DCC: fix taint-handling

1 files changed, 190 insertions, 235 deletions

diff --git a/src/src/dcc.c b/src/src/dcc.c
index 4c86c092b..055f36e93 100644
--- a/src/src/dcc.c
+++ b/src/src/dcc.c
@@ -2,17 +2,14 @@
 *     Exim - an Internet mail transport agent    *
 *************************************************/
 
-/* Copyright (c) Wolfgang Breyha 2005 - 2015
+/* Copyright (c) Wolfgang Breyha 2005 - 2019
  * Vienna University Computer Center
  * wbreyha@gmx.net
  * See the file NOTICE for conditions of use and distribution.
  *
- * Copyright (c) The Exim Maintainers 2015 - 2018
+ * Copyright (c) The Exim Maintainers 2015 - 2019
  */
 
-/* This patch is based on code from Tom Kistners exiscan (ACL integration) and
- * the DCC local_scan patch from Christopher Bodenstein */
-
 /* Code for calling dccifd. Called from acl.c. */
 
 #include "exim.h"
@@ -20,28 +17,28 @@
 #include "dcc.h"
 #include "unistd.h"
 
-uschar dcc_header_str[256];
+#define DCC_HEADER_LIMIT 120
+
 int dcc_ok = 0;
 int dcc_rc = 0;
 
 /* This function takes a file descriptor and a buffer as input and
  * returns either 0 for success or errno in case of error. */
 
-int flushbuffer (int socket, uschar *buffer)
- {
+int flushbuffer (int socket, gstring *buffer)
+{
   int retval, rsp;
-  rsp = write(socket, buffer, Ustrlen(buffer));
+  rsp = write(socket, buffer->s, buffer->ptr);
   DEBUG(D_acl)
-    debug_printf("DCC: Result of the write() = %d\n", rsp);
-  if(rsp < 0)
-  {
+    debug_printf("DCC: flushbuffer(): Result of the write() = %d\n", rsp);
+  if(rsp < 0) {
     DEBUG(D_acl)
-      debug_printf("DCC: Error writing buffer to socket: %s\n", strerror(errno));
+      debug_printf("DCC: flushbuffer(): Error writing buffer to socket: %s\n", strerror(errno));
     retval = errno;
   }
   else {
     DEBUG(D_acl)
-      debug_printf("DCC: Wrote buffer to socket:\n%s\n", buffer);
+      debug_printf("DCC: flushbuffer(): Wrote buffer to socket:\n%.*s\n", buffer->ptr, buffer->s);
     retval = 0;
   }
   return retval;
@@ -55,38 +52,32 @@ dcc_process(uschar **listptr)
   FILE *data_file;
   uschar *dcc_default_ip_option = US"127.0.0.1";
   uschar *dcc_helo_option = US"localhost";
-  uschar *dcc_reject_message = US"Rejected by DCC";
   uschar *xtra_hdrs = NULL;
   uschar *override_client_ip  = NULL;
 
   /* from local_scan */
-  int j, k, c, retval, sockfd, resp, line;
+  int dcc_resplen, retval, sockfd, resp;
   unsigned int portnr;
   struct sockaddr_un  serv_addr;
   struct sockaddr_in  serv_addr_in;
   struct hostent *ipaddress;
   uschar sockpath[128];
   uschar sockip[40], client_ip[40];
-  uschar opts[128];
-  uschar rcpt[128], from[128];
-  uschar sendbuf[4096];
-  uschar recvbuf[4096];
-  uschar dcc_return_text[1024];
-  struct header_line *dcchdr;
+  gstring *dcc_headers;
+  gstring *sendbuf;
+  uschar *dcc_return_text;
+  struct header_line *mail_headers;
   uschar *dcc_acl_options;
-  uschar dcc_acl_options_buffer[10];
-  uschar dcc_xtra_hdrs[1024];
+  gstring *dcc_xtra_hdrs;
+  gstring *dcc_header_str;
 
