lib/krb5.c - platform/external/curl - Git at Google

 /* GSSAPI/krb5 support for FTP - loosely based on old krb4.c
  *
  * Copyright (c) 1995, 1996, 1997, 1998, 1999 Kungliga Tekniska Högskolan
  * (Royal Institute of Technology, Stockholm, Sweden).
  * Copyright (c) 2004 - 2021 Daniel Stenberg
  * All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  *
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  *
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
  *    documentation and/or other materials provided with the distribution.
  *
  * 3. Neither the name of the Institute nor the names of its contributors
  *    may be used to endorse or promote products derived from this software
  *    without specific prior written permission.
  *
  * THIS SOFTWARE IS PROVIDED BY THE INSTITUTE AND CONTRIBUTORS ``AS IS'' AND
  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  * ARE DISCLAIMED.  IN NO EVENT SHALL THE INSTITUTE OR CONTRIBUTORS BE LIABLE
  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  * SUCH DAMAGE.  */

 #include "curl_setup.h"

 #if defined(HAVE_GSSAPI) && !defined(CURL_DISABLE_FTP)

 #ifdef HAVE_NETDB_H
 #include <netdb.h>
 #endif

 #include "urldata.h"
 #include "curl_base64.h"
 #include "ftp.h"
 #include "curl_gssapi.h"
 #include "sendf.h"
 #include "curl_krb5.h"
 #include "warnless.h"
 #include "non-ascii.h"
 #include "strcase.h"
 #include "strdup.h"

 /* The last 3 #include files should be in this order */
 #include "curl_printf.h"
 #include "curl_memory.h"
 #include "memdebug.h"

 static CURLcode ftpsend(struct Curl_easy *data, struct connectdata *conn,
                         const char *cmd)
 {
   ssize_t bytes_written;
 #define SBUF_SIZE 1024
   char s[SBUF_SIZE];
   size_t write_len;
   char *sptr = s;
   CURLcode result = CURLE_OK;
 #ifdef HAVE_GSSAPI
   enum protection_level data_sec = conn->data_prot;
 #endif

   if(!cmd)
     return CURLE_BAD_FUNCTION_ARGUMENT;

   write_len = strlen(cmd);
   if(!write_len || write_len > (sizeof(s) -3))
     return CURLE_BAD_FUNCTION_ARGUMENT;

   memcpy(&s, cmd, write_len);
   strcpy(&s[write_len], "\r\n"); /* append a trailing CRLF */
   write_len += 2;
   bytes_written = 0;

   result = Curl_convert_to_network(data, s, write_len);
   /* Curl_convert_to_network calls failf if unsuccessful */
   if(result)
     return result;

   for(;;) {
 #ifdef HAVE_GSSAPI
     conn->data_prot = PROT_CMD;
 #endif
     result = Curl_write(data, conn->sock[FIRSTSOCKET], sptr, write_len,
                         &bytes_written);
 #ifdef HAVE_GSSAPI
     DEBUGASSERT(data_sec > PROT_NONE && data_sec < PROT_LAST);
     conn->data_prot = data_sec;
 #endif

     if(result)
       break;

     Curl_debug(data, CURLINFO_HEADER_OUT, sptr, (size_t)bytes_written);

     if(bytes_written != (ssize_t)write_len) {
       write_len -= bytes_written;
       sptr += bytes_written;
     }
     else
       break;
   }

   return result;
 }

 static int
 krb5_init(void *app_data)
 {
   gss_ctx_id_t *context = app_data;
   /* Make sure our context is initialized for krb5_end. */
   *context = GSS_C_NO_CONTEXT;
   return 0;
 }

 static int
 krb5_check_prot(void *app_data, int level)
 {
   (void)app_data; /* unused */
   if(level == PROT_CONFIDENTIAL)
     return -1;
   return 0;
 }

 static int
 krb5_decode(void *app_data, void *buf, int len,
             int level UNUSED_PARAM,
             struct connectdata *conn UNUSED_PARAM)
 {
   gss_ctx_id_t *context = app_data;
   OM_uint32 maj, min;
   gss_buffer_desc enc, dec;

   (void)level;
   (void)conn;

   enc.value = buf;
   enc.length = len;
   maj = gss_unwrap(&min, *context, &enc, &dec, NULL, NULL);
   if(maj != GSS_S_COMPLETE) {
     if(len >= 4)
       strcpy(buf, "599 ");
     return -1;
   }

   memcpy(buf, dec.value, dec.length);
   len = curlx_uztosi(dec.length);
   gss_release_buffer(&min, &dec);

   return len;
 }

 static int
 krb5_encode(void *app_data, const void *from, int length, int level, void **to)
 {
   gss_ctx_id_t *context = app_data;
   gss_buffer_desc dec, enc;
   OM_uint32 maj, min;
   int state;
   int len;

   /* NOTE that the cast is safe, neither of the krb5, gnu gss and heimdal
    * libraries modify the input buffer in gss_wrap()
    */
   dec.value = (void *)from;
   dec.length = length;
   maj = gss_wrap(&min, *context,
                  level == PROT_PRIVATE,
                  GSS_C_QOP_DEFAULT,
                  &dec, &state, &enc);

   if(maj != GSS_S_COMPLETE)
     return -1;

   /* malloc a new buffer, in case gss_release_buffer doesn't work as
      expected */
   *to = malloc(enc.length);
   if(!*to)
     return -1;
   memcpy(*to, enc.value, enc.length);
   len = curlx_uztosi(enc.length);
   gss_release_buffer(&min, &enc);
   return len;
 }

 static int
 krb5_auth(void *app_data, struct Curl_easy *data, struct connectdata *conn)
 {
   int ret = AUTH_OK;
   char *p;
   const char *host = conn->host.name;
   ssize_t nread;
   curl_socklen_t l = sizeof(conn->local_addr);
   CURLcode result;
   const char *service = data->set.str[STRING_SERVICE_NAME] ?
                         data->set.str[STRING_SERVICE_NAME] :
                         "ftp";
   const char *srv_host = "host";
   gss_buffer_desc input_buffer, output_buffer, _gssresp, *gssresp;
   OM_uint32 maj, min;
   gss_name_t gssname;
   gss_ctx_id_t *context = app_data;
   struct gss_channel_bindings_struct chan;
   size_t base64_sz = 0;
   struct sockaddr_in **remote_addr =
     (struct sockaddr_in **)&conn->ip_addr->ai_addr;
   char *stringp;

   if(getsockname(conn->sock[FIRSTSOCKET],
                  (struct sockaddr *)&conn->local_addr, &l) < 0)
     perror("getsockname()");

   chan.initiator_addrtype = GSS_C_AF_INET;
   chan.initiator_address.length = l - 4;
   chan.initiator_address.value = &conn->local_addr.sin_addr.s_addr;
   chan.acceptor_addrtype = GSS_C_AF_INET;
   chan.acceptor_address.length = l - 4;
   chan.acceptor_address.value = &(*remote_addr)->sin_addr.s_addr;
   chan.application_data.length = 0;
   chan.application_data.value = NULL;

