check: report invalid pack names instead of crashing

src/borg/repository.py

@@ -1,5 +1,6 @@
 import io
 import os
+import re
 import sys
 import threading
 import time
@@ -34,6 +35,9 @@
 
 logger = create_logger(__name__)
 
+# an object name is its sha256 as 64 lowercase hex digits.
+_valid_object_name = re.compile(r"[0-9a-f]{64}").fullmatch
+
 
 def repo_lister(repository, *, limit=None):
     marker = None
@@ -1046,6 +1050,16 @@ def store_list(namespace):
         if index_errors == 0:
             # packs are the bulk of the work and the part --max-duration spreads over several checks.
             pack_infos = store_list("packs")
+            # drop objects whose name is not a valid pack name and count them as errors; the code
+            # below decodes each name via hex_to_bin, which only accepts valid names.
+            valid_pack_infos = []
+            for info in pack_infos:
+                if _valid_object_name(info.name):
+                    valid_pack_infos.append(info)
+                else:
+                    logger.error(f"Store object packs/{info.name} has an invalid name.")
+                    pack_errors += 1
+            pack_infos = valid_pack_infos
             if partial:
                 # a partial check stops after max_duration; verify the least-recently-checked packs
                 # first so repeated runs cover every pack. sort by recorded check time, unrecorded

src/borg/testsuite/repository_test.py

@@ -1056,6 +1056,21 @@ def test_check_detects_index_corruption(tmp_path):
         assert repository.check(repair=False) is False  # mismatch between content hash and name detected
 
 
+def test_check_reports_invalid_pack_name(tmp_path, caplog):
+    # an object in packs/ whose name is not 64 hex digits is reported as an error, and the other
+    # packs are still checked.
+    with Repository(str(tmp_path / "repo"), exclusive=True, create=True) as repository:
+        intact_id, _ = _store_intact_pack(repository)
+        repository.store_store("packs/not-a-hex-name", b"stray junk")
+
+        with caplog.at_level(logging.ERROR, logger="borg.repository"):
+            assert repository.check(repair=False) is False
+
+        assert "packs/not-a-hex-name has an invalid name" in caplog.text
+        after = PackTracker.load(repository.store)
+        assert after.table[intact_id].result == 1  # the valid pack was checked
+
+
 def test_check_warns_on_invalid_chunk_index(tmp_path, caplog):
     # check warns about an invalid chunk index but does not fail, since the index is not part of
     # the repository's object integrity.