   /* grep 1st option */
-  if ((dcc_acl_options = string_nextinlist(&list, &sep,
-		   dcc_acl_options_buffer, sizeof(dcc_acl_options_buffer))))
-    {
+  if ((dcc_acl_options = string_nextinlist(&list, &sep, NULL, 0))) {
     /* parse 1st option */
     if (  strcmpic(dcc_acl_options, US"false") == 0
-       || Ustrcmp(dcc_acl_options, "0") == 0
-       )
+       || Ustrcmp(dcc_acl_options, "0") == 0)
       return FAIL;	/* explicitly no matching */
-    }
+  }
   else
     return FAIL;	/* empty means "don't match anything" */
 
@@ -97,23 +88,20 @@ dcc_process(uschar **listptr)
     return dcc_rc;
 
   /* open the spooled body */
-  for (int i = 0; i < 2; i++)
-    {
+  for (int i = 0; i < 2; i++) {
     uschar message_subdir[2];
     set_subdir_str(message_subdir, message_id, i);
     if ((data_file = Ufopen(
-	    spool_fname(US"input", message_subdir, message_id, US"-D"),
-	    "rb")))
+	    spool_fname(US"input", message_subdir, message_id, US"-D"), "rb")))
       break;
-    }
+  }
 
-  if (!data_file)
-    {
+  if (!data_file) {
     /* error while spooling */
     log_write(0, LOG_MAIN|LOG_PANIC,
-           "dcc acl condition: error while opening spool file");
+           "DCC: error while opening spool file");
     return DEFER;
-    }
+  }
 
   /* Initialize the variables */
 
@@ -124,16 +112,15 @@ dcc_process(uschar **listptr)
     else
       if( sscanf(CS dccifd_address, "%s %u", sockip, &portnr) != 2) {
         log_write(0, LOG_MAIN,
-          "dcc acl condition: warning - invalid dccifd address: '%s'", dccifd_address);
+          "DCC: warning - invalid dccifd address: '%s'", dccifd_address);
         (void)fclose(data_file);
         return DEFER;
       }
   }
 
-  /* opts is what we send as dccifd options - see man dccifd */
+  /* dcc_headers is what we send as dccifd options - see man dccifd */
   /* We don't support any other option than 'header' so just copy that */
-  bzero(opts,sizeof(opts));
-  Ustrncpy(opts, dccifd_options, sizeof(opts)-1);
+  dcc_headers = string_cat(NULL, dccifd_options);
   /* if $acl_m_dcc_override_client_ip is set use it */
   if (((override_client_ip = expand_string(US"$acl_m_dcc_override_client_ip")) != NULL) &&
        (override_client_ip[0] != '\0')) {
@@ -153,42 +140,30 @@ dcc_process(uschar **listptr)
     DEBUG(D_acl)
       debug_printf("DCC: Client IP (default): %s\n", client_ip);
   }
-  /* strncat(opts, my_request, strlen(my_request)); */
-  Ustrcat(opts, US"\n");
-  Ustrncat(opts, client_ip, sizeof(opts)-Ustrlen(opts)-1);
-  Ustrncat(opts, US"\nHELO ", sizeof(opts)-Ustrlen(opts)-1);
-  Ustrncat(opts, dcc_helo_option, sizeof(opts)-Ustrlen(opts)-2);
-  Ustrcat(opts, US"\n");
+  /* build options block */
+  dcc_headers = string_append(dcc_headers, 5, US"\n", client_ip, US"\nHELO ", dcc_helo_option, US"\n");
 
   /* initialize the other variables */
-  dcchdr = header_list;
+  mail_headers = header_list;
   /* we set the default return value to DEFER */
   retval = DEFER;
 
-  bzero(sendbuf,sizeof(sendbuf));
-  bzero(dcc_header_str,sizeof(dcc_header_str));
-  bzero(rcpt,sizeof(rcpt));
-  bzero(from,sizeof(from));
-
   /* send a null return path as "<>". */
-  if (Ustrlen(sender_address) > 0)
-    Ustrncpy(from, sender_address, sizeof(from));
-  else
-    Ustrncpy(from, US"<>", sizeof(from));
-  Ustrncat(from, US"\n", sizeof(from)-Ustrlen(from)-1);
+  dcc_headers = string_cat (dcc_headers, *sender_address ? sender_address : US"<>");
+  dcc_headers = string_catn(dcc_headers, US"\n", 1);
 
