auth.c

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#include "config.h"
#include <stdbool.h>
#include <stdio.h>
#include <string.h>
#include "private.h"
#include "mutt/lib.h"
#include "address/lib.h"
#include "config/lib.h"
#include "core/lib.h"
#include "conn/lib.h"
#include "adata.h"
#ifdef USE_SASL_CYRUS
#include <sasl/sasl.h>
#include <sasl/saslutil.h>
#endif
#ifdef USE_SASL_GNU
#include <gsasl.h>
#endif
 
#ifdef USE_SASL_GNU
static enum PopAuthRes pop_auth_gsasl(struct PopAccountData *adata, const char *method)
{
  Gsasl_session *gsasl_session = NULL;
  struct Buffer *output_buf = NULL;
  struct Buffer *input_buf = NULL;
  int rc = POP_A_FAILURE;
  int gsasl_rc = GSASL_OK;
  int first_challenge = 1;
 
  const char *chosen_mech = mutt_gsasl_get_mech(method, buf_string(&adata->auth_list));
  if (!chosen_mech)
  {
    mutt_debug(LL_DEBUG2, "returned no usable mech\n");
    return POP_A_UNAVAIL;
  }
 
  mutt_debug(LL_DEBUG2, "using mech %s\n", chosen_mech);
 
  if (mutt_gsasl_client_new(adata->conn, chosen_mech, &gsasl_session) < 0)
  {
    mutt_debug(LL_DEBUG1, "Error allocating GSASL connection\n");
    return POP_A_UNAVAIL;
  }
 
  mutt_message(_("Authenticating (%s)..."), chosen_mech);
 
  output_buf = buf_pool_get();
  input_buf = buf_pool_get();
  buf_printf(output_buf, "AUTH %s\r\n", chosen_mech);
 
  do
  {
    if (mutt_socket_send(adata->conn, buf_string(output_buf)) < 0)
    {
      adata->status = POP_DISCONNECTED;
      rc = POP_A_SOCKET;
      goto fail;
    }
 
    if (mutt_socket_buffer_readln(input_buf, adata->conn) < 0)
    {
      adata->status = POP_DISCONNECTED;
      rc = POP_A_SOCKET;
      goto fail;
    }
 
    if (!mutt_strn_equal(buf_string(input_buf), "+ ", 2))
      break;
 
    const char *pop_auth_data = buf_string(input_buf) + 2;
 
    /* Workaround for broken POP3 servers. See pop_auth_sasl() above. */
    if (first_challenge)
    {
      first_challenge = 0;
      // Reuse output_buf as a temporary decode buffer
      if (mutt_b64_buffer_decode(output_buf, pop_auth_data) < 0)
        pop_auth_data = "";
    }
 
    char *gsasl_step_output = NULL;
    gsasl_rc = gsasl_step64(gsasl_session, pop_auth_data, &gsasl_step_output);
    if ((gsasl_rc == GSASL_NEEDS_MORE) || (gsasl_rc == GSASL_OK))
    {
      buf_strcpy(output_buf, gsasl_step_output);
      buf_addstr(output_buf, "\r\n");
      gsasl_free(gsasl_step_output);
    }
    else
    {
      mutt_debug(LL_DEBUG1, "gsasl_step64() failed (%d): %s\n", gsasl_rc,
                 gsasl_strerror(gsasl_rc));
    }
  } while ((gsasl_rc == GSASL_NEEDS_MORE) || (gsasl_rc == GSASL_OK));
 
  if (mutt_strn_equal(buf_string(input_buf), "+ ", 2))
  {
    mutt_socket_send(adata->conn, "*\r\n");
    goto fail;
  }
 
  if (mutt_strn_equal(buf_string(input_buf), "+OK", 3) && (gsasl_rc == GSASL_OK))
    rc = POP_A_SUCCESS;
 
fail:
  buf_pool_release(&input_buf);
  buf_pool_release(&output_buf);
  mutt_gsasl_client_finish(&gsasl_session);
 
