dccp: Resolve dependencies of features on choice of CCID

[deliverable/linux.git] / net / dccp / feat.c

/*
 *  net/dccp/feat.c
 *
 *  An implementation of the DCCP protocol
 *  Andrea Bittau <a.bittau@cs.ucl.ac.uk>
 *
 *  ASSUMPTIONS
 *  -----------
 *  o Feature negotiation is coordinated with connection setup (as in TCP), wild
 *    changes of parameters of an established connection are not supported.
 *  o All currently known SP features have 1-byte quantities. If in the future
 *    extensions of RFCs 4340..42 define features with item lengths larger than
 *    one byte, a feature-specific extension of the code will be required.
 *
 *  This program is free software; you can redistribute it and/or
 *  modify it under the terms of the GNU General Public License
 *  as published by the Free Software Foundation; either version
 *  2 of the License, or (at your option) any later version.
 */

#include <linux/module.h>

#include "ccid.h"
#include "feat.h"

#define DCCP_FEAT_SP_NOAGREE (-123)

static const struct {
        u8                      feat_num;               /* DCCPF_xxx */
        enum dccp_feat_type     rxtx;                   /* RX or TX  */
        enum dccp_feat_type     reconciliation;         /* SP or NN  */
        u8                      default_value;          /* as in 6.4 */
/*
 *    Lookup table for location and type of features (from RFC 4340/4342)
 *  +--------------------------+----+-----+----+----+---------+-----------+
 *  | Feature                  | Location | Reconc. | Initial |  Section  |
 *  |                          | RX | TX  | SP | NN |  Value  | Reference |
 *  +--------------------------+----+-----+----+----+---------+-----------+
 *  | DCCPF_CCID               |    |  X  | X  |    |   2     | 10        |
 *  | DCCPF_SHORT_SEQNOS       |    |  X  | X  |    |   0     |  7.6.1    |
 *  | DCCPF_SEQUENCE_WINDOW    |    |  X  |    | X  | 100     |  7.5.2    |
 *  | DCCPF_ECN_INCAPABLE      | X  |     | X  |    |   0     | 12.1      |
 *  | DCCPF_ACK_RATIO          |    |  X  |    | X  |   2     | 11.3      |
 *  | DCCPF_SEND_ACK_VECTOR    | X  |     | X  |    |   0     | 11.5      |
 *  | DCCPF_SEND_NDP_COUNT     |    |  X  | X  |    |   0     |  7.7.2    |
 *  | DCCPF_MIN_CSUM_COVER     | X  |     | X  |    |   0     |  9.2.1    |
 *  | DCCPF_DATA_CHECKSUM      | X  |     | X  |    |   0     |  9.3.1    |
 *  | DCCPF_SEND_LEV_RATE      | X  |     | X  |    |   0     | 4342/8.4  |
 *  +--------------------------+----+-----+----+----+---------+-----------+
 */
} dccp_feat_table[] = {
        { DCCPF_CCID,            FEAT_AT_TX, FEAT_SP, 2 },
        { DCCPF_SHORT_SEQNOS,    FEAT_AT_TX, FEAT_SP, 0 },
        { DCCPF_SEQUENCE_WINDOW, FEAT_AT_TX, FEAT_NN, 100 },
        { DCCPF_ECN_INCAPABLE,   FEAT_AT_RX, FEAT_SP, 0 },
        { DCCPF_ACK_RATIO,       FEAT_AT_TX, FEAT_NN, 2 },
        { DCCPF_SEND_ACK_VECTOR, FEAT_AT_RX, FEAT_SP, 0 },
        { DCCPF_SEND_NDP_COUNT,  FEAT_AT_TX, FEAT_SP, 0 },
        { DCCPF_MIN_CSUM_COVER,  FEAT_AT_RX, FEAT_SP, 0 },
        { DCCPF_DATA_CHECKSUM,   FEAT_AT_RX, FEAT_SP, 0 },
        { DCCPF_SEND_LEV_RATE,   FEAT_AT_RX, FEAT_SP, 0 },
};
#define DCCP_FEAT_SUPPORTED_MAX         ARRAY_SIZE(dccp_feat_table)

/**
 * dccp_feat_index  -  Hash function to map feature number into array position
 * Returns consecutive array index or -1 if the feature is not understood.
 */
static int dccp_feat_index(u8 feat_num)
{
        /* The first 9 entries are occupied by the types from RFC 4340, 6.4 */
        if (feat_num > DCCPF_RESERVED && feat_num <= DCCPF_DATA_CHECKSUM)
                return feat_num - 1;