   /* this loop will execute twice (once for service, once for host) */
   for(;;) {
     /* this really shouldn't be repeated here, but can't help it */
     if(service == srv_host) {
       result = ftpsend(data, conn, "AUTH GSSAPI");
       if(result)
         return -2;

       if(Curl_GetFTPResponse(data, &nread, NULL))
         return -1;

       if(data->state.buffer[0] != '3')
         return -1;
     }

     stringp = aprintf("%s@%s", service, host);
     if(!stringp)
       return -2;

     input_buffer.value = stringp;
     input_buffer.length = strlen(stringp);
     maj = gss_import_name(&min, &input_buffer, GSS_C_NT_HOSTBASED_SERVICE,
                           &gssname);
     free(stringp);
     if(maj != GSS_S_COMPLETE) {
       gss_release_name(&min, &gssname);
       if(service == srv_host) {
         failf(data, "Error importing service name %s@%s", service, host);
         return AUTH_ERROR;
       }
       service = srv_host;
       continue;
     }
     /* We pass NULL as |output_name_type| to avoid a leak. */
     gss_display_name(&min, gssname, &output_buffer, NULL);
     infof(data, "Trying against %s", output_buffer.value);
     gssresp = GSS_C_NO_BUFFER;
     *context = GSS_C_NO_CONTEXT;

     do {
       /* Release the buffer at each iteration to avoid leaking: the first time
          we are releasing the memory from gss_display_name. The last item is
          taken care by a final gss_release_buffer. */
       gss_release_buffer(&min, &output_buffer);
       ret = AUTH_OK;
       maj = Curl_gss_init_sec_context(data,
                                       &min,
                                       context,
                                       gssname,
                                       &Curl_krb5_mech_oid,
                                       &chan,
                                       gssresp,
                                       &output_buffer,
                                       TRUE,
                                       NULL);

       if(gssresp) {
         free(_gssresp.value);
         gssresp = NULL;
       }

       if(GSS_ERROR(maj)) {
         infof(data, "Error creating security context");
         ret = AUTH_ERROR;
         break;
       }

       if(output_buffer.length) {
         char *cmd;

         result = Curl_base64_encode(data, (char *)output_buffer.value,
                                     output_buffer.length, &p, &base64_sz);
         if(result) {
           infof(data, "base64-encoding: %s", curl_easy_strerror(result));
           ret = AUTH_ERROR;
           break;
         }

         cmd = aprintf("ADAT %s", p);
         if(cmd)
           result = ftpsend(data, conn, cmd);
         else
           result = CURLE_OUT_OF_MEMORY;

         free(p);
         free(cmd);

         if(result) {
           ret = -2;
           break;
         }

         if(Curl_GetFTPResponse(data, &nread, NULL)) {
           ret = -1;
           break;
         }

         if(data->state.buffer[0] != '2' && data->state.buffer[0] != '3') {
           infof(data, "Server didn't accept auth data");
           ret = AUTH_ERROR;
           break;
         }

         _gssresp.value = NULL; /* make sure it is initialized */
         p = data->state.buffer + 4;
         p = strstr(p, "ADAT=");
         if(p) {
           result = Curl_base64_decode(p + 5,
                                       (unsigned char **)&_gssresp.value,
                                       &_gssresp.length);
           if(result) {
             failf(data, "base64-decoding: %s", curl_easy_strerror(result));
             ret = AUTH_CONTINUE;
             break;
           }
         }

         gssresp = &_gssresp;
       }
     } while(maj == GSS_S_CONTINUE_NEEDED);

     gss_release_name(&min, &gssname);
     gss_release_buffer(&min, &output_buffer);

     if(gssresp)
       free(_gssresp.value);

     if(ret == AUTH_OK || service == srv_host)
       return ret;

     service = srv_host;
   }
   return ret;
 }

 static void krb5_end(void *app_data)
 {
     OM_uint32 min;
     gss_ctx_id_t *context = app_data;
     if(*context != GSS_C_NO_CONTEXT) {
       OM_uint32 maj = gss_delete_sec_context(&min, context, GSS_C_NO_BUFFER);
       (void)maj;
       DEBUGASSERT(maj == GSS_S_COMPLETE);
     }
 }

 static const struct Curl_sec_client_mech Curl_krb5_client_mech = {
   "GSSAPI",
   sizeof(gss_ctx_id_t),
   krb5_init,
   krb5_auth,
   krb5_end,
   krb5_check_prot,

   krb5_encode,
   krb5_decode
 };

 static const struct {
   enum protection_level level;
   const char *name;
 } level_names[] = {
   { PROT_CLEAR, "clear" },
   { PROT_SAFE, "safe" },
   { PROT_CONFIDENTIAL, "confidential" },
   { PROT_PRIVATE, "private" }
 };

 static enum protection_level
 name_to_level(const char *name)
 {
   int i;
   for(i = 0; i < (int)sizeof(level_names)/(int)sizeof(level_names[0]); i++)
     if(curl_strequal(name, level_names[i].name))
       return level_names[i].level;
   return PROT_NONE;
 }

 /* Convert a protocol |level| to its char representation.
    We take an int to catch programming mistakes. */
 static char level_to_char(int level)
 {
   switch(level) {
   case PROT_CLEAR:
     return 'C';
   case PROT_SAFE:
     return 'S';
   case PROT_CONFIDENTIAL:
     return 'E';
   case PROT_PRIVATE:
     return 'P';
   case PROT_CMD:
     /* Fall through */
   default:
     /* Those 2 cases should not be reached! */
     break;
   }
   DEBUGASSERT(0);
   /* Default to the most secure alternative. */
   return 'P';
 }

 /* Send an FTP command defined by |message| and the optional arguments. The
    function returns the ftp_code. If an error occurs, -1 is returned. */
 static int ftp_send_command(struct Curl_easy *data, const char *message, ...)
 {
   int ftp_code;
   ssize_t nread = 0;
   va_list args;
   char print_buffer[50];

   va_start(args, message);
   mvsnprintf(print_buffer, sizeof(print_buffer), message, args);
   va_end(args);

   if(ftpsend(data, data->conn, print_buffer)) {
     ftp_code = -1;
   }
   else {
     if(Curl_GetFTPResponse(data, &nread, &ftp_code))
       ftp_code = -1;
   }

