[Issue 9430] mdb_put() with MDB_RESERVE | MDB_NOOVERWRITE sets 'data' to invalid memory

https://bugs.openldap.org/show_bug.cgi?id=9430

--- Comment #1 from Howard Chu hyc@openldap.org --- (In reply to kenta from comment #0)

Running on NixOS (x86_64-linux).

The following sequence of methods was called with an MDB_env and MDB_txn created with default flags, with the MDB_txn open on MAIN_DBI.

The following code is pseudocode - should the code not be clear enough, happy to provide the original test case which was written in Zig (https://ziglang.org).

// Put KV pair ('hello', 'test').

var k: MDB_val = .{ .mv_size = "hello".len, .mv_data = &"hello" };
var v: MDB_val = .{ .mv_size = "test".len, .mv_data = &"test" };
mdb_put(txn, MAIN_DBI, &k, &v, 0);

// Attempt to put KV pair ('hello', 'world!') with MDB_RESERVE |

MDB_NOOVERWRITE, and assert that it fails.

var k2: MDB_val = .{ .mv_size = "hello".len, .mv_data = &"hello" };
var v2: MDB_val = .{ .mv_size = "world!".len, .mv_data = null };
assert(mdb_put(txn, MAIN_DBI, &k2, &v2, MDB_RESERVE | MDB_NOOVERWRITE)

== MDB_KEYEXIST);

// Assertion fails.
assert(v2 == v);

After these steps, it is expected that v2's 'mv_data' points to 'test' with a 'mv_size' of 4 (the previously, successfully-written KV pair).

What actually happened was that v2's 'mv_size' was correctly set to 4, though 'mv_data' points to garbage memory.

Unable to reproduce, code works and returns the expected value for me.