Implement digest algorithm support.

[people/ms/dnsmasq.git] / src / dnssec.c

#include "dnsmasq.h"
#include "dnssec-crypto.h"
#include <assert.h>

/* Maximum length in octects of a domain name, in wire format */
#define MAXCDNAME  256

#define SERIAL_UNDEF  -100
#define SERIAL_EQ        0
#define SERIAL_LT       -1
#define SERIAL_GT        1

/* Implement RFC1982 wrapped compare for 32-bit numbers */
static int serial_compare_32(unsigned long s1, unsigned long s2)
{
  if (s1 == s2)
    return SERIAL_EQ;

  if ((s1 < s2 && (s2 - s1) < (1UL<<31)) ||
      (s1 > s2 && (s1 - s2) > (1UL<<31)))
    return SERIAL_LT;
  if ((s1 < s2 && (s2 - s1) > (1UL<<31)) ||
      (s1 > s2 && (s1 - s2) < (1UL<<31)))
    return SERIAL_GT;
  return SERIAL_UNDEF;
}

/* Extract a DNS name from wire format, without handling compression. This is
   faster than extract_name() and does not require access to the full dns
   packet. */
static int extract_name_no_compression(unsigned char *rr, int maxlen, char *buf)
{
  unsigned char *start=rr, *end = rr+maxlen;
  int count;
  
  while (rr < end && *rr != 0)
    {
      count = *rr++;
      while (count-- > 0 && rr < end)
        {
          *buf = *rr++;
          if (!isascii(*buf) || iscntrl(*buf) || *buf == '.')
            return 0;
          if (*buf >= 'A' && *buf <= 'Z')
            *buf += 'a' - 'A';
          buf++;
        }
      *buf++ = '.';
    }
  /* Remove trailing dot (if any) */
  if (rr != start)
    *(--buf) = 0;
  if (rr == end)
    return 0;
  /* Trailing \0 in source data must be consumed */
  return rr-start+1;
}

/* process_domain_name() - do operations with domain names in canonicalized wire format.
 *
 * Handling domain names in wire format can be done with buffers as large as MAXCDNAME (256),
 * while the representation format (as created by, eg., extract_name) requires MAXDNAME (1024).
 *
 * With "canonicalized wire format", we mean the standard DNS wire format, eg:
 *
 *   <3>www<7>example<3>org<0>
 *
 * with all ÅSCII letters converted to lowercase, and no wire-level compression.
 *
 * The function works with two different buffers:
 *    - Input buffer: 'rdata' is a pointer to the actual wire data, and 'rdlen' is
 *      the total length till the end of the rdata or DNS packet section. Both
 *      variables are updated after processing the domain name, so that rdata points
 *      after it, and rdlen is decreased by the amount of the processed octects.
 *    - Output buffer: 'out' points to it. In some cases, this buffer can be prefilled
 *      and used as additional input (see below).
 *
 * The argument "action" decides what to do with the submitted domain name:
 *
 *    PDN_EXTRACT:
 *       Extract the domain name from input buffer into the output buffer, possibly uncompressing it.
 *       Return the length of the domain name in the output buffer in octects, or zero if error.
 *
 *    PDN_COMPARE:
 *       Compare the domain name in the input buffer and the one in the output buffer (ignoring
 *       differences in compression). Returns 0 in case of error, a positive number
 *       if they are equal, or a negative number if they are different. This function always
 *       consumes the whole name in the input buffer (there is no early exit).
 *
 *    PDN_ORDER:
 *       Order between the domain name in the input buffer and the domain name in the output buffer.
 *       Returns 0 if the names are equal, 1 if input > output, or -1 if input < output. This
 *       function early-exits when it finds a difference, so rdata might not be fully updated.
 *
 * Notice: because of compression, rdata/rdlen might be updated with a different quantity than
 * the returned number of octects. For instance, if we extract a compressed domain name, rdata/rdlen
 * might be updated only by 2 bytes (that is, rdata is incresed by 2, and rdlen decreased by 2),
 * because it then reuses existing data elsewhere in the DNS packet, while the return value might be
 * larger, reflecting the total number of octects composing the domain name.
 *
 */
#define PWN_EXTRACT   0
#define PWN_COMPARE   1
#define PWN_ORDER     2
static int process_domain_name(struct dns_header *header, size_t pktlen,
                               unsigned char** rdata, size_t* rdlen,
                               unsigned char *out, int action)
{
  int hops = 0, total = 0, i;
  unsigned char label_type;
  unsigned char *end = (unsigned char *)header + pktlen;
  unsigned char count; unsigned char *p = *rdata;
  int nonequal = 0;

