FreeTDS Development Group

["Thompson, William" <bill.d.thompson AT baml.com>]

Hi All,

I've had a new issue reported to me on freebcp.
This has come from someone migrating from Sybase to SQL Server, using freetds 
as their "enabler" - an increasing trend in the use of freetds, I'm told.
So we have some solid evidence - "This works using Sybase bcp, but it doesn't 
work with freebcp" - and although it's an edge case, I think it should be 
fixed.

So the problem occurs with freebcp using a format file. It evidences itself 
as a dbconvert() overflow error...

The problematic column is CHAR(6) on the database
The line from the format file for the column looks like this:

22      SYBCHAR 0       6       "~"     22      cost_center

and a snippet from the problematic line from the data file, showing the 
problematic host file data looks like this:

...~123456  ~...

So in the format file, we've given a host file data length as 6 (the fourth 
token in the format file), but we've also said the data is terminated  (by a 
"~")
However, there's a couple of extra spaces on the end of that data in the data 
file, giving it a total length of 8 characters.

Well I took a look at this, and the Sybase manual pages for format files 
tells me the following about the host file data length:


"Host file data length refers to the maximum number of bytes to copy for the 
field. To decide how much data to copy in or out, bcp uses one of:

- The maximum field length
- The prefix length, if any
- The field terminator string, if any

If more than one method of field length specification is given, bcp chooses 
the one that copies the least amount of data."
This caused me to delve into _bcp_read_hostfile()  (in src/dblib/bcp.c). To 
be honest, it shows the signs of having "evolved" to deal with the myriad of 
possibilities available to the innocent or pragmatic user. I'm probably to 
blame for much of that ad-hoc evolution, and here's another mutation to add 
to the mix. It works, and doesn't make things significantly worse than they 
they currently are:
Add the following lines to the function after approximately line 1421 of 
bcp.c (some context given):

               /*
                * FIXME bcpcol->bcp_column_data->data && bcpcol->column_size 
??
                * It seems a buffer overflow waiting...
                */

+              /* If column length specified (in a format file), then it 
*might*   */
+              /* be less than the data read from file (if the column was 
also     */
+              /* described as a terminated field...) in this case we need to 
only */
+              /* take the number of characters specified in the column 
length     */
+
+              if (hostcol->column_len > 0) {
+                     collen = (hostcol->column_len < collen) ? 
hostcol->column_len : collen;
+              }

               bcpcol->bcp_column_data->datalen =
                    dbconvert(dbproc, hostcol->datatype, (const BYTE *) 
coldata, collen, desttype,
                              bcpcol->bcp_column_data->data, 
bcpcol->column_size);

               if (bcpcol->bcp_column_data->datalen == -1) {


In penance, I may re-work the function at some point soon. The code is going 
to keep me awake at nights otherwise...

Bill



.


Bill Thompson

GMO Technology
Bank of America Merrill Lynch
5 Canada Square
London E14 5AQ
Phone: +44 (0)207 995 8307
Email: bill.d.thompson AT baml.com


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