dccp_feat_insert_opts(struct dccp_sock *dp, struct dccp_request_sock *dreq,
 630			  struct sk_buff *skb)
 631{
 632	struct list_head *fn = dreq ? &dreq->dreq_featneg : &dp->dccps_featneg;
 633	struct dccp_feat_entry *pos, *next;
 634	u8 opt, type, len, *ptr, nn_in_nbo[DCCP_OPTVAL_MAXLEN];
 635	bool rpt;
 636
 637	/* put entries into @skb in the order they appear in the list */
 638	list_for_each_entry_safe_reverse(pos, next, fn, node) {
 639		opt  = dccp_feat_genopt(pos);
 640		type = dccp_feat_type(pos->feat_num);
 641		rpt  = false;
 642
 643		if (pos->empty_confirm) {
 644			len = 0;
 645			ptr = NULL;
 646		} else {
 647			if (type == FEAT_SP) {
 648				len = pos->val.sp.len;
 649				ptr = pos->val.sp.vec;
 650				rpt = pos->needs_confirm;
 651			} else if (type == FEAT_NN) {
 652				len = dccp_feat_valid_nn_length(pos->feat_num);
 653				ptr = nn_in_nbo;
 654				dccp_encode_value_var(pos->val.nn, ptr, len);
 655			} else {
 656				DCCP_BUG("unknown feature %u", pos->feat_num);
 657				return -1;
 658			}
 659		}
 660		dccp_feat_print_opt(opt, pos->feat_num, ptr, len, 0);
 661
 662		if (dccp_insert_fn_opt(skb, opt, pos->feat_num, ptr, len, rpt))
 663			return -1;
 664		if (pos->needs_mandatory && dccp_insert_option_mandatory(skb))
 665			return -1;
 666
 667		if (skb->sk->sk_state == DCCP_OPEN &&
 668		    (opt == DCCPO_CONFIRM_R || opt == DCCPO_CONFIRM_L)) {
 669			/*
 670			 * Confirms don't get retransmitted (6.6.3) once the
 671			 * connection is in state OPEN
 672			 */
 673			dccp_feat_list_pop(pos);
 674		} else {
 675			/*
 676			 * Enter CHANGING after transmitting the Change
 677			 * option (6.6.2).
 678			 */
 679			if (pos->state == FEAT_INITIALISING)
 680				pos->state = FEAT_CHANGING;
 681		}
 682	}
 683	return 0;
 684}
 685
 686/**
 687 * __feat_register_nn  -  Register new NN value on socket
 688 * @fn: feature-negotiation list to register with
 689 * @feat: an NN feature from %dccp_feature_numbers
 690 * @mandatory: use Mandatory option if 1
 691 * @nn_val: value to register (restricted to 4 bytes)
 692 *
 693 * Note that NN features are local by definition (RFC 4340, 6.3.2).
 694 */
 695static int __feat_register_nn(struct list_head *fn, u8 feat,
 696			      u8 mandatory, u64 nn_val)
 697{
 698	dccp_feat_val fval = { .nn = nn_val };
 699
 700	if (dccp_feat_type(feat) != FEAT_NN ||
 701	    !dccp_feat_is_valid_nn_val(feat, nn_val))
 702		return -EINVAL;
 703
 704	/* Don't bother with default values, they will be activated anyway. */
 705	if (nn_val - (u64)dccp_feat_default_value(feat) == 0)
 706		return 0;
 707
 708	return dccp_feat_push_change(fn, feat, 1, mandatory, &fval);
 709}
 710
 711/**
 712 * __feat_register_sp  -  Register new SP value/list on socket
 713 * @fn: feature-negotiation list to register with
 714 * @feat: an SP feature from %dccp_feature_numbers
 715 * @is_local: whether the local (1) or the remote (0) @feat is meant
 716 * @mandatory: use Mandatory option if 1
 717 * @sp_val: SP value followed by optional preference list
 718 * @sp_len: length of @sp_val in bytes
 719 */
 720static int __feat_register_sp(struct list_head *fn, u8 feat, u8 is_local,
 721			      u8 mandatory, u8 const *sp_val, u8 sp_len)
 722{
 723	dccp_feat_val fval;
 724
 725	if (dccp_feat_type(feat) != FEAT_SP ||
 726	    !dccp_feat_sp_list_ok(feat, sp_val, sp_len))
 727		return -EINVAL;
 728
 729	/* Avoid negotiating alien CCIDs by only advertising supported ones */
 730	if (feat == DCCPF_CCID && !ccid_support_check(sp_val, sp_len))
 731		return -EOPNOTSUPP;
 732
 733	if (dccp_feat_clone_sp_val(&fval, sp_val, sp_len))
 734		return -ENOMEM;
 735
 736	if (dccp_feat_push_change(fn, feat, is_local, mandatory, &fval)) {
 737		kfree(fval.sp.vec);
 738		return -ENOMEM;
 739	}
 740
 741	return 0;
 742}
 743
 744/**
 745 * dccp_feat_register_sp  -  Register requests to change SP feature values
 746 * @sk: client or listening socket
 747 * @feat: one of %dccp_feature_numbers
 748 * @is_local: whether the local (1) or remote (0) @feat is meant
 749 * @list: array of preferred values, in descending order of preference
 750 * @len: length of @list in bytes
 751 */
 752int dccp_feat_register_sp(struct sock *sk, u8 feat, u8 is_local,
 753			  u8 const *list, u8 len)
 754{	 /* any changes must be registered before establishing the connection */
 755	if (sk->sk_state != DCCP_CLOSED)
 756		return -EISCONN;
 757	if (dccp_feat_type(feat) != FEAT_SP)
 758		return -EINVAL;
 759	return __feat_register_sp(&dccp_sk(sk)->dccps_featneg, feat, is_local,
 760				  0, list, len);
 761}
 762
 763/**
 764 * dccp_feat_nn_get  -  Query current/pending value of NN feature
 765 * @sk: DCCP socket of an established connection
 766 * @feat: NN feature number from %dccp_feature_numbers
 767 *
 768 * For a known NN feature, returns value currently being negotiated, or
 769 * current (confirmed) value if no negotiation is going on.