#define PROCESS(ch) \
  do { \
    if (action == PWN_EXTRACT) \
      *out++ = ch; \
    else if (action == PWN_COMPARE) \
      { \
        if (*out++ != ch) \
          nonequal = 1; \
      } \
    else if (action == PWN_ORDER) \
      { \
        char _ch = *out++; \
        if (ch < _ch) \
          return -1; \
        else if (_ch > ch) \
          return 1; \
      } \
  } while (0)

  while (1)
    {
      if (p >= end)
        return 0;
      if (!(count = *p++))
        break;
      label_type = count & 0xC0;
      if (label_type == 0xC0)
        {
          int l2;
          if (p >= end)
            return 0;
          l2 = *p++;
          if (hops == 0)
            {
              if (p - *rdata > *rdlen)
                return 0;
              *rdlen -= p - *rdata;
              *rdata = p;
            }
          if (++hops == 256)
            return 0;
          p = (unsigned char*)header + (count & 0x3F) * 256 + l2;
        }
      else if (label_type == 0x00)
        {
          if (p+count-1 >= end)
            return 0;
          total += count+1;
          if (total >= MAXCDNAME)
            return 0;
          PROCESS(count);
          for (i = 0; i < count; ++i)
            {
              unsigned char ch = *p++;
              if (ch >= 'A' && ch <= 'Z')
                ch += 'a' - 'A';
              PROCESS(ch);
            }
        }
      else
        return 0; /* unsupported label_type */
    }

  if (hops == 0)
    {
      if (p - *rdata > *rdlen)
        return 0;
      *rdlen -= p - *rdata;
      *rdata = p;
    }
  ++total;
  if (total >= MAXCDNAME)
    return 0;
  PROCESS(0);

  /* If we arrived here without early-exit, they're equal */
  if (action == PWN_ORDER)
    return 0;
  return nonequal ? -total : total;

  #undef PROCESS
}


/* RDATA meta-description.
 *
 * RFC4034 §6.2 introduces the concept of a "canonical form of a RR". This canonical
 * form is used in two important points within the DNSSEC protocol/algorithm:
 *
 * 1) When computing the hash for verifying the RRSIG signature, we need to do it on
 *    the canonical form.
 * 2) When ordering a RRset in canonical order (§6.3), we need to lexicographically sort
 *    the RRs in canonical form.
 *
 * The canonical form of a RR is specifically tricky because it also affects the RDATA,
 * which is different for each RR type; in fact, RFC4034 says that "domain names in
 * RDATA must be canonicalized" (= uncompressed and lower-cased).
 *
 * To handle this correctly, we then need a way to describe how the RDATA section is
 * composed for each RR type; we don't need to describe every field, but just to specify
 * where domain names are. The following array contains this description, and it is
 * used by rrset_canonical_order() and verifyalg_add_rdata(), to adjust their behaviour
 * for each RR type.
 *
 * The format of the description is very easy, for instance:
 *
 *   { 12, RDESC_DOMAIN, RDESC_DOMAIN, 4, RDESC_DOMAIN, RDESC_END }
 *
 * This means that this (ficticious) RR type has a RDATA section containing 12 octects
 * (we don't care what they contain), followed by 2 domain names, followed by 4 octects,
 * followed by 1 domain name, and then followed by an unspecificied number of octects (0
 * or more).
 */

#define RDESC_DOMAIN   -1
#define RDESC_END       0
static const int rdata_description[][8] =
{
  /**/            { RDESC_END },
  /* 1: A */      { RDESC_END },
  /* 2: NS */     { RDESC_DOMAIN, RDESC_END },
  /* 3: .. */     { RDESC_END },
  /* 4: .. */     { RDESC_END },
  /* 5: CNAME */  { RDESC_DOMAIN, RDESC_END },
  /* 6: SOA */    { RDESC_DOMAIN, RDESC_DOMAIN, RDESC_END },
  /* 7: */        { RDESC_END },
  /* 8: */        { RDESC_END },
  /* 9: */        { RDESC_END },
  /* 10: */       { RDESC_END },
  /* 11: */       { RDESC_END },
  /* 12: */       { RDESC_END },
  /* 13: */       { RDESC_END },
  /* 14: */       { RDESC_END },
  /* 15: MX */    { 2, RDESC_DOMAIN, RDESC_END },
};


