Re: klp: make object/func-walking helpers more robust

[Jessica Yu]

+++ Miroslav Benes [28/04/16 16:34 +0200]:
> Current object-walking helper checks the presence of obj->funcs to
> determine the end of objs array in klp_object structure. This is
> somewhat fragile because one can easily forget about funcs definition
> during livepatch creation. In such a case the livepatch module is
> successfully loaded and all objects after the incorrect one are omitted.
> This is very confusing. Let's make the helper more robust and check also
> for the other external member, name. Thus the helper correctly stops on
> an empty item of the array. We need to have a check for obj->funcs in
> klp_init_object() to make it work.
>
> The same applies to a func-walking helper.
>
> As a benefit we'll check for new_func member definition during the
> livepatch initialization. There is no such check anywhere in the code
> now.
>
> Signed-off-by: Miroslav Benes <mbenes@xxxxxxx>
> ---
> include/linux/livepatch.h | 6 ++++--
> kernel/livepatch/core.c   | 3 +++
> 2 files changed, 7 insertions(+), 2 deletions(-)
>
> diff --git a/include/linux/livepatch.h b/include/linux/livepatch.h
> index 0933ca47791c..a93a0b23dc8d 100644
> --- a/include/linux/livepatch.h
> +++ b/include/linux/livepatch.h
> @@ -104,10 +104,12 @@ struct klp_patch {
> };
>
> #define klp_for_each_object(patch, obj) \
> -	for (obj = patch->objs; obj->funcs; obj++)
> +	for (obj = patch->objs; obj->funcs || obj->name; obj++)

Remember that for patches to vmlinux, obj->name and obj->mod will also
both be NULL. So if someone happens to forget to fill in obj->funcs
for a vmlinux patch, we won't catch that case here. Perhaps we need a
better way of determining whether we've reached the end of the array,
or determining that the struct is truly empty..

Jessica