 770 */
 771u64 dccp_feat_nn_get(struct sock *sk, u8 feat)
 772{
 773	if (dccp_feat_type(feat) == FEAT_NN) {
 774		struct dccp_sock *dp = dccp_sk(sk);
 775		struct dccp_feat_entry *entry;
 776
 777		entry = dccp_feat_list_lookup(&dp->dccps_featneg, feat, 1);
 778		if (entry != NULL)
 779			return entry->val.nn;
 780
 781		switch (feat) {
 782		case DCCPF_ACK_RATIO:
 783			return dp->dccps_l_ack_ratio;
 784		case DCCPF_SEQUENCE_WINDOW:
 785			return dp->dccps_l_seq_win;
 786		}
 787	}
 788	DCCP_BUG("attempt to look up unsupported feature %u", feat);
 789	return 0;
 790}
 791EXPORT_SYMBOL_GPL(dccp_feat_nn_get);
 792
 793/**
 794 * dccp_feat_signal_nn_change  -  Update NN values for an established connection
 795 * @sk: DCCP socket of an established connection
 796 * @feat: NN feature number from %dccp_feature_numbers
 797 * @nn_val: the new value to use
 798 *
 799 * This function is used to communicate NN updates out-of-band.
 800 */
 801int dccp_feat_signal_nn_change(struct sock *sk, u8 feat, u64 nn_val)
 802{
 803	struct list_head *fn = &dccp_sk(sk)->dccps_featneg;
 804	dccp_feat_val fval = { .nn = nn_val };
 805	struct dccp_feat_entry *entry;
 806
 807	if (sk->sk_state != DCCP_OPEN && sk->sk_state != DCCP_PARTOPEN)
 808		return 0;
 809
 810	if (dccp_feat_type(feat) != FEAT_NN ||
 811	    !dccp_feat_is_valid_nn_val(feat, nn_val))
 812		return -EINVAL;
 813
 814	if (nn_val == dccp_feat_nn_get(sk, feat))
 815		return 0;	/* already set or negotiation under way */
 816
 817	entry = dccp_feat_list_lookup(fn, feat, 1);
 818	if (entry != NULL) {
 819		dccp_pr_debug("Clobbering existing NN entry %llu -> %llu\n",
 820			      (unsigned long long)entry->val.nn,
 821			      (unsigned long long)nn_val);
 822		dccp_feat_list_pop(entry);
 823	}
 824
 825	inet_csk_schedule_ack(sk);
 826	return dccp_feat_push_change(fn, feat, 1, 0, &fval);
 827}
 828EXPORT_SYMBOL_GPL(dccp_feat_signal_nn_change);
 829
 830/*
 831 *	Tracking features whose value depend on the choice of CCID
 832 *
 833 * This is designed with an extension in mind so that a list walk could be done
 834 * before activating any features. However, the existing framework was found to
 835 * work satisfactorily up until now, the automatic verification is left open.
 836 * When adding new CCIDs, add a corresponding dependency table here.
 837 */
 838static const struct ccid_dependency *dccp_feat_ccid_deps(u8 ccid, bool is_local)
 839{
 840	static const struct ccid_dependency ccid2_dependencies[2][2] = {
 841		/*
 842		 * CCID2 mandates Ack Vectors (RFC 4341, 4.): as CCID is a TX
 843		 * feature and Send Ack Vector is an RX feature, `is_local'
 844		 * needs to be reversed.
