Add a special-case to squshfs image extraction to not fail if we are not root....

Add a special-case to squshfs image extraction to not fail if we are not root. (Closes: Debian:#991059)

Don't treat a failure to extract all entries from squashfs images as a failure that requires falling back to xxd(1) --

diffoscope/comparators/squashfs.py

@@ -35,7 +35,7 @@ from .device import Device
 from .symlink import Symlink
 from .directory import Directory
 from .utils.archive import Archive, ArchiveMember
-from .utils.command import Command, our_check_output
+from .utils.command import Command
 
 logger = logging.getLogger(__name__)
 
@@ -260,20 +260,47 @@ class SquashfsContainer(Archive):
 
         logger.debug("Extracting %s to %s", self.source.path, self._temp_dir)
 
-        output = our_check_output(
-            (
-                "unsquashfs",
-                "-n",
-                "-f",
-                "-no",
-                "-li",
-                "-d",
-                ".",
-                os.path.abspath(self.source.path),
-            ),
+        cmd = (
+            "unsquashfs",
+            "-n",
+            "-f",
+            "-no",
+            "-li",
+            "-d",
+            ".",
+            os.path.abspath(self.source.path),
+        )
+
+        p = subprocess.Popen(
+            cmd,
+            stdout=subprocess.PIPE,
             stderr=subprocess.PIPE,
             cwd=self._temp_dir,
         )
+        output, stderr = p.communicate()
+
+        if p.returncode != 0:
+            # unsquashfs(1) exits with 1 (with a suitable logging messages that
+            # we can check for) if it could not extract, for example, character
+            # devices that require superuser privileges. In this case, don't
+            # treat this as a failure that requires reverting to xxd(1), but do
+            # let the user know via a comment.
+            if (
+                p.returncode == 1
+                and b"because you're not superuser" in stderr
+                and b"\n\ncreated " in output
+            ):
+                logger.debug("Ignoring unsquashfs return code")
+
+                self.source.add_comment(
+                    "Differences may be incomplete: {}".format(
+                        stderr.decode("utf-8")
+                    )
+                )
+            else:
+                raise subprocess.CalledProcessError(
+                    p.returncode, cmd, output, stderr
+                )
 
         output = iter(output.decode("utf-8").rstrip("\n").split("\n"))
 

tests/comparators/test_squashfs.py

@@ -2,7 +2,7 @@
 # diffoscope: in-depth comparison of files, archives, and directories
 #
 # Copyright © 2015 Jérémy Bobbio <lunar@debian.org>
-# Copyright © 2015-2017, 2019-2020 Chris Lamb <lamby@debian.org>
+# Copyright © 2015-2017, 2019-2021 Chris Lamb <lamby@debian.org>
 #
 # diffoscope is free software: you can redistribute it and/or modify
 # it under the terms of the GNU General Public License as published by
@@ -22,7 +22,7 @@ import subprocess
 
 from diffoscope.comparators.squashfs import SquashfsFile
 
-from ..utils.data import load_fixture, get_data
+from ..utils.data import load_fixture, assert_diff
 from ..utils.tools import skip_unless_tools_exist, skip_unless_tool_is_at_least
 from ..utils.nonexisting import assert_non_existing
 
@@ -63,25 +63,38 @@ def differences(squashfs1, squashfs2):
 
 @skip_unless_tool_is_at_least("unsquashfs", unsquashfs_version, "4.4")
 def test_superblock(differences):
-    expected_diff = get_data("squashfs_superblock_expected_diff")
-    assert differences[0].unified_diff == expected_diff
+    assert_diff(differences[0], "squashfs_superblock_expected_diff")
 
 
 @skip_unless_tools_exist("unsquashfs")
 def test_symlink(differences):
     assert differences[2].comment == "symlink"
-    expected_diff = get_data("symlink_expected_diff")
-    assert differences[2].unified_diff == expected_diff
+    assert_diff(differences[2], "symlink_expected_diff")
 
 
 @skip_unless_tools_exist("unsquashfs")
 def test_compressed_files(differences):
     assert differences[3].source1 == "/text"
     assert differences[3].source2 == "/text"
-    expected_diff = get_data("text_ascii_expected_diff")
-    assert differences[3].unified_diff == expected_diff
+    assert_diff(differences[3], "text_ascii_expected_diff")
 
 
 @skip_unless_tools_exist("unsquashfs")
 def test_compare_non_existing(monkeypatch, squashfs1):
     assert_non_existing(monkeypatch, squashfs1)
+
+
+# Test things that require root
+
+squashfs1_root = load_fixture("test1_root.squashfs")
+squashfs2_root = load_fixture("test2_root.squashfs")
+
+
+@pytest.fixture
+def differences_root(squashfs1_root, squashfs2_root):
+    return squashfs1_root.compare(squashfs2_root).details
+
+
+@skip_unless_tools_exist("unsquashfs")
+def test_symlink_root(differences_root):
+    assert_diff(differences_root[1], "squashfs_root_expected_diff")

tests/data/squashfs_root_expected_diff

+@@ -1,7 +1,7 @@
+ Parallel unsquashfs: Using 8 processors
+ 3 inodes (3 blocks) to write
+ 
+-drwxr-xr-x lamby/lamby              51 2015-06-24 14:47 
+-lrwxrwxrwx lamby/lamby               6 2015-06-24 14:47 /link -> broken
++drwxr-xr-x lamby/lamby              51 2015-06-24 14:50 
++lrwxrwxrwx lamby/lamby              13 2015-06-24 14:50 /link -> really-broken
+ crw-r--r-- root/root             1,  3 2015-06-24 14:47 /null
+--rw-r--r-- lamby/lamby             446 2015-06-24 14:49 /text
++-rw-r--r-- lamby/lamby             671 2015-06-24 14:49 /text

tests/test_source.py

@@ -135,6 +135,7 @@ ALLOWED_TEST_FILES = {
     "test1.rpm",
     "test1.sqlite3",
     "test1.squashfs",
+    "test1_root.squashfs",
     "test1.tar",
     "test1.xml",
     "test1.xsb",
@@ -195,6 +196,7 @@ ALLOWED_TEST_FILES = {
     "test2.rpm",
     "test2.sqlite3",
     "test2.squashfs",
+    "test2_root.squashfs",
     "test2.tar",
     "test2.xml",
     "test2.xsb",