Add page limit of 10000

Theoretically the max pages would be 65536 (2byte unsigned int.
However this limit is much higher than practical documents have
and larger ones can lead to unforseen problems, for example RAM
limitations.

We thus opted to use a lower limit of 10K. The limit must be
detected client-side, given that the server is distrusted. However
we also check it in the server, just as a fail-early mechanism.

dangerzone/conversion/doc_to_pixels.py

@@ -239,6 +239,9 @@ async def convert(self) -> None:
         else:
             raise errors.NoPageCountException()
 
+        if num_pages > errors.MAX_PAGES:
+            raise errors.MaxPagesException()
+
         # Get a more precise timeout, based on the number of pages
         timeout = self.calculate_timeout(size, num_pages)
 

dangerzone/conversion/errors.py

@@ -2,6 +2,7 @@
 
 # XXX: errors start at 128 for conversion-related issues
 ERROR_SHIFT = 128
+MAX_PAGES = 10000
 
 
 class ConversionException(Exception):
@@ -53,6 +54,14 @@ class NoPageCountException(PagesException):
     error_message = "Number of pages could not be extracted from PDF"
 
 
+class MaxPagesException(PagesException):
+    """Max number of pages enforced by the client (to fail early) but also the
+    server, which distrusts the client"""
+
+    error_code = ERROR_SHIFT + 42
+    error_message = f"Number of pages exceeds maximum ({MAX_PAGES})"
+
+
 class PDFtoPPMException(ConversionException):
     error_code = ERROR_SHIFT + 50
     error_message = "Error converting PDF to Pixels (pdftoppm)"

dangerzone/isolation_provider/qubes.py

@@ -125,9 +125,8 @@ def __convert(
             os.set_blocking(self.proc.stdout.fileno(), False)
 
             n_pages = read_int(self.proc.stdout, timeout)
-            if n_pages == 0:
-                # FIXME: Fail loudly in that case
-                return False
+            if n_pages == 0 or n_pages > errors.MAX_PAGES:
+                raise errors.MaxPagesException()
             if ocr_lang:
                 percentage_per_page = 50.0 / n_pages
             else:

tests/__init__.py

@@ -1,4 +1,5 @@
 import sys
+import zipfile
 from pathlib import Path
 from typing import Callable, List
 
@@ -13,7 +14,11 @@
 BASIC_SAMPLE_PDF = "sample-pdf.pdf"
 BASIC_SAMPLE_DOC = "sample-doc.doc"
 SAMPLE_EXTERNAL_DIRECTORY = "test_docs_external"
+SAMPLE_COMPRESSED_DIRECTORY = "test_docs_compressed"
+
 test_docs_dir = Path(__file__).parent.joinpath(SAMPLE_DIRECTORY)
+test_docs_compressed_dir = Path(__file__).parent.joinpath(SAMPLE_COMPRESSED_DIRECTORY)
+
 test_docs = [
     p
     for p in test_docs_dir.rglob("*")
@@ -73,6 +78,20 @@ def unreadable_pdf(tmp_path: Path) -> str:
     return str(file_path)
 
 
+@pytest.fixture
+def pdf_11k_pages(tmp_path: Path) -> str:
+    """11K page document with pages of 1x1 px. Generated with the command:
+
+    gs -sDEVICE=pdfwrite -o sample-11k-pages.pdf -dDEVICEWIDTHPOINTS=1 -dDEVICEHEIGHTPOINTS=1 -c 11000 {showpage} repeat
+    """
+
+    filename = "sample-11k-pages.pdf"
+    zip_path = test_docs_compressed_dir / f"{filename}.zip"
+    with zipfile.ZipFile(zip_path, "r") as zip_file:
+        zip_file.extractall(tmp_path)
+    return str(tmp_path / filename)
+
+
 @pytest.fixture
 def uncommon_text() -> str:
     """Craft a string with Unicode characters that are considered not common.

tests/isolation_provider/base.py

@@ -2,10 +2,11 @@
 from colorama import Style
 from pytest_mock import MockerFixture
 
+from dangerzone.conversion import errors
 from dangerzone.document import Document
 from dangerzone.isolation_provider import base
 
-from .. import sanitized_text, uncommon_text
+from .. import pdf_11k_pages, sanitized_text, uncommon_text
 
 
 class IsolationProviderTest:
@@ -48,3 +49,15 @@ def test_print_progress(
             else:
                 assert log_info_spy.call_args[0][0].endswith(sanitized_text)
                 log_error_spy.assert_not_called()
+
+    def test_max_pages_received(
+        self,
+        pdf_11k_pages: str,
+        provider: base.IsolationProvider,
+        mocker: MockerFixture,
+    ) -> None:
+        provider.progress_callback = mocker.MagicMock()
+        doc = Document(pdf_11k_pages)
+        with pytest.raises(errors.MaxPagesException):
+            success = provider._convert(doc, ocr_lang=None)
+            assert not success

tests/isolation_provider/test_container.py

@@ -8,7 +8,8 @@
 from dangerzone.document import Document
 from dangerzone.isolation_provider.container import Container
 
-from .. import sanitized_text, uncommon_text
+# XXX Fixtures used in abstract Test class need to be imported regardless
+from .. import pdf_11k_pages, sanitized_text, uncommon_text
 from .base import IsolationProviderTest
 
 

tests/isolation_provider/test_qubes.py

@@ -2,7 +2,8 @@
 
 from dangerzone.isolation_provider.qubes import Qubes
 
-from .. import sanitized_text, uncommon_text
+# XXX Fixtures used in abstract Test class need to be imported regardless
+from .. import pdf_11k_pages, sanitized_text, uncommon_text
 from .base import IsolationProviderTest