Linux: improve acl_get / acl_set error handling, see #4049

src/borg/platform/linux.pyx

@@ -251,9 +251,13 @@ def acl_get(path, item, st, numeric_ids=False, fd=None):
             access_acl = acl_get_fd(fd)
         else:
             access_acl = acl_get_file(path, ACL_TYPE_ACCESS)
+        if access_acl == NULL:
+            raise OSError(errno.errno, os.strerror(errno.errno), os.fsdecode(path))
         if stat.S_ISDIR(st.st_mode):
             # only directories can have a default ACL. there is no fd-based api to get it.
             default_acl = acl_get_file(path, ACL_TYPE_DEFAULT)
+            if default_acl == NULL:
+                raise OSError(errno.errno, os.strerror(errno.errno), os.fsdecode(path))
         if access_acl:
             access_text = acl_to_text(access_acl, NULL)
             if access_text:
@@ -289,9 +293,11 @@ def acl_set(path, item, numeric_ids=False, fd=None):
             access_acl = acl_from_text(<bytes>converter(access_text))
             if access_acl:
                 if fd is not None:
-                    acl_set_fd(fd, access_acl)
+                    if acl_set_fd(fd, access_acl) == -1:
+                        raise OSError(errno.errno, os.strerror(errno.errno), os.fsdecode(path))
                 else:
-                    acl_set_file(path, ACL_TYPE_ACCESS, access_acl)
+                    if acl_set_file(path, ACL_TYPE_ACCESS, access_acl) == -1:
+                        raise OSError(errno.errno, os.strerror(errno.errno), os.fsdecode(path))
         finally:
             acl_free(access_acl)
     default_text = item.get('acl_default')
@@ -300,7 +306,8 @@ def acl_set(path, item, numeric_ids=False, fd=None):
             default_acl = acl_from_text(<bytes>converter(default_text))
             if default_acl:
                 # only directories can get a default ACL. there is no fd-based api to set it.
-                acl_set_file(path, ACL_TYPE_DEFAULT, default_acl)
+                if acl_set_file(path, ACL_TYPE_DEFAULT, default_acl) == -1:
+                    raise OSError(errno.errno, os.strerror(errno.errno), os.fsdecode(path))
         finally:
             acl_free(default_acl)