[freetds] bugreport: possible crash when reading empty text field from mssql database using odbc

Frediano Ziglio freddy77 at gmail.com
Tue Dec 8 06:02:12 EST 2009


Il giorno lun, 07/12/2009 alle 12.29 +0100, Michal Seliga ha scritto:
> problem is in function SQLGetData in odbc.c on line 4715 (in my version)
> 
> its this context, error line is marked with /*!!!*/
> 
> switch (nSybType) {
> case SYBCHAR:
> case SYBVARCHAR:
> case SYBTEXT:
> case XSYBCHAR:
> case XSYBVARCHAR:
> /*!!!*/	nread = (src[0] == '0' && toupper(src[1]) == 'X')? 2 : 0;  /*!!!*/
> 		
> 	while ((nread < colinfo->column_cur_size) && (src[nread] == ' ' || src[nread]
> == '\0'))
> 		nread++;
> 
> 	nread += colinfo->column_text_sqlgetdatapos * 2;
> 	
> 	if (nread && nread >= colinfo->column_cur_size)
> 		ODBC_RETURN(stmt, SQL_NO_DATA);
> 
> 
> problem is that on my database i get:
> nSybType = 35
> colinfo.column_cur_size=0
> src= 0x0
> 
> but its not recognized as empty or null value, instead it tries to read src[0]
> and it causes crash
> 
> attached is patch which fixed issue for me, but of course i didn't studied
> internals of freetds before doing it and i can't guarantee its correct, please,
> someone review it...
> 
> 
> Documento in testo semplice allegato (odbc.diff)
> --- odbc.c.orig	2009-12-04 14:47:39.000000000 +0100
> +++ odbc.c	2009-12-07 12:26:23.709681867 +0100
> @@ -4623,7 +4623,7 @@
>  	}
>  	colinfo = resinfo->columns[icol - 1];
>  
> -	if (colinfo->column_cur_size < 0) {
> +	if (colinfo->column_cur_size <= 0) {
>  		*pcbValue = SQL_NULL_DATA;
>  	} else {
>  		nSybType = tds_get_conversion_type(colinfo->column_type, colinfo->column_size);

Fixed in CVS, test added too. CVS HEAD didn't have this problem. Your
patch handle in this specific case threat empty like NULLs, I added a
test to avoid invalid memory access instead.

Thanks for pointing out,
  Frediano





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