Modify libpq's string-escaping routines to be aware of encoding considerations

and standard_conforming_strings.  The encoding changes are needed for proper
escaping in multibyte encodings, as per the SQL-injection vulnerabilities
noted in CVE-2006-2313 and CVE-2006-2314.  Concurrent fixes are being applied
to the server to ensure that it rejects queries that may have been corrupted
by attempted SQL injection, but this merely guarantees that unpatched clients
will fail rather than allow injection.  An actual fix requires changing the
client-side code.  While at it we have also fixed these routines to understand
about standard_conforming_strings, so that the upcoming changeover to SQL-spec
string syntax can be somewhat transparent to client code.

Since the existing API of PQescapeString and PQescapeBytea provides no way to
inform them which settings are in use, these functions are now deprecated in
favor of new functions PQescapeStringConn and PQescapeByteaConn.  The new
functions take the PGconn to which the string will be sent as an additional
parameter, and look inside the connection structure to determine what to do.
So as to provide some functionality for clients using the old functions,
libpq stores the latest encoding and standard_conforming_strings values
received from the backend in static variables, and the old functions consult
these variables.  This will work reliably in clients using only one Postgres
connection at a time, or even multiple connections if they all use the same
encoding and string syntax settings; which should cover many practical
scenarios.

Clients that use homebrew escaping methods, such as PHP's addslashes()
function or even hardwired regexp substitution, will require extra effort
to fix :-(.  It is strongly recommended that such code be replaced by use of
PQescapeStringConn/PQescapeByteaConn if at all feasible.

1 files changed, 193 insertions, 74 deletions

diff --git a/doc/src/sgml/libpq.sgml b/doc/src/sgml/libpq.sgml
index f0cb3cdb674..f9f67ed818d 100644
--- a/doc/src/sgml/libpq.sgml
+++ b/doc/src/sgml/libpq.sgml
@@ -1,5 +1,5 @@
 <!--
-$Header: /cvsroot/pgsql/doc/src/sgml/libpq.sgml,v 1.98.2.5 2003/01/30 19:50:07 tgl Exp $
+$Header: /cvsroot/pgsql/doc/src/sgml/libpq.sgml,v 1.98.2.6 2006/05/21 20:20:48 tgl Exp $
 -->
 
  <chapter id="libpq">
@@ -880,115 +880,234 @@ as with a <structname>PGresult</structname> returned by <application>libpq</appl
 </sect2>
 
 <sect2 id="libpq-exec-escape-string">
-  <title>Escaping strings for inclusion in SQL queries</title>
+  <title>Escaping Strings for Inclusion in SQL Commands</title>
 
+   <indexterm zone="libpq-exec-escape-string"><primary>PQescapeStringConn</></>
+   <indexterm zone="libpq-exec-escape-string"><primary>PQescapeString</></>
    <indexterm zone="libpq-exec-escape-string"><primary>escaping strings</></>
 
 <para>
-<function>PQescapeString</function>
-          Escapes a string for use within an SQL query.
+<function>PQescapeStringConn</function> escapes a string for use within an SQL
+command.  This is useful when inserting data values as literal constants
+in SQL commands.  Certain characters (such as quotes and backslashes) must
+be escaped to prevent them from being interpreted specially by the SQL parser.
+<function>PQescapeStringConn</> performs this operation.
+</para>
+
+<tip>
+<para>
+It is especially important to do proper escaping when handling strings that
+were received from an untrustworthy source.  Otherwise there is a security
+risk: you are vulnerable to <quote>SQL injection</> attacks wherein unwanted
+SQL commands are fed to your database.
+</para>
+</tip>
+
+<para>
 <synopsis>
-size_t PQescapeString (char *to, const char *from, size_t length);
+size_t PQescapeStringConn (PGconn *conn,
+                           char *to, const char *from, size_t length,
+                           int *error);
 </synopsis>
-If you want to include strings that have been received
-from a source that is not trustworthy (for example, because a random user
-entered them), you cannot directly include them in SQL
-queries for security reasons.  Instead, you have to quote special
-characters that are otherwise interpreted by the SQL parser.
 </para>
+
 <para>
-<function>PQescapeString</> performs this operation.  The
-<parameter>from</> points to the first character of the string that
-is to be escaped, and the <parameter>length</> parameter counts the
-number of characters in this string (a terminating zero byte is
-neither necessary nor counted).  <parameter>to</> shall point to a
-buffer that is able to hold at least one more character than twice
-the value of <parameter>length</>, otherwise the behavior is
-undefined.  A call to <function>PQescapeString</> writes an escaped
+<function>PQescapeStringConn</> writes an escaped
 version of the <parameter>from</> string to the <parameter>to</>
-buffer, replacing special characters so that they cannot cause any
+buffer, escaping special characters so that they cannot cause any
 harm, and adding a terminating zero byte.  The single quotes that
-must surround <productname>PostgreSQL</> string literals are not part of the result
-string.
+must surround <productname>PostgreSQL</> string literals are not
+included in the result string; they should be provided in the SQL
+command that the result is inserted into.
+The parameter <parameter>from</> points to the first character of the string
+that is to be escaped, and the <parameter>length</> parameter gives the
+number of bytes in this string.  A terminating zero byte is not
+required, and should not be counted in <parameter>length</>.  (If
+a terminating zero byte is found before <parameter>length</> bytes are
+processed, <function>PQescapeStringConn</> stops at the zero; the behavior
+is thus rather like <function>strncpy</>.)
+<parameter>to</> shall point to a
+buffer that is able to hold at least one more byte than twice
+the value of <parameter>length</>, otherwise the behavior is
+undefined.
+Behavior is likewise undefined if the <parameter>to</> and <parameter>from</>
+strings overlap.
+</para>
+<para>
+If the <parameter>error</> parameter is not NULL, then <literal>*error</>
+is set to zero on success, nonzero on error.  Presently the only possible
+error conditions involve invalid multibyte encoding in the source string.
+The output string is still generated on error, but it can be expected that
+the server will reject it as malformed.  On error, a suitable message is
+stored in the <parameter>conn</> object, whether or not <parameter>error</>
+is NULL.
 </para>
 <para>
-<function>PQescapeString</> returns the number of characters written
+<function>PQescapeStringConn</> returns the number of bytes written
 to <parameter>to</>, not including the terminating zero byte.
-Behavior is undefined when the <parameter>to</> and <parameter>from</>
-strings overlap.
+</para>
+
+<para>
+<synopsis>
+size_t PQescapeString (char *to, const char *from, size_t length);
+</synopsis>
+</para>
+
+<para>
+<function>PQescapeString</> is an older, deprecated version of
+<function>PQescapeStringConn</>; the difference is that it does not
+take <parameter>conn</> or <parameter>error</> parameters.  Because of this,
+it cannot adjust its behavior depending on the connection properties (such as
+character encoding) and therefore <emphasis>it may give the wrong results</>.
+Also, it has no way to report error conditions.
+</para>
+<para>
+<function>PQescapeString</> can be used safely in single-threaded client
+programs that work with only one <productname>PostgreSQL</> connection at
+a time (in this case it can find out what it needs to know <quote>behind the
+scenes</>).  In other contexts it is a security hazard and should be avoided
+in favor of <function>PQescapeStringConn</>.
 </para>
 </sect2>
 
