path: root/src/spf.c

#include "spf.h"

#include "alloc.h"
#include "byte.h"
#include "case.h"
#include "fmt.h"
#include "ip.h"
#include "scan.h"
#include "str.h"
#include "stralloc.h"

#include "dns.h"
#include "ipalloc.h"
#include "ipme.h"
#include "now.h"

/* long lived SPF variables (output) */

stralloc spfinfo = {0};   /* SPF results - see spf.h */
stralloc spfrecord = {0}; /* Used for diagnostics */

/* s/qmail control SPF variables (input) */

stralloc spflocalrules; /* Local rules provided here */
stralloc spfexplain;    /* Default SPF_EXPMSG in spf.h */

stralloc spfmf = {0};    /* aka envelopefrom = clientid */
stralloc spfhelo = {0};  /* helo or domain part for spfmf */
stralloc dnsname = {0};  /* FQDN of client host in DNS */
stralloc spflocal = {0}; /* Receiving host */

stralloc spfexpmsg = {0}; /* additional explanation given as 5xx SMTP response */
stralloc expdomain = {0}; /* the domain, for which explanation is given */
int flagip6;

stralloc domain = {0};
stralloc identity = {0};

static int recursion;
char ip4remote[4] = {0, 0, 0, 0};
char ip6remote[16] = {16 * 0};

/* Sample SPF TXT records:
Standard example:   example.net TXT "v=spf1 mx a:pluto.example.net include:aspmx.googlemail.com -all"
Fehcom's example:   fehcom.net TXT "v=spf1 ip4:85.25.149.179/32 ip6:2001:4dd0:ff00:3d4::2/64 -all" 
Include example:    mailing.com TXT "v=spf1 a:smtpout.mailing.com include:spf.nl2go.com ~all"
Exists+Expand:      exists.com TXT "v=spf1 exists:%{ir}.%{l1r+-}._spf.%{d} -all" 
*/

/* Entry point: -------------------------------------- Go for SPF */

/**
 @brief  spf_query
         prepares the SPF TXT record query
 @param  input:  pointer to remoteip, helo, mf, localhost, and flagIP6 
 @return int r = SPF return code
 */


int spf_query(
    const char *remoteip, const char *helo, const char *mf, const char *local, const int flagip)
{
  int at;
  int r = SPF_INIT;
  flagip6 = flagip;

  if (!stralloc_copys(&spfinfo, " ")) return SPF_NOMEM;

  switch (flagip6) {
    case -1:
      if (!spf_info("MLocal=", remoteip)) return SPF_NOMEM;
      if (!spf_info("R:", "+")) return SPF_NOMEM;
      break;
    case 0:
      if (!ip4_scan(remoteip, ip4remote)) return SPF_SYNTAX;
      if (ipme_is4(ip4remote) == 1) {
        if (!spf_info("MLocal=", remoteip)) return SPF_NOMEM;
        if (!spf_info("R:", "+")) return SPF_NOMEM;
        return SPF_ME;
      }
      break;
    case 1:
      if (!ip6_scan(remoteip, ip6remote)) return SPF_SYNTAX;
      if (ipme_is6(ip6remote) == 1) {
        if (!spf_info("MLocal=", remoteip)) return SPF_NOMEM;
        if (!spf_info("R:", "+")) return SPF_NOMEM;
        return SPF_ME;
      }
      break;
  }

  if (helo && str_len(helo)) {
    if (!stralloc_copys(&spfhelo, helo)) return SPF_NOMEM;
  } else {
    if (!stralloc_copys(&spfhelo, "unknown")) return SPF_NOMEM;
  }
  if (!stralloc_0(&spfhelo)) return SPF_NOMEM;

  if (mf && str_len(mf)) {
    if (!stralloc_copys(&spfmf, mf)) return SPF_NOMEM;
    if (!stralloc_0(&spfmf)) return SPF_NOMEM;
    at = str_rchr(spfmf.s, '@');
    if (spfmf.s[at] == '@') {
      if (!stralloc_copys(&domain, spfmf.s + at + 1)) return SPF_NOMEM;
    } else {
      //      if (!stralloc_0(&spfhelo)) return SPF_NOMEM;
      if (!stralloc_copys(&domain, &spfhelo)) return SPF_NOMEM;
    }
    if (!stralloc_copy(&identity, &domain)) return SPF_NOMEM;
  }
  if (!stralloc_0(&identity)) return SPF_NOMEM;