   (void)nread; /* Unused */
   return ftp_code;
 }

 /* Read |len| from the socket |fd| and store it in |to|. Return a CURLcode
    saying whether an error occurred or CURLE_OK if |len| was read. */
 static CURLcode
 socket_read(curl_socket_t fd, void *to, size_t len)
 {
   char *to_p = to;
   CURLcode result;
   ssize_t nread = 0;

   while(len > 0) {
     result = Curl_read_plain(fd, to_p, len, &nread);
     if(!result) {
       len -= nread;
       to_p += nread;
     }
     else {
       if(result == CURLE_AGAIN)
         continue;
       return result;
     }
   }
   return CURLE_OK;
 }


 /* Write |len| bytes from the buffer |to| to the socket |fd|. Return a
    CURLcode saying whether an error occurred or CURLE_OK if |len| was
    written. */
 static CURLcode
 socket_write(struct Curl_easy *data, curl_socket_t fd, const void *to,
              size_t len)
 {
   const char *to_p = to;
   CURLcode result;
   ssize_t written;

   while(len > 0) {
     result = Curl_write_plain(data, fd, to_p, len, &written);
     if(!result) {
       len -= written;
       to_p += written;
     }
     else {
       if(result == CURLE_AGAIN)
         continue;
       return result;
     }
   }
   return CURLE_OK;
 }

 static CURLcode read_data(struct connectdata *conn,
                           curl_socket_t fd,
                           struct krb5buffer *buf)
 {
   int len;
   CURLcode result;

   result = socket_read(fd, &len, sizeof(len));
   if(result)
     return result;

   if(len) {
     /* only realloc if there was a length */
     len = ntohl(len);
     buf->data = Curl_saferealloc(buf->data, len);
   }
   if(!len || !buf->data)
     return CURLE_OUT_OF_MEMORY;

   result = socket_read(fd, buf->data, len);
   if(result)
     return result;
   buf->size = conn->mech->decode(conn->app_data, buf->data, len,
                                  conn->data_prot, conn);
   buf->index = 0;
   return CURLE_OK;
 }

 static size_t
 buffer_read(struct krb5buffer *buf, void *data, size_t len)
 {
   if(buf->size - buf->index < len)
     len = buf->size - buf->index;
   memcpy(data, (char *)buf->data + buf->index, len);
   buf->index += len;
   return len;
 }

 /* Matches Curl_recv signature */
 static ssize_t sec_recv(struct Curl_easy *data, int sockindex,
                         char *buffer, size_t len, CURLcode *err)
 {
   size_t bytes_read;
   size_t total_read = 0;
   struct connectdata *conn = data->conn;
   curl_socket_t fd = conn->sock[sockindex];

   *err = CURLE_OK;

   /* Handle clear text response. */
   if(conn->sec_complete == 0 || conn->data_prot == PROT_CLEAR)
     return sread(fd, buffer, len);

   if(conn->in_buffer.eof_flag) {
     conn->in_buffer.eof_flag = 0;
     return 0;
   }

   bytes_read = buffer_read(&conn->in_buffer, buffer, len);
   len -= bytes_read;
   total_read += bytes_read;
   buffer += bytes_read;

   while(len > 0) {
     if(read_data(conn, fd, &conn->in_buffer))
       return -1;
     if(conn->in_buffer.size == 0) {
       if(bytes_read > 0)
         conn->in_buffer.eof_flag = 1;
       return bytes_read;
     }
     bytes_read = buffer_read(&conn->in_buffer, buffer, len);
     len -= bytes_read;
     total_read += bytes_read;
     buffer += bytes_read;
   }
   return total_read;
 }

 /* Send |length| bytes from |from| to the |fd| socket taking care of encoding
    and negotiating with the server. |from| can be NULL. */
 static void do_sec_send(struct Curl_easy *data, struct connectdata *conn,
                         curl_socket_t fd, const char *from, int length)
 {
   int bytes, htonl_bytes; /* 32-bit integers for htonl */
   char *buffer = NULL;
   char *cmd_buffer;
   size_t cmd_size = 0;
   CURLcode error;
   enum protection_level prot_level = conn->data_prot;
   bool iscmd = (prot_level == PROT_CMD)?TRUE:FALSE;

   DEBUGASSERT(prot_level > PROT_NONE && prot_level < PROT_LAST);

   if(iscmd) {
     if(!strncmp(from, "PASS ", 5) || !strncmp(from, "ACCT ", 5))
       prot_level = PROT_PRIVATE;
     else
       prot_level = conn->command_prot;
   }
   bytes = conn->mech->encode(conn->app_data, from, length, prot_level,
                              (void **)&buffer);
   if(!buffer || bytes <= 0)
     return; /* error */

   if(iscmd) {
     error = Curl_base64_encode(data, buffer, curlx_sitouz(bytes),
                                &cmd_buffer, &cmd_size);
     if(error) {
       free(buffer);
       return; /* error */
     }
     if(cmd_size > 0) {
       static const char *enc = "ENC ";
       static const char *mic = "MIC ";
       if(prot_level == PROT_PRIVATE)
         socket_write(data, fd, enc, 4);
       else
         socket_write(data, fd, mic, 4);

       socket_write(data, fd, cmd_buffer, cmd_size);
       socket_write(data, fd, "\r\n", 2);
       infof(data, "Send: %s%s", prot_level == PROT_PRIVATE?enc:mic,
             cmd_buffer);
       free(cmd_buffer);
     }
   }
   else {
     htonl_bytes = htonl(bytes);
     socket_write(data, fd, &htonl_bytes, sizeof(htonl_bytes));
     socket_write(data, fd, buffer, curlx_sitouz(bytes));
   }
   free(buffer);
 }

 static ssize_t sec_write(struct Curl_easy *data, struct connectdata *conn,
                          curl_socket_t fd, const char *buffer, size_t length)
 {
   ssize_t tx = 0, len = conn->buffer_size;

   if(len <= 0)
     len = length;
   while(length) {
     if(length < (size_t)len)
       len = length;

     do_sec_send(data, conn, fd, buffer, curlx_sztosi(len));
     length -= len;
     buffer += len;
     tx += len;
   }
   return tx;
 }

 /* Matches Curl_send signature */
 static ssize_t sec_send(struct Curl_easy *data, int sockindex,
                         const void *buffer, size_t len, CURLcode *err)
 {
   struct connectdata *conn = data->conn;
   curl_socket_t fd = conn->sock[sockindex];
   *err = CURLE_OK;
   return sec_write(data, conn, fd, buffer, len);
 }

 int Curl_sec_read_msg(struct Curl_easy *data, struct connectdata *conn,
                       char *buffer, enum protection_level level)
 {
   /* decoded_len should be size_t or ssize_t but conn->mech->decode returns an
      int */
   int decoded_len;
   char *buf;
   int ret_code = 0;
   size_t decoded_sz = 0;
   CURLcode error;

