options.c

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/*
 *  net/dccp/options.c
 *
 *  An implementation of the DCCP protocol
 *  Copyright (c) 2005 Aristeu Sergio Rozanski Filho <[email protected]>
 *  Copyright (c) 2005 Arnaldo Carvalho de Melo <[email protected]>
 *  Copyright (c) 2005 Ian McDonald <[email protected]>
 *
 *      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/dccp.h>
#include <linux/module.h>
#include <linux/types.h>
#include <asm/unaligned.h>
#include <linux/kernel.h>
#include <linux/skbuff.h>

#include "ackvec.h"
#include "ccid.h"
#include "dccp.h"
#include "feat.h"

u64 dccp_decode_value_var(const u8 *bf, const u8 len)
{
    u64 value = 0;

    if (len >= DCCP_OPTVAL_MAXLEN)
        value += ((u64)*bf++) << 40;
    if (len > 4)
        value += ((u64)*bf++) << 32;
    if (len > 3)
        value += ((u64)*bf++) << 24;
    if (len > 2)
        value += ((u64)*bf++) << 16;
    if (len > 1)
        value += ((u64)*bf++) << 8;
    if (len > 0)
        value += *bf;

    return value;
}

int dccp_parse_options(struct sock *sk, struct dccp_request_sock *dreq,
               struct sk_buff *skb)
{
    struct dccp_sock *dp = dccp_sk(sk);
    const struct dccp_hdr *dh = dccp_hdr(skb);
    const u8 pkt_type = DCCP_SKB_CB(skb)->dccpd_type;
    unsigned char *options = (unsigned char *)dh + dccp_hdr_len(skb);
    unsigned char *opt_ptr = options;
    const unsigned char *opt_end = (unsigned char *)dh +
                    (dh->dccph_doff * 4);
    struct dccp_options_received *opt_recv = &dp->dccps_options_received;
    unsigned char opt, len;
    unsigned char *uninitialized_var(value);
    u32 elapsed_time;
    __be32 opt_val;
    int rc;
    int mandatory = 0;

    memset(opt_recv, 0, sizeof(*opt_recv));

    opt = len = 0;
    while (opt_ptr != opt_end) {
        opt   = *opt_ptr++;
        len   = 0;
        value = NULL;

        /* Check if this isn't a single byte option */
        if (opt > DCCPO_MAX_RESERVED) {
            if (opt_ptr == opt_end)
                goto out_nonsensical_length;

            len = *opt_ptr++;
            if (len < 2)
                goto out_nonsensical_length;
            /*
             * Remove the type and len fields, leaving
             * just the value size
             */
            len -= 2;
            value   = opt_ptr;
            opt_ptr += len;

            if (opt_ptr > opt_end)
                goto out_nonsensical_length;
        }

        /*
         * CCID-specific options are ignored during connection setup, as
         * negotiation may still be in progress (see RFC 4340, 10.3).
         * The same applies to Ack Vectors, as these depend on the CCID.
         */
        if (dreq != NULL && (opt >= DCCPO_MIN_RX_CCID_SPECIFIC ||
            opt == DCCPO_ACK_VECTOR_0 || opt == DCCPO_ACK_VECTOR_1))
            goto ignore_option;

        switch (opt) {
        case DCCPO_PADDING:
            break;
        case DCCPO_MANDATORY:
            if (mandatory)
                goto out_invalid_option;
            if (pkt_type != DCCP_PKT_DATA)
                mandatory = 1;
            break;
        case DCCPO_NDP_COUNT:
            if (len > 6)
                goto out_invalid_option;

            opt_recv->dccpor_ndp = dccp_decode_value_var(value, len);
            dccp_pr_debug("%s opt: NDP count=%llu\n", dccp_role(sk),
                      (unsigned long long)opt_recv->dccpor_ndp);
            break;
        case DCCPO_CHANGE_L ... DCCPO_CONFIRM_R:
            if (pkt_type == DCCP_PKT_DATA)      /* RFC 4340, 6 */
                break;
            if (len == 0)
                goto out_invalid_option;
            rc = dccp_feat_parse_options(sk, dreq, mandatory, opt,
                            *value, value + 1, len - 1);
            if (rc)
                goto out_featneg_failed;
            break;
        case DCCPO_TIMESTAMP:
            if (len != 4)
                goto out_invalid_option;
            /*
             * RFC 4340 13.1: "The precise time corresponding to
             * Timestamp Value zero is not specified". We use
             * zero to indicate absence of a meaningful timestamp.
             */
            opt_val = get_unaligned((__be32 *)value);
            if (unlikely(opt_val == 0)) {
                DCCP_WARN("Timestamp with zero value\n");
                break;
            }