        /*
         * Other features: add cases for new feature types here after adding
         * them to the above table.
         */
        switch (feat_num) {
        case DCCPF_SEND_LEV_RATE:
                        return DCCP_FEAT_SUPPORTED_MAX - 1;
        }
        return -1;
}

static u8 dccp_feat_type(u8 feat_num)
{
        int idx = dccp_feat_index(feat_num);

        if (idx < 0)
                return FEAT_UNKNOWN;
        return dccp_feat_table[idx].reconciliation;
}

static int dccp_feat_default_value(u8 feat_num)
{
        int idx = dccp_feat_index(feat_num);

        return idx < 0 ? : dccp_feat_table[idx].default_value;
}

/* copy constructor, fval must not already contain allocated memory */
static int dccp_feat_clone_sp_val(dccp_feat_val *fval, u8 const *val, u8 len)
{
        fval->sp.len = len;
        if (fval->sp.len > 0) {
                fval->sp.vec = kmemdup(val, len, gfp_any());
                if (fval->sp.vec == NULL) {
                        fval->sp.len = 0;
                        return -ENOBUFS;
                }
        }
        return 0;
}

static void dccp_feat_val_destructor(u8 feat_num, dccp_feat_val *val)
{
        if (unlikely(val == NULL))
                return;
        if (dccp_feat_type(feat_num) == FEAT_SP)
                kfree(val->sp.vec);
        memset(val, 0, sizeof(*val));
}

static struct dccp_feat_entry *
              dccp_feat_clone_entry(struct dccp_feat_entry const *original)
{
        struct dccp_feat_entry *new;
        u8 type = dccp_feat_type(original->feat_num);

        if (type == FEAT_UNKNOWN)
                return NULL;

        new = kmemdup(original, sizeof(struct dccp_feat_entry), gfp_any());
        if (new == NULL)
                return NULL;

        if (type == FEAT_SP && dccp_feat_clone_sp_val(&new->val,
                                                      original->val.sp.vec,
                                                      original->val.sp.len)) {
                kfree(new);
                return NULL;
        }
        return new;
}

static void dccp_feat_entry_destructor(struct dccp_feat_entry *entry)
{
        if (entry != NULL) {
                dccp_feat_val_destructor(entry->feat_num, &entry->val);
                kfree(entry);
        }
}

/*
 * List management functions
 *
 * Feature negotiation lists rely on and maintain the following invariants:
 * - each feat_num in the list is known, i.e. we know its type and default value
 * - each feat_num/is_local combination is unique (old entries are overwritten)
 * - SP values are always freshly allocated
 * - list is sorted in increasing order of feature number (faster lookup)
 */
static struct dccp_feat_entry *dccp_feat_list_lookup(struct list_head *fn_list,
                                                     u8 feat_num, bool is_local)
{
        struct dccp_feat_entry *entry;

        list_for_each_entry(entry, fn_list, node)
                if (entry->feat_num == feat_num && entry->is_local == is_local)
                        return entry;
                else if (entry->feat_num > feat_num)
                        break;
        return NULL;
}

/**
 * dccp_feat_entry_new  -  Central list update routine (called by all others)
 * @head:  list to add to
 * @feat:  feature number
 * @local: whether the local (1) or remote feature with number @feat is meant
 * This is the only constructor and serves to ensure the above invariants.
 */
static struct dccp_feat_entry *
              dccp_feat_entry_new(struct list_head *head, u8 feat, bool local)
{
        struct dccp_feat_entry *entry;

        list_for_each_entry(entry, head, node)
                if (entry->feat_num == feat && entry->is_local == local) {
                        dccp_feat_val_destructor(entry->feat_num, &entry->val);
                        return entry;
                } else if (entry->feat_num > feat) {
                        head = &entry->node;
                        break;
                }

        entry = kmalloc(sizeof(*entry), gfp_any());
        if (entry != NULL) {
                entry->feat_num = feat;
                entry->is_local = local;
                list_add_tail(&entry->node, head);
        }
        return entry;
}

/**
 * dccp_feat_push_change  -  Add/overwrite a Change option in the list
 * @fn_list: feature-negotiation list to update
 * @feat: one of %dccp_feature_numbers
 * @local: whether local (1) or remote (0) @feat_num is meant
 * @needs_mandatory: whether to use Mandatory feature negotiation options
 * @fval: pointer to NN/SP value to be inserted (will be copied)
 */
static int dccp_feat_push_change(struct list_head *fn_list, u8 feat, u8 local,
                                 u8 mandatory, dccp_feat_val *fval)
{
        struct dccp_feat_entry *new = dccp_feat_entry_new(fn_list, feat, local);

        if (new == NULL)
                return -ENOMEM;

        new->feat_num        = feat;
        new->is_local        = local;
        new->state           = FEAT_INITIALISING;
        new->needs_confirm   = 0;
        new->empty_confirm   = 0;
        new->val             = *fval;
        new->needs_mandatory = mandatory;

        return 0;
}

/**
 * dccp_feat_push_confirm  -  Add a Confirm entry to the FN list
 * @fn_list: feature-negotiation list to add to
 * @feat: one of %dccp_feature_numbers
 * @local: whether local (1) or remote (0) @feat_num is being confirmed
 * @fval: pointer to NN/SP value to be inserted or NULL
 * Returns 0 on success, a Reset code for further processing otherwise.
 */
static int dccp_feat_push_confirm(struct list_head *fn_list, u8 feat, u8 local,
                                  dccp_feat_val *fval)
{
        struct dccp_feat_entry *new = dccp_feat_entry_new(fn_list, feat, local);

        if (new == NULL)
                return DCCP_RESET_CODE_TOO_BUSY;

        new->feat_num        = feat;
        new->is_local        = local;
        new->state           = FEAT_STABLE;     /* transition in 6.6.2 */
        new->needs_confirm   = 1;
        new->empty_confirm   = (fval == NULL);
        new->val.nn          = 0;               /* zeroes the whole structure */
        if (!new->empty_confirm)
                new->val     = *fval;
        new->needs_mandatory = 0;

        return 0;
}

static int dccp_push_empty_confirm(struct list_head *fn_list, u8 feat, u8 local)
{
        return dccp_feat_push_confirm(fn_list, feat, local, NULL);
}

static inline void dccp_feat_list_pop(struct dccp_feat_entry *entry)
{
        list_del(&entry->node);
        dccp_feat_entry_destructor(entry);
}

void dccp_feat_list_purge(struct list_head *fn_list)
{
        struct dccp_feat_entry *entry, *next;

        list_for_each_entry_safe(entry, next, fn_list, node)
                dccp_feat_entry_destructor(entry);
        INIT_LIST_HEAD(fn_list);
}
EXPORT_SYMBOL_GPL(dccp_feat_list_purge);