   (void) data;

   if(!conn->mech)
     /* not initialized, return error */
     return -1;

   DEBUGASSERT(level > PROT_NONE && level < PROT_LAST);

   error = Curl_base64_decode(buffer + 4, (unsigned char **)&buf, &decoded_sz);
   if(error || decoded_sz == 0)
     return -1;

   if(decoded_sz > (size_t)INT_MAX) {
     free(buf);
     return -1;
   }
   decoded_len = curlx_uztosi(decoded_sz);

   decoded_len = conn->mech->decode(conn->app_data, buf, decoded_len,
                                    level, conn);
   if(decoded_len <= 0) {
     free(buf);
     return -1;
   }

   {
     buf[decoded_len] = '\n';
     Curl_debug(data, CURLINFO_HEADER_IN, buf, decoded_len + 1);
   }

   buf[decoded_len] = '\0';
   if(decoded_len <= 3)
     /* suspiciously short */
     return 0;

   if(buf[3] != '-')
     /* safe to ignore return code */
     (void)sscanf(buf, "%d", &ret_code);

   if(buf[decoded_len - 1] == '\n')
     buf[decoded_len - 1] = '\0';
   strcpy(buffer, buf);
   free(buf);
   return ret_code;
 }

 static int sec_set_protection_level(struct Curl_easy *data)
 {
   int code;
   struct connectdata *conn = data->conn;
   enum protection_level level = conn->request_data_prot;

   DEBUGASSERT(level > PROT_NONE && level < PROT_LAST);

   if(!conn->sec_complete) {
     infof(data, "Trying to change the protection level after the"
                 " completion of the data exchange.");
     return -1;
   }

   /* Bail out if we try to set up the same level */
   if(conn->data_prot == level)
     return 0;

   if(level) {
     char *pbsz;
     unsigned int buffer_size = 1 << 20; /* 1048576 */

     code = ftp_send_command(data, "PBSZ %u", buffer_size);
     if(code < 0)
       return -1;

     if(code/100 != 2) {
       failf(data, "Failed to set the protection's buffer size.");
       return -1;
     }
     conn->buffer_size = buffer_size;

     pbsz = strstr(data->state.buffer, "PBSZ=");
     if(pbsz) {
       /* ignore return code, use default value if it fails */
       (void)sscanf(pbsz, "PBSZ=%u", &buffer_size);
       if(buffer_size < conn->buffer_size)
         conn->buffer_size = buffer_size;
     }
   }

   /* Now try to negotiate the protection level. */
   code = ftp_send_command(data, "PROT %c", level_to_char(level));

   if(code < 0)
     return -1;

   if(code/100 != 2) {
     failf(data, "Failed to set the protection level.");
     return -1;
   }

   conn->data_prot = level;
   if(level == PROT_PRIVATE)
     conn->command_prot = level;

   return 0;
 }

 int
 Curl_sec_request_prot(struct connectdata *conn, const char *level)
 {
   enum protection_level l = name_to_level(level);
   if(l == PROT_NONE)
     return -1;
   DEBUGASSERT(l > PROT_NONE && l < PROT_LAST);
   conn->request_data_prot = l;
   return 0;
 }

 static CURLcode choose_mech(struct Curl_easy *data, struct connectdata *conn)
 {
   int ret;
   void *tmp_allocation;
   const struct Curl_sec_client_mech *mech = &Curl_krb5_client_mech;

   tmp_allocation = realloc(conn->app_data, mech->size);
   if(!tmp_allocation) {
     failf(data, "Failed realloc of size %zu", mech->size);
     mech = NULL;
     return CURLE_OUT_OF_MEMORY;
   }
   conn->app_data = tmp_allocation;

   if(mech->init) {
     ret = mech->init(conn->app_data);
     if(ret) {
       infof(data, "Failed initialization for %s. Skipping it.",
             mech->name);
       return CURLE_FAILED_INIT;
     }
   }

   infof(data, "Trying mechanism %s...", mech->name);
   ret = ftp_send_command(data, "AUTH %s", mech->name);
   if(ret < 0)
     return CURLE_COULDNT_CONNECT;

   if(ret/100 != 3) {
     switch(ret) {
     case 504:
       infof(data, "Mechanism %s is not supported by the server (server "
             "returned ftp code: 504).", mech->name);
       break;
     case 534:
       infof(data, "Mechanism %s was rejected by the server (server returned "
             "ftp code: 534).", mech->name);
       break;
     default:
       if(ret/100 == 5) {
         infof(data, "server does not support the security extensions");
         return CURLE_USE_SSL_FAILED;
       }
       break;
     }
     return CURLE_LOGIN_DENIED;
   }

   /* Authenticate */
   ret = mech->auth(conn->app_data, data, conn);

   if(ret != AUTH_CONTINUE) {
     if(ret != AUTH_OK) {
       /* Mechanism has dumped the error to stderr, don't error here. */
       return CURLE_USE_SSL_FAILED;
     }
     DEBUGASSERT(ret == AUTH_OK);

     conn->mech = mech;
     conn->sec_complete = 1;
     conn->recv[FIRSTSOCKET] = sec_recv;
     conn->send[FIRSTSOCKET] = sec_send;
     conn->recv[SECONDARYSOCKET] = sec_recv;
     conn->send[SECONDARYSOCKET] = sec_send;
     conn->command_prot = PROT_SAFE;
     /* Set the requested protection level */
     /* BLOCKING */
     (void)sec_set_protection_level(data);
   }

   return CURLE_OK;
 }

 CURLcode
 Curl_sec_login(struct Curl_easy *data, struct connectdata *conn)
 {
   return choose_mech(data, conn);
 }


 void
 Curl_sec_end(struct connectdata *conn)
 {
   if(conn->mech != NULL && conn->mech->end)
     conn->mech->end(conn->app_data);
   free(conn->app_data);
   conn->app_data = NULL;
   if(conn->in_buffer.data) {
     free(conn->in_buffer.data);
     conn->in_buffer.data = NULL;
     conn->in_buffer.size = 0;
     conn->in_buffer.index = 0;
     conn->in_buffer.eof_flag = 0;
   }
   conn->sec_complete = 0;
   conn->data_prot = PROT_CLEAR;
   conn->mech = NULL;
 }