  if (local && str_len(local)) {
    if (!stralloc_copys(&spflocal, local)) return SPF_NOMEM;
  } else {
    if (!stralloc_copys(&spflocal, "localhost")) return SPF_NOMEM;
  }
  if (!stralloc_0(&spflocal)) return SPF_NOMEM;

  if (!spf_info("S=", remoteip)) return SPF_NOMEM;
  if (!spf_info("O=", spfmf.s)) return SPF_NOMEM;
  if (!spf_info("C=", identity.s)) return SPF_NOMEM;
  if (!spf_info("H=", spfhelo.s)) return SPF_NOMEM;

  if (!stralloc_copy(&spfexpmsg, &spfexplain)) return SPF_NOMEM;
  if (!stralloc_0(&spfexpmsg)) return SPF_NOMEM;

  recursion = 0;
  dnsname.len = 0;

  if (r == SPF_INIT) r = spf_lookup(&domain);
  if (r == SPF_LOOP) {
    if (!spf_info("P=", "Maximum nesting level exceeded; possible loop")) return SPF_NOMEM;
    if (!spf_info("R:", "e")) return SPF_NOMEM;
  }
  if (r < 0) r = SPF_UNKNOWN; /* return 2main */

  return r;
}

/* SPF Lookup:  -------------------------------------- Return cases */

static struct spf_aliases {
  char *alias;
  int defrc;
} spf_aliases[] = {
    {   "allow",       SPF_OK},
    {    "pass",       SPF_OK},
    {    "deny",     SPF_FAIL},
    {"softdeny", SPF_SOFTFAIL},
    {    "fail",     SPF_FAIL},
    {"softfail", SPF_SOFTFAIL},
    { "unknown",  SPF_NEUTRAL},
    {         0,  SPF_UNKNOWN}
};

/**
 @brief  spf_lookup
         calles the actual (recursive) SPF DNS query
 @param  input:  pointer to stralloc domain (fqdn) 
 @input  stralloc spflocalrules (if provided -- for artificial results)
 @output stralloc spfdata with RDATA (+ artificial information)
 @return int r = SPF return code
 */

int spf_lookup(stralloc *domain)
{
  stralloc spfdata = {0};
  stralloc sa = {0};
  struct spf_aliases *da;
  int first = !recursion;
  int local_pos = -1;
  int localrules = 0;
  int q = -1;
  int i, r;
  int begin, pos;
  int spfrc;
  int done;
  char *p;

  /* Fallthrough result */

REDIRECT:
  if (++recursion > LOOKUP_LIMIT) return SPF_EXHAUST;

  if (!stralloc_copys(&expdomain, domain->s)) return SPF_NOMEM;  // *FIXME */

  if (!stralloc_copys(&spfdata, "")) return SPF_NOMEM;
  r = spf_records(&spfdata, domain);

  if (!stralloc_0(domain)) return SPF_NOMEM;
  if (first)
    if (!stralloc_copys(&spfrecord, "")) return SPF_NOMEM;
  if (!stralloc_cats(&spfrecord, "(")) return SPF_NOMEM;
  if (!stralloc_cat(&spfrecord, domain)) return SPF_NOMEM;
  if (!stralloc_cats(&spfrecord, ")")) return SPF_NOMEM;
  if (!stralloc_cats(&spfrecord, " => ")) return SPF_NOMEM;
  if (!stralloc_cat(&spfrecord, &spfdata)) return SPF_NOMEM;
  if (!stralloc_cats(&spfrecord, "\n")) return SPF_NOMEM;
  if (!stralloc_0(&spfrecord)) return SPF_NOMEM;

  /* In spite of none-existing SPF data, use local rules as substitude */

  if (r == SPF_NONE) { /* No SPF records published */
    if (!first) {
      return r;
    } else {
      spfdata.len = 0;
    }
    if (localrules) { /* append local ruleset */
      local_pos = spfdata.len;
      if (!stralloc_cats(&spfdata, spflocalrules.s)) return SPF_NOMEM;
    }
    if (!stralloc_0(&spfdata)) return SPF_NOMEM;

    if (!stralloc_copys(&expdomain, "")) return SPF_NOMEM;