 
  <sect2 id="libpq-exec-escape-bytea">
-  <title>Escaping binary strings for inclusion in SQL queries</title>
+  <title>Escaping Binary Strings for Inclusion in SQL Commands</title>
+
   <indexterm zone="libpq-exec-escape-bytea">
-   <primary>escaping binary strings</primary>
+   <primary>bytea</>
+   <secondary sortas="libpq">in libpq</>
   </indexterm>
+
+  <variablelist>
+  <varlistentry>
+  <term><function>PQescapeByteaConn</function><indexterm><primary>PQescapeByteaConn</></></term>
+  <listitem>
   <para>
-   <function>PQescapeBytea</function>
-   Escapes a binary string (<type>bytea</type> type) for use within an SQL query.
-   <synopsis>
-    unsigned char *PQescapeBytea(unsigned char *from,
-                                         size_t from_length,
-                                         size_t *to_length);
-   </synopsis>
-
-   Certain <acronym>ASCII</acronym> characters <emphasis>must</emphasis>
-   be escaped (but all characters <emphasis>may</emphasis> be escaped)
-   when used as part of a <type>bytea</type>
-   string literal in an <acronym>SQL</acronym> statement. In general, to
-   escape a character, it is converted into the three digit octal number
-   equal to the decimal <acronym>ASCII</acronym> value, and preceded by
-   two backslashes. The single quote (') and backslash (\) characters have
-   special alternate escape sequences. See the <citetitle>User's Guide</citetitle>
-   for more information. <function>PQescapeBytea
-   </function> performs this operation, escaping only the minimally
-   required characters.
+   Escapes binary data for use within an SQL command with the type
+   <type>bytea</type>.
+<synopsis>
+unsigned char *PQescapeByteaConn(PGconn *conn,
+                                 const unsigned char *from,
+                                 size_t from_length,
+                                 size_t *to_length);
+</synopsis>
+</para>
+
+<para>
+   Certain byte values <emphasis>must</emphasis> be escaped (but all
+   byte values <emphasis>can</emphasis> be escaped) when used as part
+   of a <type>bytea</type> literal in an <acronym>SQL</acronym>
+   statement. In general, to escape a byte, it is converted into the
+   three digit octal number equal to the octet value, and preceded by
+   one or two backslashes. The single quote (<literal>'</>) and backslash
+   (<literal>\</>) characters have special alternative escape
+   sequences. <function>PQescapeByteaConn</function> performs this
+   operation, escaping only the minimally required bytes.
   </para>
 
   <para>
    The <parameter>from</parameter> parameter points to the first
-   character of the string that is to be escaped, and the
-   <parameter>from_length</parameter> parameter reflects the number of
-   characters in this binary string (a terminating zero byte is
-   neither necessary nor counted).  The <parameter>to_length</parameter>
-   parameter shall point to a buffer suitable to hold the resultant
-   escaped string length. The result string length includes the terminating
+   byte of the string that is to be escaped, and the
+   <parameter>from_length</parameter> parameter gives the number of
+   bytes in this binary string.  (A terminating zero byte is
+   neither necessary nor counted.)  The <parameter>to_length</parameter>
+   parameter points to a variable that will hold the resultant
+   escaped string length. This result string length includes the terminating
    zero byte of the result.
   </para>
 
