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

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Message-ID: <84d6b0fa-4948-fe58-c766-17f87c2a2dba@omp.ru>
Date: Tue, 10 Sep 2024 20:38:31 +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 9/10/24 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...

>> Fixes: 7d30198ee24f ("keys: X.509 public key issuer lookup without AKID")
> 
> I would still call this an improvement. It overuses warn but I don't
> think this a bug. 

   I think warning about passing all NULL ptrs but then causing a NULL ptr
deref anyway wasn't really intended -- seems like a bug to me...
 
>> Suggested-by: Sergey Shtylyov <s.shtylyov@....ru>
>> Signed-off-by: Roman Smirnov <r.smirnov@....ru>
>> Reviewed-by: Sergey Shtylyov <s.shtylyov@....ru>
>> ---

   I forgot to tell Roman to place the changelog here when doing an internal
review. Anyway, here is some from me:

Changed in v2:
- kept the WARN_ON() call, just moved it to avoid extra prr checks, updated
  the patch description accordingly;
- reworded the patch description according to feedback.

[...]

>> diff --git a/crypto/asymmetric_keys/asymmetric_type.c b/crypto/asymmetric_keys/asymmetric_type.c
>> index a5da8ccd353e..43af5fa510c0 100644
>> --- a/crypto/asymmetric_keys/asymmetric_type.c
>> +++ b/crypto/asymmetric_keys/asymmetric_type.c
>> @@ -60,17 +60,18 @@ struct key *find_asymmetric_key(struct key *keyring,
>>  	char *req, *p;
>>  	int len;
>>  
>> -	WARN_ON(!id_0 && !id_1 && !id_2);
>> -
>>  	if (id_0) {
>>  		lookup = id_0->data;
>>  		len = id_0->len;
>>  	} else if (id_1) {
>>  		lookup = id_1->data;
>>  		len = id_1->len;
>> -	} else {
>> +	} else if (id_2) {
>>  		lookup = id_2->data;
>>  		len = id_2->len;
>> +	} else {
>> +		WARN_ON(1);
> 
> This is totally fine. It is an improvement to the current situation.

   That update also fixes a kernel oops...

>> +		return ERR_PTR(-EINVAL);
>>  	}
>>  
>>  	/* Construct an identifier "id:<keyid>". */
> 
> Can be applied as an improvement and with the added bits about
> panic_on_warn to the commit message.

   We no longer care about panic_on_warn...

> BR, Jarkko

MBR, Sergey