 #endif /* HAVE_GSSAPI && !CURL_DISABLE_FTP */
	/* GSSAPI/krb5 support for FTP - loosely based on old krb4.c
	*
	* Copyright (c) 1995, 1996, 1997, 1998, 1999 Kungliga Tekniska Högskolan
	* (Royal Institute of Technology, Stockholm, Sweden).
	* Copyright (c) 2004 - 2021 Daniel Stenberg
	* All rights reserved.
	*
	* Redistribution and use in source and binary forms, with or without
	* modification, are permitted provided that the following conditions
	* are met:
	*
	* 1. Redistributions of source code must retain the above copyright
	* notice, this list of conditions and the following disclaimer.
	*
	* 2. Redistributions in binary form must reproduce the above copyright
	* notice, this list of conditions and the following disclaimer in the
	* documentation and/or other materials provided with the distribution.
	*
	* 3. Neither the name of the Institute nor the names of its contributors
	* may be used to endorse or promote products derived from this software
	* without specific prior written permission.
	*
	* THIS SOFTWARE IS PROVIDED BY THE INSTITUTE AND CONTRIBUTORS ``AS IS'' AND
	* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
	* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
	* ARE DISCLAIMED. IN NO EVENT SHALL THE INSTITUTE OR CONTRIBUTORS BE LIABLE
	* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
	* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
	* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
	* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
	* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
	* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
	* SUCH DAMAGE. */

	#include "curl_setup.h"

	#if defined(HAVE_GSSAPI) && !defined(CURL_DISABLE_FTP)

	#ifdef HAVE_NETDB_H
	#include <netdb.h>
	#endif

	#include "urldata.h"
	#include "curl_base64.h"
	#include "ftp.h"
	#include "curl_gssapi.h"
	#include "sendf.h"
	#include "curl_krb5.h"
	#include "warnless.h"
	#include "non-ascii.h"
	#include "strcase.h"
	#include "strdup.h"

	/* The last 3 #include files should be in this order */
	#include "curl_printf.h"
	#include "curl_memory.h"
	#include "memdebug.h"

	static CURLcode ftpsend(struct Curl_easy data, struct connectdata conn,
	const char *cmd)
	{
	ssize_t bytes_written;
	#define SBUF_SIZE 1024
	char s[SBUF_SIZE];
	size_t write_len;
	char *sptr = s;
	CURLcode result = CURLE_OK;
	#ifdef HAVE_GSSAPI
	enum protection_level data_sec = conn->data_prot;
	#endif

	if(!cmd)
	return CURLE_BAD_FUNCTION_ARGUMENT;

	write_len = strlen(cmd);
	if(!write_len \|\| write_len > (sizeof(s) -3))
	return CURLE_BAD_FUNCTION_ARGUMENT;

	memcpy(&s, cmd, write_len);
	strcpy(&s[write_len], "\r\n"); /* append a trailing CRLF */
	write_len += 2;
	bytes_written = 0;

	result = Curl_convert_to_network(data, s, write_len);
	/* Curl_convert_to_network calls failf if unsuccessful */
	if(result)
	return result;

	for(;;) {
	#ifdef HAVE_GSSAPI
	conn->data_prot = PROT_CMD;
	#endif
	result = Curl_write(data, conn->sock[FIRSTSOCKET], sptr, write_len,
	&bytes_written);
	#ifdef HAVE_GSSAPI
	DEBUGASSERT(data_sec > PROT_NONE && data_sec < PROT_LAST);
	conn->data_prot = data_sec;
	#endif

	if(result)
	break;

	Curl_debug(data, CURLINFO_HEADER_OUT, sptr, (size_t)bytes_written);

	if(bytes_written != (ssize_t)write_len) {
	write_len -= bytes_written;
	sptr += bytes_written;
	}
	else
	break;
	}

	return result;
	}

	static int
	krb5_init(void *app_data)
	{
	gss_ctx_id_t *context = app_data;
	/* Make sure our context is initialized for krb5_end. */
	*context = GSS_C_NO_CONTEXT;
	return 0;
	}

	static int
	krb5_check_prot(void *app_data, int level)
	{
	(void)app_data; /* unused */
	if(level == PROT_CONFIDENTIAL)
	return -1;
	return 0;
	}

	static int
	krb5_decode(void app_data, void buf, int len,
	int level UNUSED_PARAM,
	struct connectdata *conn UNUSED_PARAM)
	{
	gss_ctx_id_t *context = app_data;
	OM_uint32 maj, min;
	gss_buffer_desc enc, dec;

	(void)level;
	(void)conn;

	enc.value = buf;
	enc.length = len;
	maj = gss_unwrap(&min, *context, &enc, &dec, NULL, NULL);
	if(maj != GSS_S_COMPLETE) {
	if(len >= 4)
	strcpy(buf, "599 ");
	return -1;
	}

	memcpy(buf, dec.value, dec.length);
	len = curlx_uztosi(dec.length);
	gss_release_buffer(&min, &dec);

	return len;
	}

	static int
	krb5_encode(void app_data, const void from, int length, int level, void **to)
	{
	gss_ctx_id_t *context = app_data;
	gss_buffer_desc dec, enc;
	OM_uint32 maj, min;
	int state;
	int len;

	/* NOTE that the cast is safe, neither of the krb5, gnu gss and heimdal
	* libraries modify the input buffer in gss_wrap()
	*/
	dec.value = (void *)from;
	dec.length = length;
	maj = gss_wrap(&min, *context,
	level == PROT_PRIVATE,
	GSS_C_QOP_DEFAULT,
	&dec, &state, &enc);

	if(maj != GSS_S_COMPLETE)
	return -1;

	/* malloc a new buffer, in case gss_release_buffer doesn't work as
	expected */
	*to = malloc(enc.length);
	if(!*to)
	return -1;
	memcpy(*to, enc.value, enc.length);
	len = curlx_uztosi(enc.length);
	gss_release_buffer(&min, &enc);
	return len;
	}

	static int
	krb5_auth(void app_data, struct Curl_easy data, struct connectdata *conn)
	{
	int ret = AUTH_OK;
	char *p;
	const char *host = conn->host.name;
	ssize_t nread;
	curl_socklen_t l = sizeof(conn->local_addr);
	CURLcode result;
	const char *service = data->set.str[STRING_SERVICE_NAME] ?
	data->set.str[STRING_SERVICE_NAME] :
	"ftp";
	const char *srv_host = "host";
	gss_buffer_desc input_buffer, output_buffer, _gssresp, *gssresp;
	OM_uint32 maj, min;
	gss_name_t gssname;
	gss_ctx_id_t *context = app_data;
	struct gss_channel_bindings_struct chan;
	size_t base64_sz = 0;
	struct sockaddr_in **remote_addr =
	(struct sockaddr_in **)&conn->ip_addr->ai_addr;
	char *stringp;

	if(getsockname(conn->sock[FIRSTSOCKET],
	(struct sockaddr *)&conn->local_addr, &l) < 0)
	perror("getsockname()");

	chan.initiator_addrtype = GSS_C_AF_INET;
	chan.initiator_address.length = l - 4;
	chan.initiator_address.value = &conn->local_addr.sin_addr.s_addr;
	chan.acceptor_addrtype = GSS_C_AF_INET;
	chan.acceptor_address.length = l - 4;
	chan.acceptor_address.value = &(*remote_addr)->sin_addr.s_addr;
	chan.application_data.length = 0;
	chan.application_data.value = NULL;

