rbd: Reset positive result codes to zero in object map update path

rbd: Reset positive result codes to zero in object map update path

In a reply message to an RBD request, a positive result code indicates
a data payload, which is not allowed for writes. While
rbd_osd_req_callback() already resets a positive result code for writes
to zero, rbd_object_map_callback() does not. This allows a corrupted
reply to an object map update to trigger the rbd_assert(*result < 0) in
__rbd_obj_handle_request(). This happens, because
rbd_object_map_callback() calls rbd_obj_handle_request() ->
__rbd_obj_handle_request() and passes this positive result code. From
__rbd_obj_handle_request(), rbd_obj_advance_write() is called, which
leaves the positive result code unchanged and returns true. Therefore,
the if(done && *result) branch is executed in __rbd_obj_handle_request()
and the assertion triggers.

This patch fixes the issue by adjusting the logic in the
rbd_object_map_callback() path. A positive result code for an object map
update is now reset to zero (similar to rbd_osd_req_callback()), and the
message is subsequently handled the same way as if the result code was
zero from the beginning. Additionally, a WARN_ON_ONCE() is added for
this case.

Cc: stable@vger.kernel.org
Fixes: 22e8bd51bb04 ("rbd: support for object-map and fast-diff")
Signed-off-by: Raphael Zimmer <raphael.zimmer@tu-ilmenau.de>
Reviewed-by: Ilya Dryomov <idryomov@gmail.com>
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>