Fix #80783: PDO ODBC truncates BLOB records at every 256th byte

It is not guaranteed, that the driver inserts only a single NUL byte at
the end of the buffer.  Apparently, there is no way to find out the
actual data length in the buffer after calling `SQLGetData()`, so we
adjust after the next `SQLGetData()` call.

We also prevent PDO::ODBC_ATTR_ASSUME_UTF8 from fetching garbage, by
fetching all chunks with the same C type.

Closes GH-6716.

Author: cmb69

NEWS

@@ -5,6 +5,10 @@ PHP                                                                        NEWS
 - DOM:
   . Fixed bug #66783 (UAF when appending DOMDocument to element). (cmb)
 
+- PDO_ODBC:
+  . Fixed bug #80783 (PDO ODBC truncates BLOB records at every 256th byte).
+    (cmb)
+
 01 Apr 2021, PHP 7.4.17
 
 - Core:

ext/pdo_odbc/odbc_stmt.c

@@ -652,6 +652,7 @@ static int odbc_stmt_get_col(pdo_stmt_t *stmt, int colno, char **ptr, zend_ulong
 
 	/* if it is a column containing "long" data, perform late binding now */
 	if (C->is_long) {
+		SQLLEN orig_fetched_len = SQL_NULL_DATA;
 		zend_ulong used = 0;
 		char *buf;
 		RETCODE rc;
@@ -662,6 +663,7 @@ static int odbc_stmt_get_col(pdo_stmt_t *stmt, int colno, char **ptr, zend_ulong
 
 		rc = SQLGetData(S->stmt, colno+1, C->is_unicode ? SQL_C_BINARY : SQL_C_CHAR, C->data,
  			256, &C->fetched_len);
+		orig_fetched_len = C->fetched_len;
 
 		if (rc == SQL_SUCCESS) {
 			/* all the data fit into our little buffer;
@@ -673,7 +675,8 @@ static int odbc_stmt_get_col(pdo_stmt_t *stmt, int colno, char **ptr, zend_ulong
 			/* this is a 'long column'
 
 			 read the column in 255 byte blocks until the end of the column is reached, reassembling those blocks
-			 in order into the output buffer
+			 in order into the output buffer; 255 bytes are an optimistic assumption, since the driver may assert
+			 more or less NUL bytes at the end; we cater to that later, if actual length information is available
 
 			 this loop has to work whether or not SQLGetData() provides the total column length.
 			 calling SQLDescribeCol() or other, specifically to get the column length, then doing a single read
@@ -687,7 +690,14 @@ static int odbc_stmt_get_col(pdo_stmt_t *stmt, int colno, char **ptr, zend_ulong
 			do {
 				C->fetched_len = 0;
 				/* read block. 256 bytes => 255 bytes are actually read, the last 1 is NULL */
-				rc = SQLGetData(S->stmt, colno+1, SQL_C_CHAR, buf2, 256, &C->fetched_len);
+				rc = SQLGetData(S->stmt, colno+1, C->is_unicode ? SQL_C_BINARY : SQL_C_CHAR, buf2, 256, &C->fetched_len);
+
+				/* adjust `used` in case we have length info from the driver */
+				if (orig_fetched_len >= 0 && C->fetched_len >= 0) {
+					SQLLEN fixed_used = orig_fetched_len - C->fetched_len;
+					ZEND_ASSERT(fixed_used <= used + 1);
+					used = fixed_used;
+				}
 
 				/* resize output buffer and reassemble block */
 				if (rc==SQL_SUCCESS_WITH_INFO) {

ext/pdo_odbc/tests/bug80783.phpt

@@ -0,0 +1,32 @@
+--TEST--
+Bug #80783 (PDO ODBC truncates BLOB records at every 256th byte)
+--SKIPIF--
+<?php
+if (!extension_loaded('pdo_odbc')) die('skip pdo_odbc extension not available');
+require 'ext/pdo/tests/pdo_test.inc';
+PDOTest::skip();
+?>
+--FILE--
+<?php
+require 'ext/pdo/tests/pdo_test.inc';
+$db = PDOTest::test_factory(dirname(__FILE__) . '/common.phpt');
+$db->exec("CREATE TABLE bug80783 (name IMAGE)");
+
+$string = str_repeat("0123456789", 50);
+$db->exec("INSERT INTO bug80783 VALUES('$string')");
+
+$stmt = $db->prepare("SELECT name FROM bug80783");
+$stmt->bindColumn(1, $data, PDO::PARAM_LOB);
+$stmt->execute();
+$stmt->fetch(PDO::FETCH_BOUND);
+
+var_dump($data === bin2hex($string));
+?>
+--CLEAN--
+<?php
+require 'ext/pdo/tests/pdo_test.inc';
+$db = PDOTest::test_factory(dirname(__FILE__) . '/common.phpt');
+$db->exec("DROP TABLE bug80783");
+?>
+--EXPECT--
+bool(true)

ext/pdo_odbc/tests/bug80783a.phpt

@@ -0,0 +1,33 @@
+--TEST--
+Bug #80783 (PDO ODBC truncates BLOB records at every 256th byte)
+--SKIPIF--
+<?php
+if (!extension_loaded('pdo_odbc')) die('skip pdo_odbc extension not available');
+require 'ext/pdo/tests/pdo_test.inc';
+PDOTest::skip();
+?>
+--FILE--
+<?php
+require 'ext/pdo/tests/pdo_test.inc';
+$db = PDOTest::test_factory(dirname(__FILE__) . '/common.phpt');
+$db->exec("CREATE TABLE bug80783a (name NVARCHAR(MAX))");
+
+$string = str_repeat("0123456789", 50);
+$db->exec("INSERT INTO bug80783a VALUES('$string')");
+
+$stmt = $db->prepare("SELECT name FROM bug80783a");
+$stmt->setAttribute(PDO::ODBC_ATTR_ASSUME_UTF8, true);
+$stmt->bindColumn(1, $data, PDO::PARAM_STR);
+$stmt->execute();
+$stmt->fetch(PDO::FETCH_BOUND);
+
+var_dump($data === $string);
+?>
+--CLEAN--
+<?php
+require 'ext/pdo/tests/pdo_test.inc';
+$db = PDOTest::test_factory(dirname(__FILE__) . '/common.phpt');
+$db->exec("DROP TABLE bug80783a");
+?>
+--EXPECT--
+bool(true)