Does SQLite leak memory with the SQLCipher extension?

Question

I'm using SQLCipher to store an encrypted SQLite database. However, when I use sqlite3_key to encrypt the database, I start getting a memory leak. Observe the following sample:

#include <sqlite3.h>    

int main()
{
    sqlite3 * connection;
    sqlite3_open_v2(":memory:", &connection, SQLITE_OPEN_READWRITE | SQLITE_OPEN_CREATE, NULL);
    sqlite3_key(connection, "passphrase", 10);
    sqlite3_close(connection);
}

This sample produces a memory leak. If I remove the call to sqlite3_key, the memory leak disappears.

I've narrowed down some possible culprits:

Although the sample uses an in-memory database (hence ":memory:"), I see the same result when using file-based databases.
All of the return codes from the sqlite3_* calls are SQLITE_OK, meaning there aren't any errors.
The buffer length of 10 for "passphrase" is not the problem.

However, no matter how many connections I create or how many different encryption keys I use, the memory leak is always about 8 kilobytes. This leads me to suspect that this is not actually a memory leak, but just some constant global memory in SQLite/SQLCipher that doesn't get freed manually.

Has anyone experienced this before? Is there a way to get rid of the leak? Even if this is not an official memory leak, it's hard to detect real memory leaks with this present.

I'm using a SQLCipher library for Windows.

No issues with the above code on Linux running the latest repo code. — netcoder, Aug 02 '12 at 20:16
Its worth noting that SQLCipher also has an test suite that we run before each release that checks for memory leaks on all operations, and it is showing no leaks with the current code base. IIRC, _CrtDumpMemoryLeaks() is somewhat notorious for erroneously reporting leaks that aren't really leaks. — Stephen Lombardo, Aug 02 '12 at 21:18
@StephenLombardo : On my Ubuntu machine it leaks too, i'm using valgrind to check memory leak (I use the same code as above). — TOC, Sep 09 '12 at 16:35

score 3 · Accepted Answer · edited Oct 02 '12 at 20:09

I've looked into this a bit further, and these reported leaks are a result of memory allocated by OpenSSL. Since SQLCipher doesn't know when the app is strictly done using it, EVP_cleanup() is not called, and the memory is reported by valgrind as a leak. We're working towards a simple fix that will try to identify when the OpenSSL structures are no longer in use by SQLCipher with some simple reference counting, so EVP_cleanup() can be called automatically.

As a quick workaround for this before the next release of SQLCipher, you could call EVP_cleanup() manually in the program before exiting.

Does SQLite leak memory with the SQLCipher extension?

1 Answers1