/* generate @to as full clone of @from - @to must not contain any nodes */
int dccp_feat_clone_list(struct list_head const *from, struct list_head *to)
{
        struct dccp_feat_entry *entry, *new;

        INIT_LIST_HEAD(to);
        list_for_each_entry(entry, from, node) {
                new = dccp_feat_clone_entry(entry);
                if (new == NULL)
                        goto cloning_failed;
                list_add_tail(&new->node, to);
        }
        return 0;

cloning_failed:
        dccp_feat_list_purge(to);
        return -ENOMEM;
}

static u8 dccp_feat_is_valid_nn_val(u8 feat_num, u64 val)
{
        switch (feat_num) {
        case DCCPF_ACK_RATIO:
                return val <= DCCPF_ACK_RATIO_MAX;
        case DCCPF_SEQUENCE_WINDOW:
                return val >= DCCPF_SEQ_WMIN && val <= DCCPF_SEQ_WMAX;
        }
        return 0;       /* feature unknown - so we can't tell */
}

/* check that SP values are within the ranges defined in RFC 4340 */
static u8 dccp_feat_is_valid_sp_val(u8 feat_num, u8 val)
{
        switch (feat_num) {
        case DCCPF_CCID:
                return val == DCCPC_CCID2 || val == DCCPC_CCID3;
        /* Type-check Boolean feature values: */
        case DCCPF_SHORT_SEQNOS:
        case DCCPF_ECN_INCAPABLE:
        case DCCPF_SEND_ACK_VECTOR:
        case DCCPF_SEND_NDP_COUNT:
        case DCCPF_DATA_CHECKSUM:
        case DCCPF_SEND_LEV_RATE:
                return val < 2;
        case DCCPF_MIN_CSUM_COVER:
                return val < 16;
        }
        return 0;                       /* feature unknown */
}

static u8 dccp_feat_sp_list_ok(u8 feat_num, u8 const *sp_list, u8 sp_len)
{
        if (sp_list == NULL || sp_len < 1)
                return 0;
        while (sp_len--)
                if (!dccp_feat_is_valid_sp_val(feat_num, *sp_list++))
                        return 0;
        return 1;
}

/**
 * __feat_register_nn  -  Register new NN value on socket
 * @fn: feature-negotiation list to register with
 * @feat: an NN feature from %dccp_feature_numbers
 * @mandatory: use Mandatory option if 1
 * @nn_val: value to register (restricted to 4 bytes)
 * Note that NN features are local by definition (RFC 4340, 6.3.2).
 */
static int __feat_register_nn(struct list_head *fn, u8 feat,
                              u8 mandatory, u64 nn_val)
{
        dccp_feat_val fval = { .nn = nn_val };

        if (dccp_feat_type(feat) != FEAT_NN ||
            !dccp_feat_is_valid_nn_val(feat, nn_val))
                return -EINVAL;

        /* Don't bother with default values, they will be activated anyway. */
        if (nn_val - (u64)dccp_feat_default_value(feat) == 0)
                return 0;

        return dccp_feat_push_change(fn, feat, 1, mandatory, &fval);
}

/**
 * __feat_register_sp  -  Register new SP value/list on socket
 * @fn: feature-negotiation list to register with
 * @feat: an SP feature from %dccp_feature_numbers
 * @is_local: whether the local (1) or the remote (0) @feat is meant
 * @mandatory: use Mandatory option if 1
 * @sp_val: SP value followed by optional preference list
 * @sp_len: length of @sp_val in bytes
 */
static int __feat_register_sp(struct list_head *fn, u8 feat, u8 is_local,
                              u8 mandatory, u8 const *sp_val, u8 sp_len)
{
        dccp_feat_val fval;

        if (dccp_feat_type(feat) != FEAT_SP ||
            !dccp_feat_sp_list_ok(feat, sp_val, sp_len))
                return -EINVAL;

        /* Avoid negotiating alien CCIDs by only advertising supported ones */
        if (feat == DCCPF_CCID && !ccid_support_check(sp_val, sp_len))
                return -EOPNOTSUPP;

        if (dccp_feat_clone_sp_val(&fval, sp_val, sp_len))
                return -ENOMEM;

        return dccp_feat_push_change(fn, feat, is_local, mandatory, &fval);
}

int dccp_feat_change(struct dccp_minisock *dmsk, u8 type, u8 feature,
                     u8 *val, u8 len, gfp_t gfp)
{
        struct dccp_opt_pend *opt;

        dccp_feat_debug(type, feature, *val);

        if (len > 3) {
                DCCP_WARN("invalid length %d\n", len);
                return -EINVAL;
        }
        /* XXX add further sanity checks */

