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

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Message-Id: <D43HH3XOAXFO.2MX7FA48VOLE9@kernel.org>
Date: Wed, 11 Sep 2024 16:19:23 +0300
From: "Jarkko Sakkinen" <jarkko@...nel.org>
To: "Jarkko Sakkinen" <jarkko@...nel.org>, "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 Wed Sep 11, 2024 at 4:18 PM EEST, Jarkko Sakkinen wrote:
> On Tue Sep 10, 2024 at 8:38 PM EEST, Sergey Shtylyov wrote:
> > On 9/10/24 4:38 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."
>
> Yep, and it changes no situation with WARN_ON() macro for better or
> worse. It would logically separate issue to discuss and address so
> as far as I'm concerned, with this clarification I think the change
> makes sense to me.

Actually explicitly stating that call paths leading to WARN_ON()
invocation are intact by the commit (as a reminder for future).

BR, Jarkko