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Buffer overrun in handle_notice_message()

From: Bart Samwel <bart(at)samwel(dot)tk>
To: pgsql-odbc(at)postgresql(dot)org
Subject: Buffer overrun in handle_notice_message()
Date: 2006-08-18 14:13:29
Message-ID: 44E5CB09.1040005@samwel.tk (view raw or flat)
Thread:
Lists: pgsql-odbc
Hi all,

I'd like to report a buffer overrun in handle_notice_message(). 
Analysis: when I run a query >4096 characters that has a 'C' at a 
specific location (at a specific, small offset before a multiple of 
4096), then the stack is trashed and the driver crashes. The code fragment:

for (;;)
{
	truncated = SOCK_get_string(sock, msgbuffer, sizeof(msgbuffer));
	if (!msgbuffer[0])
		break;

	mylog("%s: 'N' - %s\n", comment, msgbuffer);
	qlog("NOTICE from backend during %s: '%s'\n", comment, msgbuffer);
	switch (msgbuffer[0])
	{
		case 'S':
			strncat(msgbuf, msgbuffer + 1, buflen);
			strncat(msgbuf, ": ", buflen);
			buflen -= (strlen(msgbuffer) + 1);
			break;
		case 'M':
			strncat(msgbuf, msgbuffer + 1, buflen);
			msg_truncated = truncated;
			break;
		case 'C':
			if (sqlstate && !sqlstate[0] && strcmp(msgbuffer + 1, "00000"))
				strcpy(sqlstate, msgbuffer + 1);
			break;
	}
}



The problem is that PostgreSQL replies to the query with a "LOG"-type 
message, quoting the _complete_ query. This loop retrieves the message 
in chunks of 4096 bytes (i.e., sizeof(msgbuffer)) and normally just 
outputs things to mylog and qlog, _except_ if the first character of a 
chunk just happens to be 'S', 'M' or 'C'. In the 'S' or 'M' cases, 
nothing bad happens, but in the 'C' case, the 
strcpy(sqlstate,msgbuffer+1) copies 4 kbytes of data into the 8-byte 
sqlstate buffer.

The way I understand it, the switch on msgbuffer[0] should only happen 
on the first iteration, not on subsequent iterations. After I changed 
the loop like that, my application ran without any problems.

Oh, in case you're wondering: protocol is 7.4+, PostgreSQL server 
version is 8.1.4.

Cheers,
Bart

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