/* On-the-fly rdata canonicalization
 *
 * This set of functions allow the user to iterate over the rdata section of a RR
 * while canonicalizing it on-the-fly. This is a great memory saving since the user
 * doesn't need to allocate memory for a copy of the whole rdata section.
 *
 * Sample usage:
 *
 *    RDataCFrom cf;
 *    rdata_cfrom_init(
 *       &cf,
 *       header, pktlen,     // dns_header
 *       rdata,              // pointer to rdata section
 *       rrtype,             // RR tyep
 *       tmpbuf);            // temporary buf (MAXCDNAME)
 *
 *    while ((p = rdata_cfrom_next(&cf, &len))
 *      {
 *         // Process p[0..len]
 *      }
 *
 *    if (rdata_cfrom_error(&cf))
 *      // error occurred while parsing
 *
 */
typedef struct
{
  struct dns_header *header;
  size_t pktlen;
  unsigned char *rdata;
  unsigned char *tmpbuf;
  size_t rdlen;
  int rrtype;
  int cnt;
} RDataCForm;

static void rdata_cform_init(RDataCForm *ctx, struct dns_header *header, size_t pktlen,
                             unsigned char *rdata, int rrtype, unsigned char *tmpbuf)
{
  if (rrtype >= countof(rdata_description))
    rrtype = 0;
  ctx->header = header;
  ctx->pktlen = pktlen;
  ctx->rdata = rdata;
  ctx->rrtype = rrtype;
  ctx->tmpbuf = tmpbuf;
  ctx->cnt = -1;
  GETSHORT(ctx->rdlen, ctx->rdata);
}

static int rdata_cform_error(RDataCForm *ctx)
{
  return ctx->cnt == -2;
}

static unsigned char *rdata_cform_next(RDataCForm *ctx, size_t *len)
{
  if (ctx->cnt != -1 && rdata_description[ctx->rrtype][ctx->cnt] == RDESC_END)
    return NULL;

  int d = rdata_description[ctx->rrtype][++ctx->cnt];
  if (d == RDESC_DOMAIN)
    {
      *len = process_domain_name(ctx->header, ctx->pktlen, &ctx->rdata, &ctx->rdlen, ctx->tmpbuf, PWN_EXTRACT);
      if (!*len)
        {
          ctx->cnt = -2;
          return NULL;
        }
      return ctx->tmpbuf;
    }
  else if (d == RDESC_END)
    {
      *len = ctx->rdlen;
      return ctx->rdata;
    }
  else
    {
      unsigned char *ret = ctx->rdata;
      ctx->rdlen -= d;
      ctx->rdata += d;
      *len = d;
      return ret;
    }
}


/* Check whether today/now is between date_start and date_end */
static int check_date_range(unsigned long date_start, unsigned long date_end)
{
  /* TODO: double-check that time(0) is the correct time we are looking for */
  /* TODO: dnssec requires correct timing; implement SNTP in dnsmasq? */
  unsigned long curtime = time(0);

  /* We must explicitly check against wanted values, because of SERIAL_UNDEF */
  return serial_compare_32(curtime, date_start) == SERIAL_GT
         && serial_compare_32(curtime, date_end) == SERIAL_LT;
}


/* Sort RRs within a RRset in canonical order, according to RFC4034, §6.3
   Notice that the RRDATA sections have been already normalized, so a memcpy
   is sufficient.
   NOTE: r1/r2 point immediately after the owner name. */

struct {
  struct dns_header *header;
  size_t pktlen;
} rrset_canonical_order_ctx;

static int rrset_canonical_order(const void *r1, const void *r2)
{
  size_t r1len, r2len;
  int rrtype;
  unsigned char *pr1=*(unsigned char**)r1, *pr2=*(unsigned char**)r2;
  unsigned char tmp1[MAXCDNAME], tmp2[MAXCDNAME];   /* TODO: use part of daemon->namebuff */
  
  GETSHORT(rrtype, pr1);
  pr1 += 6; pr2 += 8;

  RDataCForm cf1, cf2;
  rdata_cform_init(&cf1, rrset_canonical_order_ctx.header, rrset_canonical_order_ctx.pktlen,
                   pr1, rrtype, tmp1);
  rdata_cform_init(&cf2, rrset_canonical_order_ctx.header, rrset_canonical_order_ctx.pktlen,
                   pr2, rrtype, tmp2);
  while ((pr1 = rdata_cform_next(&cf1, &r1len)) &&
         (pr2 = rdata_cform_next(&cf2, &r2len)))
    {
      int res = memcmp(pr1, pr2, MIN(r1len,r2len));
      if (res != 0)
        return res;
      if (r1len < r2len)
        return -1;
      if (r2len > r1len)
        return 1;
    }