   <para>
-   <function>PQescapeBytea</> returns an escaped version of the
-   <parameter>from</parameter> parameter binary string, to a caller-provided
-    buffer. The return string has all special characters replaced
-   so that they can be properly processed by the PostgreSQL string literal
-   parser, and the <type>bytea</type> input function. A terminating zero
-   byte is also added.  The single quotes that must surround
-   PostgreSQL string literals are not part of the result string.
+   <function>PQescapeByteaConn</> returns an escaped version of the
+   <parameter>from</parameter> parameter binary string in memory
+   allocated with <function>malloc()</>.  This memory must be freed using
+   <function>free()</> when the result is no longer needed.  The
+   return string has all special characters replaced so that they can
+   be properly processed by the <productname>PostgreSQL</productname>
+   string literal parser, and the <type>bytea</type> input function. A
+   terminating zero byte is also added.  The single quotes that must
+   surround <productname>PostgreSQL</productname> string literals are
+   not part of the result string.
+  </para>
+
+  <para>
+   On error, a NULL pointer is returned, and a suitable error message
+   is stored in the <parameter>conn</> object.  Currently, the only
+   possible error is insufficient memory for the result string.
+  </para>
+  </listitem>
+  </varlistentry>
+
+  <varlistentry>
+  <term><function>PQescapeBytea</function><indexterm><primary>PQescapeBytea</></></term>
+  <listitem>
+  <para>
+   <function>PQescapeBytea</> is an older, deprecated version of
+   <function>PQescapeByteaConn</>.
+<synopsis>
+unsigned char *PQescapeBytea(unsigned char *from,
+                             size_t from_length,
+                             size_t *to_length);
+</synopsis>
+</para>
+
+<para>
+   The only difference from <function>PQescapeByteaConn</> is that
+   <function>PQescapeBytea</> does not
+   take a <structname>PGconn</> parameter.  Because of this, it cannot adjust
+   its behavior depending on the connection properties
+   and therefore <emphasis>it may give the wrong results</>.  Also, it
+   has no way to return an error message on failure.
   </para>
 
   <para>
-   <function>PQunescapeBytea</function>
-   Converts an escaped string representation of binary data into binary
-   data - the reverse of <function>PQescapeBytea</function>.
-   <synopsis>
-    unsigned char *PQunescapeBytea(unsigned char *from, size_t *to_length);
-   </synopsis>
-
-   The <parameter>from</parameter> parameter points to an escaped string
-   such as might be returned by <function>PQgetvalue</function> of a
-   <type>BYTEA</type> column. <function>PQunescapeBytea</function> converts
-   this string representation into its binary representation, filling the supplied buffer.
-   It returns a pointer to the buffer which is NULL on error, and the size
-   of the buffer in <parameter>to_length</parameter>. The pointer may
-   subsequently be used as an argument to the function
-   <function>free(3)</function>.
+   <function>PQescapeBytea</> can be used safely in single-threaded client
+   programs that work with only one <productname>PostgreSQL</> connection at
+   a time (in this case it can find out what it needs to know <quote>behind the
+   scenes</>).  In other contexts it is a security hazard and should be
+   avoided in favor of <function>PQescapeByteaConn</>.
   </para>
+  </listitem>
+  </varlistentry>
+
+  <varlistentry>
+  <term><function>PQunescapeBytea</function><indexterm><primary>PQunescapeBytea</></></term>
+  <listitem>
+  <para>
+   Converts a string representation of binary data into binary
+   data --- the reverse of <function>PQescapeBytea</function>.
+   This is needed when retrieving <type>bytea</type> data in text format,
+   but not when retrieving it in binary format.
+
+<synopsis>
+unsigned char *PQunescapeBytea(unsigned char *from, size_t *to_length);
+</synopsis>
+</para>
+
+  <para>
+   The <parameter>from</parameter> parameter points to a string
+   such as might be returned by <function>PQgetvalue</function> when applied
+   to a <type>bytea</type> column. <function>PQunescapeBytea</function>
+   converts this string representation into its binary representation.
+   It returns a pointer to a buffer allocated with
+   <function>malloc()</function>, or null on error, and puts the size of
+   the buffer in <parameter>to_length</parameter>. The result must be
+   freed using <function>free()</> when it is no longer needed.
+  </para>
+
+  <para>
+   This conversion is not exactly the inverse of
+   <function>PQescapeBytea</function>, because the string is not expected
+   to be <quote>escaped</> when received from <function>PQgetvalue</function>.
+   In particular this means there is no need for string quoting considerations,
+   and so no need for a <structname>PGconn</> parameter.
+  </para>
+  </listitem>
+  </varlistentry>
+  </variablelist>
    
  </sect2>
 
-
 <sect2 id="libpq-exec-select-info">
   <title>Retrieving SELECT Result Information</title>