Re: [HACKERS] PQescapeIdentifier - Mailing list pgsql-patches

Hang on a second.  Has someone considered the encoding issues this might
suffer from, same as PQescapeString? I remember we discussed it briefly
and I mentioned it's outta my league to prove one way or the other...

Bruce Momjian wrote:
> Christopher Kings-Lynne wrote:
>> TODO item done for 8.2:
>>
>> * Add PQescapeIdentifier() to libpq
>>
>> Someone probably needs to check this :)
>
> Updated patch applied.  Thanks.
>
>
>
> ------------------------------------------------------------------------
>
> Index: doc/src/sgml/libpq.sgml
> ===================================================================
> RCS file: /cvsroot/pgsql/doc/src/sgml/libpq.sgml,v
> retrieving revision 1.211
> diff -c -c -r1.211 libpq.sgml
> *** doc/src/sgml/libpq.sgml    23 May 2006 22:13:19 -0000    1.211
> --- doc/src/sgml/libpq.sgml    26 Jun 2006 23:54:12 -0000
> ***************
> *** 2279,2284 ****
> --- 2279,2347 ----
>   </para>
>   </sect2>
>
> + <sect2 id="libpq-exec-escape-identifier">
> +   <title>Escaping Identifier for Inclusion in SQL Commands</title>
> +
> +    <indexterm zone="libpq-exec-escape-identifier"><primary>PQescapeIdentifier</></>
> +    <indexterm zone="libpq-exec-escape-identifier"><primary>escaping strings</></>
> +
> + <para>
> + <function>PQescapeIdentifier</function> escapes a string for use
> + as an identifier name within an SQL command.  For example; table names,
> + column names, view names and user names are all identifiers.
> + Double quotes (") must be escaped to prevent them from being interpreted
> + specially by the SQL parser. <function>PQescapeIdentifier</> 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>
> + Note that it is still necessary to do escaping of identifiers when
> + using functions that support parameterized queries such as <function>PQexecParams</> or
> + its sibling routines. Only literal values are automatically escaped
> + using these functions, not identifiers.
> +
> + <synopsis>
> + size_t PQescapeIdentifier (char *to, const char *from, size_t length);
> + </synopsis>
> + </para>
> +
> + <para>
> + 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 characters 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>PQescapeIdentifier</> 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 character than twice
> + the value of <parameter>length</>, otherwise the behavior is
> + undefined.  A call to <function>PQescapeIdentifier</> writes an escaped
> + version of the <parameter>from</> string to the <parameter>to</>
> + buffer, replacing special characters so that they cannot cause any
> + harm, and adding a terminating zero byte.  The double quotes that
> + may surround <productname>PostgreSQL</> identifiers are not
> + included in the result string; they should be provided in the SQL
> + command that the result is inserted into.
> + </para>
> + <para>
> + <function>PQescapeIdentifier</> returns the number of characters written
> + to <parameter>to</>, not including the terminating zero byte.
> + </para>
> + <para>
> + Behavior is undefined if the <parameter>to</> and <parameter>from</>
> + strings overlap.
> + </para>
> + </sect2>
>
>    <sect2 id="libpq-exec-escape-bytea">
>     <title>Escaping Binary Strings for Inclusion in SQL Commands</title>
> Index: src/interfaces/libpq/exports.txt
> ===================================================================
> RCS file: /cvsroot/pgsql/src/interfaces/libpq/exports.txt,v
> retrieving revision 1.11
> diff -c -c -r1.11 exports.txt
> *** src/interfaces/libpq/exports.txt    28 May 2006 22:42:05 -0000    1.11
> --- src/interfaces/libpq/exports.txt    26 Jun 2006 23:54:20 -0000
> ***************
> *** 130,132 ****
> --- 130,134 ----
>   PQencryptPassword         128
>   PQisthreadsafe            129
>   enlargePQExpBuffer        130
> + PQescapeIdentifier        131
> +
> Index: src/interfaces/libpq/fe-exec.c
> ===================================================================
> RCS file: /cvsroot/pgsql/src/interfaces/libpq/fe-exec.c,v
> retrieving revision 1.186
> diff -c -c -r1.186 fe-exec.c
> *** src/interfaces/libpq/fe-exec.c    28 May 2006 21:13:54 -0000    1.186
> --- src/interfaces/libpq/fe-exec.c    26 Jun 2006 23:54:21 -0000
> ***************
> *** 2516,2521 ****
> --- 2516,2557 ----
>   }
>
>   /*
> +  * Escaping arbitrary strings to get valid SQL identifier strings.
> +  *
> +  * Replaces " with "".
> +  *
> +  * length is the length of the source string.  (Note: if a terminating NUL
> +  * is encountered sooner, PQescapeIdentifier stops short of "length"; the behavior
> +  * is thus rather like strncpy.)
> +  *
> +  * For safety the buffer at "to" must be at least 2*length + 1 bytes long.
> +  * A terminating NUL character is added to the output string, whether the
> +  * input is NUL-terminated or not.
> +  *
> +  * Returns the actual length of the output (not counting the terminating NUL).
> +  */
> + size_t
> + PQescapeIdentifier(char *to, const char *from, size_t length)
> + {
> +     const char *source = from;
> +     char       *target = to;
> +     size_t        remaining = length;
> +
> +     while (remaining > 0 && *source != '\0')
> +     {
> +         if (*source  == '"')
> +             *target++ = *source;
> +         *target++ = *source++;
> +         remaining--;
> +     }
> +
> +     /* Write the terminating NUL character. */
> +     *target = '\0';
> +
> +     return target - to;
> + }
> +
> + /*
>    *        PQescapeBytea    - converts from binary string to the
>    *        minimal encoding necessary to include the string in an SQL
>    *        INSERT statement with a bytea type column as the target.
> Index: src/interfaces/libpq/libpq-fe.h
> ===================================================================
> RCS file: /cvsroot/pgsql/src/interfaces/libpq/libpq-fe.h,v
> retrieving revision 1.129
> diff -c -c -r1.129 libpq-fe.h
> *** src/interfaces/libpq/libpq-fe.h    23 May 2006 22:13:19 -0000    1.129
> --- src/interfaces/libpq/libpq-fe.h    26 Jun 2006 23:54:21 -0000
> ***************
> *** 436,441 ****
> --- 436,443 ----
>                     size_t *to_length);
>   extern unsigned char *PQunescapeBytea(const unsigned char *strtext,
>                   size_t *retbuflen);
> + extern size_t PQescapeIdentifier(char *to, const char *from, size_t length);
> +
>   /* These forms are deprecated! */
>   extern size_t PQescapeString(char *to, const char *from, size_t length);
>   extern unsigned char *PQescapeBytea(const unsigned char *from, size_t from_length,