  /* If we reached this point, the two RRs are identical (or an error occurred).
     RFC2181 says that an RRset is not allowed to contain duplicate
     records. If it happens, it is a protocol error and anything goes. */
  return 1;
}

typedef struct PendingRRSIGValidation
{
  VerifyAlgCtx *alg;
  char *signer_name;
  int keytag;
} PendingRRSIGValidation;

/* strchrnul - like strchr, but when character is not found, returns a pointer to the terminating \0.

   This is an existing C GNU extension, but it's easier to reimplement it,
   rather than tweaking with configure. */
static char *strchrnul(char *str, char ch)
{
  while (*str && *str != ch)
    str++;
  return str;
}

/* Convert a domain name to wire format */
static int convert_domain_to_wire(char *name, unsigned char* out)
{
  unsigned char len;
  unsigned char *start = out;
  char *p;

  do
    {
      p = strchrnul(name, '.');
      if ((len = p-name))
        {
          *out++ = len;
          memcpy(out, name, len);
          out += len;
        }
      name = p+1;
    }
  while (*p);

  *out++ = '\0';
  return out-start;
}


/* Pass a resource record's rdata field through a verification hash function.

   We must pass the record in DNS wire format, but if the record contains domain names,
   they must be uncompressed. This makes things very tricky, because  */
static int verifyalg_add_rdata(VerifyAlgCtx *alg, int sigtype, struct dns_header *header, size_t pktlen,
                               unsigned char *rdata)
{
  size_t len;
  unsigned char *p;
  unsigned short total;
  unsigned char tmpbuf[MAXDNAME]; /* TODO: reuse part of daemon->namebuff */
  RDataCForm cf1, cf2;

  /* Initialize two iterations over the canonical form*/
  rdata_cform_init(&cf1, header, pktlen, rdata, sigtype, tmpbuf);
  cf2 = cf1;

  /* Iteration 1: go through the canonical record and count the total octects.
     This number might be different from the non-canonical rdata length
     because of domain names compression. */
  total = 0;
  while ((p = rdata_cform_next(&cf1, &len)))
    total += len;
  if (rdata_cform_error(&cf1))
    return 0;

  /* Iteration 2: process the canonical record through the hash function */
  total = htons(total);
  alg->vtbl->add_data(alg, &total, 2);

  while ((p = rdata_cform_next(&cf2, &len)))
    alg->vtbl->add_data(alg, p, len);

  return 1;
}


static int begin_rrsig_validation(struct dns_header *header, size_t pktlen,
                                  unsigned char *reply, int count, char *owner,
                                  int sigclass, int sigrdlen, unsigned char *sig,
                                  PendingRRSIGValidation *out)
{
  int i, res;
  int sigtype, sigalg, siglbl;
  unsigned char *sigrdata = sig;
  unsigned long sigttl, date_end, date_start;
  unsigned char* p = reply;
  char* signer_name = daemon->namebuff;
  int signer_name_rdlen;
  int keytag;
  void *rrset[16];  /* TODO: max RRset size? */
  int rrsetidx = 0;
  
  if (sigrdlen < 18)
    return 0;
  GETSHORT(sigtype, sig);
  sigalg = *sig++;
  siglbl = *sig++;
  GETLONG(sigttl, sig);
  GETLONG(date_end, sig);
  GETLONG(date_start, sig);
  GETSHORT(keytag, sig);
  sigrdlen -= 18;
  
  if (!verifyalg_supported(sigalg))
    {
      printf("RRSIG algorithm not supported: %d\n", sigalg);
      return 0;
    }

  if (!check_date_range(date_start, date_end))
    {
      printf("RRSIG outside date range\n");
      return 0;
    }

  /* Iterate within the answer and find the RRsets matching the current RRsig */
  for (i = 0; i < count; ++i)
    {    
      int qtype, qclass, rdlen;
      if (!(res = extract_name(header, pktlen, &p, owner, 0, 10)))
        return 0;
      rrset[rrsetidx] = p;
      GETSHORT(qtype, p);
      GETSHORT(qclass, p);
      p += 4; /* skip ttl */
      GETSHORT(rdlen, p);
      if (res == 1 && qtype == sigtype && qclass == sigclass)
        {
          ++rrsetidx;
          if (rrsetidx == countof(rrset))
            {
              /* Internal buffer too small */
              printf("internal buffer too small for this RRset\n");
              return 0;
            }
        }
      p += rdlen;
    }
  
