Messages in this thread Patch in this message | | | Date | Fri, 29 Apr 2016 12:11:18 -0400 | From | Jessica Yu <> | Subject | Re: klp: make object/func-walking helpers more robust |
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+++ Miroslav Benes [29/04/16 09:48 +0200]: >On Thu, 28 Apr 2016, Josh Poimboeuf wrote: > >> On Thu, Apr 28, 2016 at 02:21:31PM -0400, Jessica Yu wrote: >> > +++ 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@suse.cz> >> > > --- >> > > 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. > >Yes, that is true. My reasoning is that if someone even accidently writes >{ } somewhere in the middle of the array, there is nothing we can do to >help :). I consider it improbable whereas an omission of one field is >possible. > >> > 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.. >> >> That would be nice, but I'm not sure how we could do that. I suppose we >> could add a patch->nr_objs field. But that might arguably be even >> easier for the user to mess up. > >Yeah, that is perhaps the only way (ARRAY_SIZE won't work here) besides >introducing some special mark. I think this is not worth it. I agree it is >even more error-prone. > >The idea behind this patch is that there is at least something we can do >to help without imposing much on the user.
Yeah, agreed. Then no more objections from me :-)
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