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SubjectRe: [PATCH] net: sched: Fix memory exposure from short TCA_U32_SEL
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On Sun, 2018-08-26 at 18:32 +0100, Al Viro wrote:
> On Sat, Aug 25, 2018 at 11:19:30PM -0700, Kees Cook wrote:
> > > > - n = kzalloc(sizeof(*n) + s->nkeys*sizeof(struct tc_u32_key), GFP_KERNEL);
> > > > + n = kzalloc(offsetof(typeof(*n), sel) + sel_size, GFP_KERNEL);
> > >
> > > ITYM
> > > n = kzalloc(offsetof(struct tc_u_common, sel.keys[s->nkeys]), GFP_KERNEL);
> >
> > I prefer to reuse sel_size and keep typeof() to keep things tied to
> > "n" more directly. *shrug*
>
> This is rather search-hostile, though. Fresh example from the same
> area: where are struct tcf_proto instances created? Is it true that
> each is followed by ->ops->init()? Is it true that ->ops->init()
> is never called twice for the same instance? Is it true that
> ->ops->destroy() is called exactly once between successful ->ops->init()
> and freeing the object?
>
> That's precisely the kind of questions you end up asking when learning
> a new area. Your variant makes those harder to answer; it does make
> it easier to catch local problems on casual grep, but it's hell both
> on the newbies trying to make sense of an area and on the old hands
> from different areas.
>
> That, BTW, is why I hate the use of sizeof(*p) in kmalloc, etc.
> arguments. typeof is even worse in that respect.

True. Semantic searches via tools like coccinelle could help here
but those searches are quite a bit slower than straightforward greps.

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