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kenifor wants to merge 2 commits into from
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detect: guard rate filter callback registration #15380

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detect: guard rate filter callback registration
May 12, 2026
a550dae
detect: return bool from rate filter callback registration, guard exa…
May 26, 2026
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4 changes: 3 additions & 1 deletion examples/lib/custom/main.c
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Original file line number Diff line number Diff line change
Expand Up @@ -253,7 +253,9 @@ int main(int argc, char **argv)
* ThreadVars will be ready. */
SuricataInit();

SCDetectEngineRegisterRateFilterCallback(RateFilterCallback, NULL);
if (DetectEngineEnabled()) {
SCDetectEngineRegisterRateFilterCallback(RateFilterCallback, NULL);

@jasonish jasonish May 28, 2026

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I would look a warning here, and in the other plugin as well on failure, just for completeness of the examples.

}

/* Spawn our worker threads. */
pthread_t worker;
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4 changes: 3 additions & 1 deletion examples/lib/live/main.c
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Expand Up @@ -306,7 +306,9 @@ int main(int argc, char **argv)
* ThreadVars will be ready. */
SuricataInit();

SCDetectEngineRegisterRateFilterCallback(RateFilterCallback, NULL);
if (DetectEngineEnabled()) {
SCDetectEngineRegisterRateFilterCallback(RateFilterCallback, NULL);
}

/* Spawn our worker threads, one for each interface. */
pthread_t workers[MAX_INTERFACES];
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8 changes: 7 additions & 1 deletion src/detect-engine.c
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Expand Up @@ -5122,12 +5122,18 @@ void DetectLowerSetupCallback(
}
}

void SCDetectEngineRegisterRateFilterCallback(SCDetectRateFilterFunc fn, void *arg)
bool SCDetectEngineRegisterRateFilterCallback(SCDetectRateFilterFunc fn, void *arg)
{
DetectEngineCtx *de_ctx = DetectEngineGetCurrent();
if (de_ctx == NULL) {

@victorjulien victorjulien May 13, 2026

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I'm really curious how we would get here with a NULL de_ctx. The only call site:

            if (de_ctx->RateFilterCallback && original_action != pa->action) {
                pa->action = de_ctx->RateFilterCallback(p, sid, gid, rev, original_action,
                        pa->action, de_ctx->rate_filter_callback_arg);

So there a detect engine when this is called. It's also a full engine as this is only called on a signature match AFAICS.

@catenacyber catenacyber May 17, 2026

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It is also called in plugins see

examples/lib/custom/main.c:    SCDetectEngineRegisterRateFilterCallback(RateFilterCallback, NULL);
examples/lib/live/main.c:    SCDetectEngineRegisterRateFilterCallback(RateFilterCallback, NULL);

cc @jasonish

@jasonish jasonish May 18, 2026

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Is this actually a scenario a plugin could end up in?

@jasonish jasonish May 18, 2026

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And if it can, where should a plugin attempt to reregister these callbacks again?

@kenifor kenifor May 19, 2026

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Yes. SCDetectEngineRegisterRateFilterCallback() is a documented public
extension API. A plugin author following the bundled examples
(examples/lib/custom/main.c, examples/lib/live/main.c) will naturally
call it during plugin/library initialization — before DetectEngineCtxInit()
has run and registered an engine as current. In that window,
DetectEngineGetCurrent() returns NULL and the original code dereferences it
unconditionally. In multi-tenant or delayed-detect configurations the window
is even wider.

The runtime call-site that @victorjulien points to (inside the signature-match
path) is indeed safe, because there a live engine is guaranteed. But this
function is also a registration entry-point called by external code that has
no visibility into the engine lifecycle — that is the path Svace flags.

Where should a plugin reregister?

That is a fair follow-up. The current fix (guard + log + early return) prevents
the crash, but since the function is void the caller has no way to detect
that registration was silently dropped.

Two options, in order of invasiveness:

  1. Change the return type to bool/int so the caller knows the
    registration failed and can retry after the engine is ready. This is a
    small API change but requires updating the devguide and the two bundled
    examples.

  2. Keep void, document the constraint — add a note to the devguide
    stating that this API must be called after the detect engine is initialized.
    The guard then acts purely as a defensive belt-and-suspenders measure.

SCLogError("no detection engine available for rate filter callback registration");
return false;
}

de_ctx->RateFilterCallback = fn;
de_ctx->rate_filter_callback_arg = arg;
DetectEngineDeReference(&de_ctx);
return true;
}

int DetectEngineThreadCtxGetJsonContext(DetectEngineThreadCtx *det_ctx)
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2 changes: 1 addition & 1 deletion src/detect.h
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Expand Up @@ -1175,7 +1175,7 @@ typedef struct DetectEngineCtx_ {
* This callback is added to the current detection engine and will be
* copied to all future detection engines over rule reloads.
*/
void SCDetectEngineRegisterRateFilterCallback(SCDetectRateFilterFunc cb, void *arg);
bool SCDetectEngineRegisterRateFilterCallback(SCDetectRateFilterFunc cb, void *arg);

/* Engine groups profiles (low, medium, high, custom) */
enum {
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