Potential Memory Leak in string_configuration_get Due to Ownership Mismatch

[dgershko]

There seems to be a mismatch in ownership semantics between valkeymodule-rs and the Valkey C API when handling string config getters, which may be causing a memory leak.

Problem:

• The Rust function string_configuration_get returns a *mut RedisModuleString using .take(), which appears to transfer ownership.
• The C function getModuleStringConfig calls this getter and duplicates the string (sdsdup(val->ptr)), assuming the original remains valid.
• This is done on purpose, as Valkey’s documentation states that "On string config gets, the string will not be consumed and will be valid after execution."
• Since the C code does not free the original, and Rust seems to allocate a new copy, this could lead to a memory leak.

Reproduction Steps:

1. Compile Valkey with AddressSanitizer (ASan).
2. Run Valkey with a module that registers string configs (e.g., valkey-bloom).
3. In the CLI, run CONFIG GET bf.bloom-fp-rate (or another registered config).
4. Stop the server – ASan should report a memory leak.

Additional Context:

I'm not a Rust expert, but based on my understanding, .take() combined with ConfigurationContext::new() might be the cause.

valkeymodule-rs/src/configuration.rs

Line 306 in 6497ac4

extern "C" fn string_configuration_get<T: ConfigurationValue<ValkeyString> + 'static>(

[zackcam]

Hi,
I took a look at recreating this and wasn't able to find a memory leak. Let me know if I compiled Valkey in a different way than you
Commmand used to compile the valkey server:
make -j4 SANITIZER=address SERVER_CFLAGS='-Werror' BUILD_TLS=module
I then ran this to load the module:
./src/valkey-server --loadmodule ../valkey-bloom/target/release/libvalkey_bloom.so
Finally i did step 3 and 4 above:

I don't see any memory leak messages let me know if I should try and recreate this in a different way

[dgershko]

Hi Zack!
Please try the following:

make distclean
make -j4 SANITIZER=address
./src/valkey-server --loadmodule ../valkey-bloom/target/release/libvalkey_bloom.so

here's the exact error I got when compiling like this and calling the CONFIG GET:

20781:M 23 Feb 2025 12:00:58.571 # Valkey is now ready to exit, bye bye...

=================================================================
==20781==ERROR: LeakSanitizer: detected memory leaks

Direct leak of 24 byte(s) in 1 object(s) allocated from:
    #0 0x7f87501e657d in malloc (/lib64/libasan.so.4+0xd857d)
    #1 0x5947a6 in ztrymalloc_usable_internal /home/dgershko/workplace/valkey/src/zmalloc.c:155
    #2 0x5947a6 in zmalloc_usable /home/dgershko/workplace/valkey/src/zmalloc.c:199
    #3 0x76a130 in createEmbeddedStringObjectWithKeyAndExpire.constprop.226 /home/dgershko/workplace/valkey/src/object.c:167
    #4 0x55e873 in VM_CreateStringFromString /home/dgershko/workplace/valkey/src/module.c:2794
    #5 0x7f874557bf07 in _$LT$valkey_module..redismodule..ValkeyString$u20$as$u20$core..clone..Clone$GT$::clone::hf82e8ed8ededebd7 (../valkey-bloom/target/release/libvalkey_bloom.so+0x2df07)
    #6 0x70dce0 in configGetCommand /home/dgershko/workplace/valkey/src/config.c:994
    #7 0x53e634 in call /home/dgershko/workplace/valkey/src/server.c:3735
    #8 0x54062c in processCommand /home/dgershko/workplace/valkey/src/server.c:4358
    #9 0x61b667 in processCommandAndResetClient /home/dgershko/workplace/valkey/src/networking.c:3044
    #10 0x61b667 in processInputBuffer /home/dgershko/workplace/valkey/src/networking.c:3172
    #11 0x62363a in readQueryFromClient /home/dgershko/workplace/valkey/src/networking.c:3277
    #12 0x634615 in callHandler /home/dgershko/workplace/valkey/src/connhelpers.h:79
    #13 0x634615 in connSocketEventHandler.lto_priv.378 /home/dgershko/workplace/valkey/src/socket.c:300
    #14 0x47a833 in aeProcessEvents /home/dgershko/workplace/valkey/src/ae.c:486
    #15 0x47b5c4 in aeMain /home/dgershko/workplace/valkey/src/ae.c:543
    #16 0x452960 in main /home/dgershko/workplace/valkey/src/server.c:7211
    #17 0x7f874f418139 in __libc_start_main (/lib64/libc.so.6+0x21139)

SUMMARY: AddressSanitizer: 24 byte(s) leaked in 1 allocation(s).

[zackcam]

Thanks for giving the commands you used! Trying that returned the memory leak you showed I will now take a look at fixing it.

[KarthikSubbarao]

We found the source of the leak in the SDK's config interface and Cameron is working on the fix