        /* check if that feature is already being negotiated */
        list_for_each_entry(opt, &dmsk->dccpms_pending, dccpop_node) {
                /* ok we found a negotiation for this option already */
                if (opt->dccpop_feat == feature && opt->dccpop_type == type) {
                        dccp_pr_debug("Replacing old\n");
                        /* replace */
                        BUG_ON(opt->dccpop_val == NULL);
                        kfree(opt->dccpop_val);
                        opt->dccpop_val  = val;
                        opt->dccpop_len  = len;
                        opt->dccpop_conf = 0;
                        return 0;
                }
        }

        /* negotiation for a new feature */
        opt = kmalloc(sizeof(*opt), gfp);
        if (opt == NULL)
                return -ENOMEM;

        opt->dccpop_type = type;
        opt->dccpop_feat = feature;
        opt->dccpop_len  = len;
        opt->dccpop_val  = val;
        opt->dccpop_conf = 0;
        opt->dccpop_sc   = NULL;

        BUG_ON(opt->dccpop_val == NULL);

        list_add_tail(&opt->dccpop_node, &dmsk->dccpms_pending);
        return 0;
}

EXPORT_SYMBOL_GPL(dccp_feat_change);

/*
 *      Tracking features whose value depend on the choice of CCID
 *
 * This is designed with an extension in mind so that a list walk could be done
 * before activating any features. However, the existing framework was found to
 * work satisfactorily up until now, the automatic verification is left open.
 * When adding new CCIDs, add a corresponding dependency table here.
 */
static const struct ccid_dependency *dccp_feat_ccid_deps(u8 ccid, bool is_local)
{
        static const struct ccid_dependency ccid2_dependencies[2][2] = {
                /*
                 * CCID2 mandates Ack Vectors (RFC 4341, 4.): as CCID is a TX
                 * feature and Send Ack Vector is an RX feature, `is_local'
                 * needs to be reversed.
                 */
                {       /* Dependencies of the receiver-side (remote) CCID2 */
                        {
                                .dependent_feat = DCCPF_SEND_ACK_VECTOR,
                                .is_local       = true,
                                .is_mandatory   = true,
                                .val            = 1
                        },
                        { 0, 0, 0, 0 }
                },
                {       /* Dependencies of the sender-side (local) CCID2 */
                        {
                                .dependent_feat = DCCPF_SEND_ACK_VECTOR,
                                .is_local       = false,
                                .is_mandatory   = true,
                                .val            = 1
                        },
                        { 0, 0, 0, 0 }
                }
        };
        static const struct ccid_dependency ccid3_dependencies[2][5] = {
                {       /*
                         * Dependencies of the receiver-side CCID3
                         */
                        {       /* locally disable Ack Vectors */
                                .dependent_feat = DCCPF_SEND_ACK_VECTOR,
                                .is_local       = true,
                                .is_mandatory   = false,
                                .val            = 0
                        },
                        {       /* see below why Send Loss Event Rate is on */
                                .dependent_feat = DCCPF_SEND_LEV_RATE,
                                .is_local       = true,
                                .is_mandatory   = true,
                                .val            = 1
                        },
                        {       /* NDP Count is needed as per RFC 4342, 6.1.1 */
                                .dependent_feat = DCCPF_SEND_NDP_COUNT,
                                .is_local       = false,
                                .is_mandatory   = true,
                                .val            = 1
                        },
                        { 0, 0, 0, 0 },
                },
                {       /*
                         * CCID3 at the TX side: we request that the HC-receiver
                         * will not send Ack Vectors (they will be ignored, so
                         * Mandatory is not set); we enable Send Loss Event Rate
                         * (Mandatory since the implementation does not support
                         * the Loss Intervals option of RFC 4342, 8.6).
                         * The last two options are for peer's information only.
                        */
                        {
                                .dependent_feat = DCCPF_SEND_ACK_VECTOR,
                                .is_local       = false,
                                .is_mandatory   = false,
                                .val            = 0
                        },
                        {
                                .dependent_feat = DCCPF_SEND_LEV_RATE,
                                .is_local       = false,
                                .is_mandatory   = true,
                                .val            = 1
                        },
                        {       /* this CCID does not support Ack Ratio */
                                .dependent_feat = DCCPF_ACK_RATIO,
                                .is_local       = true,
                                .is_mandatory   = false,
                                .val            = 0
                        },
                        {       /* tell receiver we are sending NDP counts */
                                .dependent_feat = DCCPF_SEND_NDP_COUNT,
                                .is_local       = true,
                                .is_mandatory   = false,
                                .val            = 1
                        },
                        { 0, 0, 0, 0 }
                }
        };
        switch (ccid) {
        case DCCPC_CCID2:
                return ccid2_dependencies[is_local];
        case DCCPC_CCID3:
                return ccid3_dependencies[is_local];
        default:
                return NULL;
        }
}

