Bug#58165: "my_empty_string" gets modified and causes LOAD DATA to fail and

other crashes

Some string manipulating SQL functions use a shared string object intended to
contain an immutable empty string. This object was used by the SQL function
SUBSTRING_INDEX() to return an empty string when one argument was of the wrong
datatype. If the string object was then modified by the sql function INSERT(),
undefined behavior ensued.

Fixed by instead modifying the string object representing the function's
result value whenever string manipulating SQL functions return an empty
string.

Relevant code has also been documented.

1 files changed, 23 insertions, 22 deletions

diff --git a/sql/item_strfunc.cc b/sql/item_strfunc.cc
index fd5c47d25cb..204a2dfc663 100644
--- a/sql/item_strfunc.cc
+++ b/sql/item_strfunc.cc
@@ -39,6 +39,9 @@ C_MODE_START
 #include "../mysys/my_static.h"			// For soundex_map
 C_MODE_END
 
+/**
+   @todo Remove this. It is not safe to use a shared String object.
+ */
 String my_empty_string("",default_charset_info);
 
 
@@ -461,7 +464,7 @@ String *Item_func_des_encrypt::val_str(String *str)
   if ((null_value= args[0]->null_value))
     return 0;                                   // ENCRYPT(NULL) == NULL
   if ((res_length=res->length()) == 0)
-    return &my_empty_string;
+    return make_empty_result();
 
   if (arg_count == 1)
   {
@@ -652,7 +655,7 @@ String *Item_func_concat_ws::val_str(String *str)
     }
 
   if (i ==  arg_count)
-    return &my_empty_string;
+    return make_empty_result();
 
   for (i++; i < arg_count ; i++)
   {
@@ -803,7 +806,7 @@ String *Item_func_reverse::val_str(String *str)
     return 0;
   /* An empty string is a special case as the string pointer may be null */
   if (!res->length())
-    return &my_empty_string;
+    return make_empty_result();
   if (tmp_value.alloced_length() < res->length() &&
       tmp_value.realloc(res->length()))
   {
@@ -1143,8 +1146,7 @@ String *Item_func_left::val_str(String *str)
 
   /* if "unsigned_flag" is set, we have a *huge* positive number. */
   if ((length <= 0) && (!args[1]->unsigned_flag))
-    return &my_empty_string;
-
+    return make_empty_result();
   if ((res->length() <= (ulonglong) length) ||
       (res->length() <= (char_pos= res->charpos((int) length))))
     return res;
@@ -1187,7 +1189,7 @@ String *Item_func_right::val_str(String *str)
 
   /* if "unsigned_flag" is set, we have a *huge* positive number. */
   if ((length <= 0) && (!args[1]->unsigned_flag))
-    return &my_empty_string; /* purecov: inspected */
+    return make_empty_result(); /* purecov: inspected */
 
   if (res->length() <= (ulonglong) length)
     return res; /* purecov: inspected */
@@ -1226,7 +1228,7 @@ String *Item_func_substr::val_str(String *str)
   /* Negative or zero length, will return empty string. */
   if ((arg_count == 3) && (length <= 0) && 
       (length == 0 || !args[2]->unsigned_flag))
-    return &my_empty_string;
+    return make_empty_result();
 
   /* Assumes that the maximum length of a String is < INT_MAX32. */
   /* Set here so that rest of code sees out-of-bound value as such. */
@@ -1237,12 +1239,12 @@ String *Item_func_substr::val_str(String *str)
   /* Assumes that the maximum length of a String is < INT_MAX32. */
   if ((!args[1]->unsigned_flag && (start < INT_MIN32 || start > INT_MAX32)) ||
       (args[1]->unsigned_flag && ((ulonglong) start > INT_MAX32)))
-    return &my_empty_string;
+    return make_empty_result();
 
   start= ((start < 0) ? res->numchars() + start : start - 1);
   start= res->charpos((int) start);
   if ((start < 0) || ((uint) start + 1 > res->length()))
-    return &my_empty_string;
+    return make_empty_result();
 
   length= res->charpos((int) length, (uint32) start);
   tmp_length= res->length() - start;
@@ -1305,7 +1307,7 @@ String *Item_func_substr_index::val_str(String *str)
   null_value=0;
   uint delimiter_length= delimiter->length();
   if (!res->length() || !delimiter_length || !count)
-    return &my_empty_string;		// Wrong parameters
+    return make_empty_result();		// Wrong parameters
 
   res->set_charset(collation.collation);
 