  if (rc == POP_A_FAILURE)
  {
    mutt_debug(LL_DEBUG2, "%s failed\n", chosen_mech);
    mutt_error(_("SASL authentication failed"));
  }
 
  return rc;
}
#endif
 
#ifdef USE_SASL_CYRUS
static enum PopAuthRes pop_auth_sasl(struct PopAccountData *adata, const char *method)
{
  sasl_conn_t *saslconn = NULL;
  sasl_interact_t *interaction = NULL;
  int rc;
  int first_challenge = 1;
  char inbuf[1024] = { 0 };
  const char *mech = NULL;
  const char *pc = NULL;
  unsigned int len = 0, olen = 0;
 
  if (mutt_account_getpass(&adata->conn->account) || !adata->conn->account.pass[0])
    return POP_A_FAILURE;
 
  if (mutt_sasl_client_new(adata->conn, &saslconn) < 0)
  {
    mutt_debug(LL_DEBUG1, "Error allocating SASL connection\n");
    return POP_A_FAILURE;
  }
 
  if (!method)
    method = adata->auth_list.data;
 
  while (true)
  {
    rc = sasl_client_start(saslconn, method, &interaction, &pc, &olen, &mech);
    if (rc != SASL_INTERACT)
      break;
    mutt_sasl_interact(interaction);
  }
 
  if ((rc != SASL_OK) && (rc != SASL_CONTINUE))
  {
    mutt_debug(LL_DEBUG1, "Failure starting authentication exchange. No shared mechanisms?\n");
 
    /* SASL doesn't support suggested mechanisms, so fall back */
    sasl_dispose(&saslconn);
    return POP_A_UNAVAIL;
  }
 
  /* About client_start:  If sasl_client_start() returns data via pc/olen,
   * the client is expected to send this first (after the AUTH string is sent).
   * sasl_client_start() may in fact return SASL_OK in this case.  */
  unsigned int client_start = olen;
 
  // L10N: (%s) is the method name, e.g. Anonymous, CRAM-MD5, GSSAPI, SASL
  mutt_message(_("Authenticating (%s)..."), "SASL");
 
  size_t bufsize = MAX((olen * 2), 1024);
  char *buf = MUTT_MEM_MALLOC(bufsize, char);
 
  snprintf(buf, bufsize, "AUTH %s", mech);
  olen = strlen(buf);
 
  /* looping protocol */
  while (true)
  {
    mutt_str_copy(buf + olen, "\r\n", bufsize - olen);
    mutt_socket_send(adata->conn, buf);
    if (mutt_socket_readln_d(inbuf, sizeof(inbuf), adata->conn, MUTT_SOCK_LOG_FULL) < 0)
    {
      sasl_dispose(&saslconn);
      adata->status = POP_DISCONNECTED;
      FREE(&buf);
      return POP_A_SOCKET;
    }
 
    /* Note we don't exit if rc==SASL_OK when client_start is true.
     * This is because the first loop has only sent the AUTH string, we
     * need to loop at least once more to send the pc/olen returned
     * by sasl_client_start().  */
    if (!client_start && (rc != SASL_CONTINUE))
      break;
 
    if (mutt_str_startswith(inbuf, "+ ") &&
        (sasl_decode64(inbuf + 2, strlen(inbuf + 2), buf, bufsize - 1, &len) != SASL_OK))
    {
      mutt_debug(LL_DEBUG1, "error base64-decoding server response\n");
 
      /* Some server implementations may send non-base64-encoded challenge,
       * which is against RFC 5034. However, for certain SASL mechanism, e.g.
       * PLAIN, the content of challenge doesn't really matter, thus we try to
       * keep going to improve compatibility if the first challenge fails to
       * decode.
       */
      if (first_challenge)
        len = 0;
      else
        goto bail;
    }
 
    first_challenge = 0;
 
    if (client_start)
    {
      olen = client_start;
      client_start = 0;
    }
    else
    {
      while (true)
      {
        rc = sasl_client_step(saslconn, buf, len, &interaction, &pc, &olen);
        if (rc != SASL_INTERACT)
          break;
        mutt_sasl_interact(interaction);
      }
    }
 
