mirror of
https://github.com/tursodatabase/libsql.git
synced 2024-11-27 06:58:59 +00:00
143 lines
6.3 KiB
Markdown
143 lines
6.3 KiB
Markdown
# The new-security-options branch
|
|
|
|
## The problem that the [new-security-options](/timeline?r=new-security-options) branch tries to solve
|
|
|
|
An attacker might modify the schema of an SQLite database by adding
|
|
structures that cause code to run when some other application opens and
|
|
reads the database. For example, the attacker might replace a table
|
|
definition with a view. Or the attacker might add triggers to tables
|
|
or views, or add new CHECK constraints or generated columns or indexes
|
|
with expressions in the index list or in the WHERE clause. If the
|
|
added features invoke SQL functions or virtual tables with side effects,
|
|
that might cause harm to the system if run by a high-privilege victim.
|
|
Or, the added features might exfiltrate information if the database is
|
|
read by a high-privilege victim.
|
|
|
|
The changes in this branch strive to make it easier for high-privilege
|
|
applications to safely read SQLite database files that might have been
|
|
maliciously corrupted by an attacker.
|
|
|
|
## Overview of changes in [new-security-options](/timeline?r=new-security-options)
|
|
|
|
The basic idea is to tag every SQL function and virtual table with one
|
|
of three risk levels:
|
|
|
|
1. Innocuous
|
|
2. Normal
|
|
3. Direct-Only
|
|
|
|
Innocuous functions/vtabs are safe and can be used at any time.
|
|
Direct-only elements, in contrast, might have cause side-effects and
|
|
should only be used from top-level SQL, not from within triggers or views nor
|
|
in elements of the schema such as CHECK constraint, DEFAULT values,
|
|
generated columns, index expressions, or in the WHERE clause of a
|
|
partial index that are potentially under the control of an attacker.
|
|
Normal elements behave like Innocuous if TRUSTED\_SCHEMA=on
|
|
and behave like direct-only if TRUSTED\_SCHEMA=off.
|
|
|
|
Application-defined functions and virtual tables go in as Normal unless
|
|
the application takes deliberate steps to change the risk level.
|
|
|
|
For backwards compatibility, the default is TRUSTED\_SCHEMA=on. Documentation
|
|
will be updated to recommend applications turn TRUSTED\_SCHEMA to off.
|
|
|
|
An innocuous function or virtual table is one that can only read content
|
|
from the database file in which it resides, and can only alter the database
|
|
in which it resides. Most SQL functions are innocuous. For example, there
|
|
is no harm in an attacker running the abs() function.
|
|
|
|
Direct-only elements that have side-effects that go outside the database file
|
|
in which it lives, or return information from outside of the database file.
|
|
Examples of direct-only elements include:
|
|
|
|
1. The fts3\_tokenizer() function
|
|
2. The writefile() function
|
|
3. The readfile() function
|
|
4. The zipvfs virtual table
|
|
5. The csv virtual table
|
|
|
|
We do not want an attacker to be able to add these kinds of things to
|
|
the database schema and possibly trick a high-privilege application
|
|
from performing any of these actions. Therefore, functions and vtabs
|
|
with side-effects are marked as Direct-Only.
|
|
|
|
Legacy applications might add other risky functions or vtabs. Those will
|
|
go in as "Normal" by default. For optimal security, we want those risky
|
|
app-defined functions and vtabs to be direct-only, but making that the
|
|
default might break some legacy applications. Hence, all app-defined
|
|
functions and vtabs go in as Normal, but the application can switch them
|
|
over to "Direct-Only" behavior using a single pragma.
|
|
|
|
The restrictions on the use of functions and virtual tables do not apply
|
|
to TEMP. A TEMP VIEW or a TEMP TRIGGER can use any valid SQL function
|
|
or virtual table. The idea is that TEMP views and triggers must be
|
|
directly created by the application and are thus under the control of the
|
|
application. TEMP views and triggers cannot be created by an attacker who
|
|
corrupts the schema of a persistent database file. Hence TEMP views and
|
|
triggers are safe.
|
|
|
|
## Specific changes
|
|
|
|
1. New sqlite3\_db\_config() option SQLITE\_DBCONFIG\_TRUSTED\_SCHEMA for
|
|
turning TRUSTED\_SCHEMA on and off. It defaults to ON.
|
|
|
|
2. Compile-time option -DSQLITE\_TRUSTED\_SCHEMA=0 causes the default
|
|
TRUSTED\_SCHEMA setting to be off.
|
|
|
|
3. New pragma "PRAGMA trusted\_schema=(ON\|OFF);". This provides access
|
|
to the TRUSTED_SCHEMA setting for application coded using scripting
|
|
languages or other secondary languages where they are unable to make
|
|
calls to sqlite3\_db\_config().
|
|
|
|
4. New options for the "enc" parameter to sqlite3\_create\_function() and
|
|
its kin:
|
|
<ol type="a">
|
|
<li> _SQLITE\_INNOCUOUS_ → tags the new functions as Innocuous
|
|
<li> _SQLITE\_DIRECTONLY_ → tags the new functions as Direct-Only
|
|
</ol>
|
|
|
|
5. New options to sqlite3\_vtab\_config():
|
|
<ol type="a">
|
|
<li> _SQLITE\_VTAB\_INNOCUOUS_ → tags the vtab as Innocuous
|
|
<li> _SQLITE\_VTAB\_DIRECTONLY_ → tags the vtab as Direct-Only
|
|
</ol>
|
|
|
|
6. Change many of the functions and virtual tables in the SQLite source
|
|
tree to use one of the tags above.
|
|
|
|
7. Enhanced PRAGMA function\_list and virtual-table "pragma\_function\_list"
|
|
with additional columns. The columns now are:
|
|
<ul>
|
|
<li> _name_ → Name of the function
|
|
<li> _builtin_ → 1 for built-in functions. 0 otherwise.
|
|
<li> _type_ → 's'=Scalar, 'a'=Aggregate, 'w'=Window
|
|
<li> _enc_ → 'utf8', 'utf16le', or 'utf16be'
|
|
<li> _narg_ → number of argument
|
|
<li> _flags_ → Bitmask of SQLITE\_INNOCUOUS, SQLITE\_DIRECTONLY,
|
|
SQLITE\_DETERMINISTIC, SQLITE\_SUBTYPE, and
|
|
SQLITE\_FUNC\_INTERNAL flags.
|
|
</ul>
|
|
<p>The last four columns are new.
|
|
|
|
8. The function\_list PRAGMA now also shows all entries for each function.
|
|
So, for example, if a function can take either 2 or 3 arguments,
|
|
there are separate rows for the 2-argument and 3-argument versions of
|
|
the function.
|
|
|
|
## Additional Notes
|
|
|
|
The function_list enhancements allow the application to query the set
|
|
of SQL functions that meet various criteria. For example, to see all
|
|
SQL functions that are never allowed to be used in the schema or in
|
|
trigger or views:
|
|
|
|
~~~
|
|
SELECT DISTINCT name FROM pragma_function_list
|
|
WHERE (flags & 0x80000)!=0
|
|
ORDER BY name;
|
|
~~~
|
|
|
|
Doing the same is not possible for virtual tables, as a virtual table
|
|
might be Innocuous, Normal, or Direct-Only depending on the arguments
|
|
passed into the xConnect method.
|