 845		 */
 846		{	/* Dependencies of the receiver-side (remote) CCID2 */
 847			{
 848				.dependent_feat	= DCCPF_SEND_ACK_VECTOR,
 849				.is_local	= true,
 850				.is_mandatory	= true,
 851				.val		= 1
 852			},
 853			{ 0, 0, 0, 0 }
 854		},
 855		{	/* Dependencies of the sender-side (local) CCID2 */
 856			{
 857				.dependent_feat	= DCCPF_SEND_ACK_VECTOR,
 858				.is_local	= false,
 859				.is_mandatory	= true,
 860				.val		= 1
 861			},
 862			{ 0, 0, 0, 0 }
 863		}
 864	};
 865	static const struct ccid_dependency ccid3_dependencies[2][5] = {
 866		{	/*
 867			 * Dependencies of the receiver-side CCID3
 868			 */
 869			{	/* locally disable Ack Vectors */
 870				.dependent_feat	= DCCPF_SEND_ACK_VECTOR,
 871				.is_local	= true,
 872				.is_mandatory	= false,
 873				.val		= 0
 874			},
 875			{	/* see below why Send Loss Event Rate is on */
 876				.dependent_feat	= DCCPF_SEND_LEV_RATE,
 877				.is_local	= true,
 878				.is_mandatory	= true,
 879				.val		= 1
 880			},
 881			{	/* NDP Count is needed as per RFC 4342, 6.1.1 */
 882				.dependent_feat	= DCCPF_SEND_NDP_COUNT,
 883				.is_local	= false,
 884				.is_mandatory	= true,
 885				.val		= 1
 886			},
 887			{ 0, 0, 0, 0 },
 888		},
 889		{	/*
 890			 * CCID3 at the TX side: we request that the HC-receiver
 891			 * will not send Ack Vectors (they will be ignored, so
 892			 * Mandatory is not set); we enable Send Loss Event Rate
 893			 * (Mandatory since the implementation does not support
 894			 * the Loss Intervals option of RFC 4342, 8.6).
 895			 * The last two options are for peer's information only.
 896			*/
 897			{
 898				.dependent_feat	= DCCPF_SEND_ACK_VECTOR,
 899				.is_local	= false,
 900				.is_mandatory	= false,
 901				.val		= 0
 902			},
 903			{
 904				.dependent_feat	= DCCPF_SEND_LEV_RATE,
 905				.is_local	= false,
 906				.is_mandatory	= true,
 907				.val		= 1
 908			},
 909			{	/* this CCID does not support Ack Ratio */
 910				.dependent_feat	= DCCPF_ACK_RATIO,
 911				.is_local	= true,
 912				.is_mandatory	= false,
 913				.val		= 0
 914			},
 915			{	/* tell receiver we are sending NDP counts */
 916				.dependent_feat	= DCCPF_SEND_NDP_COUNT,
 917				.is_local	= true,
 918				.is_mandatory	= false,
 919				.val		= 1
 920			},
 921			{ 0, 0, 0, 0 }
 922		}
 923	};
 924	switch (ccid) {
 925	case DCCPC_CCID2:
 926		return ccid2_dependencies[is_local];
 927	case DCCPC_CCID3:
 928		return ccid3_dependencies[is_local];
 929	default:
 930		return NULL;
 931	}
 932}
 933
 934/**
 935 * dccp_feat_propagate_ccid - Resolve dependencies of features on choice of CCID
 936 * @fn: feature-negotiation list to update
 937 * @id: CCID number to track
 938 * @is_local: whether TX CCID (1) or RX CCID (0) is meant
 939 *
 940 * This function needs to be called after registering all other features.
 941 */
 942static int dccp_feat_propagate_ccid(struct list_head *fn, u8 id, bool is_local)
 943{
 944	const struct ccid_dependency *table = dccp_feat_ccid_deps(id, is_local);
 945	int i, rc = (table == NULL);
 946
 947	for (i = 0; rc == 0 && table[i].dependent_feat != DCCPF_RESERVED; i++)
 948		if (dccp_feat_type(table[i].dependent_feat) == FEAT_SP)
 949			rc = __feat_register_sp(fn, table[i].dependent_feat,
 950						    table[i].is_local,
 951						    table[i].is_mandatory,
 952						    &table[i].val, 1);
 953		else
 954			rc = __feat_register_nn(fn, table[i].dependent_feat,
 955						    table[i].is_mandatory,
 956						    table[i].val);
 957	return rc;
 958}
 959
 960/**
 961 * dccp_feat_finalise_settings  -  Finalise settings before starting negotiation
 962 * @dp: client or listening socket (settings will be inherited)
 963 *
 964 * This is called after all registrations (socket initialisation, sysctls, and
 965 * sockopt calls), and before sending the first packet containing Change options
 966 * (ie. client-Request or server-Response), to ensure internal consistency.
 967 */
 968int dccp_feat_finalise_settings(struct dccp_sock *dp)
 969{
 970	struct list_head *fn = &dp->dccps_featneg;
 971	struct dccp_feat_entry *entry;
 972	int i = 2, ccids[2] = { -1, -1 };
 973
 974	/*
 975	 * Propagating CCIDs:
 976	 * 1) not useful to propagate CCID settings if this host advertises more
 977	 *    than one CCID: the choice of CCID  may still change - if this is
 978	 *    the client, or if this is the server and the client sends
 979	 *    singleton CCID values.
 980	 * 2) since is that propagate_ccid changes the list, we defer changing
 981	 *    the sorted list until after the traversal.
