Re: [exim-dev] [Bug 1706] New: wrong escaping for PostgreSQL…

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Autor: Viktor Dukhovni
Data:  
A: exim-dev
Assumpte: Re: [exim-dev] [Bug 1706] New: wrong escaping for PostgreSQL "%" and "_"
On Tue, Oct 27, 2015 at 10:10:21PM +0000, admin@??? wrote:

> When using "_" or "%" characters in lookups to PostgreSQL databases, the
> characters are escaped when they shouldn't, thus causing issues with PostgreSQL
> 9.x (or any version where standard_conforming_strings = on , which has been the
> default for quite a few years now)
>
>
> This issue was already coming up in 2012 on the dev-list:
>
> https://lists.exim.org/lurker/message/20120921.150112.993f28a2.en.html
>
>
> Using E'' for the queries as suggested in bug 932 is also not a good idea, see
>
> https://lists.exim.org/lurker/message/20120926.153049.a091c952.en.html
>
> And a simple solution was suggested and somehow probably forgotten..:


Postfix quotes input to Postgres queries by using the corresponding
Posgres interface, you can ignore the "vstring" bits, that's just
a bit of Postfix-specific buffer management:

src/global/dict_pgsql.c:

    /*
     * Escape the input string, using PQescapeStringConn(), because the older
     * PQescapeString() is not safe anymore, as stated by the documentation.
     *
     * From current libpq (8.1.4) documentation:
     *
     * PQescapeStringConn writes an escaped version of the from string to the to
     * buffer, escaping special characters so that they cannot cause any
     * harm, and adding a terminating zero byte.
     *
     * ...
     *
     * The parameter from points to the first character of the string that is to
     * be escaped, and the length parameter gives the number of bytes in this
     * string. A terminating zero byte is not required, and should not be
     * counted in length.
     *
     * ...
     *
     * (The parameter) to shall point to a buffer that is able to hold at least
     * one more byte than twice the value of length, otherwise the behavior
     * is undefined.
     *
     * ...
     *
     * If the error parameter is not NULL, then *error is set to zero on
     * success, nonzero on error ... 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 conn object,
     * whether or not error is NULL.
     */
    VSTRING_SPACE(result, buflen);
    PQescapeStringConn(active_host->db, vstring_end(result), name, len, &err);
    if (err == 0) {
        VSTRING_SKIP(result);
    } else {


        /*
         * PQescapeStringConn() failed. According to the docs, we still have
         * a valid, null-terminated output string, but we need not rely on
         * this behavior.
         */
        msg_warn("dict pgsql: (host %s) cannot escape input string: %s",
                 active_host->hostname, PQerrorMessage(active_host->db));
        active_host->stat = STATFAIL;
        VSTRING_TERMINATE(result);
    }


Bottom line, instead of hand-coding the quoting, use PQescapeStringConn(),
which does correct quoting in the context of the current database
connection.

-- 
    Viktor.