@@ -1654,7 +1656,7 @@ String *Item_func_password::val_str(String *str)
   if ((null_value=args[0]->null_value))
     return 0;
   if (res->length() == 0)
-    return &my_empty_string;
+    return make_empty_result();
   my_make_scrambled_password(tmp_value, res->ptr(), res->length());
   str->set(tmp_value, SCRAMBLED_PASSWORD_CHAR_LENGTH, res->charset());
   return str;
@@ -1678,7 +1680,7 @@ String *Item_func_old_password::val_str(String *str)
   if ((null_value=args[0]->null_value))
     return 0;
   if (res->length() == 0)
-    return &my_empty_string;
+    return make_empty_result();
   my_make_scrambled_password_323(tmp_value, res->ptr(), res->length());
   str->set(tmp_value, SCRAMBLED_PASSWORD_CHAR_LENGTH_323, res->charset());
   return str;
@@ -1706,8 +1708,7 @@ String *Item_func_encrypt::val_str(String *str)
   if ((null_value=args[0]->null_value))
     return 0;
   if (res->length() == 0)
-    return &my_empty_string;
-
+    return make_empty_result();
   if (arg_count == 1)
   {					// generate random salt
     time_t timestamp=current_thd->query_start();
@@ -1967,7 +1968,7 @@ String *Item_func_soundex::val_str(String *str)
   for ( ; ; ) /* Skip pre-space */
   {
     if ((rc= cs->cset->mb_wc(cs, &wc, (uchar*) from, (uchar*) end)) <= 0)
-      return &my_empty_string; /* EOL or invalid byte sequence */
+      return make_empty_result(); /* EOL or invalid byte sequence */
     
     if (rc == 1 && cs->ctype)
     {
@@ -1992,7 +1993,7 @@ String *Item_func_soundex::val_str(String *str)
         {
           /* Extra safety - should not really happen */
           DBUG_ASSERT(false);
-          return &my_empty_string;
+          return make_empty_result();
         }
         to+= rc;
         break;
@@ -2289,7 +2290,7 @@ String *Item_func_make_set::val_str(String *str)
 	  else
 	  {
 	    if (tmp_str.copy(*res))		// Don't use 'str'
-	      return &my_empty_string;
+              return make_empty_result();
 	    result= &tmp_str;
 	  }
 	}
@@ -2299,11 +2300,11 @@ String *Item_func_make_set::val_str(String *str)
 	  {					// Copy data to tmp_str
 	    if (tmp_str.alloc(result->length()+res->length()+1) ||
 		tmp_str.copy(*result))
-	      return &my_empty_string;
+              return make_empty_result();
 	    result= &tmp_str;
 	  }
 	  if (tmp_str.append(STRING_WITH_LEN(","), &my_charset_bin) || tmp_str.append(*res))
-	    return &my_empty_string;
+            return make_empty_result();
 	}
       }
     }
@@ -2442,7 +2443,7 @@ String *Item_func_repeat::val_str(String *str)
   null_value= 0;
 
   if (count <= 0 && (count == 0 || !args[1]->unsigned_flag))
-    return &my_empty_string;
+    return make_empty_result();
 
   /* Assumes that the maximum length of a String is < INT_MAX32. */
   /* Bounds check on count:  If this is triggered, we will error. */
@@ -2750,7 +2751,7 @@ String *Item_func_conv::val_str(String *str)
 
   ptr= longlong2str(dec, ans, to_base);
   if (str->copy(ans, (uint32) (ptr-ans), default_charset()))
-    return &my_empty_string;
+    return make_empty_result();
   return str;
 }
 
@@ -2917,7 +2918,7 @@ String *Item_func_hex::val_str(String *str)
       return 0;
     ptr= longlong2str(dec,ans,16);
     if (str->copy(ans,(uint32) (ptr-ans),default_charset()))
-      return &my_empty_string;			// End of memory
+      return make_empty_result();			// End of memory
     return str;
   }