 982	 */
 983	list_for_each_entry(entry, fn, node)
 984		if (entry->feat_num == DCCPF_CCID && entry->val.sp.len == 1)
 985			ccids[entry->is_local] = entry->val.sp.vec[0];
 986	while (i--)
 987		if (ccids[i] > 0 && dccp_feat_propagate_ccid(fn, ccids[i], i))
 988			return -1;
 989	dccp_feat_print_fnlist(fn);
 990	return 0;
 991}
 992
 993/**
 994 * dccp_feat_server_ccid_dependencies  -  Resolve CCID-dependent features
 995 * It is the server which resolves the dependencies once the CCID has been
 996 * fully negotiated. If no CCID has been negotiated, it uses the default CCID.
 997 */
 998int dccp_feat_server_ccid_dependencies(struct dccp_request_sock *dreq)
 999{
1000	struct list_head *fn = &dreq->dreq_featneg;
1001	struct dccp_feat_entry *entry;
1002	u8 is_local, ccid;
1003
1004	for (is_local = 0; is_local <= 1; is_local++) {
1005		entry = dccp_feat_list_lookup(fn, DCCPF_CCID, is_local);
1006
1007		if (entry != NULL && !entry->empty_confirm)
1008			ccid = entry->val.sp.vec[0];
1009		else
1010			ccid = dccp_feat_default_value(DCCPF_CCID);
1011
1012		if (dccp_feat_propagate_ccid(fn, ccid, is_local))
1013			return -1;
1014	}
1015	return 0;
1016}
1017
1018/* Select the first entry in @servlist that also occurs in @clilist (6.3.1) */
1019static int dccp_feat_preflist_match(u8 *servlist, u8 slen, u8 *clilist, u8 clen)
1020{
1021	u8 c, s;
1022
1023	for (s = 0; s < slen; s++)
1024		for (c = 0; c < clen; c++)
1025			if (servlist[s] == clilist[c])
1026				return servlist[s];
1027	return -1;
1028}
1029
1030/**
1031 * dccp_feat_prefer  -  Move preferred entry to the start of array
1032 * Reorder the @array_len elements in @array so that @preferred_value comes
1033 * first. Returns >0 to indicate that @preferred_value does occur in @array.
1034 */
1035static u8 dccp_feat_prefer(u8 preferred_value, u8 *array, u8 array_len)
1036{
1037	u8 i, does_occur = 0;
1038
1039	if (array != NULL) {
1040		for (i = 0; i < array_len; i++)
1041			if (array[i] == preferred_value) {
1042				array[i] = array[0];
1043				does_occur++;
1044			}
1045		if (does_occur)
1046			array[0] = preferred_value;
1047	}
1048	return does_occur;
1049}
1050
1051/**
1052 * dccp_feat_reconcile  -  Reconcile SP preference lists
1053 *  @fv: SP list to reconcile into
1054 *  @arr: received SP preference list
1055 *  @len: length of @arr in bytes
1056 *  @is_server: whether this side is the server (and @fv is the server's list)
1057 *  @reorder: whether to reorder the list in @fv after reconciling with @arr
1058 * When successful, > 0 is returned and the reconciled list is in @fval.
1059 * A value of 0 means that negotiation failed (no shared entry).
1060 */
1061static int dccp_feat_reconcile(dccp_feat_val *fv, u8 *arr, u8 len,
1062			       bool is_server, bool reorder)
1063{
1064	int rc;
1065
1066	if (!fv->sp.vec || !arr) {
1067		DCCP_CRIT("NULL feature value or array");
1068		return 0;
1069	}
1070
1071	if (is_server)
1072		rc = dccp_feat_preflist_match(fv->sp.vec, fv->sp.len, arr, len);
1073	else
1074		rc = dccp_feat_preflist_match(arr, len, fv->sp.vec, fv->sp.len);
1075
1076	if (!reorder)
1077		return rc;
1078	if (rc < 0)
1079		return 0;
1080
1081	/*
1082	 * Reorder list: used for activating features and in dccp_insert_fn_opt.
1083	 */
1084	return dccp_feat_prefer(rc, fv->sp.vec, fv->sp.len);
1085}
1086
1087/**
1088 * dccp_feat_change_recv  -  Process incoming ChangeL/R options
1089 * @fn: feature-negotiation list to update
1090 * @is_mandatory: whether the Change was preceded by a Mandatory option
1091 * @opt: %DCCPO_CHANGE_L or %DCCPO_CHANGE_R
1092 * @feat: one of %dccp_feature_numbers
1093 * @val: NN value or SP value/preference list
1094 * @len: length of @val in bytes
1095 * @server: whether this node is the server (1) or the client (0)
1096 */
1097static u8 dccp_feat_change_recv(struct list_head *fn, u8 is_mandatory, u8 opt,
1098				u8 feat, u8 *val, u8 len, const bool server)
1099{
1100	u8 defval, type = dccp_feat_type(feat);
1101	const bool local = (opt == DCCPO_CHANGE_R);
1102	struct dccp_feat_entry *entry;
1103	dccp_feat_val fval;
1104
1105	if (len == 0 || type == FEAT_UNKNOWN)		/* 6.1 and 6.6.8 */
1106		goto unknown_feature_or_value;
1107
1108	dccp_feat_print_opt(opt, feat, val, len, is_mandatory);
1109
1110	/*
1111	 *	Negotiation of NN features: Change R is invalid, so there is no
1112	 *	simultaneous negotiation; hence we do not look up in the list.
