[PNG] IndexError is raised when the sRGB chunk is broken

[ks888sk]

What did you do?

from PIL import Image
import io

# assumes the current directory is the root of this repository.
with open('Tests/images/imagedraw_polygon_1px_high.png', 'rb') as f:
    data = bytearray(f.read())

# insert the sRGB chunk after the IDAT chunk. Its length, chunk type and crc are valid, but the sRGB chunk should contain more data.
data[61:61] = b"\x00\x00\x00\x00sRGB\x10\x1c\xd3\xce"

# IndexError is raised
with Image.open(io.BytesIO(data)) as img:
    img.load()

What did you expect to happen?

IndexError is a little conusing. Maybe ValueError is better.

What actually happened?

Traceback (most recent call last):
  File "issue_index_error_simplified.py", line 14, in <module>
    img.load()
  File "/usr/local/lib/python3.8/dist-packages/PIL/ImageFile.py", line 268, in load
    self.load_end()
  File "/usr/local/lib/python3.8/dist-packages/PIL/PngImagePlugin.py", line 978, in load_end
    self.png.call(cid, pos, length)
  File "/usr/local/lib/python3.8/dist-packages/PIL/PngImagePlugin.py", line 202, in call
    return getattr(self, "chunk_" + cid.decode("ascii"))(pos, length)
  File "/usr/local/lib/python3.8/dist-packages/PIL/PngImagePlugin.py", line 512, in chunk_sRGB
    self.im_info["srgb"] = s[0]
IndexError: index out of range

What are your OS, Python and Pillow versions?

• OS: ubuntu:focal-20220426
• Python: 3.8.10
• Pillow: 9.2.0

[radarhere]

Your request is similar to the change in #6253, so this makes sense to me.

I've created PR #6431 to resolve this.