    /* Even if sasl_client_step() returns SASL_OK, we should send at
     * least one more line to the server.  */
    if ((rc != SASL_CONTINUE) && (rc != SASL_OK))
      break;
 
    /* send out response, or line break if none needed */
    if (pc)
    {
      if ((olen * 2) > bufsize)
      {
        bufsize = olen * 2;
        MUTT_MEM_REALLOC(&buf, bufsize, char);
      }
      if (sasl_encode64(pc, olen, buf, bufsize, &olen) != SASL_OK)
      {
        mutt_debug(LL_DEBUG1, "error base64-encoding client response\n");
        goto bail;
      }
    }
  }
 
  if (rc != SASL_OK)
    goto bail;
 
  if (mutt_str_startswith(inbuf, "+OK"))
  {
    mutt_sasl_setup_conn(adata->conn, saslconn);
    FREE(&buf);
    return POP_A_SUCCESS;
  }
 
bail:
  sasl_dispose(&saslconn);
 
  /* terminate SASL session if the last response is not +OK nor -ERR */
  if (mutt_str_startswith(inbuf, "+ "))
  {
    snprintf(buf, bufsize, "*\r\n");
    if (pop_query(adata, buf, bufsize) == -1)
    {
      FREE(&buf);
      return POP_A_SOCKET;
    }
  }
 
  FREE(&buf);
  // L10N: %s is the method name, e.g. Anonymous, CRAM-MD5, GSSAPI, SASL
  mutt_error(_("%s authentication failed"), "SASL");
 
  return POP_A_FAILURE;
}
#endif

void pop_apop_timestamp(struct PopAccountData *adata, char *buf)
{
  char *p1 = NULL, *p2 = NULL;
 
  FREE(&adata->timestamp);
 
  if ((p1 = strchr(buf, '<')) && (p2 = strchr(p1, '>')))
  {
    p2[1] = '\0';
    adata->timestamp = mutt_str_dup(p1);
  }
}

static enum PopAuthRes pop_auth_apop(struct PopAccountData *adata, const char *method)
{
  struct Md5Ctx md5ctx = { 0 };
  unsigned char digest[16];
  char hash[33] = { 0 };
  char buf[1024] = { 0 };
 
  if (mutt_account_getpass(&adata->conn->account) || !adata->conn->account.pass[0])
    return POP_A_FAILURE;
 
  if (!adata->timestamp)
    return POP_A_UNAVAIL;
 
  if (!mutt_addr_valid_msgid(adata->timestamp))
  {
    mutt_error(_("POP timestamp is invalid"));
    return POP_A_UNAVAIL;
  }
 
  // L10N: (%s) is the method name, e.g. Anonymous, CRAM-MD5, GSSAPI, SASL
  mutt_message(_("Authenticating (%s)..."), "APOP");
 
  /* Compute the authentication hash to send to the server */
  mutt_md5_init_ctx(&md5ctx);
  mutt_md5_process(adata->timestamp, &md5ctx);
  mutt_md5_process(adata->conn->account.pass, &md5ctx);
  mutt_md5_finish_ctx(&md5ctx, digest);
  mutt_md5_toascii(digest, hash);
 
  /* Send APOP command to server */
  snprintf(buf, sizeof(buf), "APOP %s %s\r\n", adata->conn->account.user, hash);
 
  switch (pop_query(adata, buf, sizeof(buf)))
  {
    case 0:
      return POP_A_SUCCESS;
    case -1:
      return POP_A_SOCKET;
  }
 