/**
 * dccp_feat_propagate_ccid - Resolve dependencies of features on choice of CCID
 * @fn: feature-negotiation list to update
 * @id: CCID number to track
 * @is_local: whether TX CCID (1) or RX CCID (0) is meant
 * This function needs to be called after registering all other features.
 */
static int dccp_feat_propagate_ccid(struct list_head *fn, u8 id, bool is_local)
{
        const struct ccid_dependency *table = dccp_feat_ccid_deps(id, is_local);
        int i, rc = (table == NULL);

        for (i = 0; rc == 0 && table[i].dependent_feat != DCCPF_RESERVED; i++)
                if (dccp_feat_type(table[i].dependent_feat) == FEAT_SP)
                        rc = __feat_register_sp(fn, table[i].dependent_feat,
                                                    table[i].is_local,
                                                    table[i].is_mandatory,
                                                    &table[i].val, 1);
                else
                        rc = __feat_register_nn(fn, table[i].dependent_feat,
                                                    table[i].is_mandatory,
                                                    table[i].val);
        return rc;
}

/**
 * dccp_feat_finalise_settings  -  Finalise settings before starting negotiation
 * @dp: client or listening socket (settings will be inherited)
 * This is called after all registrations (socket initialisation, sysctls, and
 * sockopt calls), and before sending the first packet containing Change options
 * (ie. client-Request or server-Response), to ensure internal consistency.
 */
int dccp_feat_finalise_settings(struct dccp_sock *dp)
{
        struct list_head *fn = &dp->dccps_featneg;
        struct dccp_feat_entry *entry;
        int i = 2, ccids[2] = { -1, -1 };

        /*
         * Propagating CCIDs:
         * 1) not useful to propagate CCID settings if this host advertises more
         *    than one CCID: the choice of CCID  may still change - if this is
         *    the client, or if this is the server and the client sends
         *    singleton CCID values.
         * 2) since is that propagate_ccid changes the list, we defer changing
         *    the sorted list until after the traversal.
         */
        list_for_each_entry(entry, fn, node)
                if (entry->feat_num == DCCPF_CCID && entry->val.sp.len == 1)
                        ccids[entry->is_local] = entry->val.sp.vec[0];
        while (i--)
                if (ccids[i] > 0 && dccp_feat_propagate_ccid(fn, ccids[i], i))
                        return -1;
        return 0;
}

static int dccp_feat_update_ccid(struct sock *sk, u8 type, u8 new_ccid_nr)
{
        struct dccp_sock *dp = dccp_sk(sk);
        struct dccp_minisock *dmsk = dccp_msk(sk);
        /* figure out if we are changing our CCID or the peer's */
        const int rx = type == DCCPO_CHANGE_R;
        const u8 ccid_nr = rx ? dmsk->dccpms_rx_ccid : dmsk->dccpms_tx_ccid;
        struct ccid *new_ccid;

        /* Check if nothing is being changed. */
        if (ccid_nr == new_ccid_nr)
                return 0;

        new_ccid = ccid_new(new_ccid_nr, sk, rx, GFP_ATOMIC);
        if (new_ccid == NULL)
                return -ENOMEM;

        if (rx) {
                ccid_hc_rx_delete(dp->dccps_hc_rx_ccid, sk);
                dp->dccps_hc_rx_ccid = new_ccid;
                dmsk->dccpms_rx_ccid = new_ccid_nr;
        } else {
                ccid_hc_tx_delete(dp->dccps_hc_tx_ccid, sk);
                dp->dccps_hc_tx_ccid = new_ccid;
                dmsk->dccpms_tx_ccid = new_ccid_nr;
        }

        return 0;
}

static int dccp_feat_update(struct sock *sk, u8 type, u8 feat, u8 val)
{
        dccp_feat_debug(type, feat, val);

        switch (feat) {
        case DCCPF_CCID:
                return dccp_feat_update_ccid(sk, type, val);
        default:
                dccp_pr_debug("UNIMPLEMENTED: %s(%d, ...)\n",
                              dccp_feat_typename(type), feat);
                break;
        }
        return 0;
}

static int dccp_feat_reconcile(struct sock *sk, struct dccp_opt_pend *opt,
                               u8 *rpref, u8 rlen)
{
        struct dccp_sock *dp = dccp_sk(sk);
        u8 *spref, slen, *res = NULL;
        int i, j, rc, agree = 1;

        BUG_ON(rpref == NULL);

        /* check if we are the black sheep */
        if (dp->dccps_role == DCCP_ROLE_CLIENT) {
                spref = rpref;
                slen  = rlen;
                rpref = opt->dccpop_val;
                rlen  = opt->dccpop_len;
        } else {
                spref = opt->dccpop_val;
                slen  = opt->dccpop_len;
        }
        /*
         * Now we have server preference list in spref and client preference in
         * rpref
         */
        BUG_ON(spref == NULL);
        BUG_ON(rpref == NULL);

        /* FIXME sanity check vals */

        /* Are values in any order?  XXX Lame "algorithm" here */
        for (i = 0; i < slen; i++) {
                for (j = 0; j < rlen; j++) {
                        if (spref[i] == rpref[j]) {
                                res = &spref[i];
                                break;
                        }
                }
                if (res)
                        break;
        }

        /* we didn't agree on anything */
        if (res == NULL) {
                /* confirm previous value */
                switch (opt->dccpop_feat) {
                case DCCPF_CCID:
                        /* XXX did i get this right? =P */
                        if (opt->dccpop_type == DCCPO_CHANGE_L)
                                res = &dccp_msk(sk)->dccpms_tx_ccid;
                        else
                                res = &dccp_msk(sk)->dccpms_rx_ccid;
                        break;

                default:
                        DCCP_BUG("Fell through, feat=%d", opt->dccpop_feat);
                        /* XXX implement res */
                        return -EFAULT;
                }

                dccp_pr_debug("Don't agree... reconfirming %d\n", *res);
                agree = 0; /* this is used for mandatory options... */
        }