	/* this loop will execute twice (once for service, once for host) */
	for(;;) {
	/* this really shouldn't be repeated here, but can't help it */
	if(service == srv_host) {
	result = ftpsend(data, conn, "AUTH GSSAPI");
	if(result)
	return -2;

	if(Curl_GetFTPResponse(data, &nread, NULL))
	return -1;

	if(data->state.buffer[0] != '3')
	return -1;
	}

	stringp = aprintf("%s@%s", service, host);
	if(!stringp)
	return -2;

	input_buffer.value = stringp;
	input_buffer.length = strlen(stringp);
	maj = gss_import_name(&min, &input_buffer, GSS_C_NT_HOSTBASED_SERVICE,
	&gssname);
	free(stringp);
	if(maj != GSS_S_COMPLETE) {
	gss_release_name(&min, &gssname);
	if(service == srv_host) {
	failf(data, "Error importing service name %s@%s", service, host);
	return AUTH_ERROR;
	}
	service = srv_host;
	continue;
	}
	/* We pass NULL as \|output_name_type\| to avoid a leak. */
	gss_display_name(&min, gssname, &output_buffer, NULL);
	infof(data, "Trying against %s", output_buffer.value);
	gssresp = GSS_C_NO_BUFFER;
	*context = GSS_C_NO_CONTEXT;

	do {
	/* Release the buffer at each iteration to avoid leaking: the first time
	we are releasing the memory from gss_display_name. The last item is
	taken care by a final gss_release_buffer. */
	gss_release_buffer(&min, &output_buffer);
	ret = AUTH_OK;
	maj = Curl_gss_init_sec_context(data,
	&min,
	context,
	gssname,
	&Curl_krb5_mech_oid,
	&chan,
	gssresp,
	&output_buffer,
	TRUE,
	NULL);

	if(gssresp) {
	free(_gssresp.value);
	gssresp = NULL;
	}

	if(GSS_ERROR(maj)) {
	infof(data, "Error creating security context");
	ret = AUTH_ERROR;
	break;
	}

	if(output_buffer.length) {
	char *cmd;

	result = Curl_base64_encode(data, (char *)output_buffer.value,
	output_buffer.length, &p, &base64_sz);
	if(result) {
	infof(data, "base64-encoding: %s", curl_easy_strerror(result));
	ret = AUTH_ERROR;
	break;
	}

	cmd = aprintf("ADAT %s", p);
	if(cmd)
	result = ftpsend(data, conn, cmd);
	else
	result = CURLE_OUT_OF_MEMORY;

	free(p);
	free(cmd);

	if(result) {
	ret = -2;
	break;
	}

	if(Curl_GetFTPResponse(data, &nread, NULL)) {
	ret = -1;
	break;
	}

	if(data->state.buffer[0] != '2' && data->state.buffer[0] != '3') {
	infof(data, "Server didn't accept auth data");
	ret = AUTH_ERROR;
	break;
	}

	_gssresp.value = NULL; /* make sure it is initialized */
	p = data->state.buffer + 4;
	p = strstr(p, "ADAT=");
	if(p) {
	result = Curl_base64_decode(p + 5,
	(unsigned char **)&_gssresp.value,
	&_gssresp.length);
	if(result) {
	failf(data, "base64-decoding: %s", curl_easy_strerror(result));
	ret = AUTH_CONTINUE;
	break;
	}
	}

	gssresp = &_gssresp;
	}
	} while(maj == GSS_S_CONTINUE_NEEDED);

	gss_release_name(&min, &gssname);
	gss_release_buffer(&min, &output_buffer);

	if(gssresp)
	free(_gssresp.value);

	if(ret == AUTH_OK \|\| service == srv_host)
	return ret;

	service = srv_host;
	}
	return ret;
	}

	static void krb5_end(void *app_data)
	{
	OM_uint32 min;
	gss_ctx_id_t *context = app_data;
	if(*context != GSS_C_NO_CONTEXT) {
	OM_uint32 maj = gss_delete_sec_context(&min, context, GSS_C_NO_BUFFER);
	(void)maj;
	DEBUGASSERT(maj == GSS_S_COMPLETE);
	}
	}

	static const struct Curl_sec_client_mech Curl_krb5_client_mech = {
	"GSSAPI",
	sizeof(gss_ctx_id_t),
	krb5_init,
	krb5_auth,
	krb5_end,
	krb5_check_prot,

	krb5_encode,
	krb5_decode
	};

	static const struct {
	enum protection_level level;
	const char *name;
	} level_names[] = {
	{ PROT_CLEAR, "clear" },
	{ PROT_SAFE, "safe" },
	{ PROT_CONFIDENTIAL, "confidential" },
	{ PROT_PRIVATE, "private" }
	};

	static enum protection_level
	name_to_level(const char *name)
	{
	int i;
	for(i = 0; i < (int)sizeof(level_names)/(int)sizeof(level_names[0]); i++)
	if(curl_strequal(name, level_names[i].name))
	return level_names[i].level;
	return PROT_NONE;
	}

	/* Convert a protocol \|level\| to its char representation.
	We take an int to catch programming mistakes. */
	static char level_to_char(int level)
	{
	switch(level) {
	case PROT_CLEAR:
	return 'C';
	case PROT_SAFE:
	return 'S';
	case PROT_CONFIDENTIAL:
	return 'E';
	case PROT_PRIVATE:
	return 'P';
	case PROT_CMD:
	/* Fall through */
	default:
	/* Those 2 cases should not be reached! */
	break;
	}
	DEBUGASSERT(0);
	/* Default to the most secure alternative. */
	return 'P';
	}

	/* Send an FTP command defined by \|message\| and the optional arguments. The
	function returns the ftp_code. If an error occurs, -1 is returned. */
	static int ftp_send_command(struct Curl_easy data, const char message, ...)
	{
	int ftp_code;
	ssize_t nread = 0;
	va_list args;
	char print_buffer[50];

	va_start(args, message);
	mvsnprintf(print_buffer, sizeof(print_buffer), message, args);
	va_end(args);

	if(ftpsend(data, data->conn, print_buffer)) {
	ftp_code = -1;
	}
	else {
	if(Curl_GetFTPResponse(data, &nread, &ftp_code))
	ftp_code = -1;
	}