  } else if (r == SPF_OK) { /* SPF records published */
    if (!stralloc_0(&spfdata)) return SPF_NOMEM;
    r = SPF_NEUTRAL;

    if (first && localrules) { /* try to add local rules before failure of all mechs */
      pos = 0;
      p = (char *)0;
      while (pos < spfdata.len) {
        NXTOK(begin, pos, &spfdata);
        if (!spfdata.s[begin]) continue;

        if (p && spfdata.s[begin] != *p) p = (char *)0;
        if (!p && (spfdata.s[begin] == '-' || spfdata.s[begin] == '~' || spfdata.s[begin] == '?'))
          p = &spfdata.s[begin];

        if (p && p > spfdata.s && case_equals(spfdata.s + begin + 1, "all")) {
          /* ok, we can insert the local rules at p */
          local_pos = p - spfdata.s;

          if (!stralloc_readyplus(&spfdata, spflocalrules.len)) return 0;
          p = spfdata.s + local_pos;
          byte_copyr(p + spflocalrules.len, spfdata.len - local_pos, p);
          byte_copy(p, spflocalrules.len, spflocalrules.s);
          spfdata.len += spflocalrules.len;

          pos += spflocalrules.len;
          break;
        }
      }

      if (pos >= spfdata.len) pos = spfdata.len - 1;
      for (i = 0; i < pos; i++)
        if (!spfdata.s[i]) spfdata.s[i] = ' ';
    }

  } else { /* Any other SPF return code */
    return r;
  }

  /* (artificial) SPF data exist; work thru them */

  pos = 0;
  done = 0;
  while (pos < spfdata.len) {
    NXTOK(begin, pos, &spfdata);
    if (!spfdata.s[begin]) continue;

    if (!done && localrules) { /* in local ruleset? */
      if (local_pos >= 0 && begin >= local_pos) {
        if (begin < (local_pos + spflocalrules.len)) {
          if (!stralloc_copys(&expdomain, "")) return SPF_NOMEM;
        } else {
          if (!stralloc_copy(&expdomain, domain)) return SPF_NOMEM;
        }
      }
    }

    for (p = spfdata.s + begin; *p; ++p)
      if (*p == ':' || *p == '/' || *p == '=') break;

    if (*p == '=') {
      *p++ = 0;

      if (case_equals(spfdata.s + begin, "redirect")) { /* modifiers are simply handled here */
        if (done) continue;

        //        if (!stralloc_0(domain)) return SPF_NOMEM;
        if (!spf_parse(&sa, p, domain->s)) return SPF_NOMEM;
        if (!stralloc_copy(domain, &sa)) return SPF_NOMEM;
        if (!spf_info("D=", p)) return SPF_NOMEM;
        r = SPF_UNKNOWN;

        goto REDIRECT;
      } else if (case_equals(spfdata.s + begin, "default")) { /* we don't need those anymore */
        if (done) continue;

        for (da = spf_aliases; da->alias; ++da)
          if (case_equals(da->alias, p)) break;

        r = da->defrc;
      } else if (case_equals(spfdata.s + begin, "exp")) { /* exp= only on top level */
        stralloc out = {0};

        if (!first) continue;
        if (!stralloc_copys(&sa, p)) return SPF_NOMEM;

        switch (dns_txt(&out, &sa)) {
          case -1: return SPF_NOMEM;
          case 0:  continue; /* nobody @home */
        }

        if (!stralloc_copys(&spfexpmsg, out.s)) return SPF_NOMEM;
        if (!stralloc_append(&spfexpmsg, "\n")) return SPF_NOMEM;
        if (!stralloc_0(&spfexpmsg)) return SPF_NOMEM;
      }
    } else if (!done) { /* and unknown modifiers are ignored */
      if (!stralloc_copys(&sa, spfdata.s + begin)) return SPF_NOMEM;
      if (!stralloc_0(&sa)) return SPF_NOMEM;

      switch (spfdata.s[begin]) {
        case '-':
          begin++;
          spfrc = SPF_FAIL;
          break;
        case '~':
          begin++;
          spfrc = SPF_SOFTFAIL;
          break;
        case '+':
          begin++;
          spfrc = SPF_OK;
          break;
        case '?':
          begin++;
          spfrc = SPF_NEUTRAL;
          break;
        default: spfrc = SPF_OK;
      }

