Re: [PATCH v2] KEYS: prevent NULL pointer dereference in find_asymmetric_key()

Jarkko Sakkinen
2024-09-12T14:27:49Z

On Thu Sep 12, 2024 at 4:51 PM EEST, Sergey Shtylyov wrote:
> On 9/11/24 4:18 PM, Jarkko Sakkinen wrote:
> [...]
>
> >>>> In find_asymmetric_key(), if all NULLs are passed in id_{0,1,2} parameters
> >>>> the kernel will first emit WARN and then have an oops because id_2 gets
> >>>> dereferenced anyway.
> >>>>
> >>>> Found by Linux Verification Center (linuxtesting.org) with Svace static
> >>>> analysis tool.
> >>>
> >>> Weird, I recall that I've either sent a patch to address the same site
> >>> OR have commented a patch with similar reasoning. Well, it does not
> >>> matter, I think it this makes sense to me.
> >>>
> >>> You could further add to the motivation that given the panic_on_warn
> >>> kernel command-line parameter, it is for the best limit the scope and
> >>> use of the WARN-macro.
> >>
> >> I don't understand what you mean -- this version of the patch keeps
> >> the WARN_ON() call, it just moves that call, so that the duplicate id_{0,1,2}
> >> checks are avoided...
> >
> > I overlooked the code change (my bad sorry). Here's a better version of
> > the first paragraph:
> >
> > "find_asymmetric_keys() has nullity checks of id_0 and id_1 but ignores
> > validation for id_2. Check nullity also for id_2."
>
> Hm, what about WARN_ON(!id_0 && !id_1 && !id_2) -- it used to check all
> the pointers, right? I think our variant was closer to reality... :-)

Right (lazy validation, first null ignores rest)

BR, Jarkko