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

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Message-ID: <dbc7249a-7bf5-7e5f-7204-d368c052023c@omp.ru>
Date: Thu, 12 Sep 2024 20:36:08 +0300
From: Sergey Shtylyov <s.shtylyov@....ru>
To: Jarkko Sakkinen <jarkko@...nel.org>, 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 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.

> BR, Jarkko

MBR, Sergey