Documentation Source Text

different query, like this:

<codeblock>
SELECT hex(t1) FROM t1 WHERE cx MATCH $pattern;
</codeblock>

<p>
Because the pointer is passed in the t1 column of the t1
table as a BLOB (in older versions of SQLite), such a query would have 
shown the value of the
pointer in hex.  The attacker could then modify that pointer to try to
get the snippet() function to modify memory in some other part of 
the application address space instead of the fts3cursor object it 
was suppose to be operating on:

<codeblock>
SELECT snippet(x'6092310100000000') FROM t1 WHERE cx MATCH $pattern;

But there are some notable exceptions.  To wit:

<ul>
<li><p>
The [https://en.wikipedia.org/wiki/Web_SQL_Database|WebSQL] interface
to webkit allowed any webpage to to run arbitrary SQL in the browser
for Chrome and Safari.  That arbitrary SQL was suppose to be run inside
a sandbox where it could do no harm even if exploited, but that sandbox
turned out to be less secure than people supposed.  In the spring of 2017, 
one team of hackers was able to root an iMac using a long sequence of 
exploits, one of which involved corrupting the pointers passed as BLOB 
values to the snippet() FTS3 function of an SQLite database running via
the WebSQL interface inside of Safari.

<li><p>

<tcl>hd_fragment ptrleak {pointer leak} {pointer leaks}</tcl>
<h2>Pointer Leaks</h2>

<p>
The use of subtypes on pointers prevented pointer forgery using
pure SQL.  But subtypes do nothing to prevent an attacker from reading
the values of pointers.  In other words, subtypes on pointer values
prevent attacks using SQL statements like this:

<codeblock>
SELECT snippet(x'6092310100000000') FROM t1 WHERE cx MATCH $pattern;
</codeblock>

<p>
The BLOB argument to snippet() does not have the correct subtype, so the

<li>Applications need to receive a pointer to the "fts5_api" object in order
    to add extensions, such as custom tokenizers, to the [FTS5] extension.
</ul>

<li><p>
Pointers should <u>never</u> be exchanged by encoding them as some other
SQL datatype, such as integers or BLOBs.  Instead, use the interfaces
designed to facilitate secure pointer passing:
[sqlite3_bind_pointer()], [sqlite3_result_pointer()], and
[sqlite3_value_pointer()].

<li><p>
The use of pointer-passing is an advanced technique that should be used
infrequently and cautiously.  Pointer-passing should not be
used haphazardly or carelessly.  Pointer-passing is a sharp tool