	(void)nread; /* Unused */
	return ftp_code;
	}

	/* Read \|len\| from the socket \|fd\| and store it in \|to\|. Return a CURLcode
	saying whether an error occurred or CURLE_OK if \|len\| was read. */
	static CURLcode
	socket_read(curl_socket_t fd, void *to, size_t len)
	{
	char *to_p = to;
	CURLcode result;
	ssize_t nread = 0;

	while(len > 0) {
	result = Curl_read_plain(fd, to_p, len, &nread);
	if(!result) {
	len -= nread;
	to_p += nread;
	}
	else {
	if(result == CURLE_AGAIN)
	continue;
	return result;
	}
	}
	return CURLE_OK;
	}


	/* Write \|len\| bytes from the buffer \|to\| to the socket \|fd\|. Return a
	CURLcode saying whether an error occurred or CURLE_OK if \|len\| was
	written. */
	static CURLcode
	socket_write(struct Curl_easy data, curl_socket_t fd, const void to,
	size_t len)
	{
	const char *to_p = to;
	CURLcode result;
	ssize_t written;

	while(len > 0) {
	result = Curl_write_plain(data, fd, to_p, len, &written);
	if(!result) {
	len -= written;
	to_p += written;
	}
	else {
	if(result == CURLE_AGAIN)
	continue;
	return result;
	}
	}
	return CURLE_OK;
	}

	static CURLcode read_data(struct connectdata *conn,
	curl_socket_t fd,
	struct krb5buffer *buf)
	{
	int len;
	CURLcode result;

	result = socket_read(fd, &len, sizeof(len));
	if(result)
	return result;

	if(len) {
	/* only realloc if there was a length */
	len = ntohl(len);
	buf->data = Curl_saferealloc(buf->data, len);
	}
	if(!len \|\| !buf->data)
	return CURLE_OUT_OF_MEMORY;

	result = socket_read(fd, buf->data, len);
	if(result)
	return result;
	buf->size = conn->mech->decode(conn->app_data, buf->data, len,
	conn->data_prot, conn);
	buf->index = 0;
	return CURLE_OK;
	}

	static size_t
	buffer_read(struct krb5buffer buf, void data, size_t len)
	{
	if(buf->size - buf->index < len)
	len = buf->size - buf->index;
	memcpy(data, (char *)buf->data + buf->index, len);
	buf->index += len;
	return len;
	}

	/* Matches Curl_recv signature */
	static ssize_t sec_recv(struct Curl_easy *data, int sockindex,
	char buffer, size_t len, CURLcode err)
	{
	size_t bytes_read;
	size_t total_read = 0;
	struct connectdata *conn = data->conn;
	curl_socket_t fd = conn->sock[sockindex];

	*err = CURLE_OK;

	/* Handle clear text response. */
	if(conn->sec_complete == 0 \|\| conn->data_prot == PROT_CLEAR)
	return sread(fd, buffer, len);

	if(conn->in_buffer.eof_flag) {
	conn->in_buffer.eof_flag = 0;
	return 0;
	}

	bytes_read = buffer_read(&conn->in_buffer, buffer, len);
	len -= bytes_read;
	total_read += bytes_read;
	buffer += bytes_read;

	while(len > 0) {
	if(read_data(conn, fd, &conn->in_buffer))
	return -1;
	if(conn->in_buffer.size == 0) {
	if(bytes_read > 0)
	conn->in_buffer.eof_flag = 1;
	return bytes_read;
	}
	bytes_read = buffer_read(&conn->in_buffer, buffer, len);
	len -= bytes_read;
	total_read += bytes_read;
	buffer += bytes_read;
	}
	return total_read;
	}

	/* Send \|length\| bytes from \|from\| to the \|fd\| socket taking care of encoding
	and negotiating with the server. \|from\| can be NULL. */
	static void do_sec_send(struct Curl_easy data, struct connectdata conn,
	curl_socket_t fd, const char *from, int length)
	{
	int bytes, htonl_bytes; /* 32-bit integers for htonl */
	char *buffer = NULL;
	char *cmd_buffer;
	size_t cmd_size = 0;
	CURLcode error;
	enum protection_level prot_level = conn->data_prot;
	bool iscmd = (prot_level == PROT_CMD)?TRUE:FALSE;

	DEBUGASSERT(prot_level > PROT_NONE && prot_level < PROT_LAST);

	if(iscmd) {
	if(!strncmp(from, "PASS ", 5) \|\| !strncmp(from, "ACCT ", 5))
	prot_level = PROT_PRIVATE;
	else
	prot_level = conn->command_prot;
	}
	bytes = conn->mech->encode(conn->app_data, from, length, prot_level,
	(void **)&buffer);
	if(!buffer \|\| bytes <= 0)
	return; /* error */

	if(iscmd) {
	error = Curl_base64_encode(data, buffer, curlx_sitouz(bytes),
	&cmd_buffer, &cmd_size);
	if(error) {
	free(buffer);
	return; /* error */
	}
	if(cmd_size > 0) {
	static const char *enc = "ENC ";
	static const char *mic = "MIC ";
	if(prot_level == PROT_PRIVATE)
	socket_write(data, fd, enc, 4);
	else
	socket_write(data, fd, mic, 4);

	socket_write(data, fd, cmd_buffer, cmd_size);
	socket_write(data, fd, "\r\n", 2);
	infof(data, "Send: %s%s", prot_level == PROT_PRIVATE?enc:mic,
	cmd_buffer);
	free(cmd_buffer);
	}
	}
	else {
	htonl_bytes = htonl(bytes);
	socket_write(data, fd, &htonl_bytes, sizeof(htonl_bytes));
	socket_write(data, fd, buffer, curlx_sitouz(bytes));
	}
	free(buffer);
	}

	static ssize_t sec_write(struct Curl_easy data, struct connectdata conn,
	curl_socket_t fd, const char *buffer, size_t length)
	{
	ssize_t tx = 0, len = conn->buffer_size;

	if(len <= 0)
	len = length;
	while(length) {
	if(length < (size_t)len)
	len = length;

	do_sec_send(data, conn, fd, buffer, curlx_sztosi(len));
	length -= len;
	buffer += len;
	tx += len;
	}
	return tx;
	}