      if (*p == '/') {
        *p++ = 0;
        q = spf_mechanism(spfdata.s + begin, 0, p, domain->s);
      } else {
        if (*p) *p++ = 0;
        i = str_chr(p, '/');
        if (p[i] == '/') {
          p[i++] = 0;
          q = spf_mechanism(spfdata.s + begin, p, p + i, domain->s);
        } else if (i > 0) {
          q = spf_mechanism(spfdata.s + begin, p, 0, domain->s);
        } else {
          q = spf_mechanism(spfdata.s + begin, 0, 0, domain->s);
        }
      }
      if (q == SPF_OK) q = spfrc;

      switch (q) {
        case SPF_OK:
          if (!spf_info("R:", "+")) return SPF_NOMEM;
          break;
        case SPF_NEUTRAL:
          if (!spf_info("R:", "?")) return SPF_NOMEM;
          break;
        case SPF_SYNTAX:
          if (!spf_info("P=", "Unknown parse error")) return SPF_NOMEM;
          if (!spf_info("R:", "e")) return SPF_NOMEM;
          break;
        case SPF_SOFTFAIL:
          if (!spf_info("R:", "~")) return SPF_NOMEM;
          break;
        case SPF_FAIL:
          if (!spf_info("R:", "-")) return SPF_NOMEM;
          break;
        case SPF_EXT:
          if (!spf_info("P=", "Unknown SPF mechanism")) return SPF_NOMEM;
          break;
        case SPF_ERROR:
          if (localrules)
            if (local_pos >= 0 && begin >= local_pos) break;
          if (!spf_info("R:", "o")) return SPF_NOMEM;
          q = SPF_NONE;
          break;
        case SPF_NONE: continue;
      }

      r = q;
      done = 1; /* we're done, no more mechanisms */
    }
  }

  /* we fell through, no local rule applied */
  if (!done)
    if (!stralloc_copy(&expdomain, domain)) return SPF_NOMEM;

  return r;
}

/* Mechanisms:  -------------------------------------- Lookup classes */

static struct mechanisms {
  char *mechanism;
  int (*func)(char *spfspec, char *prefix);
  unsigned int use_spfspec : 1;
  unsigned int use_prefix : 1;
  unsigned int expands : 1;
  unsigned int filldomain : 1;
  int defresult : 4;
} mechanisms[] = {
    {      "all",           0, 0, 0, 0, 0,  SPF_OK},
    {  "include", spf_include, 1, 0, 1, 0,       0},
    {        "a",       spf_a, 1, 1, 1, 1,       0},
    {       "mx",      spf_mx, 1, 1, 1, 1,       0},
    {      "ptr",     spf_ptr, 1, 0, 1, 1,       0},
    {      "ip4",     spf_ip4, 1, 1, 0, 0,       0},
    {      "ip6",     spf_ip6, 1, 1, 0, 0,       0},
    {   "exists",  spf_exists, 1, 0, 1, 0,       0},
    {"extension",           0, 1, 1, 0, 0, SPF_EXT},
    {          0,           0, 1, 1, 0, 0, SPF_EXT}
};

/**
 @brief  spf_mechanism
         evaluates the provided mechanisms in the SPF record [RFC7208 Sec 5.]
 @param  input:  pointer to mechanism, SPF specification from record, CIDR prefix length, domain
 @input  stralloc spflocalrules (if provided)
 @output pointer to spfspec: data evaluated
 @return int r
 */

int spf_mechanism(char *mechanism, char *spfspec, char *prefix, char *domain)
{
  struct mechanisms *mech;
  stralloc sa = {0};
  int r;
  int pos;

  for (mech = mechanisms; mech->mechanism; mech++)
    if (case_equals(mech->mechanism, mechanism)) break;

  if (mech->use_spfspec && !spfspec && mech->filldomain) spfspec = domain;
  if (!mech->use_spfspec != !spfspec) return SPF_SYNTAX;
  if (mech->use_prefix && !get_prefix(prefix)) return SPF_SYNTAX;

  if (!mech->func) return mech->defresult;
  if (!stralloc_readyplus(&sa, 1)) return SPF_NOMEM;