        /* need to put result and our preference list */
        rlen = 1 + opt->dccpop_len;
        rpref = kmalloc(rlen, GFP_ATOMIC);
        if (rpref == NULL)
                return -ENOMEM;

        *rpref = *res;
        memcpy(&rpref[1], opt->dccpop_val, opt->dccpop_len);

        /* put it in the "confirm queue" */
        if (opt->dccpop_sc == NULL) {
                opt->dccpop_sc = kmalloc(sizeof(*opt->dccpop_sc), GFP_ATOMIC);
                if (opt->dccpop_sc == NULL) {
                        kfree(rpref);
                        return -ENOMEM;
                }
        } else {
                /* recycle the confirm slot */
                BUG_ON(opt->dccpop_sc->dccpoc_val == NULL);
                kfree(opt->dccpop_sc->dccpoc_val);
                dccp_pr_debug("recycling confirm slot\n");
        }
        memset(opt->dccpop_sc, 0, sizeof(*opt->dccpop_sc));

        opt->dccpop_sc->dccpoc_val = rpref;
        opt->dccpop_sc->dccpoc_len = rlen;

        /* update the option on our side [we are about to send the confirm] */
        rc = dccp_feat_update(sk, opt->dccpop_type, opt->dccpop_feat, *res);
        if (rc) {
                kfree(opt->dccpop_sc->dccpoc_val);
                kfree(opt->dccpop_sc);
                opt->dccpop_sc = NULL;
                return rc;
        }

        dccp_pr_debug("Will confirm %d\n", *rpref);

        /* say we want to change to X but we just got a confirm X, suppress our
         * change
         */
        if (!opt->dccpop_conf) {
                if (*opt->dccpop_val == *res)
                        opt->dccpop_conf = 1;
                dccp_pr_debug("won't ask for change of same feature\n");
        }

        return agree ? 0 : DCCP_FEAT_SP_NOAGREE; /* used for mandatory opts */
}

static int dccp_feat_sp(struct sock *sk, u8 type, u8 feature, u8 *val, u8 len)
{
        struct dccp_minisock *dmsk = dccp_msk(sk);
        struct dccp_opt_pend *opt;
        int rc = 1;
        u8 t;

        /*
         * We received a CHANGE.  We gotta match it against our own preference
         * list.  If we got a CHANGE_R it means it's a change for us, so we need
         * to compare our CHANGE_L list.
         */
        if (type == DCCPO_CHANGE_L)
                t = DCCPO_CHANGE_R;
        else
                t = DCCPO_CHANGE_L;

        /* find our preference list for this feature */
        list_for_each_entry(opt, &dmsk->dccpms_pending, dccpop_node) {
                if (opt->dccpop_type != t || opt->dccpop_feat != feature)
                        continue;

                /* find the winner from the two preference lists */
                rc = dccp_feat_reconcile(sk, opt, val, len);
                break;
        }

        /* We didn't deal with the change.  This can happen if we have no
         * preference list for the feature.  In fact, it just shouldn't
         * happen---if we understand a feature, we should have a preference list
         * with at least the default value.
         */
        BUG_ON(rc == 1);

        return rc;
}

static int dccp_feat_nn(struct sock *sk, u8 type, u8 feature, u8 *val, u8 len)
{
        struct dccp_opt_pend *opt;
        struct dccp_minisock *dmsk = dccp_msk(sk);
        u8 *copy;
        int rc;

        /* NN features must be Change L (sec. 6.3.2) */
        if (type != DCCPO_CHANGE_L) {
                dccp_pr_debug("received %s for NN feature %d\n",
                                dccp_feat_typename(type), feature);
                return -EFAULT;
        }

        /* XXX sanity check opt val */

        /* copy option so we can confirm it */
        opt = kzalloc(sizeof(*opt), GFP_ATOMIC);
        if (opt == NULL)
                return -ENOMEM;

        copy = kmemdup(val, len, GFP_ATOMIC);
        if (copy == NULL) {
                kfree(opt);
                return -ENOMEM;
        }

        opt->dccpop_type = DCCPO_CONFIRM_R; /* NN can only confirm R */
        opt->dccpop_feat = feature;
        opt->dccpop_val  = copy;
        opt->dccpop_len  = len;

        /* change feature */
        rc = dccp_feat_update(sk, type, feature, *val);
        if (rc) {
                kfree(opt->dccpop_val);
                kfree(opt);
                return rc;
        }

        dccp_feat_debug(type, feature, *copy);

        list_add_tail(&opt->dccpop_node, &dmsk->dccpms_conf);

        return 0;
}

static void dccp_feat_empty_confirm(struct dccp_minisock *dmsk,
                                    u8 type, u8 feature)
{
        /* XXX check if other confirms for that are queued and recycle slot */
        struct dccp_opt_pend *opt = kzalloc(sizeof(*opt), GFP_ATOMIC);

        if (opt == NULL) {
                /* XXX what do we do?  Ignoring should be fine.  It's a change
                 * after all =P
                 */
                return;
        }

        switch (type) {
        case DCCPO_CHANGE_L:
                opt->dccpop_type = DCCPO_CONFIRM_R;
                break;
        case DCCPO_CHANGE_R:
                opt->dccpop_type = DCCPO_CONFIRM_L;
                break;
        default:
                DCCP_WARN("invalid type %d\n", type);
                kfree(opt);
                return;
        }
        opt->dccpop_feat = feature;
        opt->dccpop_val  = NULL;
        opt->dccpop_len  = 0;