  /* Sort RRset records in canonical order. */
  rrset_canonical_order_ctx.header = header;
  rrset_canonical_order_ctx.pktlen = pktlen;
  qsort(rrset, rrsetidx, sizeof(void*), rrset_canonical_order);
  
  /* Skip through the signer name; we don't extract it right now because
     we don't want to overwrite the single daemon->namebuff which contains
     the owner name. We'll get to this later. */
  if (!(p = skip_name(sig, header, pktlen, 0)))
    return 0;
  signer_name_rdlen = p - sig;
  sig = p; sigrdlen -= signer_name_rdlen;

  /* Now initialize the signature verification algorithm and process the whole
     RRset */
  VerifyAlgCtx *alg = verifyalg_alloc(sigalg);
  if (!alg)
    return 0;
  if (!alg->vtbl->set_signature(alg, sig, sigrdlen))
    return 0;
  
  sigtype = htons(sigtype);
  sigclass = htons(sigclass);
  sigttl = htonl(sigttl);

  /* TODO: we shouldn't need to convert this to wire here. Best solution would be:
     - Use process_name() instead of extract_name() everywhere in dnssec code
     - Convert from wire format to representation format only for querying/storing cache
   */
  unsigned char owner_wire[MAXCDNAME];
  int owner_wire_len = convert_domain_to_wire(owner, owner_wire);

  alg->vtbl->begin_data(alg);
  alg->vtbl->add_data(alg, sigrdata, 18+signer_name_rdlen);
  for (i = 0; i < rrsetidx; ++i)
    {
      p = (unsigned char*)(rrset[i]);

      alg->vtbl->add_data(alg, owner_wire, owner_wire_len);
      alg->vtbl->add_data(alg, &sigtype, 2);
      alg->vtbl->add_data(alg, &sigclass, 2);
      alg->vtbl->add_data(alg, &sigttl, 4);
    
      p += 8;
      if (!verifyalg_add_rdata(alg, ntohs(sigtype), header, pktlen, p))
        return 0;
    }
  alg->vtbl->end_data(alg);

  /* We don't need the owner name anymore; now extract the signer name */
  if (!extract_name_no_compression(sigrdata+18, signer_name_rdlen, signer_name))
    return 0;

  out->alg = alg;
  out->keytag = keytag;
  out->signer_name = signer_name;
  return 1;
}

static int end_rrsig_validation(PendingRRSIGValidation *val, struct crec *crec_dnskey)
{
  /* FIXME: keydata is non-contiguous */
  return val->alg->vtbl->verify(val->alg, crec_dnskey->addr.key.keydata, crec_dnskey->uid);
}

static void dnssec_parserrsig(struct dns_header *header, size_t pktlen,
                              unsigned char *reply, int count, char *owner,
                              int sigclass, int sigrdlen, unsigned char *sig)
{
  PendingRRSIGValidation val;

  /* Initiate the RRSIG validation process. The pending state is returned into val. */
  if (!begin_rrsig_validation(header, pktlen, reply, count, owner, sigclass, sigrdlen, sig, &val))
    return;

  printf("RRSIG: querying cache for DNSKEY %s (keytag: %d)\n", val.signer_name, val.keytag);

  /* Look in the cache for *all* the DNSKEYs with matching signer_name and keytag */
  char onekey = 0;
  struct crec *crecp = NULL;
  while ((crecp = cache_find_by_name(crecp, val.signer_name, time(0), F_DNSKEY)))  /* TODO: time(0) */
    {
      onekey = 1;

      if (crecp->addr.key.keytag == val.keytag
          && crecp->addr.key.algo == verifyalg_algonum(val.alg))
        {
          printf("RRSIG: found DNSKEY %d in cache, attempting validation\n", val.keytag);

          if (end_rrsig_validation(&val, crecp))
            printf("Validation OK\n");
          else
            printf("Validation FAILED\n");
        }
    }

  if (!onekey)
    {
      printf("DNSKEY not found, need to fetch it\n");
      /* TODO: store PendingRRSIGValidation in routing table,
         fetch key (and make it go through dnssec_parskey), then complete validation. */
    }
}

