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

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Message-Id: <D44DK087Y80R.25CNND6WHJ7EE@kernel.org>
Date: Thu, 12 Sep 2024 17:27:45 +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 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