   /**************************************
    * Now creating the socket connection *
    **************************************/
 
   /* If sockip contains an ip, we use a tcp socket, otherwise a UNIX socket */
-  if(Ustrcmp(sockip, "")){
+  if(Ustrcmp(sockip, "")) {
     ipaddress = gethostbyname(CS sockip);
     bzero(CS  &serv_addr_in, sizeof(serv_addr_in));
     serv_addr_in.sin_family = AF_INET;
     bcopy(CS ipaddress->h_addr, CS &serv_addr_in.sin_addr.s_addr, ipaddress->h_length);
     serv_addr_in.sin_port = htons(portnr);
-    if ((sockfd = socket(AF_INET, SOCK_STREAM,0)) < 0){
+    if ((sockfd = socket(AF_INET, SOCK_STREAM,0)) < 0) {
       DEBUG(D_acl)
         debug_printf("DCC: Creating TCP socket connection failed: %s\n", strerror(errno));
       log_write(0,LOG_PANIC,"DCC: Creating TCP socket connection failed: %s\n", strerror(errno));
@@ -197,7 +172,7 @@ dcc_process(uschar **listptr)
       return retval;
     }
     /* Now connecting the socket (INET) */
-    if (connect(sockfd, (struct sockaddr *)&serv_addr_in, sizeof(serv_addr_in)) < 0){
+    if (connect(sockfd, (struct sockaddr *)&serv_addr_in, sizeof(serv_addr_in)) < 0) {
       DEBUG(D_acl)
         debug_printf("DCC: Connecting to TCP socket failed: %s\n", strerror(errno));
       log_write(0,LOG_PANIC,"DCC: Connecting to TCP socket failed: %s\n", strerror(errno));
@@ -205,12 +180,13 @@ dcc_process(uschar **listptr)
       (void)fclose(data_file);
       return retval;
     }
-  } else {
+  }
+  else {
     /* connecting to the dccifd UNIX socket */
     bzero(&serv_addr, sizeof(serv_addr));
     serv_addr.sun_family = AF_UNIX;
     Ustrncpy(US serv_addr.sun_path, sockpath, sizeof(serv_addr.sun_path));
-    if ((sockfd = socket(AF_UNIX, SOCK_STREAM,0)) < 0){
+    if ((sockfd = socket(AF_UNIX, SOCK_STREAM,0)) < 0) {
       DEBUG(D_acl)
         debug_printf("DCC: Creating UNIX socket connection failed: %s\n", strerror(errno));
       log_write(0,LOG_PANIC,"DCC: Creating UNIX socket connection failed: %s\n", strerror(errno));
@@ -219,9 +195,9 @@ dcc_process(uschar **listptr)
       return retval;
     }
     /* Now connecting the socket (UNIX) */
-    if (connect(sockfd, (struct sockaddr *) &serv_addr, sizeof(serv_addr)) < 0){
+    if (connect(sockfd, (struct sockaddr *) &serv_addr, sizeof(serv_addr)) < 0) {
       DEBUG(D_acl)
-                            debug_printf("DCC: Connecting to UNIX socket failed: %s\n", strerror(errno));
+        debug_printf("DCC: Connecting to UNIX socket failed: %s\n", strerror(errno));
       log_write(0,LOG_PANIC,"DCC: Connecting to UNIX socket failed: %s\n", strerror(errno));
       /* if we cannot contact the socket, defer the mail */
       (void)fclose(data_file);
@@ -230,93 +206,66 @@ dcc_process(uschar **listptr)
   }
   /* the socket is open, now send the options to dccifd*/
   DEBUG(D_acl)
-    debug_printf("\nDCC: ---------------------------\nDCC: Socket opened; now sending input\nDCC: -----------------\n");
-  /* First, fill in the input buffer */
-  Ustrncpy(sendbuf, opts, sizeof(sendbuf));
-  Ustrncat(sendbuf, from, sizeof(sendbuf)-Ustrlen(sendbuf)-1);
-
-  DEBUG(D_acl)
-  {
-    debug_printf("DCC: opts = %s\nDCC: sender = %s\nDCC: rcpt count = %d\n", opts, from, recipients_count);
-    debug_printf("DCC: Sending options:\nDCC: ****************************\n");
-  }
+    debug_printf("DCC: -----------------------------------\nDCC: Socket opened; now sending input\n"
+                 "DCC: -----------------------------------\n");
 