        /* change feature */
        dccp_pr_debug("Empty %s(%d)\n", dccp_feat_typename(type), feature);

        list_add_tail(&opt->dccpop_node, &dmsk->dccpms_conf);
}

static void dccp_feat_flush_confirm(struct sock *sk)
{
        struct dccp_minisock *dmsk = dccp_msk(sk);
        /* Check if there is anything to confirm in the first place */
        int yes = !list_empty(&dmsk->dccpms_conf);

        if (!yes) {
                struct dccp_opt_pend *opt;

                list_for_each_entry(opt, &dmsk->dccpms_pending, dccpop_node) {
                        if (opt->dccpop_conf) {
                                yes = 1;
                                break;
                        }
                }
        }

        if (!yes)
                return;

        /* OK there is something to confirm... */
        /* XXX check if packet is in flight?  Send delayed ack?? */
        if (sk->sk_state == DCCP_OPEN)
                dccp_send_ack(sk);
}

int dccp_feat_change_recv(struct sock *sk, u8 type, u8 feature, u8 *val, u8 len)
{
        int rc;

        /* Ignore Change requests other than during connection setup */
        if (sk->sk_state != DCCP_LISTEN && sk->sk_state != DCCP_REQUESTING)
                return 0;
        dccp_feat_debug(type, feature, *val);

        /* figure out if it's SP or NN feature */
        switch (feature) {
        /* deal with SP features */
        case DCCPF_CCID:
                rc = dccp_feat_sp(sk, type, feature, val, len);
                break;

        /* deal with NN features */
        case DCCPF_ACK_RATIO:
                rc = dccp_feat_nn(sk, type, feature, val, len);
                break;

        /* XXX implement other features */
        default:
                dccp_pr_debug("UNIMPLEMENTED: not handling %s(%d, ...)\n",
                              dccp_feat_typename(type), feature);
                rc = -EFAULT;
                break;
        }

        /* check if there were problems changing features */
        if (rc) {
                /* If we don't agree on SP, we sent a confirm for old value.
                 * However we propagate rc to caller in case option was
                 * mandatory
                 */
                if (rc != DCCP_FEAT_SP_NOAGREE)
                        dccp_feat_empty_confirm(dccp_msk(sk), type, feature);
        }

        /* generate the confirm [if required] */
        dccp_feat_flush_confirm(sk);

        return rc;
}

EXPORT_SYMBOL_GPL(dccp_feat_change_recv);

int dccp_feat_confirm_recv(struct sock *sk, u8 type, u8 feature,
                           u8 *val, u8 len)
{
        u8 t;
        struct dccp_opt_pend *opt;
        struct dccp_minisock *dmsk = dccp_msk(sk);
        int found = 0;
        int all_confirmed = 1;

        /* Ignore Confirm options other than during connection setup */
        if (sk->sk_state != DCCP_LISTEN && sk->sk_state != DCCP_REQUESTING)
                return 0;
        dccp_feat_debug(type, feature, *val);

        /* locate our change request */
        switch (type) {
        case DCCPO_CONFIRM_L: t = DCCPO_CHANGE_R; break;
        case DCCPO_CONFIRM_R: t = DCCPO_CHANGE_L; break;
        default:              DCCP_WARN("invalid type %d\n", type);
                              return 1;

        }
        /* XXX sanity check feature value */

        list_for_each_entry(opt, &dmsk->dccpms_pending, dccpop_node) {
                if (!opt->dccpop_conf && opt->dccpop_type == t &&
                    opt->dccpop_feat == feature) {
                        found = 1;
                        dccp_pr_debug("feature %d found\n", opt->dccpop_feat);

                        /* XXX do sanity check */

                        opt->dccpop_conf = 1;

                        /* We got a confirmation---change the option */
                        dccp_feat_update(sk, opt->dccpop_type,
                                         opt->dccpop_feat, *val);

                        /* XXX check the return value of dccp_feat_update */
                        break;
                }

                if (!opt->dccpop_conf)
                        all_confirmed = 0;
        }

        if (!found)
                dccp_pr_debug("%s(%d, ...) never requested\n",
                              dccp_feat_typename(type), feature);
        return 0;
}

EXPORT_SYMBOL_GPL(dccp_feat_confirm_recv);

void dccp_feat_clean(struct dccp_minisock *dmsk)
{
        struct dccp_opt_pend *opt, *next;

        list_for_each_entry_safe(opt, next, &dmsk->dccpms_pending,
                                 dccpop_node) {
                BUG_ON(opt->dccpop_val == NULL);
                kfree(opt->dccpop_val);

                if (opt->dccpop_sc != NULL) {
                        BUG_ON(opt->dccpop_sc->dccpoc_val == NULL);
                        kfree(opt->dccpop_sc->dccpoc_val);
                        kfree(opt->dccpop_sc);
                }

                kfree(opt);
        }
        INIT_LIST_HEAD(&dmsk->dccpms_pending);

        list_for_each_entry_safe(opt, next, &dmsk->dccpms_conf, dccpop_node) {
                BUG_ON(opt == NULL);
                if (opt->dccpop_val != NULL)
                        kfree(opt->dccpop_val);
                kfree(opt);
        }
        INIT_LIST_HEAD(&dmsk->dccpms_conf);
}