1113	 */
1114	if (type == FEAT_NN) {
1115		if (local || len > sizeof(fval.nn))
1116			goto unknown_feature_or_value;
1117
1118		/* 6.3.2: "The feature remote MUST accept any valid value..." */
1119		fval.nn = dccp_decode_value_var(val, len);
1120		if (!dccp_feat_is_valid_nn_val(feat, fval.nn))
1121			goto unknown_feature_or_value;
1122
1123		return dccp_feat_push_confirm(fn, feat, local, &fval);
1124	}
1125
1126	/*
1127	 *	Unidirectional/simultaneous negotiation of SP features (6.3.1)
1128	 */
1129	entry = dccp_feat_list_lookup(fn, feat, local);
1130	if (entry == NULL) {
1131		/*
1132		 * No particular preferences have been registered. We deal with
1133		 * this situation by assuming that all valid values are equally
1134		 * acceptable, and apply the following checks:
1135		 * - if the peer's list is a singleton, we accept a valid value;
1136		 * - if we are the server, we first try to see if the peer (the
1137		 *   client) advertises the default value. If yes, we use it,
1138		 *   otherwise we accept the preferred value;
1139		 * - else if we are the client, we use the first list element.
1140		 */
1141		if (dccp_feat_clone_sp_val(&fval, val, 1))
1142			return DCCP_RESET_CODE_TOO_BUSY;
1143
1144		if (len > 1 && server) {
1145			defval = dccp_feat_default_value(feat);
1146			if (dccp_feat_preflist_match(&defval, 1, val, len) > -1)
1147				fval.sp.vec[0] = defval;
1148		} else if (!dccp_feat_is_valid_sp_val(feat, fval.sp.vec[0])) {
1149			kfree(fval.sp.vec);
1150			goto unknown_feature_or_value;
1151		}
1152
1153		/* Treat unsupported CCIDs like invalid values */
1154		if (feat == DCCPF_CCID && !ccid_support_check(fval.sp.vec, 1)) {
1155			kfree(fval.sp.vec);
1156			goto not_valid_or_not_known;
1157		}
1158
1159		return dccp_feat_push_confirm(fn, feat, local, &fval);
1160
1161	} else if (entry->state == FEAT_UNSTABLE) {	/* 6.6.2 */
1162		return 0;
1163	}
1164
1165	if (dccp_feat_reconcile(&entry->val, val, len, server, true)) {
1166		entry->empty_confirm = false;
1167	} else if (is_mandatory) {
1168		return DCCP_RESET_CODE_MANDATORY_ERROR;
1169	} else if (entry->state == FEAT_INITIALISING) {
1170		/*
1171		 * Failed simultaneous negotiation (server only): try to `save'
1172		 * the connection by checking whether entry contains the default
1173		 * value for @feat. If yes, send an empty Confirm to signal that
1174		 * the received Change was not understood - which implies using
1175		 * the default value.
1176		 * If this also fails, we use Reset as the last resort.
1177		 */
1178		WARN_ON(!server);
1179		defval = dccp_feat_default_value(feat);
1180		if (!dccp_feat_reconcile(&entry->val, &defval, 1, server, true))
1181			return DCCP_RESET_CODE_OPTION_ERROR;
1182		entry->empty_confirm = true;
1183	}
1184	entry->needs_confirm   = true;
1185	entry->needs_mandatory = false;
1186	entry->state	       = FEAT_STABLE;
1187	return 0;
1188
1189unknown_feature_or_value:
1190	if (!is_mandatory)
1191		return dccp_push_empty_confirm(fn, feat, local);
1192
1193not_valid_or_not_known:
1194	return is_mandatory ? DCCP_RESET_CODE_MANDATORY_ERROR
1195			    : DCCP_RESET_CODE_OPTION_ERROR;
1196}
1197
1198/**
1199 * dccp_feat_confirm_recv  -  Process received Confirm options
1200 * @fn: feature-negotiation list to update
1201 * @is_mandatory: whether @opt was preceded by a Mandatory option
1202 * @opt: %DCCPO_CONFIRM_L or %DCCPO_CONFIRM_R
1203 * @feat: one of %dccp_feature_numbers
1204 * @val: NN value or SP value/preference list
1205 * @len: length of @val in bytes
1206 * @server: whether this node is server (1) or client (0)
1207 */
1208static u8 dccp_feat_confirm_recv(struct list_head *fn, u8 is_mandatory, u8 opt,
1209				 u8 feat, u8 *val, u8 len, const bool server)
1210{
1211	u8 *plist, plen, type = dccp_feat_type(feat);
1212	const bool local = (opt == DCCPO_CONFIRM_R);
1213	struct dccp_feat_entry *entry = dccp_feat_list_lookup(fn, feat, local);
1214
1215	dccp_feat_print_opt(opt, feat, val, len, is_mandatory);
1216
1217	if (entry == NULL) {	/* nothing queued: ignore or handle error */
1218		if (is_mandatory && type == FEAT_UNKNOWN)
1219			return DCCP_RESET_CODE_MANDATORY_ERROR;
1220
1221		if (!local && type == FEAT_NN)		/* 6.3.2 */
1222			goto confirmation_failed;
1223		return 0;
1224	}
1225
1226	if (entry->state != FEAT_CHANGING)		/* 6.6.2 */
1227		return 0;
1228
1229	if (len == 0) {
1230		if (dccp_feat_must_be_understood(feat))	/* 6.6.7 */
1231			goto confirmation_failed;
1232		/*
1233		 * Empty Confirm during connection setup: this means reverting
1234		 * to the `old' value, which in this case is the default. Since
1235		 * we handle default values automatically when no other values
1236		 * have been set, we revert to the old value by removing this
1237		 * entry from the list.