   /* let's send each of the recipients to dccifd */
-  for (int i = 0; i < recipients_count; i++){
+  for (int i = 0; i < recipients_count; i++) {
     DEBUG(D_acl)
       debug_printf("DCC: recipient = %s\n",recipients_list[i].address);
-    if(Ustrlen(sendbuf) + Ustrlen(recipients_list[i].address) > sizeof(sendbuf))
-    {
-      DEBUG(D_acl)
-        debug_printf("DCC: Writing buffer: %s\n", sendbuf);
-      flushbuffer(sockfd, sendbuf);
-      bzero(sendbuf, sizeof(sendbuf));
-    }
-    Ustrncat(sendbuf, recipients_list[i].address, sizeof(sendbuf)-Ustrlen(sendbuf)-1);
-    Ustrncat(sendbuf, US"\r\n", sizeof(sendbuf)-Ustrlen(sendbuf)-1);
+    dcc_headers = string_append(dcc_headers, 2, recipients_list[i].address, "\n");
   }
   /* send a blank line between options and message */
-  Ustrncat(sendbuf, US"\n", sizeof(sendbuf)-Ustrlen(sendbuf)-1);
+  dcc_headers = string_catn(dcc_headers, US"\n", 1);
   /* Now we send the input buffer */
+  (void) string_from_gstring(dcc_headers);
   DEBUG(D_acl)
-    debug_printf("DCC: %s\nDCC: ****************************\n", sendbuf);
-  flushbuffer(sockfd, sendbuf);
+    debug_printf("DCC: ***********************************\nDCC: Sending options:\n%s"
+                 "DCC: ***********************************\n", dcc_headers->s);
+  if (flushbuffer(sockfd, dcc_headers) != 0) {
+      (void)fclose(data_file);
+      return retval;
+  }
 
   /* now send the message */
-  /* Clear the input buffer */
-  bzero(sendbuf, sizeof(sendbuf));
   /* First send the headers */
-  /* Now send the headers */
   DEBUG(D_acl)
-    debug_printf("DCC: Sending headers:\nDCC: ****************************\n");
-  Ustrncpy(sendbuf, dcchdr->text, sizeof(sendbuf)-2);
-  while((dcchdr=dcchdr->next)) {
-    if(dcchdr->slen > sizeof(sendbuf)-2) {
-      /* The size of the header is bigger than the size of
-       * the input buffer, so split it up in smaller parts. */
-       flushbuffer(sockfd, sendbuf);
-       bzero(sendbuf, sizeof(sendbuf));
-       j = 0;
-       while(j < dcchdr->slen)
-       {
-        for(int i = 0; i < sizeof(sendbuf)-2; i++) {
-          sendbuf[i] = dcchdr->text[j];
-          j++;
-        }
-        flushbuffer(sockfd, sendbuf);
-        bzero(sendbuf, sizeof(sendbuf));
-       }
-    } else if(Ustrlen(sendbuf) + dcchdr->slen > sizeof(sendbuf)-2) {
-      flushbuffer(sockfd, sendbuf);
-      bzero(sendbuf, sizeof(sendbuf));
-      Ustrncpy(sendbuf, dcchdr->text, sizeof(sendbuf)-2);
-    } else {
-      Ustrncat(sendbuf, dcchdr->text, sizeof(sendbuf)-Ustrlen(sendbuf)-2);
-    }
+    debug_printf("DCC: ***********************************\nDCC: Sending headers:\n");
+  sendbuf = string_get(8192);
+  sendbuf = string_catn(sendbuf, mail_headers->text, mail_headers->slen);
+  while((mail_headers=mail_headers->next)) {
+    sendbuf = string_catn(sendbuf, mail_headers->text, mail_headers->slen);
   }
 
