Check that the gain map metadata is valid on decoding.

src/read.c

@@ -2028,6 +2028,11 @@ static avifResult avifParseToneMappedImageBox(avifGainMap * gainMap, const uint8
     if (writerVersion <= supportedMetadataVersion) {
         AVIF_CHECKERR(avifROStreamRemainingBytes(&s) == 0, AVIF_RESULT_INVALID_TONE_MAPPED_IMAGE);
     }
+
+    if (avifGainMapValidateMetadata(gainMap, diag) != AVIF_RESULT_OK) {
+        return AVIF_RESULT_INVALID_TONE_MAPPED_IMAGE;
+    }
+
     return AVIF_RESULT_OK;
 }
 #endif // AVIF_ENABLE_EXPERIMENTAL_GAIN_MAP

tests/data/README.md

@@ -648,6 +648,18 @@ Source : same as seine_sdr_gainmap_srgb.avif before commit 10b7232
 An image with a `tmap` item (i.e. a gain map) but no 'tmap' brand in the `ftyp` box.
 The gain map should be ignored by the decoder since the `tmap` brand is missing.
 
+### File [seine_sdr_gainmap_ngammazero.avif](seine_sdr_gainmap_notmapbrand.avif)
+
+![](seine_sdr_gainmap_notmapbrand.avif)
+
+License: [same as libavif](https://github.com/AOMediaCodec/libavif/blob/main/LICENSE)
+
+Source : same as seine_sdr_gainmap_srgb.avif generated with a modified avifenc that
+writes 0 instead of the gain map gamma numerator.
+
+An image with a gain map where the gain map gamma value is zero (invalid).
+
+
 ### File [seine_sdr_gainmap_big_srgb.avif](seine_sdr_gainmap_big_srgb.avif)
 
 ![](seine_sdr_gainmap_big_srgb.avif)

tests/gtest/avifgainmaptest.cc

@@ -926,6 +926,21 @@ TEST(GainMapTest, DecodeInvalidFtyp) {
   ASSERT_EQ(decoded->gainMap, nullptr);
 }
 
+TEST(GainMapTest, DecodeInvalidGamma) {
+  const std::string path =
+      std::string(data_path) + "seine_sdr_gainmap_gammazero.avif";
+  ImagePtr decoded(avifImageCreateEmpty());
+  ASSERT_NE(decoded, nullptr);
+  DecoderPtr decoder(avifDecoderCreate());
+  ASSERT_NE(decoder, nullptr);
+  decoder->enableDecodingGainMap = true;
+  decoder->enableParsingGainMapMetadata = true;
+  // Fails to decode: the gain map is ignored because the gain map gamma is zero
+  // (invalid).
+  ASSERT_EQ(avifDecoderReadFile(decoder.get(), decoded.get(), path.c_str()),
+            AVIF_RESULT_INVALID_TONE_MAPPED_IMAGE);
+}
+
 #define EXPECT_FRACTION_NEAR(numerator, denominator, expected)     \
   EXPECT_NEAR(std::abs((double)numerator / denominator), expected, \
               expected * 0.001);