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Fix DDS Timeout issues in oss-fuzz #9404

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Fix DDS Timeout issues in oss-fuzz #9404

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63ff7ca
wip 2 -- zipped parameters
wiredfool Jan 22, 2026
f15886a
WIP 3 -- do all the remaining pixels in one chunk2
wiredfool Jan 22, 2026
020f890
add a selection of test cases from oss-fuzz
wiredfool Jan 22, 2026
cd1c9f1
revert consolidated mask, all extra pixels are just 0
wiredfool Jan 22, 2026
326bfde
added test images
wiredfool Jan 22, 2026
65a9bbc
lint
wiredfool Jan 22, 2026
6a421d7
[pre-commit.ci] auto fixes from pre-commit.com hooks
pre-commit-ci[bot] Jan 22, 2026
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Binary file added Tests/images/timeout-041dd17dfde800360a47a172269df127af138c6b.dds
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Binary file added Tests/images/timeout-52d106579505547091ef69b58341351a37c23e31.dds
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Binary file added Tests/images/timeout-755a4d204f4208e3597ac3391edebee196462bd0.dds
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Binary file added Tests/images/timeout-c60a3d7314213624607bfb3e38d551a8b24a7435.dds
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16 changes: 16 additions & 0 deletions Tests/test_file_dds.py
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Original file line number Diff line number Diff line change
Expand Up @@ -15,6 +15,7 @@
assert_image_similar,
assert_image_similar_tofile,
hopper,
timeout_unless_slower_valgrind,
)

TEST_FILE_DXT1 = "Tests/images/dxt1-rgb-4bbp-noalpha_MipMaps-1.dds"
Expand Down Expand Up @@ -540,3 +541,18 @@ def test_save_large_file(tmp_path: Path, pixel_format: str, mode: str) -> None:
im = hopper(mode).resize((440, 440))
# should not error in valgrind
im.save(tmp_path / "img.dds", pixel_format=pixel_format)


@timeout_unless_slower_valgrind(1)
@pytest.mark.parametrize(
"test_file",
[
"Tests/images/timeout-041dd17dfde800360a47a172269df127af138c6b.dds",
"Tests/images/timeout-755a4d204f4208e3597ac3391edebee196462bd0.dds",
"Tests/images/timeout-52d106579505547091ef69b58341351a37c23e31.dds",
"Tests/images/timeout-c60a3d7314213624607bfb3e38d551a8b24a7435.dds",
],
)
def test_timeout(test_file) -> None:
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@radarhere radarhere Jan 23, 2026

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Suggested change
def test_timeout(test_file) -> None:
def test_timeout(test_file: str) -> None:

with Image.open(test_file) as im:
im.load()
29 changes: 21 additions & 8 deletions src/PIL/DdsImagePlugin.py
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Original file line number Diff line number Diff line change
Expand Up @@ -503,21 +503,34 @@ def decode(self, buffer: bytes | Image.SupportsArrayInterface) -> tuple[int, int
while mask >> (offset + 1) << (offset + 1) == mask:
offset += 1
mask_offsets.append(offset)
mask_totals.append(mask >> offset)
mask_total = mask >> offset
if not mask_total:
mask_totals.append(0)
else:
mask_totals.append(255 / mask_total)

data = bytearray()
bytecount = bitcount // 8
dest_length = self.state.xsize * self.state.ysize * len(masks)
while len(data) < dest_length:
value = int.from_bytes(self.fd.read(bytecount), "little")
# consume the data
has_more = True
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@radarhere radarhere Jan 23, 2026

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Suggested change
has_more = True
has_more = bytecount != 0

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@wiredfool wiredfool Jan 23, 2026

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Bytecount is number of bytes per pixel, or the number of masks. It's not the data size.

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@radarhere radarhere Jan 23, 2026

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Yes, but if bytecount is zero, then self.fd.read(bytecount) is always going to be empty.

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@wiredfool wiredfool Jan 24, 2026

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But bytecount should never be zero. It’s an image level compression property, how many bytes do we consume per pixel.

To me, this looks like a misunderstanding, so can you explain why it’s better to initialize with this rather than the simpler expression for true?

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@radarhere radarhere Jan 24, 2026

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But bytecount should never be zero

...awkwardly, it does seem to be possible. I mean, it doesn't seem helpful value, and I do think it should lead to an error.

Pillow/src/PIL/DdsImagePlugin.py

Lines 355 to 356 in bc64ccb

# pixel format
pfsize, pfflags, fourcc, bitcount = struct.unpack("<4I", header[68:84])

Pillow/src/PIL/DdsImagePlugin.py

Line 509 in bc64ccb

bytecount = bitcount // 8

Here's the documentation - https://learn.microsoft.com/en-us/windows/win32/direct3ddds/dds-pixelformat

dwRGBBitCount

Type: DWORD

Number of bits in an RGB (possibly including alpha) format. Valid when dwFlags includes DDPF_RGB, DDPF_LUMINANCE, or DDPF_YUV.

To demonstrate, I've added radarhere@c90d124 onto a fork of this branch - https://github.com/radarhere/Pillow/actions/runs/21312659863/job/61351156707#step:11:58

bitcount is set to 0 in _open
bitcount is 0 which means that bytecount is 0 within DdsRgbDecoder

while len(data) < dest_length and has_more:
chunk = self.fd.read(bytecount)
# work around BufferedIO not being seekable
has_more = len(chunk) > 0
value = int.from_bytes(chunk, "little")
for i, mask in enumerate(masks):
masked_value = value & mask
# Remove the zero padding, and scale it to 8 bits
data += o8(
int(((masked_value >> mask_offsets[i]) / mask_totals[i]) * 255)
if mask_totals[i]
else 0
)
data += o8(int((masked_value >> mask_offsets[i]) * mask_totals[i]))

# extra padding pixels -- always all 0
if len(data) < dest_length:
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@radarhere radarhere Jan 23, 2026

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If the file stopped before we were able to read all the bytes we needed, why not just let the data be shorter than expected, leading to a ValueError: not enough image data be raised? That error sounds like it is accurately describing the situation.

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@wiredfool wiredfool Jan 23, 2026

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Good question - I couldn't tell if it was intentional that it filled off the end. Given that it's plain black, it's at least a reasonable fill, but I didn't see a spec. I'd be happy enough erroring out as well. Main issue here is that I want to catch things other than dds timeouts in oss-fuzz.

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@radarhere radarhere Jan 24, 2026

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I've created #9405

pixel = bytearray()
pixel += o8(0)
ct_bytes = dest_length - len(data)
data += pixel * ct_bytes

self.set_as_raw(data)
return -1, 0

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