   /* a blank line separates header from body */
-  Ustrncat(sendbuf, US"\n", sizeof(sendbuf)-Ustrlen(sendbuf)-1);
-  flushbuffer(sockfd, sendbuf);
+  sendbuf = string_catn(sendbuf, US"\r\n", 2);
+  (void) string_from_gstring(sendbuf);
+  gstring_release_unused(sendbuf);
   DEBUG(D_acl)
-    debug_printf("\nDCC: ****************************\n%s", sendbuf);
-
-  /* Clear the input buffer */
-  bzero(sendbuf, sizeof(sendbuf));
+    debug_printf("%sDCC: ***********************************\n", sendbuf->s);
+  if (flushbuffer(sockfd, sendbuf) != 0) {
+      (void)fclose(data_file);
+      return retval;
+  }
 
   /* now send the body */
   DEBUG(D_acl)
-    debug_printf("DCC: Writing body:\nDCC: ****************************\n");
+    debug_printf("DCC: ***********************************\nDCC: Writing body:\n");
   (void)fseek(data_file, SPOOL_DATA_START_OFFSET, SEEK_SET);
-  while((fread(sendbuf, 1, sizeof(sendbuf)-1, data_file)) > 0) {
-    flushbuffer(sockfd, sendbuf);
-    bzero(sendbuf, sizeof(sendbuf));
+
+  gstring filebuf = { .size = big_buffer_size, .ptr = 0, .s = big_buffer };
+
+  while((filebuf.ptr = fread(filebuf.s, 1, filebuf.size, data_file)) > 0) {
+    if (flushbuffer(sockfd, &filebuf) != 0) {
+        (void)fclose(data_file);
+        return retval;
+    }
   }
   DEBUG(D_acl)
-    debug_printf("\nDCC: ****************************\n");
+    debug_printf("DCC: ***********************************\n");
 
   /* shutdown() the socket */
-  if(shutdown(sockfd, 1) < 0){
+  if(shutdown(sockfd, SHUT_WR) < 0) {
     DEBUG(D_acl)
       debug_printf("DCC: Couldn't shutdown socket: %s\n", strerror(errno));
     log_write(0,LOG_MAIN,"DCC: Couldn't shutdown socket: %s\n", strerror(errno));
@@ -326,13 +275,14 @@ dcc_process(uschar **listptr)
     return retval;
   }
   DEBUG(D_acl)
-    debug_printf("\nDCC: -------------------------\nDCC: Input sent.\nDCC: -------------------------\n");
+    debug_printf("DCC: Input sent.\n"
+                 "DCC: +++++++++++++++++++++++++++++++++++\n"
+                 "DCC: Now receiving output from server\n"
+                 "DCC: -----------------------------------\n");
 
-    /********************************
+  /********************************
    * receiving output from dccifd *
    ********************************/
-  DEBUG(D_acl)
-    debug_printf("\nDCC: -------------------------------------\nDCC: Now receiving output from server\nDCC: -----------------------------------\n");
 
   /******************************************************************
    * We should get 3 lines:                                         *
@@ -344,91 +294,100 @@ dcc_process(uschar **listptr)
    * 3/ Third line contains the X-DCC header.                       *
    ******************************************************************/
 
-  line = 1;    /* we start at the first line of the output */
-  j = 0;       /* will be used as index for the recipients list */
-  k = 0;       /* initializing the index of the X-DCC header: dcc_header_str[k] */
+  int line = 1;    /* we start at the first line of the output */
+  int bufoffset;
 
+  dcc_header_str = string_get(DCC_HEADER_LIMIT + 2);
   /* Let's read from the socket until there's nothing left to read */
-  bzero(recvbuf, sizeof(recvbuf));
-  while((resp = read(sockfd, recvbuf, sizeof(recvbuf)-1)) > 0) {
-    /* How much did we get from the socket */
-    c = Ustrlen(recvbuf) + 1;
+  while((dcc_resplen = read(sockfd, big_buffer, big_buffer_size-1)) > 0) {
+    /* fail on read error */
+    if(dcc_resplen < 0) {
+      DEBUG(D_acl)
+        debug_printf("DCC: Error reading from socket: %s\n", strerror(errno));
+      (void)fclose(data_file);
+      return retval;
+    }
+    /* make the answer 0-terminated. only needed for debug_printf */
     DEBUG(D_acl)
-      debug_printf("DCC: Length of the output buffer is: %d\nDCC: Output buffer is:\nDCC: ------------\nDCC: %s\nDCC: -----------\n", c, recvbuf);
+      debug_printf("DCC: Length of the output buffer is: %d\nDCC: Output buffer is:\n"
+                   "DCC: -----------------------------------\n%.*s\n"
+                   "DCC: -----------------------------------\n", dcc_resplen, dcc_resplen, big_buffer);
 