/* Compute keytag (checksum to quickly index a key). See RFC4034 */
static int dnskey_keytag(unsigned char *rdata, int rdlen)
{
  unsigned long ac;
  int i;

  ac = 0;
  for (i = 0; i < rdlen; ++i)
    ac += (i & 1) ? rdata[i] : rdata[i] << 8;
  ac += (ac >> 16) & 0xFFFF;
  return ac & 0xFFFF;
}

int dnssec_parsekey(struct dns_header *header, size_t pktlen, char *owner, unsigned long ttl,
                    int rdlen, unsigned char *rdata)
{
  int flags, proto, alg;
  struct keydata *key; struct crec *crecp;
  unsigned char *ordata = rdata; int ordlen = rdlen;

  CHECKED_GETSHORT(flags, rdata, rdlen);
  CHECKED_GETCHAR(proto, rdata, rdlen);
  CHECKED_GETCHAR(alg, rdata, rdlen);

  if (proto != 3)
    return 0;
  /* Skip non-signing keys (as specified in RFC4034 */
  if (!(flags & 0x100))
    return 0;

  key = keydata_alloc((char*)rdata, rdlen);

  /* TODO: time(0) is correct here? */
  crecp = cache_insert(owner, NULL, time(0), ttl, F_FORWARD | F_DNSKEY);
  if (crecp)
    {
      /* TODO: improve union not to name "uid" this field */
      crecp->uid = rdlen;
      crecp->addr.key.keydata = key;
      crecp->addr.key.algo = alg;
      crecp->addr.key.keytag = dnskey_keytag(ordata, ordlen);
      printf("DNSKEY: storing key for %s (keytag: %d)\n", owner, crecp->addr.key.keytag);
    }
  else
    {
      keydata_free(key);
      /* TODO: if insertion really might fail, verify we don't depend on cache
         insertion success for validation workflow correctness */
      printf("DNSKEY: cache insertion failure\n");
      return 0;
    }
  return 1;
}

int dnssec_parseds(struct dns_header *header, size_t pktlen, char *owner, unsigned long ttl,
                   int rdlen, unsigned char *rdata)
{
  return 0;
}

int dnssec_validate(struct dns_header *header, size_t pktlen)
{
  unsigned char *p, *reply;
  char *owner = daemon->namebuff;
  int i, s, qtype, qclass, rdlen;
  unsigned long ttl;
  int slen[3] = { ntohs(header->ancount), ntohs(header->nscount), ntohs(header->arcount) };

  if (slen[0] + slen[1] + slen[2] == 0)
    return 0;
  if (!(reply = p = skip_questions(header, pktlen)))
    return 0;

  /* First, process DNSKEY/DS records and add them to the cache. */
  cache_start_insert();
  for (i = 0; i < slen[0]; i++)
    {
      if (!extract_name(header, pktlen, &p, owner, 1, 10))
      	return 0;
      GETSHORT(qtype, p);
      GETSHORT(qclass, p);
      GETLONG(ttl, p);
      GETSHORT(rdlen, p);
      if (qtype == T_DS)
        {
          printf("DS found\n");
          dnssec_parseds(header, pktlen, owner, ttl, rdlen, p);
        }
      else if (qtype == T_DNSKEY)
        {
          printf("DNSKEY found\n");
          dnssec_parsekey(header, pktlen, owner, ttl, rdlen, p);
        }
      p += rdlen;
    }
  cache_end_insert();

  /* After we have cached DNSKEY/DS records, start looking for RRSIGs.
     We want to do this in a separate step because we want the cache
     to be already populated with DNSKEYs before parsing signatures. */
  p = reply;
  for (s = 0; s < 3; ++s)
    {
      reply = p;
      for (i = 0; i < slen[s]; i++)
        {
          if (!extract_name(header, pktlen, &p, owner, 1, 10))
            return 0;
          GETSHORT(qtype, p);
          GETSHORT(qclass, p);
          GETLONG(ttl, p);
          GETSHORT(rdlen, p);
          if (qtype == T_RRSIG)
            {
              printf("RRSIG found (owner: %s)\n", owner);
              /* TODO: missing logic. We should only validate RRSIGs for which we
                 have a valid DNSKEY that is referenced by a DS record upstream.
                 There is a memory vs CPU conflict here; should we validate everything
                 to save memory and thus waste CPU, or better first acquire all information
                 (wasting memory) and then doing the minimum CPU computations required? */
              dnssec_parserrsig(header, pktlen, reply, slen[s], owner, qclass, rdlen, p);
            }
          p += rdlen;
        }
    }

  return 1;
}