  if (mech->expands && case_diffs(spfspec, domain)) {
    if (!spf_parse(&sa, spfspec, domain)) return SPF_NOMEM;
    for (pos = 0; (sa.len - pos) > 255;) {
      pos += byte_chr(sa.s + pos, sa.len - pos, '.');
      if (pos < sa.len) pos++;
    }
    sa.len -= pos;
    if (pos > 0) byte_copy(sa.s, sa.len, sa.s + pos);
    if (!stralloc_0(&sa)) return SPF_NOMEM;
    spfspec = sa.s;
  }

  r = mech->func(spfspec, prefix);
  return r;
}

/**
 @brief  spf_include
         deals with recursive evaluation of SPF record [RFC7208 Sec. 5.2]
 @param  input:  pointer to included SPF specification; CIDR prefix length
 @return int r = 1 ok; 0 failure
 */

int spf_include(char *spfspec, char *prefix)
{
  stralloc sa = {0};
  int r;

  if (!stralloc_copys(&sa, spfspec)) return SPF_NOMEM;

  r = spf_lookup(&sa);
  switch (r) {
    case SPF_NONE:     r = SPF_UNKNOWN; break;
    case SPF_SYNTAX:   r = SPF_UNKNOWN; break;
    case SPF_NEUTRAL:
    case SPF_SOFTFAIL:
    case SPF_FAIL:     r = SPF_NONE; break;
  }
  if (!stralloc_0(&sa)) return SPF_NOMEM;
  if (!spf_info("I=", sa.s)) return SPF_NOMEM;

  return r;
}

/**
 @brief  spf_parse
         parses the substructure of the SPF record and calls spf_macros
 @param  input:  pointer to SPF specification, pointer to domain
         output: stralloc sa -- 
 @output pointer to spfspec: with found data
 @return int r = 1 ok; 0 failure
 */

int spf_parse(stralloc *sa, char *spfspec, char *domain)
{
  char *p;
  int pos;
  char append;

  if (!stralloc_readyplus(sa, 3)) return 0;
  if (!stralloc_copys(sa, "")) return 0;

  for (p = spfspec; *p; ++p) {
    append = *p;
    if (byte_equal(p, 1, "%")) {
      p++;
      switch (*p) {
        case '%': break;
        case '_': append = ' '; break;
        case '-':
          if (!stralloc_cats(sa, "%20")) return 0;
          continue;
        case '{':
          pos = str_chr(p, '}');
          if (p[pos] != '}') {
            p--;
            break;
          }
          p[pos] = '\0';
          if (!spf_macros(sa, p + 1, domain)) return 0;
          p += pos;
          continue;
        default: p--;
      }
    }
    if (!stralloc_append(sa, &append)) return 0;
  }

  return 1;
}

/**
 @brief  spf_macros
         deals with macros in the SPF specificaton [RFC7208 Sec. 7ff]
 @param  input:  pointer to SPF macro, pointer to domain
         output: pointer to stralloc expand(ed information)
 @return int r = 1 ok; 0 failure
 */

int spf_macros(stralloc *expand, char *macro, char *domain)
{
  static const char hextab[] = "0123456789abcdef";
  stralloc sa = {0};
  int reverse = 0;
  int ndigits = -1;
  int urlencode;
  unsigned long u;
  char ch = {0};
  char ascii;
  int pos, i, n;
  int start = expand->len;

  /* URL encoding - hidden in RFC 7208 Sec. 7.3 */

  if (*macro == 'x') {
    urlencode = -1;
    ++macro;
  } else
    urlencode = 0;
  ch = *macro;
  if (!ch) {
    return 1;
  }
  if (ch >= 'A' && ch <= 'Z') {
    ch += 32;
    urlencode = 1;
  }
  if (urlencode == -1) ch -= 32;

