Only read until the offset of the next tile (#8609)

Co-authored-by: Andrew Murray <radarhere@users.noreply.github.com>

Author: radarhere

Tests/test_imagefile.py

@@ -131,6 +131,26 @@ def test_safeblock(self) -> None:
 
  assert_image_equal(im1, im2)
 
+ def test_tile_size(self) -> None:
+ with open("Tests/images/hopper.tif", "rb") as im_fp:
+ data = im_fp.read()
+
+ reads = []
+
+ class FP(BytesIO):
+ def read(self, size: int | None = None) -> bytes:
+ reads.append(size)
+ return super().read(size)
+
+ fp = FP(data)
+ with Image.open(fp) as im:
+ assert len(im.tile) == 7
+
+ im.load()
+
+ # Despite multiple tiles, assert only one tile caused a read of maxblock size
+ assert reads.count(im.decodermaxblock) == 1
+
  def test_raise_oserror(self) -> None:
  with pytest.warns(DeprecationWarning):
  with pytest.raises(OSError):

src/PIL/ImageFile.py

@@ -345,7 +345,7 @@ def load(self) -> Image.core.PixelAccess | None:
  self.tile, lambda tile: (tile[0], tile[1], tile[3])
  )
  ]
- for decoder_name, extents, offset, args in self.tile:
+ for i, (decoder_name, extents, offset, args) in enumerate(self.tile):
  seek(offset)
  decoder = Image._getdecoder(
  self.mode, decoder_name, args, self.decoderconfig
@@ -358,8 +358,13 @@ def load(self) -> Image.core.PixelAccess | None:
  else:
  b = prefix
  while True:
+ read_bytes = self.decodermaxblock
+ if i + 1 < len(self.tile):
+ next_offset = self.tile[i + 1].offset
+ if next_offset > offset:
+ read_bytes = next_offset - offset
  try:
- s = read(self.decodermaxblock)
+ s = read(read_bytes)
  except (IndexError, struct.error) as e:
  # truncated png/gif
  if LOAD_TRUNCATED_IMAGES: