illumos/Solaris: do not open device nodes to get their xattrs

src/borg/platform/solaris.py

@@ -5,10 +5,14 @@
 attribute directory attached to that file. The attribute directory is opened by giving
 O_XATTR to open(2)/openat(2), see fsattr(7) — xattr names/values map to the names/contents
 of the files in there. There are no xattr namespaces, so names are used verbatim.
+
+Block and character device nodes are treated as not supporting extended attributes:
+reaching their attribute directory would require opening the device itself.
 """
 
 import errno
 import os
+import stat
 
 from .base import ENOATTR
 
@@ -32,6 +36,11 @@ def _open_attrdir(path, follow_symlinks):
     # referring to the file, so for a path, the file itself must be opened first.
     if isinstance(path, int):
         return os.open(".", os.O_RDONLY | O_XATTR, dir_fd=path)
+    # Opening a device node runs the open routine of its driver, which might fail (ENXIO if
+    # there is no such device), block or have side effects (e.g. a tape rewinding on close).
+    st = os.stat(path, follow_symlinks=follow_symlinks)
+    if stat.S_ISBLK(st.st_mode) or stat.S_ISCHR(st.st_mode):
+        raise OSError(errno.ENOTSUP, os.strerror(errno.ENOTSUP), path)
     flags = os.O_RDONLY | os.O_NONBLOCK  # O_NONBLOCK: do not hang on FIFOs
     if not follow_symlinks:
         flags |= os.O_NOFOLLOW

src/borg/testsuite/xattr_test.py

@@ -1,9 +1,11 @@
+import errno
 import os
+import stat
 
 import pytest
 
 from ..platform.xattr import buffer, split_lstring
-from ..xattr import is_enabled, getxattr, setxattr, listxattr, XATTR_FAKEROOT
+from ..xattr import is_enabled, getxattr, setxattr, listxattr, get_all, XATTR_FAKEROOT
 from ..platformflags import is_linux, is_sunos
 
 # Whether xattrs can be set on a symlink itself:
@@ -83,6 +85,22 @@ def test_getxattr_buffer_growth(tempfile_symlink):
     assert len(buffer) == 128
 
 
+@pytest.mark.skipif(not is_sunos, reason="illumos/Solaris only")
+@pytest.mark.parametrize("kind", [stat.S_IFBLK, stat.S_IFCHR])
+def test_device_node_is_not_opened(tmp_path, kind):
+    # Reaching the attribute directory of a device node would open the device itself,
+    # which fails with ENXIO for a device number without a driver (like this one).
+    path = os.fsencode(tmp_path / "dev")
+    try:
+        os.mknod(path, 0o600 | kind, os.makedev(30, 40))
+    except PermissionError:
+        pytest.skip("creating device nodes requires root")
+    with pytest.raises(OSError) as excinfo:
+        listxattr(path)
+    assert excinfo.value.errno == errno.ENOTSUP
+    assert get_all(path) == {}
+
+
 @pytest.mark.parametrize(
     "lstring, expected", [(b"", []), (b"\x00", [b""]), (b"\x01a", [b"a"]), (b"\x01a\x02cd", [b"a", b"cd"])]
 )