  // L10N: %s is the method name, e.g. Anonymous, CRAM-MD5, GSSAPI, SASL
  mutt_error(_("%s authentication failed"), "APOP");
 
  return POP_A_FAILURE;
}

static enum PopAuthRes pop_auth_user(struct PopAccountData *adata, const char *method)
{
  if (!adata->cmd_user)
    return POP_A_UNAVAIL;
 
  if (mutt_account_getpass(&adata->conn->account) || !adata->conn->account.pass[0])
    return POP_A_FAILURE;
 
  mutt_message(_("Logging in..."));
 
  char buf[1024] = { 0 };
  snprintf(buf, sizeof(buf), "USER %s\r\n", adata->conn->account.user);
  int rc = pop_query(adata, buf, sizeof(buf));
 
  if (adata->cmd_user == 2)
  {
    if (rc == 0)
    {
      adata->cmd_user = 1;
 
      mutt_debug(LL_DEBUG1, "set USER capability\n");
    }
 
    if (rc == -2)
    {
      adata->cmd_user = 0;
 
      mutt_debug(LL_DEBUG1, "unset USER capability\n");
      snprintf(adata->err_msg, sizeof(adata->err_msg), "%s",
               _("Command USER is not supported by server"));
    }
  }
 
  if (rc == 0)
  {
    snprintf(buf, sizeof(buf), "PASS %s\r\n", adata->conn->account.pass);
    const short c_debug_level = cs_subset_number(NeoMutt->sub, "debug_level");
    rc = pop_query_d(adata, buf, sizeof(buf),
                     /* don't print the password unless we're at the ungodly debugging level */
                     (c_debug_level < MUTT_SOCK_LOG_FULL) ? "PASS *\r\n" : NULL);
  }
 
  switch (rc)
  {
    case 0:
      return POP_A_SUCCESS;
    case -1:
      return POP_A_SOCKET;
  }
 
  mutt_error("%s %s", _("Login failed"), adata->err_msg);
 
  return POP_A_FAILURE;
}

static enum PopAuthRes pop_auth_oauth(struct PopAccountData *adata, const char *method)
{
  /* If they did not explicitly request or configure oauth then fail quietly */
  const char *const c_pop_oauth_refresh_command = cs_subset_string(NeoMutt->sub, "pop_oauth_refresh_command");
  if (!method && !c_pop_oauth_refresh_command)
    return POP_A_UNAVAIL;
 
  // L10N: (%s) is the method name, e.g. Anonymous, CRAM-MD5, GSSAPI, SASL
  mutt_message(_("Authenticating (%s)..."), "OAUTHBEARER");
 
  char *oauthbearer = mutt_account_getoauthbearer(&adata->conn->account, false);
  if (!oauthbearer)
    return POP_A_FAILURE;
 
  char *auth_cmd = NULL;
  mutt_str_asprintf(&auth_cmd, "AUTH OAUTHBEARER %s\r\n", oauthbearer);
  FREE(&oauthbearer);
 
  int rc = pop_query_d(adata, auth_cmd, strlen(auth_cmd),
#ifdef DEBUG
                       /* don't print the bearer token unless we're at the ungodly debugging level */
                       (cs_subset_number(NeoMutt->sub, "debug_level") < MUTT_SOCK_LOG_FULL) ?
                           "AUTH OAUTHBEARER *\r\n" :
#endif
                           NULL);
  FREE(&auth_cmd);
 
  switch (rc)
  {
    case 0:
      return POP_A_SUCCESS;
    case -1:
      return POP_A_SOCKET;
  }
 
