CVE-2020-28024: Heap buffer underflow in smtp_ungetc()

[exim.git] / src / src / smtp_in.c

diff --git a/src/src/smtp_in.c b/src/src/smtp_in.c
index 04d6aa4ba2791e1e9178701d5ec9b59cce82a515..258ec03e4d03e78890e8a5aa2cd85a5e2adf31f7 100644 (file)
--- a/src/src/smtp_in.c
+++ b/src/src/smtp_in.c
@@ -594,8 +594,8 @@ if (n > 0)
 
 
 /* Forward declarations */
-static void bdat_push_receive_functions(void);
-static void bdat_pop_receive_functions(void);
+static inline void bdat_push_receive_functions(void);
+static inline void bdat_pop_receive_functions(void);
 
 
 /* Get a byte from the smtp input, in CHUNKING mode.  Handle ack of the
@@ -776,7 +776,7 @@ if (chunking_state != CHUNKING_LAST)
 }
 
 
-static void
+static inline void
 bdat_push_receive_functions(void)
 {
 /* push the current receive_* function on the "stack", and
@@ -794,15 +794,22 @@ else
   }
 
 receive_getc = bdat_getc;
+receive_getbuf = bdat_getbuf;
 receive_ungetc = bdat_ungetc;
 }
 
-static void
+static inline void
 bdat_pop_receive_functions(void)
 {
+if (lwr_receive_getc == NULL)
+  {
+  DEBUG(D_receive) debug_printf("chunking double-pop receive functions\n");
+  return;
+  }
 receive_getc = lwr_receive_getc;
 receive_getbuf = lwr_receive_getbuf;
 receive_ungetc = lwr_receive_ungetc;
+
 lwr_receive_getc = NULL;
 lwr_receive_getbuf = NULL;
 lwr_receive_ungetc = NULL;
@@ -824,6 +831,9 @@ Returns:       the character
 int
 smtp_ungetc(int ch)
 {
+if (smtp_inptr <= smtp_inbuffer)
+  log_write(0, LOG_MAIN|LOG_PANIC_DIE, "buffer underflow in smtp_ungetc");
+
 *--smtp_inptr = ch;
 return ch;
 }
@@ -2024,30 +2034,35 @@ static BOOL
 extract_option(uschar **name, uschar **value)
 {
 uschar *n;
-uschar *v = smtp_cmd_data + Ustrlen(smtp_cmd_data) - 1;
-while (isspace(*v)) v--;
-v[1] = '\0';
+uschar *v;
+if (Ustrlen(smtp_cmd_data) <= 0) return FALSE;
+v = smtp_cmd_data + Ustrlen(smtp_cmd_data) - 1;
+while (v > smtp_cmd_data && isspace(*v)) v--;
+v[1] = 0;
+
 while (v > smtp_cmd_data && *v != '=' && !isspace(*v))
   {
   /* Take care to not stop at a space embedded in a quoted local-part */
-
-  if ((*v == '"') && (v > smtp_cmd_data + 1))
-    do v--; while (*v != '"' && v > smtp_cmd_data+1);
+  if (*v == '"')
+    {
+    do v--; while (v > smtp_cmd_data && *v != '"');
+    if (v <= smtp_cmd_data) return FALSE;
+    }
   v--;
   }
+if (v <= smtp_cmd_data) return FALSE;
 
 n = v;
 if (*v == '=')
   {
-  while(isalpha(n[-1])) n--;
+  while (n > smtp_cmd_data && isalpha(n[-1])) n--;
   /* RFC says SP, but TAB seen in wild and other major MTAs accept it */
-  if (!isspace(n[-1])) return FALSE;
+  if (n <= smtp_cmd_data || !isspace(n[-1])) return FALSE;
   n[-1] = 0;
   }
 else
   {
   n++;
-  if (v == smtp_cmd_data) return FALSE;
   }
 *v++ = 0;
 *name = n;
@@ -5014,6 +5029,10 @@ while (done <= 0)
 
     case RCPT_CMD:
       HAD(SCH_RCPT);
+      /* We got really to many recipients. A check against configured
+      limits is done later */
+      if (rcpt_count < 0 || rcpt_count >= INT_MAX/2)
+        log_write(0, LOG_MAIN|LOG_PANIC_DIE, "Too many recipients: %d", rcpt_count);
       rcpt_count++;
       was_rcpt = fl.rcpt_in_progress = TRUE;
 
@@ -5170,7 +5189,7 @@ while (done <= 0)
 
       /* Check maximum allowed */
 
-      if (rcpt_count > recipients_max && recipients_max > 0)
+      if (rcpt_count+1 < 0 || rcpt_count > recipients_max && recipients_max > 0)
        {
        if (recipients_max_reject)
          {
@@ -5315,7 +5334,7 @@ while (done <= 0)
       DEBUG(D_receive) debug_printf("chunking state %d, %d bytes\n",
                                    (int)chunking_state, chunking_data_left);
 
-      f.bdat_readers_wanted = TRUE;
+      f.bdat_readers_wanted = TRUE; /* FIXME: redundant vs chunking_state? */
       f.dot_ends = FALSE;
 
       goto DATA_BDAT;
@@ -5365,6 +5384,12 @@ while (done <= 0)
        sender_address = NULL;  /* This will allow a new MAIL without RSET */
        sender_address_unrewritten = NULL;
        smtp_printf("554 Too many recipients\r\n", FALSE);
+
+       if (chunking_state > CHUNKING_OFFERED)
+         {
+         bdat_push_receive_functions();
+         bdat_flush_data();
+         }
        break;
        }