  /* No. digits determine number of printed labels */

  i = 0;
  while (*macro) {
    i++;
    if (*macro == '}') break;
    if (*macro >= '0' && *macro <= '9') {
      scan_ulong(macro, &u);
      ndigits = u;
    } else if (i > 1 && *macro == 'r') {
      reverse = 1;
      break;
    } /* Reverse representation */
    macro++;
  }

  switch (ch) { /* see RFC7208 sec. 7.2 */
    case 's':
    case 'S':
      if (!stralloc_readyplus(&sa, spfmf.len)) return 0;
      if (!stralloc_copys(&sa, spfmf.s)) return 0;
      break;
    case 'l':
    case 'L':
      i = byte_rchr(spfmf.s, spfmf.len, '@');
      if (i < spfmf.len) {
        if (!stralloc_copyb(&sa, spfmf.s, i)) return 0;
      } else {
        if (!stralloc_copys(&sa, "postmaster")) return 0;
      }
      break;
    case 'o':
    case 'O':
      i = byte_rchr(spfmf.s, spfmf.len, '@') + 1;
      if (i > spfmf.len) break;
      if (!stralloc_copys(&sa, spfmf.s + i)) return 0;
      break;
    case 'd':
    case 'D':
      if (!stralloc_copys(&sa, domain)) return 0; /* the hack for 'Z'; Russions everywhere ;-) */
      break;
    case 'i':
    case 'c':
    case 'I':
    case 'C':
      if (!stralloc_ready(&sa, IPFMT)) return 0;
      if (flagip6) {
        sa.len = ip6_fmt(sa.s, ip6remote);
      } else {
        sa.len = ip4_fmt(sa.s, ip4remote);
      }
      break;
    case 'p':
    case 'P':
      if (!dnsname.len) spf_ptr(domain, 0);
      if (dnsname.len) {
        if (!stralloc_copys(&sa, dnsname.s)) return 0;
      } else {
        if (!stralloc_copys(&sa, "unknown")) return 0;
      }
      break;
    case 'h':
    case 'H':
      if (!stralloc_copys(&sa, spfhelo.s)) return 0; /* FIXME: FQDN? */
      break;
    case 't':
    case 'T':
      if (!stralloc_ready(&sa, FMT_ULONG)) return 0;
      sa.len = fmt_ulong(sa.s, (unsigned long)now());
      break;
    case 'v':
    case 'V':
      if (flagip6) {
        if (!stralloc_copys(&sa, "ip6")) return 0;
      } else {
        if (!stralloc_copys(&sa, "in-addr")) return 0;
      }
      break;
    case 'r':
    case 'R':
      if (!stralloc_copy(&sa, &spflocal)) return 0;
      break;
    default: break;
  }
  if (!stralloc_0(&sa)) return 0;  // XXX

  if (reverse) {
    n = 0;
    for (i = 1; i <= sa.len; i++) {
      if ((ndigits == -1) || (n < ndigits)) {
        if (!byte_diff(sa.s + sa.len - i - 1, 1, ".") || (i == sa.len)) {
          n++;
          if (!stralloc_cats(expand, sa.s + sa.len - i)) return 0;
          if (i < sa.len) {
            sa.s[sa.len - i - 1] = 0;
            if (!stralloc_cats(expand, ".")) return 0;
          }
        }
      }
    }
  } else if (ndigits != -1) {
    n = pos = 0;
    for (i = 1; i <= sa.len; i++) {
      if (n < ndigits) {
        if (!byte_diff(sa.s + i, 1, ".")) {
          n++;
          pos = i;
        }
      }
    }
    if (!stralloc_catb(expand, sa.s, pos)) return 0;
  } else if (!stralloc_cats(expand, sa.s))
    return 0;

  if (urlencode) {
    stralloc_copyb(&sa, expand->s + start, expand->len - start);
    expand->len = start;

    for (i = 0; i < sa.len; ++i) {
      ch = sa.s[i];
      if (urlchr_table[(unsigned char)ch]) {
        if (!stralloc_readyplus(expand, 3)) return 0;
        if (!stralloc_append(expand, "%")) return 0;
        ascii = hextab[(unsigned char)ch >> 4];
        if (!stralloc_append(expand, &ascii)) return 0;
        ascii = hextab[(unsigned char)ch & 0x0f];
        if (!stralloc_append(expand, &ascii)) return 0;
      } else {
        if (!stralloc_append(expand, &ch)) return 0;
      }
    }
  }

  return 1;
}

int spf_info(char *s, const char *t)
{
  if (!stralloc_cats(&spfinfo, s)) return 0;
  if (!stralloc_cats(&spfinfo, t)) return 0;
  if (!stralloc_cats(&spfinfo, " ")) return 0;

  return 1;
}