| # 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. | |