     /* Now let's read each character and see what we've got */
-    for(int i = 0; i < c; i++) {
+    for(bufoffset = 0; bufoffset < dcc_resplen, line <= 2; bufoffset++) {
       /* First check if we reached the end of the line and
        * then increment the line counter */
-      if(recvbuf[i] == '\n')
+      if(big_buffer[bufoffset] == '\n')
         line++;
       else {
         /* The first character of the first line is the
          * overall response. If there's another character
          * on that line it is not correct. */
         if(line == 1) {
-          if(i == 0) {
+          if(bufoffset == 0) {
             /* Now get the value and set the
              * return value accordingly */
-            if(recvbuf[i] == 'A') {
-              DEBUG(D_acl)
-                debug_printf("DCC: Overall result = A\treturning OK\n");
-              Ustrcpy(dcc_return_text, US"Mail accepted by DCC");
-              dcc_result = US"A";
-              retval = OK;
-            }
-            else if(recvbuf[i] == 'R') {
-              DEBUG(D_acl)
-                debug_printf("DCC: Overall result = R\treturning FAIL\n");
-              dcc_result = US"R";
-              retval = FAIL;
-              if(sender_host_name) {
-                log_write(0, LOG_MAIN, "H=%s [%s] F=<%s>: rejected by DCC", sender_host_name, sender_host_address, sender_address);
-              }
-              else {
-                log_write(0, LOG_MAIN, "H=[%s] F=<%s>: rejected by DCC", sender_host_address, sender_address);
-              }
-              Ustrncpy(dcc_return_text, dcc_reject_message, Ustrlen(dcc_reject_message) + 1);
-            }
-            else if(recvbuf[i] == 'S') {
-              DEBUG(D_acl)
-                debug_printf("DCC: Overall result  = S\treturning OK\n");
-              Ustrcpy(dcc_return_text, US"Not all recipients accepted by DCC");
-              /* Since we're in an ACL we want a global result
-               * so we accept for all */
-              dcc_result = US"A";
-              retval = OK;
-            }
-            else if(recvbuf[i] == 'G') {
-              DEBUG(D_acl)
-                debug_printf("DCC: Overall result  = G\treturning FAIL\n");
-              Ustrcpy(dcc_return_text, US"Greylisted by DCC");
-              dcc_result = US"G";
-              retval = FAIL;
-            }
-            else if(recvbuf[i] == 'T') {
-              DEBUG(D_acl)
-                debug_printf("DCC: Overall result = T\treturning DEFER\n");
-              retval = DEFER;
-              log_write(0,LOG_MAIN,"Temporary error with DCC: %s\n", recvbuf);
-              Ustrcpy(dcc_return_text, US"Temporary error with DCC");
-              dcc_result = US"T";
-            }
-            else {
-              DEBUG(D_acl)
-                debug_printf("DCC: Overall result = something else\treturning DEFER\n");
-              retval = DEFER;
-              log_write(0,LOG_MAIN,"Unknown DCC response: %s\n", recvbuf);
-              Ustrcpy(dcc_return_text, US"Unknown DCC response");
-              dcc_result = US"T";
+            switch(big_buffer[bufoffset]) {
+              case 'A':
+                DEBUG(D_acl)
+                  debug_printf("DCC: Overall result = A\treturning OK\n");
+                dcc_return_text = US"Mail accepted by DCC";
+                dcc_result = US"A";
+                retval = OK;
+                break;
+              case 'R':
+                DEBUG(D_acl)
+                  debug_printf("DCC: Overall result = R\treturning FAIL\n");
+                dcc_return_text = US"Rejected by DCC";
+                dcc_result = US"R";
+                retval = FAIL;
+                if(sender_host_name)
+                  log_write(0, LOG_MAIN, "H=%s [%s] F=<%s>: rejected by DCC",
+                             sender_host_name, sender_host_address, sender_address);
+                else
+                  log_write(0, LOG_MAIN, "H=[%s] F=<%s>: rejected by DCC",
+                             sender_host_address, sender_address);
+                break;
+              case 'S':
+                DEBUG(D_acl)
+                  debug_printf("DCC: Overall result  = S\treturning OK\n");