  /* The error response was a SASL continuation, so "continue" it.
   * See RFC7628 3.2.3 */
  mutt_socket_send(adata->conn, "\001");
 
  char *err = adata->err_msg;
  char decoded_err[1024] = { 0 };
  int len = mutt_b64_decode(adata->err_msg, decoded_err, sizeof(decoded_err) - 1);
  if (len >= 0)
  {
    decoded_err[len] = '\0';
    err = decoded_err;
  }
  mutt_error("%s %s", _("Authentication failed"), err);
 
  return POP_A_FAILURE;
}

static const struct PopAuth PopAuthenticators[] = {
  // clang-format off
  { pop_auth_oauth, "oauthbearer" },
#ifdef USE_SASL_CYRUS
  { pop_auth_sasl, NULL },
#endif
#ifdef USE_SASL_GNU
  { pop_auth_gsasl, NULL },
#endif
  { pop_auth_apop, "apop" },
  { pop_auth_user, "user" },
  { NULL, NULL },
  // clang-format on
};

bool pop_auth_is_valid(const char *authenticator)
{
  for (size_t i = 0; i < countof(PopAuthenticators); i++)
  {
    const struct PopAuth *auth = &PopAuthenticators[i];
    if (auth->method && mutt_istr_equal(auth->method, authenticator))
      return true;
  }
 
  return false;
}

int pop_authenticate(struct PopAccountData *adata)
{
  struct ConnAccount *cac = &adata->conn->account;
  const struct PopAuth *authenticator = NULL;
  int attempts = 0;
  int rc = POP_A_UNAVAIL;
 
  if ((mutt_account_getuser(cac) < 0) || (cac->user[0] == '\0'))
  {
    return -3;
  }
 
  const struct Slist *c_pop_authenticators = cs_subset_slist(NeoMutt->sub, "pop_authenticators");
  const bool c_pop_auth_try_all = cs_subset_bool(NeoMutt->sub, "pop_auth_try_all");
  if (c_pop_authenticators && (c_pop_authenticators->count > 0))
  {
    /* Try user-specified list of authentication methods */
    struct ListNode *np = NULL;
    STAILQ_FOREACH(np, &c_pop_authenticators->head, entries)
    {
      mutt_debug(LL_DEBUG2, "Trying method %s\n", np->data);
      authenticator = PopAuthenticators;
 
      /* Walk the built-in authenticator table looking for a match */
      while (authenticator->authenticate)
      {
        if (!authenticator->method || mutt_istr_equal(authenticator->method, np->data))
        {
          rc = authenticator->authenticate(adata, np->data);
          if (rc == POP_A_SOCKET)
          {
            /* Connection dropped; try reconnecting and retrying once */
            switch (pop_connect(adata))
            {
              case 0:
              {
                rc = authenticator->authenticate(adata, np->data);
                break;
              }
              case -2:
                rc = POP_A_FAILURE;
            }
          }
 
          if (rc != POP_A_UNAVAIL)
            attempts++;
          if ((rc == POP_A_SUCCESS) || (rc == POP_A_SOCKET) ||
              ((rc == POP_A_FAILURE) && !c_pop_auth_try_all))
          {
            break;
          }
        }
        authenticator++;
      }
    }
  }
  else
  {
    /* Fall back to default: try every authenticator in order */
    mutt_debug(LL_DEBUG2, "Using any available method\n");
    authenticator = PopAuthenticators;
 
    while (authenticator->authenticate)
    {
      rc = authenticator->authenticate(adata, NULL);
      if (rc == POP_A_SOCKET)
      {
        switch (pop_connect(adata))
        {
          case 0:
          {
            rc = authenticator->authenticate(adata, NULL);
            break;
          }
          case -2:
            rc = POP_A_FAILURE;
        }
      }
 
      if (rc != POP_A_UNAVAIL)
        attempts++;
      if ((rc == POP_A_SUCCESS) || (rc == POP_A_SOCKET) ||
          ((rc == POP_A_FAILURE) && !c_pop_auth_try_all))
      {
        break;
      }
 
      authenticator++;
    }
  }
 
  /* Map internal result code to the caller's return values */
  switch (rc)
  {
    case POP_A_SUCCESS:
      return 0;
    case POP_A_SOCKET:
      return -1;
    case POP_A_UNAVAIL:
      if (attempts == 0)
        mutt_error(_("No authenticators available"));
  }
 
  return -2;
}