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

Sergey Shtylyov
2024-09-12T17:36:24Z

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