Merge pull request #2536 from enkore/issue/2534

fuse: fix crash if empty (None) xattr is read

src/borg/fuse.py

@@ -288,7 +288,7 @@ class FuseOperations(llfuse.Operations):
     def getxattr(self, inode, name, ctx=None):
         item = self.get_item(inode)
         try:
-            return item.get('xattrs', {})[name]
+            return item.get('xattrs', {})[name] or b''
         except KeyError:
             raise llfuse.FUSEError(llfuse.ENOATTR) from None
 

src/borg/testsuite/archiver.py

@@ -326,6 +326,7 @@ class ArchiverTestCaseBase(BaseTestCase):
             # into "fakeroot space". Because the xattrs exposed by borgfs are these of an underlying file
             # (from fakeroots point of view) they are invisible to the test process inside the fakeroot.
             xattr.setxattr(os.path.join(self.input_path, 'fusexattr'), 'user.foo', b'bar')
+            xattr.setxattr(os.path.join(self.input_path, 'fusexattr'), 'user.empty', b'')
             # XXX this always fails for me
             # ubuntu 14.04, on a TMP dir filesystem with user_xattr, using fakeroot
             # same for newer ubuntu and centos.
@@ -1874,8 +1875,10 @@ class ArchiverTestCase(ArchiverTestCaseBase):
                 in_fn = 'input/fusexattr'
                 out_fn = os.path.join(mountpoint, 'input', 'fusexattr')
                 if not xattr.XATTR_FAKEROOT and xattr.is_enabled(self.input_path):
-                    assert no_selinux(xattr.listxattr(out_fn)) == ['user.foo', ]
+                    assert sorted(no_selinux(xattr.listxattr(out_fn))) == ['user.empty', 'user.foo', ]
                     assert xattr.getxattr(out_fn, 'user.foo') == b'bar'
+                    # Special case: getxattr returns None (not b'') when reading an empty xattr.
+                    assert xattr.getxattr(out_fn, 'user.empty') is None
                 else:
                     assert xattr.listxattr(out_fn) == []
                     try:

src/borg/xattr.py

@@ -35,6 +35,16 @@ def is_enabled(path=None):
 
 
 def get_all(path, follow_symlinks=True):
+    """
+    Return all extended attributes on *path* as a mapping.
+
+    *path* can either be a path (str or bytes) or an open file descriptor (int).
+    *follow_symlinks* indicates whether symlinks should be followed
+    and only applies when *path* is not an open file descriptor.
+
+    The returned mapping maps xattr names (str) to values (bytes or None).
+    None indicates, as a xattr value, an empty value, i.e. a value of length zero.
+    """
     try:
         result = {}
         names = listxattr(path, follow_symlinks=follow_symlinks)
@@ -111,7 +121,7 @@ def split_lstring(buf):
 
 
 class BufferTooSmallError(Exception):
-    """the buffer given to an xattr function was too small for the result."""
+    """the buffer given to a xattr function was too small for the result."""
 
 
 def _check(rv, path=None, detect_buffer_too_small=False):
@@ -346,10 +356,33 @@ elif sys.platform.startswith('freebsd'):  # pragma: freebsd only
 
 else:  # pragma: unknown platform only
     def listxattr(path, *, follow_symlinks=True):
+        """
+        Return list of xattr names on a file.
+
+        *path* can either be a path (str or bytes) or an open file descriptor (int).
+        *follow_symlinks* indicates whether symlinks should be followed
+        and only applies when *path* is not an open file descriptor.
+        """
         return []
 
     def getxattr(path, name, *, follow_symlinks=True):
-        pass
+        """
+        Read xattr and return its value (as bytes) or None if its empty.
+
+        *path* can either be a path (str or bytes) or an open file descriptor (int).
+        *name* is the name of the xattr to read (str).
+        *follow_symlinks* indicates whether symlinks should be followed
+        and only applies when *path* is not an open file descriptor.
+        """
 
     def setxattr(path, name, value, *, follow_symlinks=True):
-        pass
+        """
+        Write xattr on *path*.
+
+        *path* can either be a path (str or bytes) or an open file descriptor (int).
+        *name* is the name of the xattr to read (str).
+        *value* is the value to write. It is either bytes or None. The latter
+        signals that the value shall be empty (size equals zero).
+        *follow_symlinks* indicates whether symlinks should be followed
+        and only applies when *path* is not an open file descriptor.
+        """