whisper : reject audio too short for reflective padding

src/whisper.cpp

@@ -3189,6 +3189,14 @@ static bool log_mel_spectrogram(
     int64_t stage_1_pad = WHISPER_SAMPLE_RATE * 30;
     int64_t stage_2_pad = frame_size / 2;
 
+    // The reflective padding below reads samples[1 .. stage_2_pad], so an input
+    // shorter than stage_2_pad + 1 would read past the end of the buffer.
+    if (n_samples < stage_2_pad + 1) {
+        WHISPER_LOG_ERROR("%s: audio too short: %d samples, need at least %d\n",
+                __func__, n_samples, (int) stage_2_pad + 1);
+        return false;
+    }
+
     // Initialize a vector and copy data from C array to it.
     std::vector<float> samples_padded;
     samples_padded.resize(n_samples + stage_1_pad + stage_2_pad * 2);

tests/CMakeLists.txt

@@ -177,3 +177,13 @@ add_parakeet_transcription_test(
     tests/parakeet-expected-diffusion-output.txt
     0.95)
 
+# log_mel_spectrogram out-of-bounds read on very short audio (issue #3923)
+set(MEL_OOB_TEST test-log-mel-oob)
+add_executable(${MEL_OOB_TEST} ${MEL_OOB_TEST}.cpp)
+target_include_directories(${MEL_OOB_TEST} PRIVATE ../include ../ggml/include ../examples)
+target_link_libraries(${MEL_OOB_TEST} PRIVATE common)
+target_compile_definitions(${MEL_OOB_TEST} PRIVATE
+    WHISPER_MODEL_PATH="${PROJECT_SOURCE_DIR}/models/for-tests-ggml-tiny.bin")
+add_test(NAME ${MEL_OOB_TEST} COMMAND ${MEL_OOB_TEST})
+set_tests_properties(${MEL_OOB_TEST} PROPERTIES LABELS "unit;gh")
+

tests/test-log-mel-oob.cpp

@@ -0,0 +1,35 @@
+#include "whisper.h"
+
+#include <string>
+#include <vector>
+
+#ifdef NDEBUG
+#undef NDEBUG
+#endif
+#include <cassert>
+
+// Regression test for the heap out-of-bounds read in log_mel_spectrogram().
+// Reflective padding reads samples[1 .. WHISPER_N_FFT/2], so an input shorter
+// than WHISPER_N_FFT/2 + 1 (201) samples used to read past the end of the
+// caller's buffer. Such inputs must now be rejected with a non-zero return.
+
+int main() {
+    std::string model_path = WHISPER_MODEL_PATH;
+
+    struct whisper_context_params cparams = whisper_context_default_params();
+    struct whisper_context * ctx = whisper_init_from_file_with_params(model_path.c_str(), cparams);
+    assert(ctx != nullptr);
+
+    std::vector<float> samples(256, 0.0f);
+
+    // Shorter than the reflective-pad window: must be rejected, not read OOB.
+    assert(whisper_pcm_to_mel(ctx, samples.data(),   4, 1) != 0);
+    assert(whisper_pcm_to_mel(ctx, samples.data(), 200, 1) != 0);
+
+    // Long enough to pad safely: must still succeed.
+    assert(whisper_pcm_to_mel(ctx, samples.data(), 201, 1) == 0);
+
+    whisper_free(ctx);
+
+    return 0;
+}