1238		 */
1239		dccp_feat_list_pop(entry);
1240		return 0;
1241	}
1242
1243	if (type == FEAT_NN) {
1244		if (len > sizeof(entry->val.nn))
1245			goto confirmation_failed;
1246
1247		if (entry->val.nn == dccp_decode_value_var(val, len))
1248			goto confirmation_succeeded;
1249
1250		DCCP_WARN("Bogus Confirm for non-existing value\n");
1251		goto confirmation_failed;
1252	}
1253
1254	/*
1255	 * Parsing SP Confirms: the first element of @val is the preferred
1256	 * SP value which the peer confirms, the remainder depends on @len.
1257	 * Note that only the confirmed value need to be a valid SP value.
1258	 */
1259	if (!dccp_feat_is_valid_sp_val(feat, *val))
1260		goto confirmation_failed;
1261
1262	if (len == 1) {		/* peer didn't supply a preference list */
1263		plist = val;
1264		plen  = len;
1265	} else {		/* preferred value + preference list */
1266		plist = val + 1;
1267		plen  = len - 1;
1268	}
1269
1270	/* Check whether the peer got the reconciliation right (6.6.8) */
1271	if (dccp_feat_reconcile(&entry->val, plist, plen, server, 0) != *val) {
1272		DCCP_WARN("Confirm selected the wrong value %u\n", *val);
1273		return DCCP_RESET_CODE_OPTION_ERROR;
1274	}
1275	entry->val.sp.vec[0] = *val;
1276
1277confirmation_succeeded:
1278	entry->state = FEAT_STABLE;
1279	return 0;
1280
1281confirmation_failed:
1282	DCCP_WARN("Confirmation failed\n");
1283	return is_mandatory ? DCCP_RESET_CODE_MANDATORY_ERROR
1284			    : DCCP_RESET_CODE_OPTION_ERROR;
1285}
1286
1287/**
1288 * dccp_feat_handle_nn_established  -  Fast-path reception of NN options
1289 * @sk:		socket of an established DCCP connection
1290 * @mandatory:	whether @opt was preceded by a Mandatory option
1291 * @opt:	%DCCPO_CHANGE_L | %DCCPO_CONFIRM_R (NN only)
1292 * @feat:	NN number, one of %dccp_feature_numbers
1293 * @val:	NN value
1294 * @len:	length of @val in bytes
1295 *
1296 * This function combines the functionality of change_recv/confirm_recv, with
1297 * the following differences (reset codes are the same):
1298 *    - cleanup after receiving the Confirm;
1299 *    - values are directly activated after successful parsing;
1300 *    - deliberately restricted to NN features.
1301 * The restriction to NN features is essential since SP features can have non-
1302 * predictable outcomes (depending on the remote configuration), and are inter-
1303 * dependent (CCIDs for instance cause further dependencies).
1304 */
1305static u8 dccp_feat_handle_nn_established(struct sock *sk, u8 mandatory, u8 opt,
1306					  u8 feat, u8 *val, u8 len)
1307{
1308	struct list_head *fn = &dccp_sk(sk)->dccps_featneg;
1309	const bool local = (opt == DCCPO_CONFIRM_R);
1310	struct dccp_feat_entry *entry;
1311	u8 type = dccp_feat_type(feat);
1312	dccp_feat_val fval;
1313
1314	dccp_feat_print_opt(opt, feat, val, len, mandatory);
1315
1316	/* Ignore non-mandatory unknown and non-NN features */
1317	if (type == FEAT_UNKNOWN) {
1318		if (local && !mandatory)
1319			return 0;
1320		goto fast_path_unknown;
1321	} else if (type != FEAT_NN) {
1322		return 0;
1323	}
1324
1325	/*
1326	 * We don't accept empty Confirms, since in fast-path feature
1327	 * negotiation the values are enabled immediately after sending
1328	 * the Change option.
1329	 * Empty Changes on the other hand are invalid (RFC 4340, 6.1).