EXPORT_SYMBOL_GPL(dccp_feat_clean);

/* this is to be called only when a listening sock creates its child.  It is
 * assumed by the function---the confirm is not duplicated, but rather it is
 * "passed on".
 */
int dccp_feat_clone(struct sock *oldsk, struct sock *newsk)
{
        struct dccp_minisock *olddmsk = dccp_msk(oldsk);
        struct dccp_minisock *newdmsk = dccp_msk(newsk);
        struct dccp_opt_pend *opt;
        int rc = 0;

        INIT_LIST_HEAD(&newdmsk->dccpms_pending);
        INIT_LIST_HEAD(&newdmsk->dccpms_conf);

        list_for_each_entry(opt, &olddmsk->dccpms_pending, dccpop_node) {
                struct dccp_opt_pend *newopt;
                /* copy the value of the option */
                u8 *val = kmemdup(opt->dccpop_val, opt->dccpop_len, GFP_ATOMIC);

                if (val == NULL)
                        goto out_clean;

                newopt = kmemdup(opt, sizeof(*newopt), GFP_ATOMIC);
                if (newopt == NULL) {
                        kfree(val);
                        goto out_clean;
                }

                /* insert the option */
                newopt->dccpop_val = val;
                list_add_tail(&newopt->dccpop_node, &newdmsk->dccpms_pending);

                /* XXX what happens with backlogs and multiple connections at
                 * once...
                 */
                /* the master socket no longer needs to worry about confirms */
                opt->dccpop_sc = NULL; /* it's not a memleak---new socket has it */

                /* reset state for a new socket */
                opt->dccpop_conf = 0;
        }

        /* XXX not doing anything about the conf queue */

out:
        return rc;

out_clean:
        dccp_feat_clean(newdmsk);
        rc = -ENOMEM;
        goto out;
}

EXPORT_SYMBOL_GPL(dccp_feat_clone);

int dccp_feat_init(struct sock *sk)
{
        struct dccp_sock *dp = dccp_sk(sk);
        struct dccp_minisock *dmsk = dccp_msk(sk);
        int rc;

        INIT_LIST_HEAD(&dmsk->dccpms_pending);  /* XXX no longer used */
        INIT_LIST_HEAD(&dmsk->dccpms_conf);     /* XXX no longer used */

        /* CCID L */
        rc = __feat_register_sp(&dp->dccps_featneg, DCCPF_CCID, 1, 0,
                                &dmsk->dccpms_tx_ccid, 1);
        if (rc)
                goto out;

        /* CCID R */
        rc = __feat_register_sp(&dp->dccps_featneg, DCCPF_CCID, 0, 0,
                                &dmsk->dccpms_rx_ccid, 1);
        if (rc)
                goto out;

        /* Ack ratio */
        rc = __feat_register_nn(&dp->dccps_featneg, DCCPF_ACK_RATIO, 0,
                                dmsk->dccpms_ack_ratio);
out:
        return rc;
}

EXPORT_SYMBOL_GPL(dccp_feat_init);

#ifdef CONFIG_IP_DCCP_DEBUG
const char *dccp_feat_typename(const u8 type)
{
        switch(type) {
        case DCCPO_CHANGE_L:  return("ChangeL");
        case DCCPO_CONFIRM_L: return("ConfirmL");
        case DCCPO_CHANGE_R:  return("ChangeR");
        case DCCPO_CONFIRM_R: return("ConfirmR");
        /* the following case must not appear in feature negotation  */
        default:              dccp_pr_debug("unknown type %d [BUG!]\n", type);
        }
        return NULL;
}

EXPORT_SYMBOL_GPL(dccp_feat_typename);

const char *dccp_feat_name(const u8 feat)
{
        static const char *feature_names[] = {
                [DCCPF_RESERVED]        = "Reserved",
                [DCCPF_CCID]            = "CCID",
                [DCCPF_SHORT_SEQNOS]    = "Allow Short Seqnos",
                [DCCPF_SEQUENCE_WINDOW] = "Sequence Window",
                [DCCPF_ECN_INCAPABLE]   = "ECN Incapable",
                [DCCPF_ACK_RATIO]       = "Ack Ratio",
                [DCCPF_SEND_ACK_VECTOR] = "Send ACK Vector",
                [DCCPF_SEND_NDP_COUNT]  = "Send NDP Count",
                [DCCPF_MIN_CSUM_COVER]  = "Min. Csum Coverage",
                [DCCPF_DATA_CHECKSUM]   = "Send Data Checksum",
        };
        if (feat > DCCPF_DATA_CHECKSUM && feat < DCCPF_MIN_CCID_SPECIFIC)
                return feature_names[DCCPF_RESERVED];

        if (feat ==  DCCPF_SEND_LEV_RATE)
                return "Send Loss Event Rate";
        if (feat >= DCCPF_MIN_CCID_SPECIFIC)
                return "CCID-specific";

        return feature_names[feat];
}

EXPORT_SYMBOL_GPL(dccp_feat_name);
#endif /* CONFIG_IP_DCCP_DEBUG */