            if (dreq != NULL) {
                dreq->dreq_timestamp_echo = ntohl(opt_val);
                dreq->dreq_timestamp_time = dccp_timestamp();
            } else {
                opt_recv->dccpor_timestamp =
                    dp->dccps_timestamp_echo = ntohl(opt_val);
                dp->dccps_timestamp_time = dccp_timestamp();
            }
            dccp_pr_debug("%s rx opt: TIMESTAMP=%u, ackno=%llu\n",
                      dccp_role(sk), ntohl(opt_val),
                      (unsigned long long)
                      DCCP_SKB_CB(skb)->dccpd_ack_seq);
            /* schedule an Ack in case this sender is quiescent */
            inet_csk_schedule_ack(sk);
            break;
        case DCCPO_TIMESTAMP_ECHO:
            if (len != 4 && len != 6 && len != 8)
                goto out_invalid_option;

            opt_val = get_unaligned((__be32 *)value);
            opt_recv->dccpor_timestamp_echo = ntohl(opt_val);

            dccp_pr_debug("%s rx opt: TIMESTAMP_ECHO=%u, len=%d, "
                      "ackno=%llu", dccp_role(sk),
                      opt_recv->dccpor_timestamp_echo,
                      len + 2,
                      (unsigned long long)
                      DCCP_SKB_CB(skb)->dccpd_ack_seq);

            value += 4;

            if (len == 4) {     /* no elapsed time included */
                dccp_pr_debug_cat("\n");
                break;
            }

            if (len == 6) {     /* 2-byte elapsed time */
                __be16 opt_val2 = get_unaligned((__be16 *)value);
                elapsed_time = ntohs(opt_val2);
            } else {        /* 4-byte elapsed time */
                opt_val = get_unaligned((__be32 *)value);
                elapsed_time = ntohl(opt_val);
            }

            dccp_pr_debug_cat(", ELAPSED_TIME=%u\n", elapsed_time);

            /* Give precedence to the biggest ELAPSED_TIME */
            if (elapsed_time > opt_recv->dccpor_elapsed_time)
                opt_recv->dccpor_elapsed_time = elapsed_time;
            break;
        case DCCPO_ELAPSED_TIME:
            if (dccp_packet_without_ack(skb))   /* RFC 4340, 13.2 */
                break;

            if (len == 2) {
                __be16 opt_val2 = get_unaligned((__be16 *)value);
                elapsed_time = ntohs(opt_val2);
            } else if (len == 4) {
                opt_val = get_unaligned((__be32 *)value);
                elapsed_time = ntohl(opt_val);
            } else {
                goto out_invalid_option;
            }

            if (elapsed_time > opt_recv->dccpor_elapsed_time)
                opt_recv->dccpor_elapsed_time = elapsed_time;

            dccp_pr_debug("%s rx opt: ELAPSED_TIME=%d\n",
                      dccp_role(sk), elapsed_time);
            break;
        case DCCPO_MIN_RX_CCID_SPECIFIC ... DCCPO_MAX_RX_CCID_SPECIFIC:
            if (ccid_hc_rx_parse_options(dp->dccps_hc_rx_ccid, sk,
                             pkt_type, opt, value, len))
                goto out_invalid_option;
            break;
        case DCCPO_ACK_VECTOR_0:
        case DCCPO_ACK_VECTOR_1:
            if (dccp_packet_without_ack(skb))   /* RFC 4340, 11.4 */
                break;
            /*
             * Ack vectors are processed by the TX CCID if it is
             * interested. The RX CCID need not parse Ack Vectors,
             * since it is only interested in clearing old state.
             * Fall through.
             */
        case DCCPO_MIN_TX_CCID_SPECIFIC ... DCCPO_MAX_TX_CCID_SPECIFIC:
            if (ccid_hc_tx_parse_options(dp->dccps_hc_tx_ccid, sk,
                             pkt_type, opt, value, len))
                goto out_invalid_option;
            break;
        default:
            DCCP_CRIT("DCCP(%p): option %d(len=%d) not "
                  "implemented, ignoring", sk, opt, len);
            break;
        }
ignore_option:
        if (opt != DCCPO_MANDATORY)
            mandatory = 0;
    }