1330	 */
1331	if (len == 0 || len > sizeof(fval.nn))
1332		goto fast_path_unknown;
1333
1334	if (opt == DCCPO_CHANGE_L) {
1335		fval.nn = dccp_decode_value_var(val, len);
1336		if (!dccp_feat_is_valid_nn_val(feat, fval.nn))
1337			goto fast_path_unknown;
1338
1339		if (dccp_feat_push_confirm(fn, feat, local, &fval) ||
1340		    dccp_feat_activate(sk, feat, local, &fval))
1341			return DCCP_RESET_CODE_TOO_BUSY;
1342
1343		/* set the `Ack Pending' flag to piggyback a Confirm */
1344		inet_csk_schedule_ack(sk);
1345
1346	} else if (opt == DCCPO_CONFIRM_R) {
1347		entry = dccp_feat_list_lookup(fn, feat, local);
1348		if (entry == NULL || entry->state != FEAT_CHANGING)
1349			return 0;
1350
1351		fval.nn = dccp_decode_value_var(val, len);
1352		/*
1353		 * Just ignore a value that doesn't match our current value.
1354		 * If the option changes twice within two RTTs, then at least
1355		 * one CONFIRM will be received for the old value after a
1356		 * new CHANGE was sent.
1357		 */
1358		if (fval.nn != entry->val.nn)
1359			return 0;
1360
1361		/* Only activate after receiving the Confirm option (6.6.1). */
1362		dccp_feat_activate(sk, feat, local, &fval);
1363
1364		/* It has been confirmed - so remove the entry */
1365		dccp_feat_list_pop(entry);
1366
1367	} else {
1368		DCCP_WARN("Received illegal option %u\n", opt);
1369		goto fast_path_failed;
1370	}
1371	return 0;
1372
1373fast_path_unknown:
1374	if (!mandatory)
1375		return dccp_push_empty_confirm(fn, feat, local);
1376
1377fast_path_failed:
1378	return mandatory ? DCCP_RESET_CODE_MANDATORY_ERROR
1379			 : DCCP_RESET_CODE_OPTION_ERROR;
1380}
1381
1382/**
1383 * dccp_feat_parse_options  -  Process Feature-Negotiation Options
1384 * @sk: for general use and used by the client during connection setup
1385 * @dreq: used by the server during connection setup
1386 * @mandatory: whether @opt was preceded by a Mandatory option
1387 * @opt: %DCCPO_CHANGE_L | %DCCPO_CHANGE_R | %DCCPO_CONFIRM_L | %DCCPO_CONFIRM_R
1388 * @feat: one of %dccp_feature_numbers
1389 * @val: value contents of @opt
1390 * @len: length of @val in bytes
1391 *
1392 * Returns 0 on success, a Reset code for ending the connection otherwise.
1393 */
1394int dccp_feat_parse_options(struct sock *sk, struct dccp_request_sock *dreq,
1395			    u8 mandatory, u8 opt, u8 feat, u8 *val, u8 len)
1396{
1397	struct dccp_sock *dp = dccp_sk(sk);
1398	struct list_head *fn = dreq ? &dreq->dreq_featneg : &dp->dccps_featneg;
1399	bool server = false;
1400
1401	switch (sk->sk_state) {
1402	/*
1403	 *	Negotiation during connection setup
1404	 */
1405	case DCCP_LISTEN:
1406		server = true;			/* fall through */
1407	case DCCP_REQUESTING:
1408		switch (opt) {
1409		case DCCPO_CHANGE_L:
1410		case DCCPO_CHANGE_R:
1411			return dccp_feat_change_recv(fn, mandatory, opt, feat,
1412						     val, len, server);
1413		case DCCPO_CONFIRM_R:
1414		case DCCPO_CONFIRM_L:
1415			return dccp_feat_confirm_recv(fn, mandatory, opt, feat,
1416						      val, len, server);
1417		}
1418		break;
1419	/*
1420	 *	Support for exchanging NN options on an established connection.
1421	 */
1422	case DCCP_OPEN:
1423	case DCCP_PARTOPEN:
1424		return dccp_feat_handle_nn_established(sk, mandatory, opt, feat,
1425						       val, len);
1426	}
1427	return 0;	/* ignore FN options in all other states */
1428}
1429
1430/**
1431 * dccp_feat_init  -  Seed feature negotiation with host-specific defaults
1432 * This initialises global defaults, depending on the value of the sysctls.
1433 * These can later be overridden by registering changes via setsockopt calls.
1434 * The last link in the chain is finalise_settings, to make sure that between
1435 * here and the start of actual feature negotiation no inconsistencies enter.
1436 *
1437 * All features not appearing below use either defaults or are otherwise
1438 * later adjusted through dccp_feat_finalise_settings().
