linux-kernel - Re: [PATCH 1/1][BUG][IMPORTANT] KEYRINGS: find_keyring_by

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Message-Id: <20100423194547.3135efb8.toshi.okajima@jp.fujitsu.com>
Date:	Fri, 23 Apr 2010 19:45:47 +0900
From:	Toshiyuki Okajima <toshi.okajima@...fujitsu.com>
To:	David Howells <dhowells@...hat.com>
Cc:	keyrings@...ux-nfs.org, security@...nel.org,
	linux-security-module@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/1][BUG][IMPORTANT] KEYRINGS: find_keyring_by_name()
 can gain the freed keyring

Hi.
Thanks for your comments.

David Howells wrote:
> Toshiyuki Okajima <toshi.okajima@...fujitsu.com> wrote:
> 
>> With linux-2.6.34-rc5, find_keyring_by_name() can gain the keyring which has
>> been already freed. And then, its space (which is gained by
>> find_keyring_by_name()) is broken by accessing the freed keyring as the
>> available keyring.
> 
> Good catch!
> 

> I'm not sure this is the best solution, though.
This means that the keyring of which the count became 0 should not usually 
be used again?
If yes, I think so, too.

> 
> The alternative is just to ignore keys that have a zero usage count.
OK. I applied your suggestion and I remade the patch.
Then I confirmed that the system with new fix could continue to work while
I was executing my reproducer and your reproducer.
[your reproducer]
> for ((i=0; i<100000; i++)); do keyctl session wibble /bin/true || break; done

So, I think my new patch is also fixed.
Please check it.(new patch is attached into the following mail.)

Thanks,
Toshiyuki Okajima
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