+                dcc_return_text = US"Not all recipients accepted by DCC";
+                /* Since we're in an ACL we want a global result
+                 * so we accept for all */
+                dcc_result = US"A";
+                retval = OK;
+                break;
+              case 'G':
+                DEBUG(D_acl)
+                  debug_printf("DCC: Overall result  = G\treturning FAIL\n");
+                dcc_return_text = US"Greylisted by DCC";
+                dcc_result = US"G";
+                retval = FAIL;
+                break;
+              case 'T':
+                DEBUG(D_acl)
+                  debug_printf("DCC: Overall result = T\treturning DEFER\n");
+                dcc_return_text = US"Temporary error with DCC";
+                dcc_result = US"T";
+                retval = DEFER;
+                log_write(0,LOG_MAIN,"Temporary error with DCC: %s\n", big_buffer);
+                break;
+              default:
+                DEBUG(D_acl)
+                  debug_printf("DCC: Overall result = something else\treturning DEFER\n");
+		dcc_return_text = US"Unknown DCC response";
+                dcc_result = US"T";
+                retval = DEFER;
+                log_write(0,LOG_MAIN,"Unknown DCC response: %s\n", big_buffer);
+                break;
             }
           }
           else {
             /* We're on the first line but not on the first character,
              * there must be something wrong. */
-            DEBUG(D_acl) debug_printf("DCC: Line = %d but i = %d != 0"
-		"  character is %c - This is wrong!\n", line, i, recvbuf[i]);
-            log_write(0,LOG_MAIN,"Wrong header from DCC, output is %s\n", recvbuf);
+            DEBUG(D_acl) debug_printf("DCC: Line = %d but bufoffset = %d != 0"
+		"  character is %c - This is wrong!\n", line, bufoffset, big_buffer[bufoffset]);
+            log_write(0,LOG_MAIN,"Wrong header from DCC, output is %s\n", big_buffer);
           }
         }
         else if(line == 2) {
@@ -437,69 +396,65 @@ dcc_process(uschar **listptr)
            * it because we're in an acl and take the
            * global result. */
         }
-        else if(line > 2) {
-          /* The third and following lines are the X-DCC header,
-           * so we store it in dcc_header_str. */
-          /* check if we don't get more than we can handle */
-          if(k < sizeof(dcc_header_str)) {
-            dcc_header_str[k] = recvbuf[i];
-            k++;
-          }
-          else {
-            DEBUG(D_acl) debug_printf("DCC: We got more output than we can store"
-		" in the X-DCC header. Truncating at 120 characters.\n");
-          }
-        }
-        else {
-          /* Wrong line number. There must be a problem with the output. */
-          DEBUG(D_acl)
-            debug_printf("DCC: Wrong line number in output. Line number is %d\n", line);
-        }
       }
     }
-    /* we reinitialize the output buffer before we read again */
-    bzero(recvbuf,sizeof(recvbuf));
+    if(line > 2) {
+      /* The third and following lines are the X-DCC header,
+       * so we store it in dcc_header_str up to our limit. */
+      /* check if buffer contains the end of the header .."\n\n" and truncate it */
+      if ((big_buffer[dcc_resplen-1] == '\n') &&
+          (big_buffer[dcc_resplen-2] == '\n'))
+        dcc_resplen -= 2;
+      dcc_resplen -= bufoffset;
+      if (dcc_header_str->ptr + dcc_resplen > DCC_HEADER_LIMIT) {
+        dcc_resplen = DCC_HEADER_LIMIT - dcc_header_str->ptr;
+        DEBUG(D_acl) debug_printf("DCC: We got more output than we can store"
+	                   "in the X-DCC header. Truncating at 120 characters.\n");
+      }
+      dcc_header_str = string_catn(dcc_header_str, &big_buffer[bufoffset], dcc_resplen);
+    }
   }
-  /* We have read everything from the socket */
-
-  /* We need to terminate the X-DCC header with a '\n' character. This needs to be k-1
-   * since dcc_header_str[k] contains '\0'. */
-  dcc_header_str[k-1] = '\n';
+  /* We have read everything from the socket. make sure the header ends with "\n" */
+  dcc_header_str = string_catn(dcc_header_str, US"\n", 1);
 
