Generating GIFs for fuzzing a GIF Parser

coverage_gemini15.txt

File 'gifdec.c'
Lines executed:36.91% of 317
Creating 'gifdec.c.gcov'

File 'gifread.c'
Lines executed:62.50% of 56
Creating 'gifread.c.gcov'

gengif_gemini15.py

# gemini 1.5
# temperature = 2.0
# top_p = 0.4
import random
import struct
import io
from typing import BinaryIO

RANDOM_HEADER =\
b'GIF89a'\
b'\x00\x01'\
b'\x00\x01\x00\x00'

GIF_EXT_LABELS = {
    0x01: b'text',
    0xf9: b'graphic control',
    0xfe: b'comment',
    0xff: b'application',
}

RANDOM_TEXT_EXT =\
b'\x01'\
b'\x01\x01'\
b'\x01\x01'\
b'\x01\x01'\
b'\x01\x01\x01\x01'\
b'\x01\x01\x01\x01\x01\x01\x01\x01\x01'\
b'\x01'

RANDOM_GCE_EXT =\
b'\xf9'\
b'\x04'\
b'\x00'

RANDOM_COMMENT_EXT =\
b'\xfe'\
b'Comment!'

RANDOM_APPLICATION_EXT =\
b'\xff'\
b'NETSCAPE2.0'\
b'\x03'\
b'\x00\x00'

RANDOM_TERMINATOR =\
b'\x00'

def generate_random_input(out: BinaryIO):
  """Generates a random file into `out`.

  The generated input will fully exercise the parsing code.

  Generates a random header with a random width and height, then
  generates a random color table and a random image. Finally, generates
  some random extensions, including the text extension, the graphic control
  extension, the comment extension, and the application extension.
  """

  out.write(RANDOM_HEADER)

  width = random.randint(1, 1000)
  height = random.randint(1, 1000)
  depth = random.randint(1, 8)
  gct_size = 1 << (depth + 1)

  out.write(struct.pack('>H', width))
  out.write(struct.pack('>H', height))
  flags = depth | (1 << 4) | (1 << 7)
  out.write(struct.pack('B', flags))
  out.write(struct.pack('B', gct_size))
  out.write(struct.pack('B', 0))  # background color index
  out.write(struct.pack('B', 0))  # aspect ratio

  # Generate a random color table.
  for _ in range(gct_size):
    r = random.randint(0, 255)
    g = random.randint(0, 255)
    b = random.randint(0, 255)
    out.write(b"%c%c%c" % (r, g, b))

  # Generate a random image.
  for _ in range(width * height):
    index = random.randint(0, gct_size - 1)
    color = struct.pack('B', index)
    out.write(color)

  # Generate some random extensions.
  for label in GIF_EXT_LABELS.keys():
    if random.random() < 0.5:
      out.write(struct.pack('B', label))
      if label == 0x01:
        out.write(RANDOM_TEXT_EXT)
      elif label == 0xf9:
        out.write(RANDOM_GCE_EXT)
      elif label == 0xfe:
        out.write(RANDOM_COMMENT_EXT)
      elif label == 0xff:
        out.write(RANDOM_APPLICATION_EXT)
      out.write(RANDOM_TERMINATOR)

  out.write(RANDOM_TERMINATOR)


for i in range(10000):
  with open(f"gifs/random_gif_{i}.gif", "wb") as f:
      generate_random_input(f)

gengif_gpt4.py

from PIL import Image, ImageDraw, ImageSequence
import os
from io import BytesIO

# Utility function to save GIF to a BytesIO object
def save_gif(images, **kwargs):
    bio = BytesIO()
    images[0].save(bio, format='GIF', save_all=True, append_images=images[1:], **kwargs)
    bio.seek(0)
    return bio

# Generates GIFs to test the C GIF parsing code
def generate_gif_inputs():
    # Ensure the gifs directory exists
    os.makedirs('gifs', exist_ok=True)
    files = []

    # 1. Valid GIF with a simple global color table
    img1 = Image.new("RGB", (100, 100), "white")
    draw = ImageDraw.Draw(img1)
    draw.rectangle([10, 10, 90, 90], fill="blue")
    files.append(save_gif([img1], loop=0))

    # 2. GIF with no global color table (invalid per parser's expectations)
    img2 = Image.new("RGB", (100, 100), "red")
    files.append(save_gif([img2], loop=0, global_palette=False))

    # 3. GIF with a NETSCAPE looping extension
    img3 = Image.new("RGB", (50, 50), "green")
    img3.info['loop'] = 1  # Loop once
    files.append(save_gif([img3], loop=1))

    # 4. GIF with local color tables and different frames
    img4_1 = Image.new("RGB", (100, 100), "yellow")
    img4_2 = Image.new("RGB", (100, 100), "purple")
    img4_2.info['local_palette'] = True
    files.append(save_gif([img4_1, img4_2], loop=0))

    # 5. Interlaced GIF
    img5 = Image.new("RGB", (100, 100), "black")
    draw = ImageDraw.Draw(img5)
    for y in range(0, 100, 10):
        draw.line([(0, y), (99, y)], fill="white")
    files.append(save_gif([img5], interlace=True))

    # 6. GIF with a comment extension
    img6 = Image.new("RGB", (100, 100), "orange")
    img6.info['comment'] = b"This is a test comment."
    files.append(save_gif([img6]))

    # Save all BytesIO objects to files for inspection
    for i, file in enumerate(files):
        with open(f'gifs/generated_gif_{i}.gif', 'wb') as f:
            f.write(file.getvalue())

generate_gif_inputs()