	/* Matches Curl_send signature */
	static ssize_t sec_send(struct Curl_easy *data, int sockindex,
	const void buffer, size_t len, CURLcode err)
	{
	struct connectdata *conn = data->conn;
	curl_socket_t fd = conn->sock[sockindex];
	*err = CURLE_OK;
	return sec_write(data, conn, fd, buffer, len);
	}

	int Curl_sec_read_msg(struct Curl_easy data, struct connectdata conn,
	char *buffer, enum protection_level level)
	{
	/* decoded_len should be size_t or ssize_t but conn->mech->decode returns an
	int */
	int decoded_len;
	char *buf;
	int ret_code = 0;
	size_t decoded_sz = 0;
	CURLcode error;

	(void) data;

	if(!conn->mech)
	/* not initialized, return error */
	return -1;

	DEBUGASSERT(level > PROT_NONE && level < PROT_LAST);

	error = Curl_base64_decode(buffer + 4, (unsigned char **)&buf, &decoded_sz);
	if(error \|\| decoded_sz == 0)
	return -1;

	if(decoded_sz > (size_t)INT_MAX) {
	free(buf);
	return -1;
	}
	decoded_len = curlx_uztosi(decoded_sz);

	decoded_len = conn->mech->decode(conn->app_data, buf, decoded_len,
	level, conn);
	if(decoded_len <= 0) {
	free(buf);
	return -1;
	}

	{
	buf[decoded_len] = '\n';
	Curl_debug(data, CURLINFO_HEADER_IN, buf, decoded_len + 1);
	}

	buf[decoded_len] = '\0';
	if(decoded_len <= 3)
	/* suspiciously short */
	return 0;

	if(buf[3] != '-')
	/* safe to ignore return code */
	(void)sscanf(buf, "%d", &ret_code);

	if(buf[decoded_len - 1] == '\n')
	buf[decoded_len - 1] = '\0';
	strcpy(buffer, buf);
	free(buf);
	return ret_code;
	}

	static int sec_set_protection_level(struct Curl_easy *data)
	{
	int code;
	struct connectdata *conn = data->conn;
	enum protection_level level = conn->request_data_prot;

	DEBUGASSERT(level > PROT_NONE && level < PROT_LAST);

	if(!conn->sec_complete) {
	infof(data, "Trying to change the protection level after the"
	" completion of the data exchange.");
	return -1;
	}

	/* Bail out if we try to set up the same level */
	if(conn->data_prot == level)
	return 0;

	if(level) {
	char *pbsz;
	unsigned int buffer_size = 1 << 20; /* 1048576 */

	code = ftp_send_command(data, "PBSZ %u", buffer_size);
	if(code < 0)
	return -1;

	if(code/100 != 2) {
	failf(data, "Failed to set the protection's buffer size.");
	return -1;
	}
	conn->buffer_size = buffer_size;

	pbsz = strstr(data->state.buffer, "PBSZ=");
	if(pbsz) {
	/* ignore return code, use default value if it fails */
	(void)sscanf(pbsz, "PBSZ=%u", &buffer_size);
	if(buffer_size < conn->buffer_size)
	conn->buffer_size = buffer_size;
	}
	}

	/* Now try to negotiate the protection level. */
	code = ftp_send_command(data, "PROT %c", level_to_char(level));

	if(code < 0)
	return -1;

	if(code/100 != 2) {
	failf(data, "Failed to set the protection level.");
	return -1;
	}

	conn->data_prot = level;
	if(level == PROT_PRIVATE)
	conn->command_prot = level;

	return 0;
	}

	int
	Curl_sec_request_prot(struct connectdata conn, const char level)
	{
	enum protection_level l = name_to_level(level);
	if(l == PROT_NONE)
	return -1;
	DEBUGASSERT(l > PROT_NONE && l < PROT_LAST);
	conn->request_data_prot = l;
	return 0;
	}

	static CURLcode choose_mech(struct Curl_easy data, struct connectdata conn)
	{
	int ret;
	void *tmp_allocation;
	const struct Curl_sec_client_mech *mech = &Curl_krb5_client_mech;

	tmp_allocation = realloc(conn->app_data, mech->size);
	if(!tmp_allocation) {
	failf(data, "Failed realloc of size %zu", mech->size);
	mech = NULL;
	return CURLE_OUT_OF_MEMORY;
	}
	conn->app_data = tmp_allocation;

	if(mech->init) {
	ret = mech->init(conn->app_data);
	if(ret) {
	infof(data, "Failed initialization for %s. Skipping it.",
	mech->name);
	return CURLE_FAILED_INIT;
	}
	}

	infof(data, "Trying mechanism %s...", mech->name);
	ret = ftp_send_command(data, "AUTH %s", mech->name);
	if(ret < 0)
	return CURLE_COULDNT_CONNECT;

	if(ret/100 != 3) {
	switch(ret) {
	case 504:
	infof(data, "Mechanism %s is not supported by the server (server "
	"returned ftp code: 504).", mech->name);
	break;
	case 534:
	infof(data, "Mechanism %s was rejected by the server (server returned "
	"ftp code: 534).", mech->name);
	break;
	default:
	if(ret/100 == 5) {
	infof(data, "server does not support the security extensions");
	return CURLE_USE_SSL_FAILED;
	}
	break;
	}
	return CURLE_LOGIN_DENIED;
	}

	/* Authenticate */
	ret = mech->auth(conn->app_data, data, conn);

	if(ret != AUTH_CONTINUE) {
	if(ret != AUTH_OK) {
	/* Mechanism has dumped the error to stderr, don't error here. */
	return CURLE_USE_SSL_FAILED;
	}
	DEBUGASSERT(ret == AUTH_OK);

	conn->mech = mech;
	conn->sec_complete = 1;
	conn->recv[FIRSTSOCKET] = sec_recv;
	conn->send[FIRSTSOCKET] = sec_send;
	conn->recv[SECONDARYSOCKET] = sec_recv;
	conn->send[SECONDARYSOCKET] = sec_send;
	conn->command_prot = PROT_SAFE;
	/* Set the requested protection level */
	/* BLOCKING */
	(void)sec_set_protection_level(data);
	}

	return CURLE_OK;
	}

	CURLcode
	Curl_sec_login(struct Curl_easy data, struct connectdata conn)
	{
	return choose_mech(data, conn);
	}


	void
	Curl_sec_end(struct connectdata *conn)
	{
	if(conn->mech != NULL && conn->mech->end)
	conn->mech->end(conn->app_data);
	free(conn->app_data);
	conn->app_data = NULL;
	if(conn->in_buffer.data) {
	free(conn->in_buffer.data);
	conn->in_buffer.data = NULL;
	conn->in_buffer.size = 0;
	conn->in_buffer.index = 0;
	conn->in_buffer.eof_flag = 0;
	}
	conn->sec_complete = 0;
	conn->data_prot = PROT_CLEAR;
	conn->mech = NULL;
	}

	#endif /* HAVE_GSSAPI && !CURL_DISABLE_FTP */