fix: close file handle in get_file_taste using a with statement

`get_file_taste` opened a file handle with `sample_path.open("rb").read(8)`,
discarding the file object without explicitly closing it. CPython reference-
counting closes it promptly in practice, but other implementations (PyPy,
Jython) and CPython under GC pressure may defer closure. Use a `with` statement
to guarantee the handle is released immediately after reading.

CHANGELOG.md

@@ -32,6 +32,7 @@
 - fix: loader.py reads entire file for magic byte check @williballenthin #3029
 - fix: freeze/__init__.py: logically impossible condition @williballenthin #3030
 - fix: EXTENSIONS_ELF never referenced @williballenthin #3031
+- fix: close file handle in get_file_taste using a with statement @williballenthin
 - fix: correct off-by-one in dynamic analysis call_count debug log (enumerate -> explicit counter) @williballenthin
 - fix: correct capa/subscope-rule key in RuleMetadata so is_subscope_rule is no longer always False @williballenthin
 - fix: remove unreachable backports.functools_lru_cache fallback and dead dependency @williballenthin

capa/helpers.py

@@ -88,8 +88,8 @@ def hex(n: int) -> str:
 def get_file_taste(sample_path: Path) -> bytes:
     if not sample_path.exists():
         raise IOError(f"sample path {sample_path} does not exist or cannot be accessed")
-    taste = sample_path.open("rb").read(8)
-    return taste
+    with sample_path.open("rb") as f:
+        return f.read(8)
 
 
 def is_runtime_ida():

tests/test_helpers.py

@@ -27,6 +27,7 @@ from capa.helpers import (
     EXTENSIONS_BINEXPORT2,
     EXTENSIONS_SHELLCODE_32,
     EXTENSIONS_SHELLCODE_64,
+    get_file_taste,
     get_format_from_extension,
 )
 from capa.features.common import (
@@ -166,3 +167,16 @@ def test_get_format_from_extension():
     assert get_format_from_extension(Path("sample.BinExport2")) == FORMAT_BINEXPORT2
     assert get_format_from_extension(Path("sample.bndb")) == FORMAT_BINJA_DB
     assert get_format_from_extension(Path("sample.exe")) == FORMAT_UNKNOWN
+
+
+def test_get_file_taste_reads_first_bytes(tmp_path):
+    sample = tmp_path / "sample.bin"
+    sample.write_bytes(b"\x4d\x5a\x90\x00\x01\x02\x03\x04\xff\xfe")
+    taste = get_file_taste(sample)
+    assert taste == b"\x4d\x5a\x90\x00\x01\x02\x03\x04"
+    assert len(taste) == 8
+
+
+def test_get_file_taste_missing_file_raises():
+    with pytest.raises(IOError):
+        get_file_taste(Path("/nonexistent/path/sample.exe"))