    /* mandatory was the last byte in option list -> reset connection */
    if (mandatory)
        goto out_invalid_option;

out_nonsensical_length:
    /* RFC 4340, 5.8: ignore option and all remaining option space */
    return 0;

out_invalid_option:
    DCCP_INC_STATS_BH(DCCP_MIB_INVALIDOPT);
    rc = DCCP_RESET_CODE_OPTION_ERROR;
out_featneg_failed:
    DCCP_WARN("DCCP(%p): Option %d (len=%d) error=%u\n", sk, opt, len, rc);
    DCCP_SKB_CB(skb)->dccpd_reset_code = rc;
    DCCP_SKB_CB(skb)->dccpd_reset_data[0] = opt;
    DCCP_SKB_CB(skb)->dccpd_reset_data[1] = len > 0 ? value[0] : 0;
    DCCP_SKB_CB(skb)->dccpd_reset_data[2] = len > 1 ? value[1] : 0;
    return -1;
}

EXPORT_SYMBOL_GPL(dccp_parse_options);

void dccp_encode_value_var(const u64 value, u8 *to, const u8 len)
{
    if (len >= DCCP_OPTVAL_MAXLEN)
        *to++ = (value & 0xFF0000000000ull) >> 40;
    if (len > 4)
        *to++ = (value & 0xFF00000000ull) >> 32;
    if (len > 3)
        *to++ = (value & 0xFF000000) >> 24;
    if (len > 2)
        *to++ = (value & 0xFF0000) >> 16;
    if (len > 1)
        *to++ = (value & 0xFF00) >> 8;
    if (len > 0)
        *to++ = (value & 0xFF);
}

static inline u8 dccp_ndp_len(const u64 ndp)
{
    if (likely(ndp <= 0xFF))
        return 1;
    return likely(ndp <= USHRT_MAX) ? 2 : (ndp <= UINT_MAX ? 4 : 6);
}

int dccp_insert_option(struct sk_buff *skb, const unsigned char option,
               const void *value, const unsigned char len)
{
    unsigned char *to;

    if (DCCP_SKB_CB(skb)->dccpd_opt_len + len + 2 > DCCP_MAX_OPT_LEN)
        return -1;

    DCCP_SKB_CB(skb)->dccpd_opt_len += len + 2;

    to    = skb_push(skb, len + 2);
    *to++ = option;
    *to++ = len + 2;

    memcpy(to, value, len);
    return 0;
}

EXPORT_SYMBOL_GPL(dccp_insert_option);

static int dccp_insert_option_ndp(struct sock *sk, struct sk_buff *skb)
{
    struct dccp_sock *dp = dccp_sk(sk);
    u64 ndp = dp->dccps_ndp_count;

    if (dccp_non_data_packet(skb))
        ++dp->dccps_ndp_count;
    else
        dp->dccps_ndp_count = 0;

    if (ndp > 0) {
        unsigned char *ptr;
        const int ndp_len = dccp_ndp_len(ndp);
        const int len = ndp_len + 2;

        if (DCCP_SKB_CB(skb)->dccpd_opt_len + len > DCCP_MAX_OPT_LEN)
            return -1;

        DCCP_SKB_CB(skb)->dccpd_opt_len += len;

        ptr = skb_push(skb, len);
        *ptr++ = DCCPO_NDP_COUNT;
        *ptr++ = len;
        dccp_encode_value_var(ndp, ptr, ndp_len);
    }

    return 0;
}

static inline int dccp_elapsed_time_len(const u32 elapsed_time)
{
    return elapsed_time == 0 ? 0 : elapsed_time <= 0xFFFF ? 2 : 4;
}

/* FIXME: This function is currently not used anywhere */
int dccp_insert_option_elapsed_time(struct sk_buff *skb, u32 elapsed_time)
{
    const int elapsed_time_len = dccp_elapsed_time_len(elapsed_time);
    const int len = 2 + elapsed_time_len;
    unsigned char *to;

    if (elapsed_time_len == 0)
        return 0;

    if (DCCP_SKB_CB(skb)->dccpd_opt_len + len > DCCP_MAX_OPT_LEN)
        return -1;