+  (void) string_from_gstring(dcc_header_str);
   /* Now let's sum up what we've got. */
   DEBUG(D_acl)
-    debug_printf("\nDCC: --------------------------\nDCC: Overall result = %d\nDCC: X-DCC header: %sReturn message: %s\nDCC: dcc_result: %s\n", retval, dcc_header_str, dcc_return_text, dcc_result);
+    debug_printf("\nDCC: --------------------------\nDCC: Overall result = %d\n"
+                 "DCC: X-DCC header: %sReturn message: %s\nDCC: dcc_result: %s\n",
+                   retval, dcc_header_str->s, dcc_return_text, dcc_result);
 
   /* We only add the X-DCC header if it starts with X-DCC */
-  if(!(Ustrncmp(dcc_header_str, "X-DCC", 5))){
-    dcc_header = dcc_header_str;
+  if(!(Ustrncmp(dcc_header_str->s, "X-DCC", 5))) {
+    dcc_header = dcc_header_str->s;
     if(dcc_direct_add_header) {
-      header_add(' ' , "%s", dcc_header_str);
+      header_add(' ' , "%s", dcc_header_str->s);
   /* since the MIME ACL already writes the .eml file to disk without DCC Header we've to erase it */
       unspool_mbox();
     }
   }
   else {
     DEBUG(D_acl)
-      debug_printf("DCC: Wrong format of the X-DCC header: %s\n", dcc_header_str);
+      debug_printf("DCC: Wrong format of the X-DCC header: %.*s\n", dcc_header_str->ptr, dcc_header_str->s);
   }
 
   /* check if we should add additional headers passed in acl_m_dcc_add_header */
   if(dcc_direct_add_header) {
     if (((xtra_hdrs = expand_string(US"$acl_m_dcc_add_header")) != NULL) && (xtra_hdrs[0] != '\0')) {
-      Ustrncpy(dcc_xtra_hdrs, xtra_hdrs, sizeof(dcc_xtra_hdrs) - 2);
-      if (dcc_xtra_hdrs[Ustrlen(dcc_xtra_hdrs)-1] != '\n')
-        Ustrcat(dcc_xtra_hdrs, US"\n");
-      header_add(' ', "%s", dcc_xtra_hdrs);
+      dcc_xtra_hdrs = string_cat(NULL, xtra_hdrs);
+      if (dcc_xtra_hdrs->s[dcc_xtra_hdrs->ptr - 1] != '\n')
+        dcc_xtra_hdrs = string_catn(dcc_xtra_hdrs, US"\n", 1);
+      header_add(' ', "%s", string_from_gstring(dcc_xtra_hdrs));
       DEBUG(D_acl)
-        debug_printf("DCC: adding additional headers in $acl_m_dcc_add_header: %s", dcc_xtra_hdrs);
+        debug_printf("DCC: adding additional headers in $acl_m_dcc_add_header: %.*s", dcc_xtra_hdrs->ptr, dcc_xtra_hdrs->s);
     }
   }
 
   dcc_ok = 1;
   /* Now return to exim main process */
   DEBUG(D_acl)
-    debug_printf("DCC: Before returning to exim main process:\nDCC: return_text = %s - retval = %d\nDCC: dcc_result = %s\n", dcc_return_text, retval, dcc_result);
+    debug_printf("DCC: Before returning to exim main process:\nDCC: return_text = %s - retval = %d\n"
+                 "DCC: dcc_result = %s\n", dcc_return_text, retval, dcc_result);
 
   (void)fclose(data_file);
   dcc_rc = retval;