linux-kernel - Re: [PATCH v2] KEYS: prevent NULL pointer dereference in find_asymmetric

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Message-Id: <D44PO3WW3R6S.1VSJQ4AYFJW04@kernel.org>
Date: Fri, 13 Sep 2024 02:57:20 +0300
From: "Jarkko Sakkinen" <jarkko@...nel.org>
To: "Sergey Shtylyov" <s.shtylyov@....ru>, "Roman Smirnov"
 <r.smirnov@....ru>, "David Howells" <dhowells@...hat.com>, "Herbert Xu"
 <herbert@...dor.apana.org.au>, "David S. Miller" <davem@...emloft.net>,
 "Andrew Zaborowski" <andrew.zaborowski@...el.com>
Cc: <keyrings@...r.kernel.org>, <linux-crypto@...r.kernel.org>,
 <linux-kernel@...r.kernel.org>, <lvc-project@...uxtesting.org>
Subject: Re: [PATCH v2] KEYS: prevent NULL pointer dereference in
 find_asymmetric_key()

On Thu Sep 12, 2024 at 8:36 PM EEST, Sergey Shtylyov wrote:
> On 9/12/24 5:27 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)
>
>    No, contrariwise: since we use && and !, first non-NULL would ignore the rest.

Oops correct :-/

BR, Jarkko