1439 */
1440int dccp_feat_init(struct sock *sk)
1441{
1442	struct list_head *fn = &dccp_sk(sk)->dccps_featneg;
1443	u8 on = 1, off = 0;
1444	int rc;
1445	struct {
1446		u8 *val;
1447		u8 len;
1448	} tx, rx;
1449
1450	/* Non-negotiable (NN) features */
1451	rc = __feat_register_nn(fn, DCCPF_SEQUENCE_WINDOW, 0,
1452				    sysctl_dccp_sequence_window);
1453	if (rc)
1454		return rc;
1455
1456	/* Server-priority (SP) features */
1457
1458	/* Advertise that short seqnos are not supported (7.6.1) */
1459	rc = __feat_register_sp(fn, DCCPF_SHORT_SEQNOS, true, true, &off, 1);
1460	if (rc)
1461		return rc;
1462
1463	/* RFC 4340 12.1: "If a DCCP is not ECN capable, ..." */
1464	rc = __feat_register_sp(fn, DCCPF_ECN_INCAPABLE, true, true, &on, 1);
1465	if (rc)
1466		return rc;
1467
1468	/*
1469	 * We advertise the available list of CCIDs and reorder according to
1470	 * preferences, to avoid failure resulting from negotiating different
1471	 * singleton values (which always leads to failure).
1472	 * These settings can still (later) be overridden via sockopts.
1473	 */
1474	if (ccid_get_builtin_ccids(&tx.val, &tx.len))
1475		return -ENOBUFS;
1476	if (ccid_get_builtin_ccids(&rx.val, &rx.len)) {
1477		kfree(tx.val);
1478		return -ENOBUFS;
1479	}
1480
1481	if (!dccp_feat_prefer(sysctl_dccp_tx_ccid, tx.val, tx.len) ||
1482	    !dccp_feat_prefer(sysctl_dccp_rx_ccid, rx.val, rx.len))
1483		goto free_ccid_lists;
1484
1485	rc = __feat_register_sp(fn, DCCPF_CCID, true, false, tx.val, tx.len);
1486	if (rc)
1487		goto free_ccid_lists;
1488
1489	rc = __feat_register_sp(fn, DCCPF_CCID, false, false, rx.val, rx.len);
1490
1491free_ccid_lists:
1492	kfree(tx.val);
1493	kfree(rx.val);
1494	return rc;
1495}
1496
1497int dccp_feat_activate_values(struct sock *sk, struct list_head *fn_list)
1498{
1499	struct dccp_sock *dp = dccp_sk(sk);
1500	struct dccp_feat_entry *cur, *next;
1501	int idx;
1502	dccp_feat_val *fvals[DCCP_FEAT_SUPPORTED_MAX][2] = {
1503		 [0 ... DCCP_FEAT_SUPPORTED_MAX-1] = { NULL, NULL }
1504	};
1505
1506	list_for_each_entry(cur, fn_list, node) {
1507		/*
1508		 * An empty Confirm means that either an unknown feature type
1509		 * or an invalid value was present. In the first case there is
1510		 * nothing to activate, in the other the default value is used.
1511		 */
1512		if (cur->empty_confirm)
1513			continue;
1514
1515		idx = dccp_feat_index(cur->feat_num);
1516		if (idx < 0) {
1517			DCCP_BUG("Unknown feature %u", cur->feat_num);
1518			goto activation_failed;
1519		}
1520		if (cur->state != FEAT_STABLE) {
1521			DCCP_CRIT("Negotiation of %s %s failed in state %s",
1522				  cur->is_local ? "local" : "remote",
1523				  dccp_feat_fname(cur->feat_num),
1524				  dccp_feat_sname[cur->state]);
1525			goto activation_failed;
1526		}
1527		fvals[idx][cur->is_local] = &cur->val;
1528	}
1529
1530	/*
1531	 * Activate in decreasing order of index, so that the CCIDs are always
1532	 * activated as the last feature. This avoids the case where a CCID
1533	 * relies on the initialisation of one or more features that it depends
1534	 * on (e.g. Send NDP Count, Send Ack Vector, and Ack Ratio features).
1535	 */
1536	for (idx = DCCP_FEAT_SUPPORTED_MAX; --idx >= 0;)
1537		if (__dccp_feat_activate(sk, idx, 0, fvals[idx][0]) ||
1538		    __dccp_feat_activate(sk, idx, 1, fvals[idx][1])) {
1539			DCCP_CRIT("Could not activate %d", idx);
1540			goto activation_failed;
1541		}
1542
1543	/* Clean up Change options which have been confirmed already */
1544	list_for_each_entry_safe(cur, next, fn_list, node)
1545		if (!cur->needs_confirm)
1546			dccp_feat_list_pop(cur);
1547
1548	dccp_pr_debug("Activation OK\n");
1549	return 0;
1550
1551activation_failed:
1552	/*
1553	 * We clean up everything that may have been allocated, since
1554	 * it is difficult to track at which stage negotiation failed.
1555	 * This is ok, since all allocation functions below are robust
1556	 * against NULL arguments.
1557	 */
1558	ccid_hc_rx_delete(dp->dccps_hc_rx_ccid, sk);
1559	ccid_hc_tx_delete(dp->dccps_hc_tx_ccid, sk);
1560	dp->dccps_hc_rx_ccid = dp->dccps_hc_tx_ccid = NULL;
1561	dccp_ackvec_free(dp->dccps_hc_rx_ackvec);
1562	dp->dccps_hc_rx_ackvec = NULL;
1563	return -1;
1564}