    DCCP_SKB_CB(skb)->dccpd_opt_len += len;

    to    = skb_push(skb, len);
    *to++ = DCCPO_ELAPSED_TIME;
    *to++ = len;

    if (elapsed_time_len == 2) {
        const __be16 var16 = htons((u16)elapsed_time);
        memcpy(to, &var16, 2);
    } else {
        const __be32 var32 = htonl(elapsed_time);
        memcpy(to, &var32, 4);
    }

    return 0;
}

EXPORT_SYMBOL_GPL(dccp_insert_option_elapsed_time);

static int dccp_insert_option_timestamp(struct sk_buff *skb)
{
    __be32 now = htonl(dccp_timestamp());
    /* yes this will overflow but that is the point as we want a
     * 10 usec 32 bit timer which mean it wraps every 11.9 hours */

    return dccp_insert_option(skb, DCCPO_TIMESTAMP, &now, sizeof(now));
}

static int dccp_insert_option_timestamp_echo(struct dccp_sock *dp,
                         struct dccp_request_sock *dreq,
                         struct sk_buff *skb)
{
    __be32 tstamp_echo;
    unsigned char *to;
    u32 elapsed_time, elapsed_time_len, len;

    if (dreq != NULL) {
        elapsed_time = dccp_timestamp() - dreq->dreq_timestamp_time;
        tstamp_echo  = htonl(dreq->dreq_timestamp_echo);
        dreq->dreq_timestamp_echo = 0;
    } else {
        elapsed_time = dccp_timestamp() - dp->dccps_timestamp_time;
        tstamp_echo  = htonl(dp->dccps_timestamp_echo);
        dp->dccps_timestamp_echo = 0;
    }

    elapsed_time_len = dccp_elapsed_time_len(elapsed_time);
    len = 6 + elapsed_time_len;

    if (DCCP_SKB_CB(skb)->dccpd_opt_len + len > DCCP_MAX_OPT_LEN)
        return -1;

    DCCP_SKB_CB(skb)->dccpd_opt_len += len;

    to    = skb_push(skb, len);
    *to++ = DCCPO_TIMESTAMP_ECHO;
    *to++ = len;

    memcpy(to, &tstamp_echo, 4);
    to += 4;

    if (elapsed_time_len == 2) {
        const __be16 var16 = htons((u16)elapsed_time);
        memcpy(to, &var16, 2);
    } else if (elapsed_time_len == 4) {
        const __be32 var32 = htonl(elapsed_time);
        memcpy(to, &var32, 4);
    }

    return 0;
}

static int dccp_insert_option_ackvec(struct sock *sk, struct sk_buff *skb)
{
    struct dccp_sock *dp = dccp_sk(sk);
    struct dccp_ackvec *av = dp->dccps_hc_rx_ackvec;
    struct dccp_skb_cb *dcb = DCCP_SKB_CB(skb);
    const u16 buflen = dccp_ackvec_buflen(av);
    /* Figure out how many options do we need to represent the ackvec */
    const u8 nr_opts = DIV_ROUND_UP(buflen, DCCP_SINGLE_OPT_MAXLEN);
    u16 len = buflen + 2 * nr_opts;
    u8 i, nonce = 0;
    const unsigned char *tail, *from;
    unsigned char *to;

    if (dcb->dccpd_opt_len + len > DCCP_MAX_OPT_LEN) {
        DCCP_WARN("Lacking space for %u bytes on %s packet\n", len,
              dccp_packet_name(dcb->dccpd_type));
        return -1;
    }
    /*
     * Since Ack Vectors are variable-length, we can not always predict
     * their size. To catch exception cases where the space is running out
     * on the skb, a separate Sync is scheduled to carry the Ack Vector.
     */
    if (len > DCCPAV_MIN_OPTLEN &&
        len + dcb->dccpd_opt_len + skb->len > dp->dccps_mss_cache) {
        DCCP_WARN("No space left for Ack Vector (%u) on skb (%u+%u), "
              "MPS=%u ==> reduce payload size?\n", len, skb->len,
              dcb->dccpd_opt_len, dp->dccps_mss_cache);
        dp->dccps_sync_scheduled = 1;
        return 0;
    }
    dcb->dccpd_opt_len += len;

    to   = skb_push(skb, len);
    len  = buflen;
    from = av->av_buf + av->av_buf_head;
    tail = av->av_buf + DCCPAV_MAX_ACKVEC_LEN;

    for (i = 0; i < nr_opts; ++i) {
        int copylen = len;

        if (len > DCCP_SINGLE_OPT_MAXLEN)
            copylen = DCCP_SINGLE_OPT_MAXLEN;

        /*
         * RFC 4340, 12.2: Encode the Nonce Echo for this Ack Vector via
         * its type; ack_nonce is the sum of all individual buf_nonce's.
         */
        nonce ^= av->av_buf_nonce[i];

        *to++ = DCCPO_ACK_VECTOR_0 + av->av_buf_nonce[i];
        *to++ = copylen + 2;

