On Tue, Jun 9, 2026 at 9:27 PM Petr Mladek [off-list ref] wrote:

On Sun 2026-06-07 21:16:53, Yafang Shao wrote:

quoted

If a newly loaded livepatch provides a function entry with a NULL old_name,
func->old_name will be NULL when evaluated in strcmp():

klp_init_patch()
    klp_add_nops()
        klp_find_func()
            strcmp(old_func->old_name, func->old_name)

--- a/kernel/livepatch/core.c
+++ b/kernel/livepatch/core.c

@@ -92,7 +92,7 @@ static struct klp_func *klp_find_func(struct klp_object *obj,
               * Besides identical old_sympos, also consider old_sympos
               * of 0 and 1 are identical.
               */
-             if ((strcmp(old_func->old_name, func->old_name) == 0) &&
+             if ((func->old_name && strcmp(old_func->old_name, func->old_name) == 0) &&

I do not have a good feeling about this solution because it quietly
ignores a problem. As a result, klp_add_object_nops() would
call klp_alloc_func_nop() even though it does not make much sense.

A livepatch where any func->oldname is not defined should get
rejected. It will actually happen but _later_ in:

  + klp_init_patch()
    + klp_init_object()
      + klp_init_func()

I see three better possibilities.

1. We could move/add the sanity checks into klp_init_patch_early()
   and return broken livepatches earlier.

2. We could move/add the sanity check into a new klp_check_patch()
   which will be called even before klp_init_patch_early().

3. We could allow klp_find_func() to return ERR_PTR(-EINVAL).
   klp_add_object_nops() should then return the error as well.

My preference:

I would do the 3rd variant because it is much easier than
adding/moving all consistency checks between klp_init_*() and
klp_init_*_early() or klp_check_*() functions.

Thanks for the suggestion. I will update it.

-- 
Regards
Yafang