From a1255cb6c9f4d53fea8ae491da314edfabbeb108 Mon Sep 17 00:00:00 2001
From: Nicolas Ramz <nicolas.ramz@gmail.com>
Date: Fri, 12 Jan 2024 18:26:52 +0100
Subject: [PATCH] LibGfx/ILBMLoader: Don't decode bits once full row has been
 decoded

We were potentially decoding more bits than needed: this could
trash the next lines if decoder didn't zero the extra bits.
---
 Tests/LibGfx/TestImageDecoder.cpp                 |  11 +++++++++++
 Tests/LibGfx/test-inputs/ilbm/small-24bit.iff     | Bin 0 -> 678 bytes
 .../Libraries/LibGfx/ImageFormats/ILBMLoader.cpp  |   4 +++-
 3 files changed, 14 insertions(+), 1 deletion(-)
 create mode 100644 Tests/LibGfx/test-inputs/ilbm/small-24bit.iff

diff --git a/Tests/LibGfx/TestImageDecoder.cpp b/Tests/LibGfx/TestImageDecoder.cpp
index ffd47e6a3e..6c475bf8ca 100644
--- a/Tests/LibGfx/TestImageDecoder.cpp
+++ b/Tests/LibGfx/TestImageDecoder.cpp
@@ -254,6 +254,17 @@ TEST_CASE(test_brush_transparent_color)
     EXPECT_EQ(frame.image->get_pixel(114, 103), Gfx::Color::NamedColor::Black);
 }
 
+TEST_CASE(test_small_24bit)
+{
+    auto file = MUST(Core::MappedFile::map(TEST_INPUT("ilbm/small-24bit.iff"sv)));
+    EXPECT(Gfx::ILBMImageDecoderPlugin::sniff(file->bytes()));
+    auto plugin_decoder = TRY_OR_FAIL(Gfx::ILBMImageDecoderPlugin::create(file->bytes()));
+
+    auto frame = TRY_OR_FAIL(expect_single_frame_of_size(*plugin_decoder, { 10, 10 }));
+
+    EXPECT_EQ(frame.image->get_pixel(0, 4), Gfx::Color(1, 0, 1, 255));
+}
+
 TEST_CASE(test_ilbm_malformed_header)
 {
     Array test_inputs = {
diff --git a/Tests/LibGfx/test-inputs/ilbm/small-24bit.iff b/Tests/LibGfx/test-inputs/ilbm/small-24bit.iff
new file mode 100644
index 0000000000000000000000000000000000000000..39580314bc541a9037ef17da8a852a369d1af4dc
GIT binary patch
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z5Aq^Eh!A3AkY{9&2Qk?h8LSu?co`XV!HVU<0nYgUHkc>E$RNVVzz9|?$H<@n05f%^
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literal 0
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diff --git a/Userland/Libraries/LibGfx/ImageFormats/ILBMLoader.cpp b/Userland/Libraries/LibGfx/ImageFormats/ILBMLoader.cpp
index e89f6bff24..1b10f91978 100644
--- a/Userland/Libraries/LibGfx/ImageFormats/ILBMLoader.cpp
+++ b/Userland/Libraries/LibGfx/ImageFormats/ILBMLoader.cpp
@@ -220,7 +220,9 @@ static ErrorOr<ByteBuffer> planar_to_chunky(ReadonlyBytes bitplanes, ILBMLoading
                 u8 bit = bitplanes[offset_base + i];
                 u8 rgb_shift = p / 8;
 
-                for (u8 b = 0; b < 8; b++) {
+                // Some encoders don't pad bytes rows with 0: make sure we stop
+                // when enough data for current bitplane row has been read
+                for (u8 b = 0; b < 8 && (i * 8) + b < width; b++) {
                     u8 mask = 1 << (7 - b);
                     // get current plane
                     if (bit & mask) {