        /* Check if buf_head wraps */
        if (from + copylen > tail) {
            const u16 tailsize = tail - from;

            memcpy(to, from, tailsize);
            to  += tailsize;
            len -= tailsize;
            copylen -= tailsize;
            from    = av->av_buf;
        }

        memcpy(to, from, copylen);
        from += copylen;
        to   += copylen;
        len  -= copylen;
    }
    /*
     * Each sent Ack Vector is recorded in the list, as per A.2 of RFC 4340.
     */
    if (dccp_ackvec_update_records(av, dcb->dccpd_seq, nonce))
        return -ENOBUFS;
    return 0;
}

int dccp_insert_option_mandatory(struct sk_buff *skb)
{
    if (DCCP_SKB_CB(skb)->dccpd_opt_len >= DCCP_MAX_OPT_LEN)
        return -1;

    DCCP_SKB_CB(skb)->dccpd_opt_len++;
    *skb_push(skb, 1) = DCCPO_MANDATORY;
    return 0;
}

int dccp_insert_fn_opt(struct sk_buff *skb, u8 type, u8 feat,
               u8 *val, u8 len, bool repeat_first)
{
    u8 tot_len, *to;

    /* take the `Feature' field and possible repetition into account */
    if (len > (DCCP_SINGLE_OPT_MAXLEN - 2)) {
        DCCP_WARN("length %u for feature %u too large\n", len, feat);
        return -1;
    }

    if (unlikely(val == NULL || len == 0))
        len = repeat_first = false;
    tot_len = 3 + repeat_first + len;

    if (DCCP_SKB_CB(skb)->dccpd_opt_len + tot_len > DCCP_MAX_OPT_LEN) {
        DCCP_WARN("packet too small for feature %d option!\n", feat);
        return -1;
    }
    DCCP_SKB_CB(skb)->dccpd_opt_len += tot_len;

    to    = skb_push(skb, tot_len);
    *to++ = type;
    *to++ = tot_len;
    *to++ = feat;

    if (repeat_first)
        *to++ = *val;
    if (len)
        memcpy(to, val, len);
    return 0;
}

/* The length of all options needs to be a multiple of 4 (5.8) */
static void dccp_insert_option_padding(struct sk_buff *skb)
{
    int padding = DCCP_SKB_CB(skb)->dccpd_opt_len % 4;

    if (padding != 0) {
        padding = 4 - padding;
        memset(skb_push(skb, padding), 0, padding);
        DCCP_SKB_CB(skb)->dccpd_opt_len += padding;
    }
}

int dccp_insert_options(struct sock *sk, struct sk_buff *skb)
{
    struct dccp_sock *dp = dccp_sk(sk);

    DCCP_SKB_CB(skb)->dccpd_opt_len = 0;

    if (dp->dccps_send_ndp_count && dccp_insert_option_ndp(sk, skb))
        return -1;

    if (DCCP_SKB_CB(skb)->dccpd_type != DCCP_PKT_DATA) {

        /* Feature Negotiation */
        if (dccp_feat_insert_opts(dp, NULL, skb))
            return -1;

        if (DCCP_SKB_CB(skb)->dccpd_type == DCCP_PKT_REQUEST) {
            /*
             * Obtain RTT sample from Request/Response exchange.
             * This is currently used for TFRC initialisation.
             */
            if (dccp_insert_option_timestamp(skb))
                return -1;

        } else if (dccp_ackvec_pending(sk) &&
               dccp_insert_option_ackvec(sk, skb)) {
                return -1;
        }
    }

    if (dp->dccps_hc_rx_insert_options) {
        if (ccid_hc_rx_insert_options(dp->dccps_hc_rx_ccid, sk, skb))
            return -1;
        dp->dccps_hc_rx_insert_options = 0;
    }

    if (dp->dccps_timestamp_echo != 0 &&
        dccp_insert_option_timestamp_echo(dp, NULL, skb))
        return -1;

    dccp_insert_option_padding(skb);
    return 0;
}

int dccp_insert_options_rsk(struct dccp_request_sock *dreq, struct sk_buff *skb)
{
    DCCP_SKB_CB(skb)->dccpd_opt_len = 0;

    if (dccp_feat_insert_opts(NULL, dreq, skb))
        return -1;

    /* Obtain RTT sample from Response/Ack exchange (used by TFRC). */
    if (dccp_insert_option_timestamp(skb))
        return -1;

    if (dreq->dreq_timestamp_echo != 0 &&
        dccp_insert_option_timestamp_echo(NULL, dreq, skb))
        return -1;

    dccp_insert_option_padding(skb);
    return 0;
}